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Author
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Topic: Op-Amp "Mod" Survey (for Peavey 400's)
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Tom Gorr
Member From: Three Hills, Alberta
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posted 06 October 2002 11:10 PM
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For those electronics buffs/audiophiles who have tried experimenting with different op-amp selections in their Peavey products:As indicated on a previous thread, I am considering "test driving" OPA 2604's as a swap out replacement for the IC's provided in the standard Peavey Vegas 400 Mod kit. Q1: Please share any experience(s) with trials of different op-amps in your Peavey amps, including a description of the change to the sound and some technical explanation for the change in audio performance. Q2: What problems are reasonably expected to be encountered when test-driving different op-amps? Q3: What are the issues that I could expect to encounter when testing OPA 2604's? Regards,
Tom |
Mike Brown
Member From: Meridian, Mississippi USA
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posted 07 October 2002 07:27 AM
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Hello Tom,
The highly respected Burr Brown OPA2604 integrated circuit "is" a part of the Vegas 400 mod kit. Not all IC's in the circuit require the replacement chip, only those in the signal path.
Mike Brown
Peavey Electronics Corporation[This message was edited by Mike Brown on 07 October 2002 at 07:28 AM.]
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jim milewski
Member From: stowe, vermont
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posted 07 October 2002 08:33 AM
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Tom, why don't you install those OPA's as you have them sitting there, they ain't cheap at nearly 4 bucks a pop, 85 cents for the TL072's, if you open it up look at caps 13 and 14, right by the high pot, I have resistors what's in yours |
Glenn Austin
Member From: Montreal, Canada
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posted 07 October 2002 08:33 AM
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Hi Tom, I've got the Lemay mod in my Vegas 400. The Lemay mod changes the gain structure in the amp. Also , it doesn't use 2604 chips, but some other high end audio amplifier, the model number escapes me but I do know they are not class A like the 2604. As a result, the amp sounds a bit sweeter, but the reverb sounds awful now. I am seriously considering putting the amp back to stock. Some guys rave about this mod, but I just can't seem to understand what all the fuss is about. The opamp upgrade will probably make the amp sound sweeter, but if I were you, I wouldn't mess with any gain structure changing components, like feedback caps and resistors. A reCap with high quality electrolytics would probably be a good bet with a twenty year old amp, and probably do more for the sound quality. I have recapped some old pre's and compressors, and the results have been great. |
Keith Hilton
Member From: 248 Laurel Road Ozark, Missouri 65721
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posted 07 October 2002 08:56 AM
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Tom, the 2604 is a great chip. It is the dual version of the 604. I use the 604 as one of the chips in my infrared pedal. These are Burr Brown chips, but Texas Instruments bought out Burr Brown. If you are looking for some other chips to try, I suggest looking at some Analog Devices chips. In my opinion Analog Devices have some of the best sounding chips made. As for price, you get what you pay for,usually. |
Donny Hinson
Member From: Balto., Md. U.S.A.
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posted 07 October 2002 09:05 AM
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Glenn, if you're happy with the sound of the amp, then there's no point in changing it. On the other hand, players sometimes want a fuller sound, with more low end. (The un-moded amps are definitely lacking in low end response.) Now, if you're a player who doesn't use all the bass he has at present, and tends to run your mids up near 11:00 then you're right...it's no big deal. But, if you like solid "fat" tones...the ones you get from turning the mids almost completely off and the bass wide-open, you gotta have the mod! In short, if you prefer the high thin sounds...like Mooney, Brumley, or Emmons Black-Album, or even sounds that are typical in today's music ("heavy midrange" tones), then the mod will do little or nothing for you. |
jim milewski
Member From: stowe, vermont
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posted 07 October 2002 10:14 AM
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Do the chips change tonality or lower noise or both, only 5 are in the signal path, not counting on board reverb which I don't use, so I would go for best linear reproduction, I play E9th only (no cop out neck for me, ....only kiddin, only kiddin) so the amp has all the lows I need, anyway my mod is complete except for the chip change, I got digi-keys number and ready to dial when I hear from you experts, I'll let you know my findings... |
Glenn Austin
Member From: Montreal, Canada
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posted 07 October 2002 12:13 PM
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Thanks Donny, I'll try those settings out tonight. My amp does sound better, it's just that the reverb sounds real distant and hissy now.. I have changed out that chip, for a new one and still the same thing. Who knows, I'll call you guys The Mod Squad! |
Tom Gorr
Member From: Three Hills, Alberta
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posted 14 October 2002 11:01 PM
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Gentlemen:Finally made time to swap out existing op-amps with 2604's. Per Mike Brown the 2604 is the current recommended op-amp upgrade. Note: this amp had been upgraded by the previous owner, using TL072's and one NE5532. Resistors and Caps already matched the current specs. These are the things that I think have changed based on a very subjective before and after comparison:
1) slightly less amp noise.
2) EQ setting preferences may have changed slightly. Seem to now prefer to set the "mid-shift" in the 12 o'clock position rather than at 2 o'clock.
3) the mids are sweeter, I believe.
4) overall sound, especially the low end, sounds more articulated. Overall, I believe that there was some improvement over the former TL072's chips. For Mike: The mod instructions indicate that C39 was to be changed from a 2.2 uF to a 22 uF capacitor, yet the original schematic indicates that the 22 uF was standard already. Could you look into and clarify the intended design change. Jim: Per your question - I had capacitors, not resistors. Thanks.
Tom
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jim milewski
Member From: stowe, vermont
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posted 15 October 2002 03:02 AM
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I finished my mod and don't really notice much of a change, maybe side by side would reveal the improvement, the components I thought were resistors proved to be caps and I made the change there, it still doesn't match my 500 for tone, it has a BW 1502 in it |
Glenn Austin
Member From: Montreal, Canada
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posted 15 October 2002 07:46 AM
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My sentiments exactly, Jim |
Tom Gorr
Member From: Three Hills, Alberta
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posted 22 October 2002 05:02 PM
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Gents:Just wanted to update you on my OPA 2604 upgrade... I've played with the amp for a week now, and every time I light up the strings, I am totally impressed with the improvement. I think this is the first time I have been satisfied with my sound. Sweeeeeet! I am 100% convinced that the OPA 2604's were a worthwhile investment. Again, this was the amp's second mod/upgrade - the first had TL072's which were probably heavenly compared to the stock 4558's. These chips are "must haves", particularly for C6 and U12 players. Tom MSA U12/Vegas 400 | |
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