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Gear / Technical Help => Battery Boxes, Preamps, Mixers, ADCs, and Processors => Topic started by: poorlyconditioned on January 13, 2006, 06:54:47 PM

Title: DIY UA5 opamp mods
Post by: poorlyconditioned on January 13, 2006, 06:54:47 PM

Hi there, I just did some DIY UA5 mods.  It was a lot easier than I though.  I put in qty. 2 of LT6231 for the mic pres and qty. 2 LT6201 for the buffers.

I'll post some pictures showing this.

Some tips:
- surface mount parts can be removed easily by using copper "solder wick" to remove all the solder, then just (carefully) lift them off the board.
- make sure to solder new parts down completely.  I put too little solder on some of the tabs the first time.

Observations:
- Completely silent at full gain (mic and headphone) with an SM57 connected.
- Quality of sound TBD (next week)

Pictures and samples to follow.

  Richard

Title: Re: DIY UA5 opamp mods
Post by: aberg on January 13, 2006, 07:19:30 PM

Is this using my old ua-5, or a different one?

Title: Re: DIY UA5 opamp mods
Post by: poorlyconditioned on January 13, 2006, 08:00:11 PM

Quote from: aberg83 on January 13, 2006, 07:19:30 PM

Is this using my old ua-5, or a different one?

No, I'm working on mine.  I had different opamps in it last night too.  I'm living on the edge.

(I'll PM you if/when I do anything to yours...)

  Richard

Title: Re: DIY UA5 opamp mods
Post by: poorlyconditioned on January 15, 2006, 04:21:21 AM

Quote from: poorlyconditioned on January 13, 2006, 06:54:47 PM

Hi there, I just did some DIY UA5 mods.  It was a lot easier than I though.  I put in qty. 2 of LT6231 for the mic pres and qty. 2 LT6201 for the buffers.

I'll post some pictures showing this.

Some tips:
- surface mount parts can be removed easily by using copper "solder wick" to remove all the solder, then just (carefully) lift them off the board.
- make sure to solder new parts down completely.  I put too little solder on some of the tabs the first time.

Observations:
- Completely silent at full gain (mic and headphone) with an SM57 connected.
- Quality of sound TBD (next week)

Pictures and samples to follow.

  Richard

OOPS!! Don't use the LT chips above!!

I just tried it out tonight and for some reason it distorts *before* the -3dB level.  Everything just tops out there.

I have no idea why.  The chips must have some different spec (bias current?).  Maybe they are not "unity gain stable".  I don't know.

But I wasn't content to leave it at that.  So, I put in two OPA2228 chips on the front end, and the following two chips are AD8620.  Those seem to sound fine.  The OPA2228 is a "Burr-Brown" chip, optimized for gain 5 and above.  Seems good for a front end.  The second two could probably be anything, maybe even the original 4570 would be fine.

Results: Well, there is a lot less noise on the input.  And it sounds clear.  I'll have to run some shows to know for sure.

By the way, if anyone out there (Busman, Oade, or others) is willing to disclose their "secrets", feel free to speak up.  Otherwise I'll just go with what I got now.

Thanks,
  Richard

Title: Re: DIY UA5 opamp mods
Post by: cybermansrev on January 15, 2006, 02:31:48 PM

Thanks for keeping us informed of your "experiments", for those with an uncontrollable urge to tinker.
+T