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Interstage Transformer VS Coupling Caps for Tube Amps


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Hi all,

 

I am so grateful that there are so many kind members here willing to spend time to help "NOOBS" like me regarding Hifi questions. So please accept my thanks in advance! :)

 

My question is: 

 

I am about to have a tube amp made by McChanson and as part of the upgrade option is to have the coupling caps replaced by interstage transformers. I have no idea what the difference between them and what the disadvantage(s) and advantage(s) between them in terms of sound and life for the amp?. Will it be worth the $300 upgrade to have the caps changed to the interstage transformer?

 

Cheers

Edited by DMax
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When I was bread boarding my 300B SET I did experiment with IT's. It never convinced me so I went with caps. Currently running Miflex and don't have the desire to side-grade to any other brand.

My understanding is that interstage transformers (IT) can provide more ideal coupling between the driver and output stages, particularly when the output stage is a demanding load.  But, but, but  this

I liked Earle, but it is known he didn't prescribe to better caps sounding better, he viewed it as placebo and used to mention this often, so need to look at things like that when weighing up his view

My understanding is that interstage transformers (IT) can provide more ideal coupling between the driver and output stages, particularly when the output stage is a demanding load.  But, but, but  this assumes that the IT is itself of excellent quality which is HARD to do and usually means big bucks.  I remember Earle Weston posting that (IIRC) he had given up using ITs in his designs because he couldn't make them to the standard he required.

So I guess tha questions for you are: would the design benefit from IT?  And are the supplied ITs likely to be good enough?  Not easy to answer!

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46 minutes ago, RoHo said:

But, but, but  this assumes that the IT is itself of excellent quality which is HARD to do and usually means big bucks. 

 

These were the reasons years ago when valves were first invented.    Initially transformers were all they had, and caps were the hard thing to get.  But when more caps came on the market, designs switched because the equipment became lighter and less bulky, sounded better,   and cost less to make.  Win win win.  There was also the invention of circuits to produce things like push-pull driving waveforms using valves instead of a transformer.

 

These days, I would say it is still difficult and expensive to match the performance of normal circuits using interstage transformers.  Maybe  right at the very top end of the market,  transformers might just have an edge.   Haven't heard such beasts myself though.

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I'd have a great cap over a poor transformer. (but that's if I'm only looking at sonic character and looking at something in caps at a Duelund level.), but all things being equal I'd choose the transformers

 

Technically transformers are a better solution.

 

Like caps transformers will have their sonic signature, and different transformers will have different signatures like caps due to construction/materials.

 

Looking at options with Eric's amps I'd likely choose his transformer builds over his ones using caps.

Edited by muon*
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Deleted

 

Meant to edit not quote :ermm:

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12 hours ago, muon* said:

Looking at options with Eric's amps I'd likely choose his transformer builds over his ones using caps.

Are his IT better quality than his caps? 

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1 hour ago, DMax said:

Are his IT better quality than his caps? 

I think his inter-stage transformer version will sound better than the non transformer version, so it is and upgrade.

I have only heard one amp of Eric's apart from a guitar one, and that was a 300B amp with inter-stage transformers and I thought it sounded pretty nice.

 

The guitar amp was a nice thing too.

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6 hours ago, muon* said:

I think his inter-stage transformer version will sound better than the non transformer version, so it is and upgrade.

I have only heard one amp of Eric's apart from a guitar one, and that was a 300B amp with inter-stage transformers and I thought it sounded pretty nice.

 

The guitar amp was a nice thing too.

Is it worth the extra 300 bucks? 

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8 hours ago, DMax said:

Is it worth the extra 300 bucks? 

That's a value judgement and subjective, so it will vary from one opinion to another.

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10 hours ago, muon* said:

That's a value judgement and subjective, so it will vary from one opinion to another.

If it's you, would you spend the extra $300? Because I'm very tempted lol

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8 hours ago, DMax said:

If it's you, would you spend the extra $300? Because I'm very tempted lol

Probably.

 

I'd have no problem paying that to upgrade caps for better caps in an amp, and that would only get good coupling caps not great caps.

 

But some people don't hear improvements as much as some others, some don't even hear differences between caps and other things, so for those people it might be a waste of time.

 

This is why I say it is a subjective value judgement.

 

 

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if you're going to buy the amp anyway I'd ask Eric's opinion on the ITs vs better caps than he uses as standard...just a thought...I'm assuming with a custom build you would have that flexibility?

 

Really good transformers are the expensive bits in valve amps in order to have them linear across their range.

 

On 21/10/2020 at 10:10 AM, RoHo said:

I remember Earle Weston posting that (IIRC) he had given up using ITs in his designs because he couldn't make them to the standard he required.

Earle's amps are highly regarded, and my understanding is he winds all his own transformers, so for him to move away from ITs is testament to them being tricky to get right.

 

I'm not at all saying Eric's amps with ITs won't sound great, but they may sound even better (and perhaps cost more) with high end caps.

 

mike

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15 hours ago, almikel said:

if you're going to buy the amp anyway I'd ask Eric's opinion on the ITs vs better caps than he uses as standard...just a thought...I'm assuming with a custom build you would have that flexibility?

 

Really good transformers are the expensive bits in valve amps in order to have them linear across their range.

 

Earle's amps are highly regarded, and my understanding is he winds all his own transformers, so for him to move away from ITs is testament to them being tricky to get right.

 

I'm not at all saying Eric's amps with ITs won't sound great, but they may sound even better (and perhaps cost more) with high end caps.

 

mike

I liked Earle, but it is known he didn't prescribe to better caps sounding better, he viewed it as placebo and used to mention this often, so need to look at things like that when weighing up his views. His views I's imagine were based on measurements for the best part.

 

But I agree It's worth chatting with Eric on these options, but as very good transformers will be costly, so will very good capacitors. I could easily spend $600 or more! on 4x coupling caps to have very good ones..............Pick ya' poison and flavour :thumb:

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I'm going to chime in with my 2 cents worth. Cap (coupling cap) rolling in valve amp/sources is fun but never ending. You will keep going until most brand and/or capacitance value is exhausted. Interstage trannies are limited with very few options available.

 

Interstage trannies are common in Japanese valve circuit topology. There are some great brands out there that sound absolutely brilliant. Like others have said, Eric prefers the interstage topology so go with this, you won't be sorry. 👍👍👍

Edited by xlr8or
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18 minutes ago, xlr8or said:

I'm going to chime in with my 2 cents worth. Cap (coupling cap) rolling in valve amp/sources is fun but never ending. You will keep going until most brand and/or capacitance value is exhausted.

 

You gotta know when enough is enough, that is true.    Past a certain point, time to look elsewhere for fun...

 

20 minutes ago, xlr8or said:

Interstage trannies are limited with very few options available.

That is true.

 

20 minutes ago, xlr8or said:

Interstage trannies are common in Japanese valve circuit topology.

 

I always saw that as a bit of a cult thing. A bit like just trying to do it the old way because you can.  It would be  easy to replace a coupling cap in a circuit with a transformer that actually has inferior qualities.  

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On 23/10/2020 at 7:03 PM, almikel said:

if you're going to buy the amp anyway I'd ask Eric's opinion on the ITs vs better caps than he uses as standard...just a thought...I'm assuming with a custom build you would have that flexibility?

Yeah I did ask him but he said he is neutral in opinion and recommended me to do my own research and decide for myself lol

 

From what I have read here and opinions received from other sources, the IT would only be a benefit for the push and pull design? So I guess now I'm leaning towards the option of upgrading the caps.... 

Edited by DMax
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What caps would you guys recommend if I do go with the upgraded cap option rather than the IT option? 

 

At the moment I'm looking at the Mundorf Silver Oil or Mundorf Silver Gold Oil. How do they compare to each other? Would the silver gold be better and worth the more $$$. How about the Duelund? How do they compare to the Mundorf? Or is it like Earle said, it is all placebo? 

 

Cheers 

 

 

Edited by DMax
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IT's have their own problems like phase shift at low frequencies were caps display phase shift at higher frequencies. Take your pick.

Good transformers are expensive. A set of good transformers cost as much as a McChanson amp. You can draw your own conclusions from that.

Go for the caps. Miflex is an excellent alternative over the over priced boutique caps.

There is absolutely nothing wrong with caps. You will be assured of good bandwidths which will be a problem with cheap IT's. 

 

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29 minutes ago, DMax said:

What caps would you guys recommend if I do go with the upgraded cap option rather than the IT option? 

 

At the moment I'm looking at the Mundorf Silver Oil or Mundorf Silver Gold Oil. How do they compare to each other? Would the silver gold be better and worth the more $$$. How about the Duelund? How do they compare to the Mundorf? Or is it like Earle said, it is all placebo? 

 

Cheers 

 

 

 

Opinions will vary here but my vote goes towards the Jupiter copper foil wax and paper capacitors. I'd still go for the IT option though.

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Not sure if that is accurate that inter-stage transformers only suit PP amps *shrug*

 

As for good capacitors, Duelund are in the middle of a revamp or their different line ups, releasing the JDM series that will be their more affordable caps and the CAST will be their higher end lines.

 

If we compare Mundorf's best to say, Duelunds previous lower end series RS copper series, the RS are the better cap, more natural in sound.

 

Edit: my favorite is still the discontinued Copper VSF series, but they were only 400vdc.

I like Jupiter Copper foils, but still prefer Duelund over them, and I'd put both Duelund and Jupiter in front of Miflex.

So in order of my preferences:

1/ Duelund Copper Foil and oil

2/Jupiter Copper Foil and Wax

3/Miflex Copper Foil and Oil

 

I'd look at the new Duelund  JDM series if they are available, if going for a capacitor rather than interstage transformers.

 

Can inquire on the JDM availability on their facebook page https://www.facebook.com/pg/duelundcoherentaudio/posts/

Edited by muon*
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Really need to ask Eric what voltage rating the caps need to be, parts connxion still have the Duelund RS in 400vdc available at a reduced price. They have 0.47uf/400vdc for about $75usd each.

This covid thing has slowed the release of the JDM series I think as they were supposed to be available by this stage. The JDM series will be better priced than the previous RS series since Duelund has acquired the machinery from Jensen since they closed their capacitor production, and no longer need to get Jensen to handle part of the production (winding).

 

And there is another pretty nice cap in the Andyn True Copper Max, although where the others are oil or wax impregnated the Andyn is not, but an affordable nice copper foil cap all the same. About $38usd each for 0.47uf/630vdc

0.47uF 600Vdc in Jutpiter Copper/paper and Wax are $99usd each.

MIFLEX KPCU Capacitor, 0.47uF 600Vdc are $25.80usd each.

 

These are parts Connexion prices.

 

Also need to consider capacitor sizes, these copper foil caps are big for a given value, so larger than others.

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All these preferences will be very personal, as you can see each of us prefer different ones, but what you need is what YOU will prefer.

A rough guide to the sound of most of these can be read on the humblehomemadehifi cap test.

http://www.humblehomemadehifi.com/Cap.html

 

Edit: as I have said I have always preferred the Duelund Copper VSF caps, now discontinued and only by special order.

I like them due to the rich sound they have, especially in the lower end and mids are magic.

 

Some prefer the Jupiters which have a bit more up top and a tighter bass, but not as detailed (rich) in that bass.

 

Some like the Miflex, and it is up there with these others, but with a sound of It's own of course, and it is the cheapest of them if going by pricing I'm looking at.

I have a been a little dismissive of these as I have only used them as by-passes across some Andyn True Coppers, and that did not work well with the two caps having different timings or phase causing a smearing. So I have not heard the Miflex on their own to be able to judge them fairly.

 

Any of these copper foil caps are better than Mundorf caps, in my opinion of course.

 

What do I have in my amp? I unfortunate have a lower Duelund series in the older Alexander caps, more or less at a level of the old Jensen Copper Foil and Oil caps, but with the Duelund signature. So not up there with the likes of Duelund RS or Jupiter Copper Foil and Wax but a good cap, just not a great one.

 

Caps placebo? nah! far from it IMO.

Edited by muon*
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7 hours ago, muon* said:

Not sure if that is accurate that inter-stage transformers only suit PP amps *shrug*

 

Maybe it's because of the need to use air-gapped transformers to prevent core saturation when they need to tolerate DC when used single ended.   Still,  my SET amp sounds good :) 

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2 hours ago, aussievintage said:

 

Maybe it's because of the need to use air-gapped transformers to prevent core saturation when they need to tolerate DC when used single ended.   Still,  my SET amp sounds good :) 

 

Do you have the IT in your SET amp? Did they cost much to be implemented into the amp? 

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9 hours ago, muon* said:

A rough guide to the sound of most of these can be read on the humblehomemadehifi cap test.

http://www.humblehomemadehifi.com/Cap.html

 

Thank you very much for sharing this link. Even though that's just on persons test and opinion but gives a pretty good general guide and also helps me to know what are the different caps out there. 

 

I think I may go with the Mundorf Silver Oil first and then maybe try the Jupiter Copper Foil and Wax and Duelund Copper Foil and oil later on. I'll need to start learning how to do unsoldering and soldering first before that I guess lol. 

 

Ps. Where would be the best place to buy caps? 

 

Cheers 

 

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@aussievintage  I thought that would only pertain to the OPT's.

 

But you are correct where the front end is SE also.

 

But what's the difficulty in winding them to suit anyway, there are transformer manufactures catering to SE where interstage transformers are concerned. Lundahl, Sowter ect'.

Even these vintage Tamara ones are good for 30ma primary.

https://www.ebay.com/itm/Used-Pair-of-Tamura-A-342-interstage-transformer-special-order-for-Sakuma-amp-/133369582760

Edited by muon*
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42 minutes ago, DMax said:

 

Ps. Where would be the best place to buy caps? 

 

 

For 'boutique' caps, I use:

 

www.percyaudio.com

www.partsconnexion.com

www.soniccraft.com.

 

There is also at least one good supplier in the UK.

 

Andy

 

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53 minutes ago, DMax said:

 

Thank you very much for sharing this link. Even though that's just on persons test and opinion but gives a pretty good general guide and also helps me to know what are the different caps out there. 

 

I think I may go with the Mundorf Silver Oil first and then maybe try the Jupiter Copper Foil and Wax and Duelund Copper Foil and oil later on. I'll need to start learning how to do unsoldering and soldering first before that I guess lol. 

 

Ps. Where would be the best place to buy caps? 

 

Cheers 

 

 

Those Mundorf cost more than Andyn True Copper Max and the Miflex Copper n Oils.......looking at prices on partsconnxion at least, about $50usd each for 0.47uf.

But if that is the sound you desire

 

I'd also make sure you have plenty of air flow in the case if using those Mundorf's, as even though they are rated to 70c I have heard of failures in high temp conditions with them.

 

See what Eric can access and at what prices.

 

Cap Test

I have been surprised at how accurate Tony Gee is with his take on sound from different caps in that test, even without any priming I have used caps and then looked at his findings there and found consensus, likely as caps don't change in sound from one listener to the next, but only where they hear things to a greater or lesser degree.

Edited by muon*
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1 hour ago, DMax said:

Do you have the IT in your SET amp? Did they cost much to be implemented into the amp? 

 

No, but a single ended IT is much the same thing as the output transformer - just handles less current.  

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45 minutes ago, muon* said:

But what's the difficulty in winding them to suit anyway, there are transformer manufactures catering to SE where interstage transformers are concerned.

 The difficulty is only winding them with sufficient quality, and not introduce loads of distortion from the magnetic circuit, and also the capacitance and inductances in the primary and secondary, plus interwinding coupling all affecting the outcome.  It's no free lunch and capacitors are much easier to make.

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4 minutes ago, aussievintage said:

 The difficulty is only winding them with sufficient quality, and not introduce loads of distortion from the magnetic circuit, and also the capacitance and inductances in the primary and secondary, plus interwinding coupling all affecting the outcome.  It's no free lunch and capacitors are much easier to make.

Plenty available which is good.

 

More costly that most capacitors of course, depending on what transformers are compared to what capacitors, naturally. But in general more costly, but that's expected.

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24 minutes ago, muon* said:

I have been surprised at how accurate Tony Gee is with his take on sound from different caps in that test

 

Good resource

 

My suggestion, just because I believe in value for money, is learn from what rates well.  Look at the materials and construction used in the big name caps that get big scores.   Then find a less well known cap made the same way.  This will get you value for money nearly every time.   

 

For example, simply noting the dielectric that is preferred, i.e. works most often to produce a good sounding cap, then buy one of that type.  I did that and tried a very cheap polypropylene crossover cap, as a coupling cap, and even that made good improvements.

Edited by aussievintage
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1 minute ago, muon* said:

Plenty available which is good.

 

More costly that most capacitors of course, depending on what transformers are compared to what capacitors, naturally. But in general more costly, but that's expected.

 

Yes, agreed.  The cost mostly reflects the difficulty in making them.

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Transformers are much more complex than capacitors.  Look at the equivalent circuits

 

A capacitor

image.png.95bdf409edd3bdca84beaa03f4349ec4.png

 

a transformer

image.png.02fcedeba87b7ef17f7cadc4cd79ed13.png

Edited by aussievintage
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@aussievintage preaching to the choir :D

 

At one point I was going to wind my own OPT's under the guidance of a knowledgeable friend, and while I opted for the easy way out instead it informed me of what is involved in manufacturing transformers.

 

I probably should have as the experience would have been very valuable.

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4 hours ago, DMax said:

 

Thank you very much for sharing this link. Even though that's just on persons test and opinion but gives a pretty good general guide and also helps me to know what are the different caps out there. 

 

I think I may go with the Mundorf Silver Oil first and then maybe try the Jupiter Copper Foil and Wax and Duelund Copper Foil and oil later on. I'll need to start learning how to do unsoldering and soldering first before that I guess lol. 

 

Ps. Where would be the best place to buy caps? 

 

Cheers 

 

 

 

Try searching for second hand Duelunds or Jupiters using Hifishark. They will outperform the Mundorfs. You can give them to Eric to solder in. 🙂

 

Here is an example of some new JDM ones:

 

https://www.ebay.com/itm/274528530795

 

Edited by xlr8or
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When I was bread boarding my 300B SET I did experiment with IT's. It never convinced me so I went with caps.

Currently running Miflex and don't have the desire to side-grade to any other brand.

If I ever go down the path of IT's again I will be trying Lundhal transformers.

Miflex.thumb.jpg.56362dce41ec4687ec0d208a8f95feeb.jpg

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Yes, any of those copper foil caps will be good including the Miflex, just slightly different flavours :thumb:

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