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Messages - edvard

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Amplifier Discussion / Re: Peavey VSS-20 amplifier with chorus noise problem
« on: September 19, 2020, 03:38:00 PM »
Make sure you buy from a reputable seller; there are some counterfeits ever since the MN-series bucket-brigade delay chips went out of production, though on eBay you're more likely to encounter salvage chips, which are a good deal if they aren't dead.  If they're actually listed as salvage and are cheap enough, I'd order two or more to make sure you get at least one good one. 

YouTube link: (Part2) Detecting Fake Ebay ICs Chips - Sound Test

Smallbear carries genuine NOS stock at somewhat of a premium ($10.95 at the time of this posting), but at least you know you're getting the real deal. 
Xvive is making re-issues, but they may be a little hard to find, and are on the expensive side ($25 and up from what I could find).  They sound as good as the originals, from what I hear.

Amplifier Discussion / Re: Peak dissipation in class B output stage
« on: September 13, 2020, 01:24:45 AM »
Do you think Spice simulations would differ a lot from reality?
What I find annoying, is what is a practical signal for testing a guitar amp? An hifi amp won't have to produce continuous square waves. But for a guitar amp, for exemple, a larsen with a super fuzz type pedal is a possible situation, and look really more painfull for the amp.

The biggest drawback to using simulators is that they will consistently give you an ideal result; that is, any given part will have real-world variations due to many factors, but the simulation will run at exact specs every time.  That can lead to disappointing results with real parts, but as long as you're aware of that, it's not so bad. 

In LTSpice (and probably others), you can use a sound file as input to your simulation, so I sometimes record a 1 or 2 second clip of a strummed open E, or plucking of a high note as "real-world" input (the clips are short because the simulation with a sound file takes quite a bit more time to process, as you can imagine).  Your guitar and pre-amp will NEVER produce a perfect sine wave, so though a sine wave can be used as a useful baseline to see if the circuit is doing what you think it is supposed to do, it won't show you how the circuit will react to an actual guitar signal.

If you are doing your testing on a "real-world" amp, I would suggest investing in a looper pedal.  That way you can strum a few chords into it, start it looping, then jack it directly into the amp and it will repeat until you stop it while you take measurements or gawk at an oscilloscope trace.  You could even run it through a pedal of your choice.

Furthermore, what would you use for practical load? Results would vary a lot in fonction of the load used for measurments, with different impedance dips and phase shifts between real speakers.

There are circuits that simulate a speaker load with varying impedances, etc. that are very close to how a real speaker will affect the operation of the circuit it's connected to.  Try this one:
Whether you build a real one, or run it through a simulation, I think something like this will work fine.  Tonal differences between speakers are often down to the material and construction of the speaker cone itself; the engineering of the power amp is only concerned with the magnet/coil part.

The Newcomer's Forum / Re: Tda ICs Pentawatt PCB
« on: May 31, 2020, 11:48:32 PM »
The tab is connected to V-.

If you can avoid, or have no intention of, grounding the heat sink by attaching it to a metal chassis (most common)or other scheme, you can get away with mounting the chip directly to it with some thermal grease.  CAVEAT: Make absolutely sure that there isn't or won't be the opportunity for some wayward part to short the heatsink to ground or the V+ rail. 
Or just use an isolation pad.  For breadboarding, I wouldn't risk going without one.  For final assembly in a box, use some common sense (and a barrier between the heatsink and the rest of the circuit) and you can get away with it.

By the way, I've heard all the cool kids are using 1mil Kapton Tape for isolating their semiconductors nowadays.  Good thermal conductivity (not as good as Mica, better than Sil-Pads), pretty tough, and one 36 yard/~33 meter roll oughta last you a while...

P.S. All you ever wanted to know about attaching something to a heat sink:

The Newcomer's Forum / Re: Tda ICs Pentawatt PCB
« on: May 28, 2020, 10:42:58 PM »
You'll find that most chipamp packages do not line up to any pre-drill hole patterns, unless it's a DIP, and there's no such thing as a pentawatt socket as far as I can find.  I wish I had thought of that when I was younger, I bet it'd make a few bucks.

My best suggestion would be to solder solid lead wires to the legs of your chipamp, so they go from your heatsink to your breadboard; you don't want to flex the legs of the  chipamps themselves too much.  They tend to weaken and break at the chip body.  Ask me how I know... >:( 


I am studying different preamp schematics. I am inclined to minimal amps or amps with not so many parts, just the ones needed to produce a given sound for guitar practice/bedroom playing purposes. I have several questions:

1.- Is it good to add a boost stage initially before any overdrive/soft clipping in terms of sound?

It depends on the circuit.  Some circuits sound just fine creating their own gain, like discrete transistor designs and most Op-Amp designs, but oftentimes boosting into a circuit that is wired for low gain will get better tones than the circuit itself wired for high gain.  In my experience, MOSFET inverter stages are like this, perhaps some others.  Counter-intuitive, I know...

2.- Is it better to add a tone control stack before any clipping or after, in terms of sound?

Again, it depends on the circuit and what you want it to do.  Personally, I've found that tone controls before the clipping/gain stage work best with low- to mid-gain circuits, for Blues and Classic Rock.  High gain circuits can tend to be noisy and "mushy" sounding with the tone control in front, though that might sound good if you want more of a Fuzz effect from your high-gain channel.  Post-clipping tone controls can sound "sterile" with lower gain circuits (but not always, there are many exceptions, I'm sure), but can be powerful tone shaping tools after a high-gain stage.

Let's say you make: guitar, boost, tone control/tone stack, soft and/or hard clipping, out.
3.- Does it worth to add a classic tone stack with bass, trebble, mid respect a single pot tone control, or a BMP with some mid control (Jack Orman mod I believe...)?

The best answer I can give is to simply try it.  I've used single-knobs, two knobs, 5-band EQs, they all have their advantages and disadvantages.  If you want to keep it simple, then a BMP with mid control sounds like it could be nice, but as joecool85 said, it can be TOO limiting.  Give it a shot, start breadboarding and take notes on which ones you like.

It seems to me that with a simple tone control (or maybe two pots) you can get a wide range of sounds, but I am learning, and I would like to understand how many stages can have a guitar amp, and the purpose of those, to see how can I simplify or minimize them, and still get a good and wide range of sound. For instance, adding preamp stages to an LM386 can give you a good sound with control. I have tried hard clip diodes with a TL072, and the sound to me gets better. Nicer.

Thank you very much for your attention.

Regards, cheers.

Most of the "extra" stages and parts of a preamp have to do with either tone shaping, bandwidth limiting, or protection.  Solid state gear is really good at simply re-creating whatever is put into it, but that includes signals you didn't intend, and so we have a thousand schemes to clamp oscillations, eliminate sub-sonics, and protect an op-amp from frying itself.  Many of those can be eliminated, but it is oftentimes what gives certain circuits their "feel".  Would a Tube Screamer sound like it does without that famous mid-hump?  Nope, it'd sound like any other generic OD/Distortion boxes out there, but maybe that's what you like; only YOU can make that distinction.

For the record, I prefer: Op-amp clean boost to a tight (2-pole) hi-pass at about 100Hz into a chain of low-gain MOSFET inverters, just about any FMV tone control circuit, (pre-gain for clean channels, post gain for dirt), make-up gain and single pole low-pass at ~5-7kHz depending on the circuit

To me the most obvious difference in the preamps ss vs tube
Is the onset "fizz" of the opamp or generally transistor when it
Starts to clip. At least i figure this is from transistors because all ss
Amps that i have do it.  I have a marshall 3203 which, if it wasnt for
That fizziness would sound rather close to a marshall 2204 or similar.
Maybe its just bad design from the old marshall ss amps.
Maybe jfet dont fizz.

I'm inclined to believe the "fizz" is from "ringing" when the signal gets clipped.  Tubes naturally go from clean signal to squared-off clipping in a very gradual manner that doesn't "ring" like squared-off waves do.  Transistors are clean until they hit the limits, then *BAM*... Gibbs Phenomenon.  This is why people like (ab)using CMOS chips (and JFETs, to a lesser extent) for "tube-like" distortion; they exhibit a gradual onset of clipping as the signal approaches the limits, though not completely analogous.

D'Addario has released their "casein" picks.  These picks are suppose to be reminiscent or tortoiseshell picks but instead of being made of plastics, they are made of dairy proteins.  Sounds cheesy to me, but if they work, I'm all for it!  That said, at $21.99 for a single plectrum, I might stick with my Dunlop Nylons!

In all seriousness, that sounds cool.  Not 22 bucks cool, but cool nonetheless.

Schematics and Layouts / Re: Schematic sites for different brands of amps
« on: January 26, 2020, 07:52:34 PM »
I've seen this posted around the forum, but it should be here.

Schematics for Crate amplifiers (and others):

Also, for those who have a schematic for the Sunn Beta Lead and disappointed that the power amp schematic is unreadable, the schematic for the Sunn "Alpha Series" mixers is the exact same thing.  Page 3 here:
can drop in to page 1 here:

Amplifier Discussion / Re: Info on Sunn Stinger 100 amp
« on: November 06, 2019, 01:07:29 AM »
I found out that the Fender Stage Lead II amp(Japan) and the Sunn Stinger 100(Taiwan) are the same amp..guess Fender just Re-Branded the same amp for Sunn & Fender during that time frame. I could not find any reviews on the Sunn Stinger 100 Amp, but I did find reviews on the Fender Stage Lead II, which are all positive. I guess that Sunn at that time did not have a very big fan base.
Thanks to everyone for all the info..good food for thought. Respects. PoorOtis.

There's some information here:

He says email him for the Japan schematic.

EL34world has a Stage Lead II schematic, no idea if it's the "Japan" schematic or not:

Amplifier Discussion / Re: Info on Sunn Stinger 100 amp
« on: November 06, 2019, 12:54:58 AM »
hey teemuk can you throw me a schematic for the sunn stinger 60, I am working on a stinger 20, sound the the preamp is of the same design.

There's a .gif file of the Stinger 60 Rev. B here (3rd post down):

You are correct.  According to the User Manual (, the Stinger 20 and 60 were the same amp with different power sections.  I think even the power sections could be the same, but missing one pair of Power Darlingtons (TIP102 & TIP107) in the Stinger 20.

Amplifier Discussion / Re: Lab Series L3
« on: July 11, 2019, 09:33:15 PM »
Try this:!1ph3CSrY!44oxSuZl6oZOZnnXJ12ikMNFncLJ2-AqZqEFzqUrnKg

Interesting schematic, that L3; it uses a CD4007 strung up to use the top half of it's 3 inverters as P-MOSFETs running the tone controls and another for the reverb driver/master out.
I don't see anywhere that counts as adjustable bias, but I could be wrong...

Amplifier Discussion / Re: Another Randall RG100ES question
« on: May 27, 2019, 03:24:05 PM »
Schematic says it's a 2K linear.

EDIT: Ooops... 5 days too late... Have you fixed it yet?

Schematics and Layouts / Re: Dual or Split supply Audio amps
« on: May 04, 2019, 01:51:24 AM »
According to the datasheet, full power on a LM1875 requires a power supply of +/- 30 volts.   That's 60 volts across peaks.  Are you using a 60 volt power supply? Your schematic calls for a 30V supply, which is not going to give you full power.
Also Single-supply requires a virtual ground made by the junction of two equal resistors that only the amplifier component uses (this is an OLD stompbox trick when using op-amps with a 9V power supply).  On the circuit you provided, this is found at the junction of R24 and R25.  Here they are designated as 10k resistors, which I think possibly puts a bit of load on the power supply (but I could be totally wrong about that). I would try changing those to 47k or 100k to see if you can get a stiffer output.

Amplifier Discussion / Re: EBay TDA2050 boards
« on: May 04, 2019, 01:01:31 AM »
Congrats, 2 years is a long time to take on a project, but I'm not one to talk (took me 2+ years to finish building my guitar...  :loco)

The reason your TDA2050s sounded so bad could be because they are cheap knock-offs; the TDA2050 has been discontinued for a few years now, and new ones are just as likely to be filled with wet sawdust as silicon.

Counterfeit VS. Authentic TDA2050 audio amplifier ic test
Counterfeit parts have been a problem for many years. Let's do a comparison test of the TDA2050 audio IC to see the difference in performance.

Glad to hear that your Class D amplifier sounds good.  I may be going that way eventually, but haven't taken the plunge yet.

Amplifier Discussion / Re: Etching your own boards
« on: January 04, 2019, 12:23:58 AM »
I've used some thinned-down model paint and a dip pen with very good results.  Speedball "B" series or Cartographer nibs.  Sharpies always drove me nuts, though my first Big Muff box was done with a sharpie.  I drew the circuit, waited for it to dry, and drew over it to get better coverage.  Sometimes, drawing over it would erase the original, so I'd have to re-draw the trace and do a second coat with a lighter hand. 
With the dip pen and paint, I never had to re-draw any, and the traces were solid.  Depending on the nib size, I could do thick, thin, or medium lines as needed.  I used two different sizes of pencil eraser as a "stamp" to make off-board wiring pads; big pads for pots, small pads for other wires.

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