anyone use UTC A-25 in LA2A?

I scored a old preamp on Ebay a few weeks back that had an HA-100x and an A-25.
They both test good and the A-25 is in new condition. Before selling it off in favor of a more expensive A-24 I wonder if anyone has used it before, especially anyone with experience with the LA2A or any comparisons or anything. The A-25 specs are similar on paper.

It's on the list.

http://www.groupdiy.com/index.php?topic=6518&highlight=projects

use it, sell the other one.

would you agree to tell us the brand and model of this preamp ?

Hint: they are on ebay every week practically, and they are always hacked up for the iron.  They are perfectly good classic preamps, and I doubt there will be any left before long.    I see no reason to make it any easier to hasten their demise.  Anyone watching ebay at all should be able to find one with a few weeks watching.  They usually sell for the value of the iron, so there's no deal to be had most times.   

would you agree to tell us the brand and model of this preamp?

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I don't think it's much of a secret, some of the old IPC Preamps have HA-100/A-25.
On ebay they usually sell for about the same as the value of the transformers, unless you find a banged up one for cheap such as the one I bought.

thanks for the hints,
as a french guy i don't know a lot about these old US preamps,
I think i should study american radio gear from the 40's till now ! ;-)
Regards,
Francois

You won't find much US gear with stock off the shelf transformers, but worth studying all the same. 

Back to the original question....... Yes I have used a UTC A-25 on my 2nd LA2A build. As I recall the Specs stated the Frequency range cuts off slightly higher than the A-24. Although I can't say it had an adverse effect on compressing Kick Drum or Bass Guitar, However with that spec in mind I do have a tendency to use it more on guitars and vocals and I tend to use the 1st LA2A with the A-24 on Drums and Bass. Actually, These 2 LA2A builds each have A-10s on the input. If anything I tend to notice more of a difference (Gain settings) between the older "Black" A-10 and the Newer "Gray" A-10.  I don't think the A-25 is a bad choice, it may slightly color your low end response. Hope this is of some help to you on the build.... Good Luck on the Build!
Take Care,
Shawn

SAnthony said:

Back to the original question....... Yes I have used a UTC A-25 on my 2nd LA2A build. As I recall the Specs stated the Frequency range cuts off slightly higher than the A-24. Although I can't say it had an adverse effect on compressing Kick Drum or Bass Guitar, However with that spec in mind I do have a tendency to use it more on guitars and vocals and I tend to use the 1st LA2A with the A-24 on Drums and Bass. Actually, These 2 LA2A builds each have A-10s on the input. If anything I tend to notice more of a difference (Gain settings) between the older "Black" A-10 and the Newer "Gray" A-10.  I don't think the A-25 is a bad choice, it may slightly color your low end response. Hope this is of some help to you on the build.... Good Luck on the Build!
Take Care,
Shawn

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They don't necessarily roll off earlier than the 24s or 26s . . . . that number is for the max specified conditions for direct coupled output use, which was what is was designed to accommodate.  That being said,  it's deja vu - similar question today regarding the HA equivalent in another post and I'll echo emrr's advice there:  save it for circuits that require it.  Outside of that, impedance specs are the same.  Someone may have measured some A-25s under AC only - likely better than the catalog number.

azone said:

I scored a old preamp on Ebay a few weeks back that had an HA-100x and an A-25.
They both test good and the A-25 is in new condition. Before selling it off in favor of a more expensive A-24 I wonder if anyone has used it before, especially anyone with experience with the LA2A or any comparisons or anything. The A-25 specs are similar on paper.

Click to expand...

The A-25 still seems to go a little cheaper than the 24.  Given the LA2A circuit I would certainly give thought to trying an Edcor 10K:600 - and be happy when it sounds great knowing you didn't cough up 250.00 for the overpriced A-24.   

The A-25 still seems to go a little cheaper than the 24.  Given the LA2A circuit I would certainly give thought to trying an Edcor 10K:600 - and be happy when it sounds great knowing you didn't cough up 250.00 for the overpriced A-24.   

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+1. Mine sounds great.

someone can explain me how to wire the A-25 please?

I've used the A25 a few times as input traffo in limiter builds - a fairchild 660 type and an rca ba25 type ...

It does indeed rolloff the low end a little early - I found it to do  -3dB at something like 50Hz - a bit worse than the published spec
High end is fine. Not usable as a inter-stage unless driving Z is very low. Quite good for THD and overload performance.

It's VERY sensitive to placement and orientation - even with the uber-pricey shield. It needs good seperation from psu traffo.
However, with trial and error, one can find a good positioning and give good performance.

I wouldn't use without a shield if there is a non-toroidal psu traffo nearby. Might be OK with a toroid .. maybe.

I should also say I get similar result for the A25, A35 and A15 which are all 'cheaper' compromises to the A24 (which I havent used).

OK if cheaply sourced, but for inflated prices now common,  not worth bothering with - go with something good  ;D  like a sowter, jensen, cinemag etc.

The Sowters I've used  in this role show near perfect behaviour as do the Jensens and Altec

Wiring is generally the lowZ winding(s) in series for 500ohms nominal, and the highZ windings in series for 15Kohms nominal.
For the LA2A, centre-taps are not used.

Hi alexc thank you for your detailed answer

I forgot to precise, I want use it for output because I have a-10 for input

A-24 : 20hz to 40Khz - 1st Choice
Sowter : Full Bandwidth, always fine, but not vintage..
A-25 : 40hz to 20khz - Max +15dbm : Very fine, but not top specs.