ACA modification with Edcor transformer

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Hi All ,

When I was at the Edcor store for the M2 transformer I did buy also another transformer to experiment or try just in case ....
So inspired from the BAF coverage circuit I did built a version of ACA without the buffer , but with the transformer . Below you can see the schematic , and please let me know what do you think . :)

thanks ...
 

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Since you have actually built it (and listened to it I assume), we would be more interested in knowing what you think. How does it sound compared to the original ACA or any other amp you have compared it to? Does it sound tuby? Does it maintain the high frequencies?

One observation I would make, is that without the jfet you could run it at a higher voltage. Even thought laptop smps typical come in the 18v-19v range I have seen some in the 20's, 30's, and even 40's, but they need to be rated for the current (typically 2x the actual draw) for reliable operation.
 
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Well , I have been enjoying the new M2 build some time yet ...
but , below please find out the second version of this modification .

also ....I have tried to change as little as possible the original ACA this time , after some meditation ... lol

This is much better than the previous try .
Even though I don't know if the 10k:10k transformer is the best way , the amp now performs quite well , rather different in terms of musical/sound energy from the original , the gain is just slightly higher ( I am guessing ) .
Very very quiet , some detail comes to the surface , the bass at first seems a little bumped .... but after a while it is very easy to follow the music even in complex passages .

That's about it .... :)
 

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The one and only
Joined 2001
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I don't see how you will have any voltage gain with the input to Q1 taken from the junction of that 47k and 35k resisror. Won't that be almost 100% - feedback?

You are neglecting the low source impedance of the transformer, so actually
those resistors are there simply to stabilize the DC bias, as their impedance
is too high (compared to the output of the transformer to give much AC
feedback.

:cool:
 
The one and only
Joined 2001
Paid Member
BTW, with circuits like this you have to be careful that they don't "motorboat"
at low frequencies when the source impedance has a cap in series with it.

There are numerous ways to prevent that, but as is, the easiest way is to
see to it that they have a DC coupled source.

:cool:
 
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