Torpedo III Build Thread

[tomb]

 

 
How does it sound with Cinemag nickel-core transformers instead of Edcor steel?  Dsavitsk put the Cinemag prototypes on the second prototype Torpedo III we built and has had some very (very!) surprising comments. 

Hey! Way to leave us hanging!  

Yeah, I know - but I'm being honest and I also don't want to speak for Doug.

  He thinks the Cinemags will be here this next week, so we'll see.  It's no slouch with the Edcors, though and the Cinemags are not cheap.  Hopefully, the choices will keep everyone happy. 

 

[dsavitsk]

My comment to Tom about the Cinemags is that once he's heard them, he will have no interest in hearing the Edcors again.

 

[tomb]

 

 
How does it sound with Cinemag nickel-core transformers instead of Edcor steel?  Dsavitsk put the Cinemag prototypes on the second prototype Torpedo III we built and has had some very (very!) surprising comments. 

Hey! Way to leave us hanging!  

 
 

My comment to Tom about the Cinemags is that once he's heard them, he will have no interest in hearing the Edcors again.

 

I do have L2 PCBs available and the new Cinemags will fit the boards (as will the Edcors) but frankly I'd build a T3 before an L2 unless one is a glutton for punishment. The L2 build process is non-trivial, and I like the T3 better anyway.

 
OK - he said it: translated, Torpedo III + Cinemags = Summit-Fi.

 

[dsavitsk]

Here's what Spice has to say about the circuit.

[ATTACHMENT=1749]TORPEDO3.pdf (188k. pdf file)[/ATTACHMENT]

 

[HiGHFLYiN9]

Wow! Very low THD for a tube-based amp. Good to hear about the Cinemags. Edcor is a tremendous value, just not the best choice for fussy audiophiles who have a couple extra bucks in their wallet.  

 

[TheEnthusiast]

How would the Torpedo III drive some current spec LCD-2's or LCD-X's?

 

[dsavitsk]

These are very efficient headphones and the T3 has plenty of power to make them loud.

Both of the transformer types are designed for either 32 or 300 Ohm loads. Other loads should not be an issue, especially with the T3, but you can always use a resistor either in series or in parallel to make the load more optimal.

 

[cspirou]

For an amp that has a lot of differential parts to it, why is having a balanced output not an option?

 

[tomb]

For an amp that has a lot of differential parts to it, why is having a balanced output not an option?

 
I believe dsavitsk will want to weigh in on this, but my perspective is as follows - I suspect that in solid-state, the primary benefit of having differential all the way to the headphone is from the increased voltage swing that's created (slew rate, too, admittedly).  Solid-state doesn't have a lot of voltage to work from.  Tube amps have plenty.  It's kind of pointless to pursue increased voltage swing when you start from a B+ of 200V.
 
The other factor is in avoiding extreme cost.  Differential inputs - especially a differential volume pot - then differential output connectors, not to mention four output transformers(!), are all very expensive.  The result is very little to no additional common-mode distortion cancellation for a huge cost.

 

[dsavitsk]

The output from a transformer is inherently balanced. But in a high voltage amp, it is necessary for safety reasons to ground the transformer's secondary. Additionally, while a balanced headphone output is useful if you are driving 100m long cables in a noisy environment, in the short run to your head it serves no benefit. 0. None.

 

[cspirou]

The output from a transformer is inherently balanced. But in a high voltage amp, it is necessary for safety reasons to ground the transformer's secondary. Additionally, while a balanced headphone output is useful if you are driving 100m long cables in a noisy environment, in the short run to your head it serves no benefit. 0. None.

I understand the need to ground it but couldn't that be done with a center tapped secondary and grounding the tap?

As for the second point, if balanced output doesn't give a benefit for short cable runs then what is your opinion of amps(Schiit Mjolnir1/2, Headamp GS-X, etc) that have a balanced topology and a balanced output? Should the balanced output only be used for long cable runs or in a professional setting?
 
Personally I just think that having an amp balanced all the way to the end has a sort of aesthetic appeal that you don't have with one that is balanced except for the last part. But that's just my bias.

 

[cspirou]

   
I believe dsavitsk will want to weigh in on this, but my perspective is as follows - I suspect that in solid-state, the primary benefit of having differential all the way to the headphone is from the increased voltage swing that's created (slew rate, too, admittedly).  Solid-state doesn't have a lot of voltage to work from.  Tube amps have plenty.  It's kind of pointless to pursue increased voltage swing when you start from a B+ of 200V.
 
The other factor is in avoiding extreme cost.  Differential inputs - especially a differential volume pot - then differential output connectors, not to mention four output transformers(!), are all very expensive.  The result is very little to no additional common-mode distortion cancellation for a huge cost.

 
True, a balanced output is a way to double the available power, similar to a bridge tied load used in subwoofers and some Class D amps.
 
Although I think you are mistaken for the need to double everything to have a balanced output. I actually don't know of any tube amp with balanced output that uses two output transformers to create a differential signal. Even top of the line amps like the Eddie Current Balancing Act(with balance in the name) use only one output transformer per channel. Maybe if you had a stereo amp configured as a monoblock you can have 4 transformers but that's the only case I can think of.

 

[tomb]

That's part of the issue: the Balancing Act is not fully differential - only on the inputs, from what I understand.

 

[cspirou]

That's part of the issue: the Balancing Act is not fully differential - only on the inputs, from what I understand.

Balancing act has 2 XLR ports and one 4 pin balanced connection. Its pretty clear on the front panel.

http://www.eddiecurrent.com/BA.html

 

[OJNeg]

Balancing Act -> Balanced (not differential) input via input transformer, single-ended gain stage, single-ended output stage feeding transformer for balanced output
 
Torp III -> Single-ended input, LTP differential input stage, differential follower feeding transformer for balanced output (that happens to have one leg grounded)
 
A reminder that differential is not the same as balanced.