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Author Topic: "J20" (K-20X Preamp, only OD and with 071 instead of 072)  (Read 26940 times)

joecool85

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"J20" (K-20X Preamp, only OD and with 071 instead of 072)
« 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?
« Last Edit: December 02, 2010, 01:54:18 PM by joecool85 »
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J M Fahey

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #1 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?

joecool85

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #2 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".
Life is what you make it.
Still rockin' the Dean Markley K-20X
"New" amp: Fender Frontman 25 DSP (FM25DSP)
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J M Fahey

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #3 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.

joecool85

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #4 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.
Life is what you make it.
Still rockin' the Dean Markley K-20X
"New" amp: Fender Frontman 25 DSP (FM25DSP)
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J M Fahey

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #5 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.

joecool85

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #6 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?
Life is what you make it.
Still rockin' the Dean Markley K-20X
"New" amp: Fender Frontman 25 DSP (FM25DSP)
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phatt

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #7 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.

phatt

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #8 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.

joecool85

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #9 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?
Life is what you make it.
Still rockin' the Dean Markley K-20X
"New" amp: Fender Frontman 25 DSP (FM25DSP)
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phatt

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #10 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:

joecool85

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #11 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.
Life is what you make it.
Still rockin' the Dean Markley K-20X
"New" amp: Fender Frontman 25 DSP (FM25DSP)
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J M Fahey

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #12 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.

joecool85

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #13 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)?
Life is what you make it.
Still rockin' the Dean Markley K-20X
"New" amp: Fender Frontman 25 DSP (FM25DSP)
thatraymond.com

J M Fahey

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Re: "J20" (K-20X Preamp, only OD and with 071 instead of 072)
« Reply #14 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 .

 

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