Audioxpress Peavey upgrade article?

[Racket Scientist]

There was a couple of articles in AudioXpress (I think in '03) that detailed upgrading a Peavey TKO bass amp. I've been curious about it, but not curious enough to order a back issue. Anyone read that and can give me a summary? Thanks!

[kec]

I'll take a look and see if I have that issue. I'm not sure if I have '03 though.

[kec]

Sorry Racket, didn't find this article

[Racket Scientist]

I appreciate you looking for it. I've played around with "upgrading" some Peavey solid state guitar amps by replacing opamps and diodes, and have no real need to do any more of that, but just curious what others have done along those lines.

[HK26147]

It was a 2 part series:
Oct2003/Nov2003 by Charles Hansen and G.R. Koonce
Part 1 covered driver swaps
Part 2 was circuit mods.

Syd

[Racket Scientist]

Thanks for the info. Can you give a few more details? Was the goal higher fidelity, more output, more "musical" sound? Any of this generalizable to other Peavey solid state amps, or mostly peculiar to the TKO? Could you give a quick synopsis of the mods? Thanks again.

[HK26147]

From the article's conclusion:
"I am quite happy with the performance of this restored/modified TKO 80. Restoration was a big investment of time, and the not-insignificant amount of $270. Whether or not it was cost effective is up to debate. You can buy a brand new 50W Peavey Basic 112 bass amp for $360, with a 12" driver in a ported enclosure with more preamp features."
"Despite the performance problem with the (Phoenix Gold) QX108(driver),I had a lot of fun, and gained a tremendous amount of knowledge and experience about driver selection....My TKO 80 nows sound the way I want it to sound"

Overview:
The goal was to take a "pawn shop find" and restore and improve performance and functionality.
After evaluation of 15 drivers - the aforementioned driver (QX108) was initially selected based upon published T/S specs. Unfortunately the measured actual specs were too far off to be usable. A Peerless 850146 was used instead.
The TKO 80 amp is a quasi-complementary (QC) output stage, originally patented in 1956. In contrast to modern amps that use complementary-symmetrical output stages.
The authors spent a lot of focus dealing with the intrinsic issues of the QC design.
Modifications included:
All aluminum caps were replaced. Ceramics were replaced with polyester.
The preamp performance was improved and flattened with improving accuracy of the tone controls.
Power supply mods included replacing and increasing cap values 2X, diode replacement/Up-spec with additional cap mods to lower noise.
Mods to the amp proper were around the output stage to improve QC design flaws and lower distortion and improve performance linearity.
The modification list:
32 caps, 7 diodes, 2 transistors, 10 resistors
( * a dual-op amp had been replaced prior )

Syd

[Racket Scientist]

Thanks so much. Sounds like not much of this is generalizable to many other amps. I've experimented a little with upgrading Peavey solid state stuff, but limited to just upgrading the quality of some of the parts and replacing op amps with lower noise models and such.

[HK26147]

Originally Posted by Racket Scientist

Thanks so much. Sounds like not much of this is generalizable to many other amps. I've experimented a little with upgrading Peavey solid state stuff, but limited to just upgrading the quality of some of the parts and replacing op amps with lower noise models and such.

It's beyond a POOGE and requires some engineering skill ( Douglas Self provided suggestions )
From the article:
"The only other amp I could find with this topology is the 1970s Gibson SG-812"