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Author Topic: UA5 pre amp mod instructions  (Read 4536 times)

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Offline bobc

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UA5 pre amp mod instructions
« on: April 08, 2006, 03:07:01 AM »
I would like to DIY the UA5 oade or similar pre-amp mods. Would be better if the TRS inputs on the Neutriks were left available - but not a necessity. Does anybody have instructions for these mods please?

Offline poorlyconditioned

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Re: UA5 pre amp mod instructions
« Reply #1 on: April 08, 2006, 03:12:18 AM »
I would like to DIY the UA5 oade or similar pre-amp mods. Would be better if the TRS inputs on the Neutriks were left available - but not a necessity. Does anybody have instructions for these mods please?

It is not the OADE mod, but it improves the sound:
  http://www.cs.uwaterloo.ca/~mannr/UA5/ua5_poorlymodded.jpg

/begin{geek speak}
- digimod (described elsewhere)
- replace four i4580 chips with AD8620 or AD712.  (I used AD712 for the mic pres, AD8620 for the ADC drivers).
- replace eight 1uF/50V aluminum caps with four 0.47uF poly caps.  (Note: you replace two series 1uF caps with a single 0.5uF cap, which is equal, but you disable the TRS inputs in the process.)
- replace two 22uF aluminum caps near ADC with higher quality electrolytic bypassed with 0.1uF poly or film cap
/end{geek speak}

You should be able to follow those steps on the (big!) image I've linked to.

  Richard

« Last Edit: April 08, 2006, 03:14:28 AM by poorlyconditioned »
Mics: Sennheiser MKE2002 (dummy head), Studio Projects C4, AT825 (unmodded), AT822 franken mic (x2), AT853(hc,c,sc,o), Senn. MKE2, Senn MKE40, Shure MX183/5, CA Cards, homebrew Panasonic and Transsound capsules.
Pre/ADC: Presonus Firepod & Firebox, DMIC20(x2), UA5(poorly-modded, AD8620+AD8512opamps), VX440
Recorders: Edirol R4, R09, IBM X24 laptop, NJB3(x2), HiMD(x2), MD(1).
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Offline bobc

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Re: UA5 pre amp mod instructions
« Reply #2 on: April 09, 2006, 12:59:15 AM »
Richard,
Thanks very much for the info. Essentially it is an upgrade to better op-amps and caps. I don't understand the term "bypassed" as in the image it appears as though the last two cap change outs are a 100uf and 120nf set up in parallel - am I looking in the right place? Sorry if I have the values wrong - haven't got a cap conversion chart with me.
Regards,
Bob

Offline poorlyconditioned

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Re: UA5 pre amp mod instructions
« Reply #3 on: April 09, 2006, 01:43:49 AM »
Richard,
Thanks very much for the info. Essentially it is an upgrade to better op-amps and caps. I don't understand the term "bypassed" as in the image it appears as though the last two cap change outs are a 100uf and 120nf set up in parallel - am I looking in the right place? Sorry if I have the values wrong - haven't got a cap conversion chart with me.
Regards,
Bob

Bypass means put two caps in parallel.  Yes, 100uF || 120nF.  120nF is my approx for 0.1uF=100nF.

Enjoy it.  And post photos if it works for you.

Hint: to remove surface mount opamps, use a thin tip soldering iron and copper "solder wick".  Remove all of the solder, the use a small screwdriver to *gently* "peel off" the chip.  Don't do this too many times, though, or you'll damage the traces on the circuit board.

  Richard
Mics: Sennheiser MKE2002 (dummy head), Studio Projects C4, AT825 (unmodded), AT822 franken mic (x2), AT853(hc,c,sc,o), Senn. MKE2, Senn MKE40, Shure MX183/5, CA Cards, homebrew Panasonic and Transsound capsules.
Pre/ADC: Presonus Firepod & Firebox, DMIC20(x2), UA5(poorly-modded, AD8620+AD8512opamps), VX440
Recorders: Edirol R4, R09, IBM X24 laptop, NJB3(x2), HiMD(x2), MD(1).
** This individual has moved to user "illconditioned" **

Offline bobc

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Re: UA5 pre amp mod instructions
« Reply #4 on: April 10, 2006, 03:25:33 AM »
Thanks Richard,
Bob

Offline cybermansrev

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Re: UA5 pre amp mod instructions
« Reply #5 on: April 18, 2006, 10:47:53 AM »
- replace four i4580 chips with AD8620 or AD712.  (I used AD712 for the mic pres, AD8620 for the ADC drivers).
Just curious Richard why did you choose to use 2 different op amps?

Offline poorlyconditioned

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Re: UA5 pre amp mod instructions
« Reply #6 on: April 18, 2006, 11:24:55 AM »
- replace four i4580 chips with AD8620 or AD712.  (I used AD712 for the mic pres, AD8620 for the ADC drivers).
Just curious Richard why did you choose to use 2 different op amps?

Because when I got samples, I could only get two of each type :)

The 8620 are better opamps, but I only got two.  They appear most suited for line-level drivers anyway.  The 712 would work for both line and mic level signals.  I *think* this is true, though I only know only a little about opamp details.  It should work with 712's or 8620 all the way too.  The rumour is that 712 are "warm" and 8620 are "transparent", whatever these terms mean.  Anyway, *anything* is better than those 4580's that are in stock unit!

 Richard
Mics: Sennheiser MKE2002 (dummy head), Studio Projects C4, AT825 (unmodded), AT822 franken mic (x2), AT853(hc,c,sc,o), Senn. MKE2, Senn MKE40, Shure MX183/5, CA Cards, homebrew Panasonic and Transsound capsules.
Pre/ADC: Presonus Firepod & Firebox, DMIC20(x2), UA5(poorly-modded, AD8620+AD8512opamps), VX440
Recorders: Edirol R4, R09, IBM X24 laptop, NJB3(x2), HiMD(x2), MD(1).
** This individual has moved to user "illconditioned" **

Offline cybermansrev

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Re: UA5 pre amp mod instructions
« Reply #7 on: April 19, 2006, 11:09:40 AM »
Because when I got samples, I could only get two of each type :)
It's all becoming a bit clearer now!
I might have a go with 712's as I seem to be able to get hold of them in the UK, provided I can get access to a friends solder station with magnification.
Did you also write in another thread that your mod disables the 1/4" TRS inputs? If so how come if all you've done is replace the op amps and the caps?

Offline poorlyconditioned

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Re: UA5 pre amp mod instructions
« Reply #8 on: April 19, 2006, 12:42:54 PM »
Because when I got samples, I could only get two of each type :)
Did you also write in another thread that your mod disables the 1/4" TRS inputs? If so how come if all you've done is replace the op amps and the caps?
I did not describe the mod in detail.  You'll have to figure it out from the picture, I'm afraid.

Note that I put in 0.47uF poly caps instead of 1uF.  In effect, I've put in 1/2 of the capacitors, and the TRS are the ones that are omitted.

  Richard
Mics: Sennheiser MKE2002 (dummy head), Studio Projects C4, AT825 (unmodded), AT822 franken mic (x2), AT853(hc,c,sc,o), Senn. MKE2, Senn MKE40, Shure MX183/5, CA Cards, homebrew Panasonic and Transsound capsules.
Pre/ADC: Presonus Firepod & Firebox, DMIC20(x2), UA5(poorly-modded, AD8620+AD8512opamps), VX440
Recorders: Edirol R4, R09, IBM X24 laptop, NJB3(x2), HiMD(x2), MD(1).
** This individual has moved to user "illconditioned" **

Offline cybermansrev

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Re: UA5 pre amp mod instructions
« Reply #9 on: April 19, 2006, 01:04:44 PM »
I get it now!
Thanks

 

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