peavey vegas mod

jim milewski · Post by **jim milewski** » 4 Oct 2002 7:51 pm

I got the mod sheets from peavey on the vegas and did it, a couple of questions...
1. I had the caps and resistors on hand already so I just did that part, caps 13 and 14 weren't caps but resistors so they stayed in, apparently my circuit board is different than the schemetic and parts placement sheet, should I pull the resistors and put caps in their place?
2. The op amps in there are RC4558's the change calls to put in TL072's and NE5532, what is the difference, Bifet, Jfet? how does this affect the tone? and why would one be prefered over the other? (My 500 has the TL series IC's and it has a great tone)
before the mod the amp had a certain harsh midrange, not real bad, but it was there, is this what the mod is supposed to eliminate? (I'm hoping) I haven't played it yet (my son is in bed)
Just curious if anyone has done this and what they found[This message was edited by jim milewski on 04 October 2002 at 08:53 PM.][This message was edited by jim milewski on 04 October 2002 at 08:55 PM.]

Ken Fox · Post by **Ken Fox** » 4 Oct 2002 10:26 pm

Are you sure those old parts were not just caps with color bands? You might lift one end off the board and check them with an ohm meter. I have seen those before, they look like resistors, but are not![This message was edited by Ken Fox on 04 October 2002 at 11:28 PM.]

jim milewski · Post by **jim milewski** » 5 Oct 2002 3:20 am

Ken, there are those style caps on the board, that look like resistors, these are classic resistors though, I'm thinking this is a revision to the circuit I have the schemetic for, I appreciate your help,

Ken Fox · Post by **Ken Fox** » 5 Oct 2002 7:34 am

If you don't get an answer here on the Forum, call Tech Services at Peavey. They will get you helped out. The support there is second to none!

1-877-732-8391, Peavey's toll free number

Tom Gorr · Post by **Tom Gorr** » 6 Oct 2002 6:56 pm

Jim,

Good questions.

I'd be interested in the answers you are able to drum up.

Please continue to post your progress if forumites are unable to directly answer your questions.

FYI - My own research into audio ap-amps led me to the conclusion that OPA2604's were the best combination of value and quality.

Thanks,
Tom

jim milewski · Post by **jim milewski** » 6 Oct 2002 7:33 pm

Tom, are the OPA2604 op amps same pinout, my guess is they are, maybe I will order those, so far if there is a change, it is minor, and some caps are 10 times the capacitance of the originals, I will post my progress, thanks

Tom Gorr · Post by **Tom Gorr** » 6 Oct 2002 9:41 pm

Jim,

Here is a link to the Burr Brown datasheets for the 2604.
http://www.schuro.de/Daten/Burr%20Brown/OPA2604.PDF

I own a Vegas 400, with the Peavey mod, but believe that there is still more clarity and sweetness to be found. To my understanding the op-amps used in the mod are not particularly "state of the art", but the kits are certainly affordable and a step up.

BTW:

a) The technical aspect of my "research" consisted of downloading and comparing technical specifications on about 8 or 10 different op-amps.

b) My "subjective test" was simple reliance on a survey of audiophile websites that compared op-amps for various audio applications. The 2604 was most cited as best bang for the buck.

c) Also, I am a mechanical engineer, and my dabblings in electronics are at best "trial and error", armed only with a healthy respect for 120V AC and some rudimentary theoretical background in basic circuit theory (which I don't make a point of applying anyway).

d) I have had 10 OPA 2604's sitting in my desk for 6 months, and I haven't plugged them into my Vegas 400 yet!!. If I actually decide to undertake this "experiment", for all I know, my amp may go into oscillation or give other problems.

Thinking of this, perhaps I will start another related thread.

Regards,
Tom

David Rich · Post by **David Rich** » 11 Oct 2002 12:26 pm

Does the Vegas have sockets for the op amps so you can just plug the new ones in?

jim milewski · Post by **jim milewski** » 11 Oct 2002 2:34 pm

the chips have sockets