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Tube amplifiers and interstage transformers

Hi,

I have seen that a lot of very expensive tube amplifiers use interstage transformers to handle impedance between stages. There are other two methods to handle impedance between stages: capacitor coupling and RC. I would like to know if somebody with more knowledge can explain the difference in the sound of these 3 styles.

Somehow, it looks like some of the most expensive SET amplifiers have interstage transformers like Audio Note or Shindo.

I also read about the highly regarded amity and karna amplifiers that D Olsen built and they have also interstage transformers.

So, what are the benefits of using interstage transformers?

Thanks

Alan
128x128alanbrain
larryi
3,991 posts
 
I am sure that one can find a lot of people in either camps -- those that hate "iron" (limited bandwidth, phase shifts, etc) and those that hate caps. I have not personally experimented with design, so I cannot speak to theoretical advantages. It just happens to be the case that the amps I like are in the "lot of iron" camp. I have a pair of Audionote (uk) Kageki amps. These are interstage coupled.

I also own a pushpull amp based on an old Western Electric 133-A design, and a linestage that is also based on a Western Electric design. The linestage has input transformers and output transformers (no caps other than in the power supply) and the amp has input transformers, and again, no caps other than in the power supply.

My phonostage has a step up transformer in lieu of an active gain stage for low output moving coils.
charles1dad's avatar
charles1dad
10,250 posts
 
Have to agree with Larryi, definitely two opposing camps.In theory the
limited bandwidth argument against transformer use makes some sense,
until you put theory aside and actually listen.In my experience the best
sounding amps and preamps more often than not take the high quality iron
route. Tube amps with interstage transformers sould exceedingly natural
and realistic compared to other topologies.They are utterly transparent and
have superb tone and body. My 2 cents worth.One of the
very best power amps I've ever heard, the Absolare Passion PSET 845
tube has the IT and is stunning! Both my amp and preamp use them and
sound
wonderful to me.
Regards,
mechans
3,048 posts
 
Out of curiosity, it appears as though the interstage tranny is a big help with impedance matching. What I don't understand is why bandwidth is limited within the realm of human hearing i.e,why they even have this effect. Seems like you should get cleaner more powerful signal from the stage that needs to be matched to the next stage when impedance is better matched.
charles1dad's avatar
charles1dad
10,250 posts
 
Mechans,
In reality you do get the advantages you describe despite what opponents
of the IT may claim.As alan pointed out, Many of the very custom and cost
no object designs use them .For good reason, when implemented
appropriately they produce excellent sound. I do recognize that other
designs can provide excellent sound also.Interstage transformers are a
time tested and proven pathway for superb sonic results.
Regards,
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