Isolation transformers

[Galu]

Hi Jimmy!

I may be in too deep here!

I was working under the asumption that you wanted to interface an op amp with a power amp.

However, you mention an active volume control arrangement.

Where, exactly, do the op amps come in?

Can you provide a circuit diagram?

 

[jimmy audio]

Hey Gala, Thanks for your reply. The trannys i Pirated pretty much fall dramatically at about 15khz no oscillation seen yet but i will add traces and pads for the loading components in the design of my small pc boards for the trannys so i can mount them a few inches from the amps input. For the trannys primary and dc blocking you suggest using back to back electrolitics to simulate what type of cap? something you would find in a speaker crossover? non polarized electrolytic?

 

[Galu]

Yes, to simulate an NP electrolytic.


P.S. A single non-polar 47uF loudspeaker crossover electrolytic will do the same job!

 

[jimmy audio]

re replies

The volume amp portion is what i hacked. Why not use a small electrolytic in series to block dc on the primary somthing along the lines of 4.7 uf or would reactance at low freq be a problem?

 

[Galu]

To reduce bass distortion I'd go for 10 times as much.

A 47uF NP electrolytic as used in loudspeaker crossovers will do the job.

 

[Galu]

Also blocking capacitor and primary coil will resonate.
Choosing a large capacitance will ensure the resonance is below the audio band.

 

[jimmy audio]

Thanks much Galu! I did some browsing and the general consensus seems to be when using a non polarized cap to block dc bypass that cap with a film cap at least 10% of the value of the non polarized one... Am i getting that correct? Also my power amps are capacitive coupled with a small electrolytic on the inputs(4.7uf) so by adding trannys at the power amp input i should be able to get rid of them? sound correct?

 

[Galu]

I suggested a 0.1uF bypass capacitor in post #9. Probably won't make much of a difference, but including one is inexpensive!

I wouldn't modify the inputs unless I was sure I'd never use the power amps in another application!

 

[jimmy audio]

Thanks Galu I will add traces and pads for the components on the primary and secondary. the fact that its working now with excellent sound quality up to the limits of the trannys being used gives me hope that the dc is low enough not to cause problems. but that being said extending the bandwidth with new trannys could uncover problems. will order the triads and the non polarized caps. Thanks to all. Its wonderful to have such an online community. I learn something new every day!