[tanchiro58]

I would like to ask your technical knowledge about replacing the interstage transformers with capacitors at the site of input tubes (underneath the tube sockets) in my 2A3 SET amp. I have heard that the sound would have a big improvement with capacitors rather than with interstage TX.

Since I am an average listener and know a little bit of DIY so I am not sure of doing this kind of big project to me. I also do not want anything happen to my amp when doing by myself. Any help of technical advices and suggestions would be appreciated.

Regards,
Tan

[Ronw]

Imho,i would never change an interstage transformer for a capacitor,audio manufacturers use coupling capacitors because they are much cheaper than a transformer,Transformers pass the music much purer and allow the emotion of performances to emerge.I am not really an audiophile,and i agree with Nicholas at Promitheus that when accountants started making decisions rather than engineers cost became more important than sound.Long Live Transformers and Tone!! I am not associated with Promitheus Audio in any way but i do love their design philosophy.I have been associated with audio & hi-fi since the early 50's,and i think that they are surfing backwards into the new age of the best sound and value in audio! Imho.

[JoshK]

I have heard that the sound would have a big improvement with output caps in the direct heat circuit rather than interstage transformers.

You heard wrong.  I agree with the above poster, that this would be a downgrade. 

[Occam]

Tan,

Is your present interstage transformer 1:1?
You question whether (or not) replacing an interstage transformer with an appropriate cap, would be moot if that transformer isn't a 1:1. A capacitor in that coupling role isn't going to amplify, or significantly attenuate the signal. (Even if there is voltage gain in the transformer, a replacement with a cap might be possible if there is also an attenuation circuit, as long as the net gain of the trans and attenuation network is <=1). Similarly, if the transformer is providing current gain with lesser voltage swing, a cap and attenuation can adjust the voltages, but cannot amplify current.
Even if the such a substitution is possible, you need to consider how (and if) grid bias is provided to the following stage, and make appropriate adjustments.
As to the merits of transformer vs capacitor ... that would depend on the quality(s) of both components.

FWIW,
Paul

[Note - Also, is that interstage a gapped transformer, providing the plate or cathode load, or is the transformer coupled via a capacitor already? If the former, replacing an inductive load with a resistive load is going to call for a relatively significant redesign of the topology.]

[JoshK]

Paul's right.  There is a lot to consider if it is even possible without redesign.  Most likely it is a gapped 1:1 interstage transformer which provides the plate load for the preceding tube and drives the grid of the output tube with its secondary.   In which case, it also allows the output tube to be driven a bit harder even into grid current area because the interstage essentially stores energy.  This allows the tube to swing a bit more power on hard transients.  The alternative with a cap is usually blocking distortion as the preceding tube has to keep charging the cap, so theoretically the amp with the IX would avoid clipping earlier when the amp w/ cap did.

Hard to know though if it would be possible without a schematic.  If you really wanted to try the experiment and it lends itself to such, you could pretty easily solder an appropriate cap in its place and listen to the difference.  Most likely you'd reverse the mod.  But you never know.  You have to be very careful though as a 2a3 amp have voltages typically >400V dc and if there are no bleeder resistors in your PSU they can hold this voltage a while after you unplug the amp. 

[slbender]

Hi Tan

First off, and NOT to be insulting, but your phrase "interstage output transformers" makes me think you have no idea what you're talking about,  and the non-technical and simply inexperienced should not play with high voltages and power tube circuits, as they can blow up, fail unexpectedly when  you least expect it, start a fire, explode, electrocute, or otherwise hurt you!!!

Now if you are referring to 2A3 tube output transformers in your 2A3 SET amp, then no, you cannot just yank transformers and put a cap in its place. It won't work. If this is indeed an interstage transformer between a voltage amplifier and a current amplifier driver tube, its a slightly different story; it still won't work, but possibly a technician who is familiar with tubes and has years or decades of experience would be able to make sufficient changes to the circuitry to make it work. But his labor would likely cost as much or more than your amp did. Furthermore, the chances that the resulting circuit changes and outcome would sound sonically better than the original circuit would be kinda doubtful, or at best 50/50 ( still, it would definitely sound different ).

If you don't like something about the sound of your 2A3 amp, then first try and determine the actual WHY? of that.  Is it really the speakers at fault, or is it the amp?  Then get yourself other speakers, or another amp that more closely meets your audio needs.  It could be that for your speaker and room that you need an amplifier with higher output power to avoid clipping distortion. Or possibly one designed with a lower output impedance for tighter control of the bass; or one of the higher priced types with silver wire in the output transformer; and silver in oil, or polypropylene caps, or other design criteria characteristics that would change the sound for more detail, wider soundstaging, or more clarity, which might be to your liking.

There are many, many hundreds of amps out there, Vintage Tube, Modern Tube, Vintage and Modern Transistor, Mosfet, and Hybrids of all sorts, and their designers have all made different design choices in the compromises present in their particular design. Try and find a speaker or an amp where the set of compromises results in a sonic characteristic which best suits your ear and your wallet.


Steven L.. Bender,  Designer of Vintage Audio Equipment

I would like to ask your technical knowledge about replacing the interstage output transformers with output capacitors in my 2A3 SET amp. I have heard that the sound would have a big improvement with output caps in the direct heat circuit rather than interstage transformers.

Since I am an average listener and know a little bit of DIY so I am not sure of doing this kind of big project to me. I also do not want anything happen to my amp when doing by myself. Any help would be appreciated.

Regards,
Tan

[tanchiro58]

http://www.audiocircle.com/index.php?action=gallerylastup&cat=0&pos=3
http://www.audiocircle.com/index.php?action=gallerylastup&cat=0&pos=1
http://www.audiocircle.com/index.php?action=gallerylastup&cat=0&pos=2
http://www.audiocircle.com/index.php?action=gallerylastup&cat=0&pos=0

Hi Gentlemen,

I apologize I do not know how to upload pictures to this site. These are the link to my picture gallery.
Again this amp is custombuilt and I do not have any schematic. I have compared this amp with my modified SET Sun Audio 2A3 stereo amp in the same system (considered of mod Denon 2900 directly connected to both amps, anti-cable speakers and mod VR1 monitor speakers).

To my ears and my friend opinion, the Sun Audio has more soundstage, more full sound and bass than the SET parallel 2A3 stereo amp.

Mr. Steve Bender,

I was wrong using terminology. Yes, they are interstage trannies instead of interstage output TX. So the Sun Audio uses two Jensen 0.22uF Copper foil PIO but the SEA Parallel 2A3 has two interstage TX. Thanks in advance for your help.

Tan

[Daryl]

You would not want to change the design of a componet unless you were a competent designer yourself, in which case you would not be asking this question.

Transformers are both the most expensive and the worst performing of all passive componets therefore they won't likely be in a circuit if there isn't a good reason.

Transformers are used for rejecting common mode signals at the input of circuits and converting impedances/voltages at the output of circuits and in power supplies.

Capacitors cannot perform these functions.

I would prefer a differential amplifier to input transformers and an output stage capable the required current to output transformers myself.

[tanchiro58]

Capacitors cannot perform these functions.

I would prefer a differential amplifier to input transformers and an output stage capable the required current to output transformers myself.

Actually the designer of this amp told me the interstage TX design sounds constricted compared to his new design with capacitors (I noticed that too). In addition this amp has double C-core transformers which should be sounding good whereas Sun Audio has a reputation of Tamura TX (EI core).

[2wo]

Well, If you are in contact with the designer...JOhn

[Occam]

And what praytell, do you specifically expect?

To quote you from a contemporaneous thread -
http://www.audiocircle.com/index.php?topic=41093.msg391636#msg391636

To be honest it is good to learn from everyone' experiences or DIY's experiences but too much of theories of audio-engineering I have never interested.

(I left out the smileys, and caution you to never use that 'wagging finger' in the Lab Circle)
Obviously, you've no interest in extending yourself, and wonder why you should expect that effort from others.

Without a schematic, no one with any sense can provide any assistance. Even if you could, why should anyone bother? You're the first to admit that you've no interest in leaning anything of substance.

FWIW

[tanchiro58]

Without a schematic, no one with any sense can provide any assistance. Even if you could, why should anyone bother?

Occam,

I will take your advice to NOT wagging finger in this Lab circle.

To be honest I do not understand much the technical terminology back in Promi DAC posted by jb. What I would want to get the "technical advices" but not theoritical advices of the AC members who have experienced DIYing. Besides I do not have a schematic of the amp from the designer. Therefore, I have posted some pictures of the amp to show everybody what I have intended to ask and plan to modify.

[slbender]

Well Tan -

I looked at all the pix you posted, and saw no indications of any interstage transformers... in the pictures you posted.  If that was the SEA Parallel 2A3 and if it is a custom amp, and you don't have the schematic... Well you haven't revealed anything about what was driving either amplifier for your comparison - a CD player, a Passive, or Active Transistor, or Tube Preamp; or any characteristics of said Preamp. And of these amplifiers, you haven't stated what either amplifier has for input impedance; what its gain is; what the output tube's operating points; voltages; or dissipations are; you don't reveal what the tube complement in either amp is; what the ratio's employed in each interstage and output transformer are; whether there is global feedback employed (or not); what the internal output impedance or damping factor of each amplifier is (and at what frequencies); what the impedance of the speaker used is (over what frequency range) nor its resonance point in the bass; and if it has a nearly constant impedance, or is varying all over the place; how complex the crossover is; if the same wire was used too connect the speakers to each amplifier for the comparison; etc. -- so I don't think you can make ANY valid direct comparisons or sweeping generalizations between the Sun Audio versus the SEA Parallel 2A3 or between capacitor coupling and interstage transformer coupling stages given such a meager amount of information... I certainly can't, don't know either amplifier!

Maybe one amplifier does indeed sound better than the other on a given system setup, in a given room.  But change any one aspect of that system such as better or different speakers; different room placement, or a different room; or with another preamp, or different speaker cables and that evaluation could very well change.

So the only possible answer in this case would be:  Well "I see" said the blind man - to his deaf daughter ... as he walked into a tree...


-Steven L. Bender

http://www.audiocircle.com/index.php?action=gallerylastup&cat=0&pos=3
http://www.audiocircle.com/index.php?action=gallerylastup&cat=0&pos=1
http://www.audiocircle.com/index.php?action=gallerylastup&cat=0&pos=2
http://www.audiocircle.com/index.php?action=gallerylastup&cat=0&pos=0

... So the Sun Audio uses two Jensen 0.22uF Copper foil PIO but the SEA Parallel 2A3 has two interstage TX. Thanks in advance for your help.

Tan