I have an amplifier that has a 1 volt input sensitivity with a 15K input impedanxce and I need the input sensitivity to be lower.

I have a pair of Edcor 15K balanced/unbalanced to 15K balanced/unbalanced transformers and was wondering if that would work good for what I need?

I could wire the primary and secondary in series which will make it like an auto transformer. Input would go to 1/2 of the primary and I would have three fixed gain taps. I could either put a 10K volume control before the transformers or after the transformers.

Another option would be to go with a single FET per channel which would permit me to use the 100K ALPS pot I already have and in all actuality would be simpler as I don't have to drill any extra holes in the amp case. I have + and _ 15 volts to power the FET. Don't really want to use an OP-AMP if I can help it.

Well, I would think that a good quality audio opamp would be better than a single FET. Why are you opposed to it?

A single FET would be easier to put in the circuit than an OP-AMP would.

Maybe, although, by the time it's all said and done I'm not so sure it turns out that way. It depends on how much gain and just how 'good' you want the preamp. With an opamp that's already 'done' and you've got the +- 15 V supplies.

Taking a wild swag at a simple generic FET common source amplifier you'd probably end up with something on the order of .1% distortion, nominal, at 5x gain. Less with less gain, more with more. That's not necessarily 'bad', although I'm not sure that could be maintained with a 15k load, but a good audio opamp would be transparent. Just plop a couple of resistors around it to set gain and, poof, you're done.

But to get less distortion with discretes you'd probably need to start adding things like maybe a constant current source, maybe another gain stage to wrap some negative feedback around it, a low impedance follower output, etc. It begins to add up.

It's just darn hard to beat bugs for convenience but building your own is probably more fun

My only real options seem to be these;

Build a circuit with a couple op amps.

Use the Edcor transformers which have no active elements so will not introduce any noise.

Replace the volume control in my Sony TAE5450 preamp and use it.

Use a Planet Audio preamp/crossover/eq which has two inputs, front & rear outputs, a subwoofer output and more control over the tone, but does not drop the volume all the way to zero which might not even be noticeable driving an amp with a 1 volt input sensitivity.

Which do y'all think would be the best choice related to audio quality and cost?

Inputs will primarily be a cellphone, iPod, laptop & AM/FM tuner

Oh my. Well, my choice would be to repair the Sony, if possible. That's a nice vintage preamp with all the neat stuff you get on a full blown preamp; tone controls, switched inputs, etc., pretty case with lot of knobs and switches Plus it's got a phono input and switched outlet for the power amp.

I suppose the down side is no remote control but don't think I could let that thing just sit there broke.

I agree on the Sony and the phono input will be nice and if I need a powered sub or two I can drive them with the second output on the Sony given the speakers I am gonna use are a small pair of old Olson bookshelf speakers which don't have much bass below 60 Hz.

Yes the Sony seems like the best way to go. I could then simplify the amp (being built in an old ammo case) by just using a power cord without a power switch on the amp itself.

Where can I find a good 10K dual gang volume pot with shaft that takes a setscrew type knob? The original volume control was a stepped attenuator which I don't really like.

Like this? http://www.mouser.com/ProductDetail/Alp ... rWeD590%3d

Curtis Eickerman

Well, I don't know how 'good' but Mouser has a dual audio 10k with, I presume you mean, 1/4" plain round shaft. Whether it's long enough I don't know. But, if it would fit, for $2.73 you could use it till you found whatever super duper thing you'd really like.

http://www.mouser.com/ProductDetail/Alpha-Taiwan/RV24BF-10-15R1-A10K/?qs=vCz78MyBKmo3ImvmonpjEcssR%2fyTfk9oXGmjrWeD590%3d

LOWER? Then you don't need a preamp at all, just a variable resistor.

If you mean higher, and it seems you do, then I'd go with a small amp based on a BC109C/BC549C - or whatever equivalent you use in the USA. The BC109 is a very low noise transistor, use plenty of negative feedback to keep the distortion low and it'll beat most FET based preamps of similar design. The BC109C has an Hfe of some 600 btw.

I'm thinking along the lines of those ALPS pots that are square and have a blue rear plastic cover.
I have a 100K dual gang pot like that and it is pretty good.

Rk27 Blue Velvet?

http://www.ebay.com/itm/Japan-ALPS-RK27-VOLUME-Potentiometer-Dual-10K-Slotted-/320816794159?pt=US_Amplifier_Parts_Components&hash=item4ab22bca2f

Yep. That will work.

Another option I have is to go look at the flea markets for one of those smaller Radio Shack mixers. That should do what I need plus provide individual level controls for each input source.