Se Tranny used on Parafeed!!!

[Triod lover]

Hello...There
I just wonder what would be the result if SE tranny that has no air gap to use on Parafeed amp?
Thanks& Regards,
Triod Lover.

[Triod lover]

oops..i made a mistake i mean se tranny that has an air gap to use on Parafeed amp.
thanks,
Triod Lover

[dsavitsk]

There is always a compromise with a transformer coupled circuit. Either the air gap causes some problems, or the parafeed capacitor does. If you use an air gapped transformer in parafeed, it will work, but you get the worst of both worlds. So, from a sound quality perspective, it is not a good idea. The benefit of parafeed is that it gets rid of the air gap, but otherwise there isn't really any advantage to it.

[Shoog]

.

There is always a compromise with a transformer coupled circuit. Either the air gap causes some problems, or the parafeed capacitor does. If you use an air gapped transformer in parafeed, it will work, but you get the worst of both worlds. So, from a sound quality perspective, it is not a good idea. The benefit of parafeed is that it gets rid of the air gap, but otherwise there isn't really any advantage to it.

An over simplified analysis of the situation. The SE airgapped transformer will perform slightly better in parafeed because the core is free from any saturation - this will free up a small amount of inductance and hence improve the bass. You will also get the benefit of improved PSRR which the parafeed setup imparts. Worthwhile gains in themselves.

Still I would say that you will be carrying a hell of a lot of redundant iron for very little benefit. A better result could be obtained with the toroidal mains transformer (i'am starting to sound like a stuck record). which will have better bass and better highs than the airgapped SE transformer.

Shoog

[aletheian]

Originally posted by Shoog
. A better result could be obtained with the toroidal mains transformer (i'am starting to sound like a stuck record). which will have better bass and better highs than the airgapped SE transformer.

Shoog

Any specs to look for with them... i have a few lying around that i might try in that service.

[Shoog]

I can only tell you what has worked for me. All my amps have been about 7-10Watts. I have used the same toroidals which are 18V+18V:110V+110V. at about 120VA.
I would say that because mains transformers are designed to go down to 50hz, to get them down to audio ranges they need to be oversized by at least 4x. To big and the top end will suffer.
I had to unwind them to get the ratios I needed and depending on the output impedance you need this is likely to be your biggest issue. The situation is made worse for me because my speakers are 4ohm.
For 8ohm speakers the impedances you will get are as follows;

220V:6V > 11K
220V:7V > 8K
220V:8V > 6K
220V:9V > 5K
220V:10V > 3K8


110V:6V > 2K6

A fairly good range of workable values.

If you can find inductance ratings then the bigger the primary inductance the better, unfortunately these specs are usually not published for mains transformers.

One more point, because toroidals have such high bandwidth they have a tendency to ring, so a scope will be useful in judging their performance. Another thing to note is that they can sometimes ring if connected in one direction - but not in the other.

Hope that helps.

Shoog

[Tweeker]

Hi Shoog,

An over simplified analysis of the situation. The SE airgapped transformer will perform slightly better in parafeed because the core is free from any saturation - this will free up a small amount of inductance and hence improve the bass. You will also get the benefit of improved PSRR which the parafeed setup imparts. Worthwhile gains in themselves.

Im not so sure this is really much of an advantage. Your also no longer operating on the most linear part of the BH curve and the redundant iron will be more reluctant.

[Triod lover]

Thanks you all for the answers,I will try my own experiment!
Thanks and Regards,
Triod Lover.

[planet10]

Originally posted by Shoog
An over simplified analysis of the situation. The SE airgapped transformer will perform slightly better in parafeed because the core is free from any saturation - this will free up a small amount of inductance and hence improve the bass. You will also get the benefit of improved PSRR which the parafeed setup imparts. Worthwhile gains in themselves.

The monoblok parafeed amps we built using 2 pair of Grundig SE OPTs (primary of 1 used as parafeed choke for another) work well.

dave

[soundbrigade]

SO IF I ADD another suggestion/question in this PF-tranny thread:

What about 100V Line Transformers? I expect those to be w/o airgap running on a sort of 100V distribution signal and used to adopt 4 or 8 or .. ohm speakers to the distribution net.

I have a load of those bastards and wondered if I could use with with a fairly small tube like 12B4A (I have a load of those too). Either for a headphone-amp or for a tiny power amp for speakers.