Improving Peavey Decade

[MCM1910]

I have this little amp which seems to be so well built and sound pretty good. I find the saturation input to be really harsh though and I'm wondering if there's somethings I can do to improve it. It seems to me that the saturation input simply has a transistor boosting the signal into the opamp? Is this correct. I also see three pairs of diodes I the same signal with one set going to ground as hard clippers. Could I take these out or make them switchable? Would changing the diodes to LEDs or germaniums smooth it out?

Thanks in advance!

[Enzo]

Nope, look again.  There is no signal going to the transistor.  The base is wired to the jacks, but all that does is ground or unground R2, which in turn turns on and off Q1.  Q1 more or less turns on the four diodes in the feedback loop of that op amp.

CR1,2 are not involved in audio, they are reverse bias to the power rails from the input p[in.  All they do is prevent the input signal from going past the power supply voltages into the IC.  The other four are indeed clipping and you could experiment with other types if you like.

Just my opinion, but while we could fool around with it and maybe yes, maybe no, get it to sound better.  I think if it were mine, I'd run it through the clean jack and just find a pedal I like for overdrive.

[J M Fahey]

That little amp actually sounds VERY good as is,
https://www.youtube.com/watch?v=-k3XGV_di3k
the only problem it has is not electronic (so you won´t solve it by tweaking the electronics)  but acoustic: it has a very small, light speker i nside an open backed shoebox sized cabinet ... absolutely no bass and very little "warm"  low mids, so n o surprise clean sound is bright and jangly asshown in the video, that speaker is almost a tweeter, but buzzy thin with distortion.

Whay I suggest is that you drill the back panel and add a *plastic*  ("Marshall type") speaker jack, which when unused still sends sound to internal speaker, but allows you to plug an external "real"  cabinet ... day and night.

If you are on  tight budget, you can get a good speaker for cheap on local Craigslist , lots of people upgrade their amps from original speaker (which is still very good) to a shiny fancy Celestion/Jensen/"good" Eminence/etc. and have no use for the prfectly good they just pulled.

I have seen people buy a Factory original 12" speaker (usually made by Eminence) labelled Fender/Peavey/Crate/unlabelled for U$20 or so.

You can build a simple cabinet for peanuts, or become creative, I have seen inexpensive IKEA magazine holders or whatever turned into cool guitar cabs, same with any older dusty furniture piece you find in your attic.
Or any old piece of luggage:


Just as an example, here is how a simple crummy Smokey amplifier: 1/2W 9V battery powered **NO CONTROLS** amplifier sounds when hooked to a real cabinet, you´ll be surprised:
https://www.youtube.com/watch?v=og_RiEB-74U
https://www.youtube.com/watch?v=1KSWa7N1xGY
what you have is WAY better than the Smokey

[MCM1910]

Thank you for your explanation. What about cr5 and 6. Aren't those clipping to ground? So if I'm understanding you right when plug into sat input the diodes in feedback loop are turned on and create the clipping. When I'm plugged in to the regular input and it is clipping am I then hearing more cr5 and 6?

[Enzo]

CR5,6 are ALWAYS across the signal path, even on clean.   In clean you can clip the amp in multiple places.  I think CR5,6 are more about limiting signal amplitude at that point.  I could be wrong.

[J M Fahey]

That Peavey (and many others,including old Bandits) had 2 ways to distort.

1) to simulate power amp clipping but at a lower level, they added a couple diodes, CR5/CR6 , just before the master, and gave power amp such a gain factor that when power amp clipped against the rails those diodes also started clipping.
So if you rise volume enough to clip power amp and it´s too loud, you lower master volume and "nothing changes", a standard ss amp clipping and a couple diodes clipping are not that far from each other.
Somewhat dull distortion but usable.

2) to have a stronger harder distortion they had to add clipping diodes near the input, to behave similar to a pedal, enter CR3/4/17/18 , which work in a different way.

If Q1 is open, none of them works.

If Q1 grounds them, they can clip if signal surpasses 700mV peak, BUT:
CR17/18 work like in most pedals, clipping output to ground, all frequencies tye same.

CR3/4 are more subtle:
* as  I see them they soft clip and round peaks ,because they are in series with R41, also C7 cuts the clipped top highs, I guess the combination was designed to give a smoother somewhat crunchy sound.

So now you see it, Peavey DID try to smooth sound ... only problem is the tiny peaky speaker does not help.

[MCM1910]

Thanks very much for the explanation. I had replaced the speaker with a Jensen mod for awhile but it was still an 8" so maybe I'll try to get another larger 10 or 12" and build a cab

[J M Fahey]

Just curious, what difference did you notice between the original Peavey speaker and the Jensen Mod?