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-   -   input transformer for Simple SE Tubelab amp (http://www.diyaudio.com/forums/tubes-valves/174935-input-transformer-simple-se-tubelab-amp.html)

Salsero 7th October 2010 02:10 AM

input transformer for Simple SE Tubelab amp
 
Hi guys,
As with all tinkerers here, I was recently reading on the virtues of using input transformers for phase splitting in push-pull amps. Are there any gains that can be achieved by using an input transformer into a single ended amp like the Tube Lab Simple SE? If so, what are the benefits? What would be a good input transformer?
Thanks
Salsero

Steve Eddy 7th October 2010 03:37 AM

Well, you get ground isolation, good common-mode noise rejection, and the ability to feed it from either balanced or unbalanced sources. Also, even when fed from unbalanced sources, transformers offer good common-mode noise rejection.

Check out the CineMag CMLI-15/15B.

se

Salsero 10th October 2010 01:53 PM

SE,
Thanks for your reply. It seems like the input transformer will only provide ground isolation when run in single ended mode. Unless I understand this incorrectly, noise cancelation will only occur in balanced mode - therefore the only virtue of an input transformer is ground isolation and DC filtering. Will this alone improve sonics for single ended?
Thanks
Salsero

Steve Eddy 10th October 2010 02:27 PM

It provides ground isolation in both balanced and unbalanced. It also provides good common-mode noise rejection in both balanced and unbalanced. It will be a bit higher with balanced sources, but because of the transformer's exceedingly high common-mode input impedance, it also gives excellent rejection from unbalanced sources (about 107dB at 60 Hz balanced and about 100dB at 60Hz unbalanced).

As for sonics, welll, that's such a subjective issue. It's impossible to say just what someone else's experience may be. All I can say is that I'm a big fan of input transformers and wouldn't build anything without them.

se

Salsero 10th October 2010 07:00 PM

Input transformer for Tubelab Simple SE
 
SE,
What would I need to modify in my Tubelab Simple SE to use an input transformer?
Salsero

Steve Eddy 10th October 2010 07:46 PM

Do they make a schematic available for it? Wasn't able to find one on their website.

se

epitaxial 10th October 2010 08:28 PM

Transformer coupling
 
Transformer (magnetic) coupling, in the output stage, is one of the reasons tube amps have a "tame" sound compared with solid state amps.

A grid transformer will ensure correct grid impedance.

Acheiving a correct frequency response using RC charts from a tube manual is nearly impossible with RC coupled amps, even if components are chosen experimentally.

The transformer will step up the voltage, so the output gets a strong enough input with less demand on the preceeding stage.

Transistor radios (the small 9v ones once very popular) functioned very well, because every stage (not just the RF stages) was transformer coupled.

One can build a good amplifier with ease with a minimum of components when transformer coupled.

Just be careful, because nearly any transformer can be made to work, but the correct transformer is a must for great performance.

Steve Eddy 10th October 2010 09:22 PM

Quote:

Originally Posted by epitaxial (Post 2328435)
The transformer will step up the voltage, so the output gets a strong enough input with less demand on the preceeding stage.

Only if the input transformer is a step-up transformer. Most are 1:1.

se


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