Burr Brown Peavey Mod Question

Steve Stallings · Post by **Steve Stallings** » 10 Feb 2005 7:30 am

I've got an email in to amp guru Ken Fox, but I thought I'd throw this up here as well.

Ken is doing the battery chip mod for me on both my Profex II and Tubefex at the TSGA. I'm thinking about the Burr Brown Chip mod as well. Real world, does this make a big difference? I'm not using either of these units live at present as I'm using an Evans Stereo Preamp into a TC Electronics M-One, but if I could get similar quality with the Profex II or Tubefex, it would eliminate one item from the rack.

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God Bless,
Steve Stallings

Tom Gorr · Post by **Tom Gorr** » 11 Feb 2005 6:49 pm

Here's my experience with Burr Browns in my Vegas 400. I don't know how this would translate on the TubeFex, etc., as those units have a bunch of AD/DA conversion mid-path...

On the Vegas, there was more than just replacing the IC's from what I remember. Seems to me the voicing is changed too through some resistors and cap replacements.

However, to your queston - When I first got my Vegas 400, it had TLO72's. After I put in the Burr Brown 2604's it made a very subtle, but very noticeable improvement to the timbre.

Prior to, I found the sound "hard" and not particularly enjoyable. After, it was "sweet". The sound is virtually indistinguishable if not preferably to a tube preamp, from what I've been able to tell when comparing with my Mesa Formula Pre into the power amp section of the Vegas.

If I recall correctly, I bought a set of 10 OPA2604's for Cdn$40. Pretty cheap. Just go for it.
[This message was edited by Tom Gorr on 11 February 2005 at 06:52 PM.]

Bob Metzger · Post by **Bob Metzger** » 19 Feb 2005 7:03 am

I, like Tom, changed out ICs while at the same time I altered some cap values so isolating the effect of the ICs alone was not possible. The amp in question, a Nashville 400, improved drastically.

Bob M.[This message was edited by Bob Metzger on 19 February 2005 at 07:04 AM.]

Jack Stoner · Post by **Jack Stoner** » 19 Feb 2005 8:47 am

I've done the chip "mod" to several Profex II's. It is a big improvement in the sound quality and lowers the noise.

However, I had a Nashville 400 that had the tone mod installed by the factory (an early mod) but it did not have the OPA op-amps in it. I have a friend that had a Nashville 400 with older op-amps too. We bought the OPA's and installed them in our amps. Neither of us could tell a difference, and we are both electronic techs.[This message was edited by Jack Stoner on 19 February 2005 at 12:57 PM.]

James Quackenbush · Post by **James Quackenbush** » 21 Feb 2005 3:55 pm

I've had various mixing boards and various mic pre's that had Burr Brown upgrade Op amps, and the difference was like night and day ....If the difference is that drastic in the ProFex it's worth the money to do ......Jim

Ken Fox · Post by **Ken Fox** » 25 Feb 2005 9:10 am

Well, I bit the bullet and ordered 100 of these this morning. I have had a lot of request for them and need to offer that option with the memory upgrades I offer for the Profex 2 and Bassfex.

Peavey has these chips at a very reasonable price for those who want to upgrade themselves. I will not be selling the chips outright, just installed. I just wanted to add that as an option while folks have there Profex 2 or Bassfex here for memory chip (batteryless mod!) upgrade. The Burr Brown chips are not for the Tubefex or Transtubefex, just the memory chip mod is all I can do for you there.

I can tell from units I am repairing that they are quieter with the Burr Brown chips.
[This message was edited by Ken Fox on 25 February 2005 at 01:58 PM.][This message was edited by Ken Fox on 25 February 2005 at 01:58 PM.]

Mike Brown · Post by **Mike Brown** » 25 Feb 2005 11:38 am

The Burr Brown IC's are quieter. It was our intention to offer these quieter chips with our mod kits.

Ken Fox · Post by **Ken Fox** » 25 Feb 2005 1:54 pm

Thanks, Mike. I thought that was the case. I have noticed that difference for sure on units I have had in lately. I was talkin gwith Bud Harger, he has two units. He said the one with the Burr Brown chips even sounds better to his ear!

Brad Sarno · Post by **Brad Sarno** » 25 Feb 2005 2:04 pm

The Burr Brown x604 series chips are great. I've done audio mods with them for years. They are FET based and have a very clean and silky sound. They are among the best sounding opamps around. They're not just quieter, but they sound more musical.

Brad Sarno

Paddy Long · Post by **Paddy Long** » 26 Feb 2005 2:12 am

Is this similar to the lemay mod for the Profex II ??

Bill Crook · Post by **Bill Crook** » 26 Feb 2005 6:34 am

Very much so.......

Eventho the LeMay mod had the replacement chips ID numbers removed and the chips painted with red fingernail polish,

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Ken Fox · Post by **Ken Fox** » 26 Feb 2005 6:50 am

Yes the Peavey and Lemay mods were Burr Brown chips. I charge extra for the optional fingernail polish!

Jack Stoner · Post by **Jack Stoner** » 26 Feb 2005 7:24 am

But, credit needs to be given to John Lemay for the original engineering of the "mods" (but not the OPA chips).

In the component "obliteration", Goodrich also does that. The chip markings are gone in my MatchBro.[This message was edited by Jack Stoner on 26 February 2005 at 07:27 AM.]

basilh · Post by **basilh** » 26 Feb 2005 12:48 pm

A big improvement in the Profex II regarding noise..
Thanks Mike Brown and Peavey..

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Steel players do it without fretting

http://www.waikiki-islanders.com

ajm · Post by **ajm** » 1 Mar 2005 8:08 pm

Are these a drop in replacement for a 4558 dual op amp?

Does anyone have a source for these that they can recommend?

Thanks in advance.

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Artie McEwan

Bob Lawrence · Post by **Bob Lawrence** » 1 Mar 2005 9:51 pm

Jack,

I hate it when companies do that. I don't know how many versions there were for the MatchBro but the info below should help.
============================================
Motorola MC34182P Low Power, High Slew Rate, Wide Bandwidth, JFET Input Operational Amplifier.
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Transistor : J113 = NTE469
Industry Number : J113
NTE Device Number: NTE469
JFET-N-CHAN CHOPPER/SW, TO-92

============================================
Transistor: MPSA18
NTE Device Number: NTE47
T-NPN,SI LO NOISE AMP,TO-92
============================================

Anything else you need?

James Quackenbush · Post by **James Quackenbush** » 2 Mar 2005 11:26 am

Ken,
I didn't know you used fingernail polish

Jack Stoner · Post by **Jack Stoner** » 11 Apr 2005 10:28 am

Bob,

Thanks for the info. I don't know if that matches up with the model I have or not. My MatchBro is the original model, with the tone control in the bypass.

Ken Fox · Post by **Ken Fox** » 11 Apr 2005 12:50 pm

Just pink, James!

Tom Gorr · Post by **Tom Gorr** » 12 Apr 2005 6:33 pm

I would also like clarification if the OPA2604 is a drop-in replacement for a 4558.

I think I recall that the 2604 is a drop-in replacement for the TL072, but thought that going from a 4558 may require some circuit tweaking. Also recall increased potential for oscillation with the 2604 which may need some snubbers added.

Ken Fox · Post by **Ken Fox** » 13 Apr 2005 7:32 am

Good point, Tom. I was also told that by Peavey tech support. I wanted to replace the TLO74 chips in a Mace VT. I left them alone!

Just put several Burr Brown mods in the last few days and I can hear the difference in white noise level for sure. They are much quieter.

I just modded the output of a Bassfex (same as Profex 2)to double its output (a 10K resistors in parallel with both R910 and R922). It clearly doubles the output level, as I verified that with the scope and a 1000 Hz tone. To my ear it improves the signal to noise ratio as well. Makes sense, as you are increasing the amplification of the final output stages.