Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Preamps and Effects => Topic started by: joecool85 on December 02, 2010, 01:52:47 PM

Title: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 02, 2010, 01:52:47 PM
Does this look like it would work?  I would like to take just the OD circuit from the Dean Markley K-20X (as seen here: http://deanmarkley.com/Info/LegacyAmps/Schematics/D1515.pdf ).  Will this work?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: J M Fahey on December 03, 2010, 12:40:49 AM
Yes it will. It needs +/-15V (down to +/-9V).
It's practically an MXR Distortion+ with a slight buzz filtering (which you may easily add).
I'd just build the Dist+, which also has a board and layout already solved , and has higher input impedance (this one is low and will load your pickup somewhat)
Or you can build a simplified Turbo-RAT, the one with LEDs.
Are you going to drive a TDA something with this preamp?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 03, 2010, 08:31:11 AM
Yes it will. It needs +/-15V (down to +/-9V).
It's practically an MXR Distortion+ with a slight buzz filtering (which you may easily add).
I'd just build the Dist+, which also has a board and layout already solved , and has higher input impedance (this one is low and will load your pickup somewhat)
Or you can build a simplified Turbo-RAT, the one with LEDs.
Are you going to drive a TDA something with this preamp?

I was thinking I'd use it more like a pedal than a preamp, run it in front of an amplifier.

On the original dean markley version I'm not sure how the preamp works.  I was thinking that the TL072 hook ups on the left of the schematic were for "clean" and the ones on the right for overdrive.  But it looks like it always runs through the left portion and maybe for clean it skips the right portion?  Am I right in my thinking?

I really like the Dean's OD circuit.  Maybe I will take a look at the MXR Distortion Plus and make some tweaks to make it "more dean".
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: J M Fahey on December 03, 2010, 10:54:34 AM
Then use the MXR Dist+ as a base pedal, leave the "gain", bias, etc original, specially because it's already meant to be used with single +9Volts, but modify the clipping and post clipping "tuning" at will.
Dean Markleys sound *good*, even the cheapes ones, the guy obviously has ears.
I specially like the simplest one, the K15.
Driving a 10"/12" speaker and powered with a TDA2050 with +/-22 or +/-25V  it becomes loud and club capable in a very simple package.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 03, 2010, 12:11:06 PM
Then use the MXR Dist+ as a base pedal, leave the "gain", bias, etc original, specially because it's already meant to be used with single +9Volts, but modify the clipping and post clipping "tuning" at will.
Dean Markleys sound *good*, even the cheapes ones, the guy obviously has ears.
I specially like the simplest one, the K15.
Driving a 10"/12" speaker and powered with a TDA2050 with +/-22 or +/-25V  it becomes loud and club capable in a very simple package.

Sounds like a plan.  Now, post clipping I assume you're referring to the LEDs etc at the end of the circuit, correct?  As for "regular" clipping, are you referring to the gain?  If I'm correct that is the resistor between the inverted input and the output.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: J M Fahey on December 03, 2010, 04:03:49 PM
Yes. In these circuits you have a gain stage, with an OpAmp and the net of resistors, capacitors and a gain pot around it, and after that a couple clipping diodes in different configurations, resistors, and some capacitors, usually filtering high frequencies (buzz) to ground, plus an output volume pot.
You can combine the gain section from one pedal and the clipping/filtering from another.
I suggest the MXR one because it's simple yet good, it can provide clean sound by itself (The MXR Boost is just that, a Dist+ without clipping diodes), and the RAT or others can provide more control.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 03, 2010, 04:38:43 PM
Yes. In these circuits you have a gain stage, with an OpAmp and the net of resistors, capacitors and a gain pot around it, and after that a couple clipping diodes in different configurations, resistors, and some capacitors, usually filtering high frequencies (buzz) to ground, plus an output volume pot.
You can combine the gain section from one pedal and the clipping/filtering from another.
I suggest the MXR one because it's simple yet good, it can provide clean sound by itself (The MXR Boost is just that, a Dist+ without clipping diodes), and the RAT or others can provide more control.

Ok...so the dean markley has a clean preamp feeding the OD circuit?  Doesn't that mean it will probably sound different running the guitar straight into the OD circuit?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: phatt on December 04, 2010, 05:41:17 AM
Yes Joe,
            The second stage is an inverting config,, so input imp is expecting a low signal from preceding stage.
By deleting the first hi imp stage you upset the balance,,,Still works but not as good.

I just did some simulations of the first 2 stages and it certainly has a big hump at 1kHz so it will be a smooth OD sound as the high freq are surpressed giving the classic warm tone.

Sw1A is a bit confusing so I might BBoard test it and see how it works in real life.
Cheers Phil.

Phil.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: phatt on December 04, 2010, 11:35:48 PM
Hi Joe,
        Tested it and it does the job well. :tu:

Way to fuzzed up for my style so I made a few alterations to make it a little more touch responsive. See Circuit.
Did not like the big difference in freq response between the clean and drive so I added a 500p cap across the clean.

I did not bother testing the tone section as I have my *PhAbbTone unit* which is darn hard to beat. 8)

So yes it could work as a pedal if you change it to a single supply and add a reference voltage.

BTW, in my experience hanging a tone control off the end of these circuits never seems to work well.
I have had far more success with tone *In front*. Just a thought.
Cheers, Phil.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 05, 2010, 07:49:07 AM
Hi Joe,
        Tested it and it does the job well. :tu:

Way to fuzzed up for my style so I made a few alterations to make it a little more touch responsive. See Circuit.
Did not like the big difference in freq response between the clean and drive so I added a 500p cap across the clean.

I did not bother testing the tone section as I have my *PhAbbTone unit* which is darn hard to beat. 8)

So yes it could work as a pedal if you change it to a single supply and add a reference voltage.

BTW, in my experience hanging a tone control off the end of these circuits never seems to work well.
I have had far more success with tone *In front*. Just a thought.
Cheers, Phil.

Way cool Phil!  I love the sound of my K20-X, but I plan on getting rid of the "clean" portion of the preamp and just using it as a OD box.  Also, looks like it would be a good idea to keep using the TL072 to keep it as "Dean" as possible.  Thanks for the help!

**edit**
You said you tested it, did you actually build it or was it a sim?  Also, were you running it on 9v?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: phatt on December 05, 2010, 08:21:43 AM
Hi Joe,
         Yes I did both, simmed it and bread boarded it.
has a nice peak at 1kHz and rolls off the treble early, which does tend to deliver the more classic tone shape.

Impossible to get any cleanish rattle even with guitar Volume rolled back, it's all crunch so I played around with the values.

The low freq is fat due to C4/C5 but still does not fart out like some circuits do so that's nice but does make it a lot harder to make it dynamic.
Larger values for R6/R7 will make it softer/smoother but that is why I breadboard things ,,so one can find these little tricks to a given circuit.
Sadly Simms don't tell you how it will sound,, dratt!

If you don't need the clean then just delete the switching and parts involved.

I ran it from a split 6-0-6 VDC battery pack but should work the same with
a 9V Batt.
I 've never found there to be massive difference in swapping opamps,, I tend to use whatever is in my draw at the time.
Depends what the circuit does. With simple circuits like this I doubt you will hear big changes.  :tu:
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 08, 2010, 09:21:59 AM
I just realized that "LED1" is actually a two-led unit in a single case. In looking at the schematic I figured it was two separate LEDs.  Think it would sound the same with two separate LEDs or do I really need to try to find a double LED unit like they used? 

I'm thinking about applying voltage to my Dean's LEDs and seeing what colors they are so I can at least get that right.  Turns out dual LEDs are normally red and green from my research.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: J M Fahey on December 08, 2010, 12:18:56 PM
Yes, often dual leds are red/green so they can produce 3 colors (add yellow)
In this circuit they will provide a somewhat asymmetric clipping , not bad.
It's the same as using 2 separate ones, or even 2 red ones, adding a 1N4002 in series with one of them.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 08, 2010, 12:40:11 PM
Yes, often dual leds are red/green so they can produce 3 colors (add yellow)
In this circuit they will provide a somewhat asymmetric clipping , not bad.
It's the same as using 2 separate ones, or even 2 red ones, adding a 1N4002 in series with one of them.

Does it matter what colors I choose?  IE - Red, blue, green, yellow, orange?  I would think it would.

Also, does it matter which way the diodes go?  I know they go opposite each other, but does it matter if the red one "points up" and the green "down" on the schematic or vice-versa (IE - which cathode goes to ground and which goes to signal)?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: J M Fahey on December 08, 2010, 11:33:40 PM
Most popular is 2 reds , used By Marshall, Fender, and most others; I'm finding Marshall MGs with red/green.
Color isn't important but forward voltage.
Red around 1.8 or 1.9; green about 2.1.
Which one goes "up" or "down" can't be heard.
You can add one of those DIP tiny-switches to experiment .
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: phatt on December 09, 2010, 06:39:48 AM
Hi folks,
I found this led voltages listed down the page. :tu:

http://www.kpsec.freeuk.com/components/led.htm

I used little Green Leds for testing Joes circuit but I doubt it makes a lot of difference.

I tend to find the debate about the pros and cons of small details like this is hardly ever going to be noticed in live situation.

Quite frankly a lot of these opamp type OD tricks are much the same,,, in the end whether you limit the swing with a pair (or more) of diodes or let the signal slam into the supply rails it often sounds much the same.

It's more circuit design and other tone shaping tricks that tend to make the difference.

I even tried some very high voltage diodes once but I think the fv drop was likely much bigger that the 9 Volt battery the circuit ran from.  :duh
But it was all good fun to experiment, even though I was a clueless noob at the time. :lmao:
Phil.


Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 09, 2010, 09:14:22 AM
Excellent info as always fellas.  I appreciate it.  I'll probably test my LED in my K20-X to see what colors it is (apply voltage to that part of the board and watch them light up).  I'd like to keep this is original as possible but don't want to have to go to a special vendor to get parts.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 21, 2010, 09:40:47 AM
In the interest of keeping parts count low, I might try Juan's solution of using the Dist+ as the base circuit, swapping in a TL071, using "K20-X" style clipping diodes/caps/resistors etc at the tail, and then a BMP style tone control.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 29, 2010, 11:19:09 AM
So yes it could work as a pedal if you change it to a single supply and add a reference voltage.

I'm interested in doing this so I can run the circuit as a stock full fledged K20-X preamp on 9v or maybe 12v single supply.  How would I go about changing it to a single supply with a reference voltage?  Is it as simple as putting th V- pin to ground and V+ to 9-12v DC positive?  What exactly is a "reference voltage"?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: teemuk on December 29, 2010, 11:57:22 AM
It's pretty simple. really. To convert from bipolar power supply to a single-sided one all you need to do is to provide the OpAmps a reference voltage that's half of the rail-to-rail voltage.

I know you've seen this setup before numerous times.

(http://d.imagehost.org/0290/conversion.gif)
Added components are circled in red. Basically the only additions you'll only need are the voltage divider and filter for generatingthe reference voltage and one coupling cap.

Essentially, your biggest problem is not the conversion from bipolar to single-ended power supply, but that you try to decrease the rail-to-rail voltage from about 30V to only 9V. Basically, doing that will cut about 2/3 rd's of the headroom. Since the clipping of this particular circuit relies on the somewhat high forward voltage of the LEDs the result may end up being that at high levels of overdrive the OpAmps also start clipping.

I think you might have to add in some kind of DC-DC converter that generates 30VDC from a 9VDC battery supply.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 29, 2010, 12:06:53 PM
Thanks for the info Teemu, and you are right, I have seen that before but just didn't "get it".

If I was to keep a dual power supply, say two 9v batteries, could I keep the schematic the same as the original and just have ground be the intersection of the two batteries, V+ the postive and V- the negative?  If I am correct this would get rid of the need for a VREF as well as increase headroom substantially over using just a single 9v.

V+(+9v/-9v) GROUND (+9v/-9v+) V-
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: teemuk on December 29, 2010, 03:45:51 PM
I didn't really understand how you meant to connect the batteries, but yes, series connection of two of them, with the node where the terminals connect being the ground would work perfectly in that application.

VCC +[:::::] GND +[:::::] VEE

I hope you understand the crude "diagram" above.

You have 9+9=18 volts affecting between the positive and negative terminals of the battery string. Since the mid point is tied to ground reference (zero volts) the potential read from positive terminal to ground is +9V and the potential read from negative terminal to ground is
-9V. So, you have a bipolar supply.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on December 29, 2010, 04:05:00 PM
I didn't really understand how you meant to connect the batteries, but yes, series connection of two of them, with the node where the terminals connect being the ground would work perfectly in that application.

VCC +[:::::] GND +[:::::] VEE

I hope you understand the crude "diagram" above.

You have 9+9=18 volts affecting between the positive and negative terminals of the battery string. Since the mid point is tied to ground reference (zero volts) the potential read from positive terminal to ground is +9V and the potential read from negative terminal to ground is
-9V. So, you have a bipolar supply.

Your crude drawing depicts the same thing as mine, albeit a bit easier to read.  I think I'll try it this way.  I don't mind using two batteries in it.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 05, 2011, 10:40:54 AM
About the Vref:

I understand the 10k resistors are electrically in series, and the point between makes half the original supply voltage - that makes sense.

Two questions though:

Wouldn't it make sense to use 100k resistors in stead of 10k?  If I'm correct, with 10k we are bleeding out 4mw of power whereas with 100k we would only bleed out .4mw of power.

Second, I'm assuming the 22uF cap was added as a supply line filter.  Why is this necessary if we already have a filter at the 9v + line and how is this 22uF value calculated?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: J M Fahey on January 05, 2011, 03:41:24 PM
Just convenience.
You could use 1M if necessary (as in Jerry García's guitar preamp), but probably any current "eaten" by Op Amps or whatever you reference to that point will make it change, (usually going lower) and losing its symmetric status.
10K is a low enough value as to ignore any sensible load.
Remember this has been in use for ages, before Fet input Op Amps.
22uF is a generic value; 100uF would be better and 1000 or 2200 uF much more so, only they start being on the bulky side.
Remember that your problem is not only having no ripple there, but being an *audio ground* reference for many gain circuits. In fact some people use an "as large as possible" electrolytic, paralleled with a .1 ceramic or similar.
No, it does not need to be a SoZo, Mustard, Orange Drop or Silver Mica one.
No Mojo here.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 05, 2011, 03:57:55 PM
Remember that your problem is not only having no ripple there, but being an *audio ground* reference for many gain circuits. In fact some people use an "as large as possible" electrolytic, paralleled with a .1 ceramic or similar.

Could you elaborate on this "audio ground"?  Also, why would having a small .1 or so ceramic cap help?  I've seen it a lot in pedal board PSU designs but never knew why.

Thanks for the excellent explanations.  I've been doing this hobby for 5 years now and know how to do stuff, but not always why.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: phatt on January 07, 2011, 08:27:32 AM
Remember that your problem is not only having no ripple there, but being an *audio ground* reference for many gain circuits. In fact some people use an "as large as possible" electrolytic, paralleled with a .1 ceramic or similar.

Could you elaborate on this "audio ground"?  Also, why would having a small .1 or so ceramic cap help?  I've seen it a lot in pedal board PSU designs but never knew why.

Thanks for the excellent explanations.  I've been doing this hobby for 5 years now and know how to do stuff, but not always why.

Hi Joe,
In a nut shell, you are lifting your AC signal *Common* above the DC Ground. you are Floating it at a bias point higher than ground,,  it's biased at a different quisient point.

The really tecky part (Why Capacitor on the bias voltage) I'll leave for the experts to explain but what helped me big time was *Simulation* as you get to see stuff that, done in real time would cost a small fortune in scopes, sig gens and half a dozen DMMs just to take all the readings.

For a hobbist it really opens up a whole new world that you would not see outside of working in a repair shop.

Sims will show you just how the AC signal is moved up and down on the DC line (the Q point).
Quite frankly I would still be messing around with 2 or 3 transistor circuits and wondering why it does not work if it was not for Sims.

Heck the MaxiVerb, the PhAbbTone, The DDC circuit. None of these would not have been possible without the help of simulation software.

I use Circuitmaker (student edition) which is free up to 50 commponents.
I now have 100's of sim files I can call up if I need to reference something.

Now sims are not perfect and Absolutely nothing beats years of experience from qualified teck folk. (You know,,those smarty guys that brag about building 10,000 Amplifiers and make there own speakers) :loco ;)
We  hobby types will never be able to reach such dizzying heights,,  :'(
But as a hobby tool sims will save you 100's of hours of building waste of time circuits.
Just think of the solder you will save. LOL.
----
Ed,,, whoops Did I  mention Circuitmaker student is *FREE* ?
http://my.ece.ucsb.edu/bobsclass/2C/Simulation/circuit_maker.htm

I think this still works if not just google it I'm quite sure it's floating about just waiting to save you from hard labour.  Oh yes it even has some Valves to play around with. :tu:
Cheers, Phil.

Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: DJPhil on January 07, 2011, 01:30:19 PM
Could you elaborate on this "audio ground"?  Also, why would having a small .1 or so ceramic cap help?  I've seen it a lot in pedal board PSU designs but never knew why.
Audio ground means the same as 'virtual ground (http://tangentsoft.net/elec/vgrounds.html)'. In a single supply system it sets a point near or at the middle of the supply for the AC audio signal to ride on. Because it will have to source and sink (a little) current you want it to have a very low impedance. If it were high impedance then the ground would follow the signal as it moved up and down, anywhere from slightly (causing frequency dependent attenuation) to horribly (almost no signal and badly distorted). The lower the impedance the better the virtual ground's compliance as a (sort of) regulator.
The choice of resistors is a balance between getting that low impedance and wasting lots of power on smoking hot ten ohm resistors. 10k is a nice middle ground (sorry for the pun) and is often used. The 22uF capacitor and it's 100nF friend help keep noise off of the virtual ground by providing it a low impedance path to ground. They serve a similar purpose to the bypass capacitors in a voltage regulator, and help insure that the virtual ground is as flat and stable a DC value as possible. The extra smaller cap helps with higher frequency noise and RF interference in a manner I can't easily describe. This is where joecool85's simulations come in very handy, otherwise you find yourself doing the hard math.
This all becomes academic if you choose to use a 2x9V battery setup, as you can leave the circuit as it was originally. The virtual ground link above has some additional details on various methods that go beyond a simple voltage divider if you like.

Regarding simulation, I'm a fan of LTSpice (http://ltspice.linear.com/software/LTspiceIV.exe) (also free), though it took me a few weeks of tinkering to get used to. I'd recommend playing around with a few of the free ones out there and seeing what works for you. Simulators shouldn't be trusted for everything, but they are indispensable for quickly working out simple things like the above. Their ability to graph output gives you access to the sort of information you might not have the equipment to see in practice (oscope, spectrum analyzer, etc.).

I hope that helps some. As usual, always double check my work against the pros to be sure. :)
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 07, 2011, 02:16:45 PM
You guys always have the best answers.  I will probably build a full K-20X preamp with clean and OD and run it off a "normal" transformer/PSU board situation, maybe only as little as +/- 6v though depending on what I can find for a transformer cheap.  Think it would sound ok with such little voltage?

Eventually I will get around to playing with the circuit and building a TL071 Distortion Plus with K-20X style clipping and maybe some other mods.

**edit**
Also, I'm thinking I may eventually build this as a pedal with two 9v batteries and have two stomp switches.  One for bypass and one for clean/OD circuits.  It'd be pretty cool I think.  I might try it with a single 9v at some point though, it is a strong point running on just 1 battery.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 11, 2011, 08:17:22 AM
Quick question.  On the schematic it shows C19's value as "223".  Does this mean 223pF?  223nF?  And what about C7's value of 333M?  I know it can't mean 333mF because that would be a huge electrolytic.

All the capacitors in question are brown film-type caps and regardless of the M or not they are all about the same physical size.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: phatt on January 11, 2011, 09:46:22 AM
Yep a pain until you get how it works,, and darn I still get tricked some times.  :loco
223 would most likely mean, 22nF or .022uF or 22,000 pF all the same.

First two numbers are the *Value* 3rd number is the multiplier.
in this case it's 22 now just add 3 zeros and presto it's 22nF

333 same again 33nF
Phil.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 11, 2011, 09:54:39 AM
So 333M and 333 would both be 33nF?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: phatt on January 11, 2011, 10:00:57 AM
Yep I'd say so,
M is the voltage rating of the device.
Can't remember them all off hand but I think *J* means a 100volt rating.

Some makers use different codes but after a while you catch on to the tricks.
Phil.

Ed;
the code Works like this;

 uF  nF  pF
000,000,000

So a 100nF would read 104,, that's 10 and just add 4 zeros
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 11, 2011, 10:02:02 AM
Yep I'd say so,
M is the voltage rating of the device.
Can't remember them all off hand but I think *J* means a 100volt rating.

Some makers use different codes but after a while you catch on to the tricks.
Phil.

Thanks!
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: DJPhil on January 11, 2011, 10:36:06 AM
Wow you guys work fast! Well, that and I'm long winded too.  :duh
Here's a link to a page on cap codes (http://www.solarbotics.net/library/pieces/parts_elect_pass_cap_code.html), and a quick online calculator (http://www.electronics2000.co.uk/calc/capacitor-code-calculator.php). The letter codes can be a number of things, but the letters used for voltage ratings are from an old military scale that's probably not used here. If so, it would mean 4KV rated cap!
The letter codes are often tolerance ratings. An 'M' would be +/- 20%, which is the standard tolerance for cheap caps. Sometimes you'll see a 'J' or 'K' rated cap (5% or 10%) to signify that the cap needs to be better than cheap. Capacitors will definitely teach you to forgive sloppy tolerances, especially when you imagine how many things out there are stuffed to the gills with +/- 20% parts and 1% resistors! It's a rare circuit that will need better than 5% on a cap, though it's a bit more common to need a well matched pair (twin T filters (http://www.radio-electronics.com/info/circuits/rc_notch_filter/twin_t_notch_filter.php) for example).

Included is a picture from when I thought I'd be the first to respond. The codes discussed above are commonly used for through hole small caps of all types.
You never know what you'll run into on an old schematic. :)
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: J M Fahey on January 11, 2011, 04:03:04 PM
 :o
Been watching Australian floods on TV
WOW !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Becoming worried about Phatt and a couple other Aussies which frequent this virtual smoky joint.
All right pals ????
We want proof of life !!!
Post something or at least let go some bubbles, so we can see them in the surface.
Just in case, I'm getting my Scuba equipment ready.
Good luck. :tu:
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 11, 2011, 04:30:45 PM
:o
Been watching Australian floods on TV
WOW !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Becoming worried about Phatt and a couple other Aussies which frequent this virtual smoky joint.
All right pals ????
We want proof of life !!!
Post something or at least let go some bubbles, so we can see them in the surface.
Just in case, I'm getting my Scuba equipment ready.
Good luck. :tu:

No kidding, hope you guys are alright!
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: DJPhil on January 11, 2011, 11:52:19 PM
Yes, stay safe over there guys!
If you need help or need to check on someone you know I'd recommend contacting the Australian Red Cross. I worked with the Red Cross here locally when we had some flooding in 1993 and there's no better bunch of folks when you need a hand.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: phatt on January 12, 2011, 11:05:16 AM
First,,, Bubbles ,, yes I'm alive and well. ;D

2nd thanks *DJ Phil*. You are quite right the Letter is the Tolerance not the Voltage,,, late at night I get confused. :loco

And thanks All of you for your concern. :tu:

Nambour is about 80 mile north of the Capital of Queensland, Brisbane.

The great Dividing range runs right down the East Coast of Auz and when we get rain in Queensland on both sides of that range not only does it flood on the coastal towns but it also moves inland.

Some ends up in Lake Eyre ( it's a salt lake in the middle below sea level)

The rest ends up in the Murray River and the water from mid land Queensland actually takes 6 to 9 months to reach the mouth of the Murray River in South Australia.

When all the rivers from the middle of Qland join up, The Condermine, Darling,(to name 2 of many) they ultimately join into the Murray River.
That basin *is then* very close to the same size as the Missisippi. Of course nowhere near as much water flows but it is a very big system none the less.

Australia being so boring and flat in the middle the water just runs outwards and hence town after town gets flooded out.

By now some of you will know the Town of Towoomba because of that freak wave.
Well it's about 80mile west of Brisbane right on the very edge of the great diving range.

Yes I 've driven through that town many times,, that very street that you may have seen on TV.

My Father lived through the bad Floods of 1954 in my home town of Rockhampton which has also been Flooded again.
So yes you could say The East coast of Queensland is really behind the 8 ball.

I lived through the Brisbane flood 1974 so I know what they are in for. I helped many elderly folks in my area clean out the mess afterwards, The smell afterwards is horendous. I will never forget it.

Nambour got away with only some carpark being ripped away and 4 feet of mud in the main shops.  This town is very hilly up and down so water gets away fast.

It has been observed that this Flood may well be Australia's worst natural disaster and It is certainly starting to look that way. :'(

Having witnessed the 74 floods,,, I make a point of living on top of hills rather than low lying areas. 8|
Phil.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 12, 2011, 11:33:27 AM
Having witnessed the 74 floods,,, I make a point of living on top of hills rather than low lying areas. 8|
Phil.

Good to hear you are alright, and learning all the time  :tu: lol

Back on topic, I have a vero layout almost complete for the whole K20-X preamp.  The original, as it is in the schematic, not with any of the changes we have talked about.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 14, 2011, 05:23:27 AM
Alright, who wants to build a vero K20-X preamp?  It's all verified electronically on paper, but hasn't been built yet.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 14, 2011, 11:25:55 AM
Just realized teemu had a resistor and cap going to ground at the end of the circuit that I left off, how important would those be?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: phatt on January 15, 2011, 09:44:49 AM
Hi Joe,
         A suggestion if I may.
As a stand alone unit it would be wise to hang a buffer at the end of this.

It's a low imp tone stack which are not as lossy as high impeadance TStacks but just the same the circuit is some what dependant on what it plugs into.

A buffer will fix any interface issues that may arise.

There are a few well known pedals that do as you have done but it's not good design practise.
 Cheers Phil.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 15, 2011, 04:56:49 PM
Hi Joe,
         A suggestion if I may.
As a stand alone unit it would be wise to hang a buffer at the end of this.

It's a low imp tone stack which are not as lossy as high impeadance TStacks but just the same the circuit is some what dependant on what it plugs into.

A buffer will fix any interface issues that may arise.

There are a few well known pedals that do as you have done but it's not good design practise.
 Cheers Phil.

Ok, what about the resistor and cap that teemu had on the end of the circuit that I didn't add in?  The schematic had a resistor inline as well as one to ground and a cap to ground originally right before going into the poweramp circuit - should I put these in?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: DJPhil on January 15, 2011, 09:07:24 PM
Ok, what about the resistor and cap that teemu had on the end of the circuit that I didn't add in?
I went back and found a schematic in this post (http://www.ssguitar.com/index.php?topic=1885.msg12647#msg12647), let me know if I should be looking at another.
R12 and C11?
I believe these act as a lowpass filter and help set the output impedance. It starts rolling the impedance down at about 14kHz, and this helps keep ultrasonics out of the following stage (presumably a power amp) which aids in stability. It certainly wouldn't hurt to put it in, and if need be you can just solder the parts to the output jack.

The schematic had a resistor inline as well as one to ground and a cap to ground originally right before going into the poweramp circuit - should I put these in?
I'm not sure about this one. Do you mean preamp as opposed to power amp? Could you say which components in the above schematic?

Hope that helps. :)
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: phatt on January 16, 2011, 09:41:33 AM
My guess is you can take the signal out straight from the treble wiper,,,
BUT you are then totally dependant on what you plug into next.

My point is sure it works *asis* but why build something and cost cut if it is likely to cause pain and frustration somewhere in the future?

One only has to read the constant flow of interface issues with pedal boards to see that cheap short cuts like this are trouble in the making.

Having simulated the circuit I can see why Joe cool likes it so up to him how he wants to build it but if I did build it,, NoWay I would leave it hanging out like that.

If you want stuff to interface with almost anything then *Buffer* or wear the pain somewhere down the track.
Phil.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on January 16, 2011, 10:55:28 AM
Ok, sounds good guys.  I'll probably add a buffer into the next version which will be set up to run on 9v.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: anttyj on October 27, 2011, 09:54:22 AM
Alright, who wants to build a vero K20-X preamp?  It's all verified electronically on paper, but hasn't been built yet.
I've been building this veroboard version of preamp and in doing that I noted one needs to cut the copper strip at c12 or c13 in order to prevent short-circuiting parallel-connected C5 and R5. Unless you do that, you will also directly connect pins 1 and 2 of IC1 together. This is not good from the viewpoint of gain of the first half of the IC.
I've notified joecool85 of this and he says hasn't got the time to check it just now but urges me to report my observation on this list.
In a few days I'll be testing the preamp once I've got my +/- 12 V power supply working...
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on October 27, 2011, 09:59:14 AM
Thanks anttyj for posting this, I look forward to hearing how the preamp works out for you once it is fully built.  Maybe even a pic and a sound clip?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: anttyj on November 07, 2011, 09:00:07 PM
Thanks anttyj for posting this, I look forward to hearing how the preamp works out for you once it is fully built.  Maybe even a pic and a sound clip?
Well, I've got it built now and it works nicely. I followed your parts placement otherwise to the letter but moved all other components but the IC to the non-copper side of the veroboard (as a slight mental exercise). In addition, the cutting of copper strip at c12 was indeed necessary, as indicated in my previous post.
I put the preamp into an aluminium diecast box together with a small 8-watt TDA2030 PA built from a kit. The latter provides plenty of volume for home rehearsing.
Overdrive works well, too, and you can see the red LEDs blinking when a guitar string is struck.
Having built a number of solid-state ham radio transmitters in the past, I was slightly concerned of eventual self-oscillations due to proximity of the input and output copper strips of the TL072 but these concerns proved unfounded. There is no sign of instability of any sort.
With my guitar disconnected from the input jack and with the lid of the box in place, the amp is amazingly quiet, no hum, no noise, not anything. Nevertheless, with the guitar connected, the sensitivity is more than ample for full-blast blockbuster operation.
I'm attaching a mediocre-quality picture of the preamp and PA in the aluminium box. The camera of my Nokia C5 mobile phone isn't very well suited for close-up work...
The two not-yet-connected jacks at the rear wall are for connection to an effects box (in my case the t.c. electronic G-Major guitar processor).
The dual-voltage power supply is external and, it is heavy-duty enough to supply power for a TDA2050 power amplifier I'm planning to build for gig use. As the amp is now, I'll try it at our band's rehearsal location the coming Sunday.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on November 08, 2011, 07:15:56 AM
I followed your parts placement otherwise to the letter but moved all other components but the IC to the non-copper side of the veroboard (as a slight mental exercise). In addition, the cutting of copper strip at c12 was indeed necessary, as indicated in my previous post.

anttyj, it was designed for ALL parts to be placed on the non-copper side.  I'm not sure how you could even solder them down if you put them on the copper side.  The "tracks" are shown on the diagram for reference, just like most all vero layouts.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: anttyj on November 09, 2011, 11:52:12 AM
anttyj, it was designed for ALL parts to be placed on the non-copper side.
Yes, of course. It was my first assumption but then flipping the veroboard upside down to cut copper tracks at the right locations becomes another mental exercise. Therefore I chose to consider the layout as copper-side illustration to be sure I cut the tracks at the right places. After that there was no alternative but to solder the IC on the copper side.
Quote
I'm not sure how you could even solder them down if you put them on the copper side.  The "tracks" are shown on the diagram for reference, just like most all vero layouts.
Okay. Though I've got more than 50 years of solid-state building experience, I admit most of it has been dealing with printed circuit boards and much less with veroboards. It is possible to solder  components on the copper side but you have to be very careful not to short-circuit the tracks with bare component leads.
With PCBs, it is customary to publish both the component-side and the foil-side pictures to help avoid confusion.Perhaps you could assist potential builders of this preamp by publishing the layout also seen from the copper side?
Now that I've succeeded once, I'll build the next one according to your original design.
I'll try to provide the sound clip you requested a little later after I've figured out how to best connect my effect box to the preamp...
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: J M Fahey on November 09, 2011, 01:21:34 PM
Dear anttyj.
Most Vero designs you´ll find in these Forums (and many others) are drawn using the *excellent* Bancika´s "Do it yourself Layout Creator".
I suggest you search for it and download a copy for your own enjoyment.
I much prefer the somewhat older Windows version rather then the newer Java based multiplatform one, specially because 99% of published designs are compatible with the older one.
It´s a full fledged PCB design package, which has the exact needed functions and no more, to shorten the learning time (it´s very intuitive even for non electronics guys) *but* it shows Vero designs component side only.(what others would call "from above")
Enjoy.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: anttyj on November 10, 2011, 10:48:06 PM
Thank you, J M. I downloaded the program but it seems to be a Windows-only thing. As I'm 99% of the time in Linux (Fedora), I didn't try it out as yet. However, I have got XP in one of my computers so I'll try the program in the near future.
Circuit diagram CADs and PCB layout design programs have been around for some time but I never felt the necessity to learn to use one. This is probably because I seldom design circuits or PCBs myself. This might be as good a time to start as any...
Thanks again - and thanks to Joe whose preamp layout prompted me to build something after several years of resting on the proverbial laurels!
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: J M Fahey on November 11, 2011, 04:57:03 AM
Yes, *there is* a Java based version which runs on anything, including Linux, but designs are not compatible with the old, Windows one.
Fact is, there is a ton of designs around, made with the old one, which became the de facto standard.
Just check http://aronnelson.com/gallery/main.php
There are *thousands* of designs and layouts there, most of them made with DIY Layout Creator.
It´s very intuitive and quick to learn.
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: anttyj on November 12, 2011, 02:10:50 AM
Well, I tried the diylc-3.0.9-beta but it won't run in Fedora-15-x86_64 Linux. Googling around a bit showed it *does* run in some flavour of Linux, such as Puppy Linux. Fedora just flatly declares: "Permission denied", even when trying to start it as superuser (root). This may be because Fedora is _the_ "bleeding edge" Linux distro with advanced built-in precautions. My guess is it won't accept other libraries than its own, but I didn't really look into it closer.
One possibility would be running DIY Layout Creator in a Windows emulator such as Wine or qemu but installing those emulators may bring along their own problems.
Anyway, all this is probably somewhat beyond the scope of this forum. I'll install diylc in Windows XP where it probably will run "out of the box". Thanks for your input, J M!
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on November 18, 2011, 05:31:50 PM
Thanks again - and thanks to Joe whose preamp layout prompted me to build something after several years of resting on the proverbial laurels!

Your welcome!
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: runce on December 25, 2011, 05:51:02 AM
hello from Lithuania! I have sereos problems building my op-amp/tone/buil-in effects. will this schematic work with fender tone schematic? will the Rin and Rout match? and can I use gainclone? I olready have gainclone and cab with V12. second question, what should I do to get realy high-gain distortion?
Title: Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
Post by: joecool85 on March 17, 2020, 07:15:57 AM
Not sure how I missed this, but the Mid pot should be 500 ohm, not 500k !!!  I finally got a chance to play with the tone stack in a sim and found the error.  It makes a HUGE difference!

You can get away with a much more common 1k potentiometer though.