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October 02, 2022, 02:38:10 AM

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Adafruit PAM8302 Amplifer

Started by Carriage, July 12, 2022, 04:22:47 AM

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Loudthud

This effect is not what I would call "Diode hash". It's not any fault with the diodes. The circuit is doing exactly what the math says it will do. To get rid of the "1+" effect, use the inverting form of feedback. See attached. The one disadvantage is the low input impedance, so you really need an input buffer like the TS pedal.
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Carriage

Parts have arrived from tayda.
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joecool85

Quote from: Carriage on July 18, 2022, 05:38:17 AMParts have arrived from tayda.
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How's it sound?
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

Carriage

It wasn't amazing. It's just the first stage into the flat channel on my THR. I'm thinking I perhaps instead play with the tonestack first to get a pleasing enough clean tone and then add the gainy tone on top.

This all assumes the THR's flat channel is going to be similar to the PAM8302. That's still in the post and I need to get my speaker cab back from a friend too.

Carriage

So I added the tonemender tonestack to the breadboard and with the gain down in the first stage it sounds like advertised.

With the gain up I still wasn't so happy with it. At very specific gains it sounded okay but past that it sounded kind of like the clean with a fuzz/noise behind it. I don't know if the analysis is leading me to think that but it's not particularly pleasing.

I put the clipping diodes after the tonestack to not much difference. I then removed the ones in the first stage and it's  heaps better to my ear.

There's still a few things I want to fiddle with plus I realised the op amps I've bought aren't designed for single sided supply, though they're working. I'll try and get some sound samples too when I get some time
 

Carriage

#20
Here are some samples. The first file is the yamaha thr on its own for reference (usb out). The difference between the other two is the feedback resistor in the first stage. The second gain stage isnt included yet. The tonestack pots are somewhere vaguely pleasing. Guitar is a strat bridge pickup

I think I'm reasonably happy with it at lower gain but at higher gain there's this fizzy distortion on top. I think that may be the op amp distorting (based on some Spice sims) so I'm thinking about putting a unity buffer in front of some other clipping diodes in the front as a boosted/hotter signal is going to make it worse. Not sure yet though. Maybe some filtering would be better but I think I'm struggling with no headroom and then the OP07 isn't rail to rail to make things worse.

It's also unclear how much the Yamaha is helping. Still waiting for the 8302 board.

Yamaha
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200k
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500k
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phatt

Hey it's not too bad but likely to struggle if you want distortion.

Hey you have a BBoard,,Maybe test some of the Marshall circuits that *TassieViking* mentioned on first page?
FWIW,
     In My 30 plus years of building guitar circuits I can say that if you just want to strum a few clean chords then bandwidth and tone shaping will not be much of an issue but if you want OD/Distortion, crunch, big fat sweet singing leed guitar tones then you will spend years building land fill if you don't research the bandwidth issues of Distortion,, an Why do I know this,,Well I have draws full of land fill circuits that went nowhere. In all those years I've only had a few success circuits that actually worked well. It's a long journey but I'm glad I persevered in spite of all my failures as those fails taught me stuff that I may never have known otherwise.
Phil.

phatt

Quote from: Loudthud on July 18, 2022, 04:04:16 AMThis effect is not what I would call "Diode hash". It's not any fault with the diodes. The circuit is doing exactly what the math says it will do. To get rid of the "1+" effect, use the inverting form of feedback. See attached. The one disadvantage is the low input impedance, so you really need an input buffer like the TS pedal.
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Hi , thanks for that, yes I worked out years back that using inverting circuits tends to produce a better result, but was never quite sure why, so ta that makes sense.
I think I got slewed with the term crossover and Expansion at zero crossing. I'm Still not totally clear on that point and also, if I remove the diodes in the sim then the jagged edge on peaks is gone. Of course it just square waves but the flat top peaks show no hash. A bit hard to compare because it hits the rails so early.
It's certainly and interesting subject.