Torpedo III Build Thread

[badf00d]

@dsavitsk, @tomb : Wow, I built mine with Cinemags and the sound is fantastic. Been grooving on it all last night and today. It was a lot of fun to build as well. You guys are great.

 

[tomb]

Great!  Glad you're enjoying it.
 
I think we can add the 12AV7 to the list of quite nice tubes to use in the Torpedo.  I received a pair today and tried them for the first time.  I have more coming in and will report back when I try them, but so far, this pair is outstanding.

 

[badf00d]

  I think we can add the 12AV7 to the list of quite nice tubes to use in the Torpedo.  I received a pair today and tried them for the first time.  I have more coming in and will report back when I try them, but so far, this pair is outstanding.

 
Which manufacturer?

 

[tomb]

RCA

That said, there are a few others that may offer a substantial improvement, perhaps similar to the difference between 6J6 vs 5920 (E90CC) in the Torpedo I. First listens seem to confirm this, but again - I have more coming in and will report for certain soon.

 

[amtgamt1]

Could you explain a bit about how the power supply outputs 225V to the tube and 2mA to the filament as mentioned in your website? I am a newer in diy but i'm kinda interested how this power supply works. Thanks.

 

[dsavitsk]

Could you explain a bit about how the power supply outputs 225V to the tube

R3, D3, D4, and D5 form a voltage divider. D3-D5 will always drop a fixed (~225) voltage as they are Zener diodes, and that's what Zeners do. R3 drops the remaining voltage and limits the amount of current flowing through the diodes. That 225V biases the gate of Q1, and the source stays at a fixed voltage from Q1. C5 shunts Zener and residual power supply noise.

and 2mA to the filament

There are no filaments here. Directly heated tubes have filaments, these tubes have heaters. At any rate, there is a constant current source connected to the tube's cathodes that is set at 2mA. The CCS connects to the -6.3V power supply which does double duty powering the heaters.

 

[badf00d]

The more I listen to this amp, the more I love it. The bass has some serious attitude, and the highs are very resolving. Can't wait to try some tube rolling... first time for me.

 

[tomb]

  The more I listen to this amp, the more I love it. The bass has some serious attitude, and the highs are very resolving. Can't wait to try some tube rolling... first time for me.

 
For me personally, I have never had an amp that sounds this good.  It's really something wonderful to think that I can build (and sell) an amp with this kind of quality.  THANKS DOUG!!
 
I have been busy building several "built" versions of the Torpedo III.  In between time, I have been listening to every different tube I can get my hands on.  Unfortunately, my ears are over-whelmed at this point.  There are a few tubes that are obvious to me as not-so-good-fits, but the rest are completely confused in my mind.  The not-so-good-fits I've already mentioned - the 12AX7 is so-so but acceptable if you need wildly high gain; the 12AZ7 I did not like very much.
 
The rest have obvious differences, others not so much.  I can say with certainty that the 12AT7's are a great alternative with an obvious difference, but am at a loss to really explain that difference at the moment.  Here are some of the others I've tried, in no particular order:

1. 6072
2. 6201
3. 12AV7
4. 5965
5. 12AT7 (both NOS and NEW EH)
6. 6829
7. 6414

 
I suspect the 6829 and 6414 may have super-potential, but the pairs that I have are not matched very well and it makes it difficult to tell.  There is also the E180CC/7062, but it seems destined for audiophile-sticker-price-stratosphere.  Similarly, the pair of 5965's I have are not well matched.  There are flashes of greatness, but then my ears get tired and I start questioning whether I've really heard something different or not.
 
I am going to suspend all listening soon and do some RMAA's, which is a quite good tool (despited NWAVGUY's accusations) if you use it for direct comparisons.  The plan is to come up with some graphs that show a number of these tubes together, assuming all else is held constant.
 
P.S. Most every 12AU7 tube - including the 5963 - sound great in the amp, but that's with Grados. As Dsavitsk mentioned, they probably don't have enough gain for typical high-impedance phones.

 

[tomb]

 
P.S. Most every 12AU7 tube - including the 5963 - sound great in the amp, but that's with Grados. As Dsavitsk mentioned, they probably don't have enough gain for typical high-impedance phones.

 
Dsavistk wanted me to clarify that with transformer output, power is pretty much the same at low impedance vs. high impedance.  I understood that, but I'm always talking about Senn HD580's/600's (which I own) vs. HD650's (which he owns).  There's a 6dB improvement in efficiency going from HD600's to HD650's.

 

[fierce_freak]

 
P.S. Most every 12AU7 tube - including the 5963 - sound great in the amp, but that's with Grados. As Dsavitsk mentioned, they probably don't have enough gain for typical high-impedance phones.

 
I have some 5963's cooking in mine now. Way more than enough gain for HD650 (for me).
 
Got the case powdercoated. Take a look at the grill and where the tubes protrude from the top - trying to decide whether or not to keep the rings around the tubes. Thoughts?
 

 

 

[AndreYew]

That looks pretty good. An easier route might have been drilling a bunch of holes above the caps.

 

[tomb]

Well with the Thanksgiving holidays, I've had a chance to do some fairly thorough tube rolling tests.  I will post all of this sometime this weekend in excruciating detail on the Torpedo III website.  Also, please note the noise figures may be at the limits of the device used for testing - see the post below for an explanation.  For now - here are the highlights.*
 
First, results at 32R:

 
Second, results at 300R:

 
In order to make some sense out of this, here are some plots of S/N ratio (same as Noise in RMAA) and %THD vs. tube type.  Again, one for 32R and one for 300R.
 
32R:

 
300R:

 
So what can be gleaned from all of this?  A few conclusions that I've drawn, but again realize that opinion strongly guides my conclusions.  Data can be manipulated, depending on how you display it and how the base settings and assumptions were applied in the beginning.  More on how to manipulate data later.  For now, here are my personal conclusions:
 

1. The Torpedo III has an extraordinary frequency response for a tube/tube-hybrid amplifier, especially with output transformers (all tests were done with Cinemags):
   300R -.025dB at 20Hz and -0.25dB at 20KHz; ruler-flat inbetween.  The M-Audio Audiophile USB shows the very same drop at 20KHz (so no drop for the Torpedo), and only slightly less at 20Hz.
   32R -0.25dB at 20Hz and -1 dB at 20KHz; ruler-flat inbetween.  This is still outstanding, but shows that frequency response is a bit better at 300R.
2. Bottom line, frequency response was the same with every tube.  There was no deviation.  The only change in frequency response occurred between 32R vs. 300R.  All other tube differences were in distortion and noise.
3. Distortion with the Torpedo III rivals some solid-state amps.  Distortion of 0.0062% was measured with the 12AY7 EH tubes at 300R.  However, the King of low distortion was the GE 12AZ7 at 0.0031% at 300R!
4. We made the right decision in supplying the 12AY7 EH with the kits.  This tube is consistently superior at both 32R and 300R.
5. Dsavitsk was also correct in highlighting the 12AZ7 as a tube with promise for the Torpedo III.  I don't know what was going on when I personally first listened to a pair, but I missed the boat - big time.  Distortion for the 12AZ7 tube at 300R is simply incredible.  At 32R, the EH 12AY7 bests it quite a bit, but still - lots of potential perhaps with this tube.
6. Distortion is consistently higher at 32R, while S/N is ~10dB greater.  Noise is in the low-to-mid -90dB's all across the board at 32R.  At 300R, noise is in the mid-to-high -80db's.
7. 12AT7 is a viable alternative, although numbers are slightly worse than 12AY7 all around.  The 6829 may be somewhere inbetween, but also shows promise.  Again, the 12AZ7 may be superior at 300R and competitive at 32R.

 
Other conclusions somewhat related:

1. Don't believe "matching" for tube pairs on ebay.  I found extremely wide disparities, almost none of which were consistent with my own personal testing and matching.
2. At least for the Torpedo III, NEW construction tubes (EH anyway) are superior to most NOS tubes in every respect.  They really are better, at least with run-of-the-mill, non-boutique tubes.
3. I could not even test the 12AU7 at 300R.  The output was not strong enough under any adjustment to meet the levels required to run an RMAA test.  I suspect that may even mean negative gain?

 
* (Non-brand-specified tubes in the two tables are Electro-Harmonix.) 

 

[tomb]

One thing to note about the noise figures is that generally speaking, the noise floor hovers around -130dB.  There are artifacts in using the M-Audio Audiophile USB that contribute to higher noise values, I'm afraid.  Here's a graph of the M-Audio in loopback mode:
 

This is a noise of -95.1dB because of those peaks.
 
Here is a plot of the Torpedo III with EH 12AY7's at 32R:

This is  a noise of -94.0 for the Torpedo III - because of almost identical peaks.
 
So, the Torpedo III measurement is very close to the limits of the M-Audio device, if not THE limits due to variances in measuring.  The M-Audio Audiophile USB actually "looks" worse than my M-Audio Transit, but the straight-line noise floor is in a lower octave.  The M-Audio Audiophile USB is separately powered with an AC walwart.  That makes it overall more quiet than the Transit, but it's obvious that they don't have a power supply good enough to remove the 60 Hz and its harmonics.  In the first plot above, it's easy to see a peak at 60Hz, 120Hz, and unfortunately, another one at 180 Hz and then a few others as well.
 
So, I would take the noise values with a huge dose of salt when it comes to the Torpedo III.  I think we are way into the limits of the Audiophile USB's performance.

 

[tomb]

I am speechless.  n_maher and Tyll mentioned the Torpedo III on Innerfidelity.com:
http://www.innerfidelity.com/content/2015-innerfidelity-holiday-gift-guide-nate-maher
 

 

[dpump]

Tomb,
 
Will you be able to try the Cinemags in the Torpedo II with Telefunken E90CC's and compare to the Torpedo III? Wandering how close the II would then be to the III. Could mean some sales of the Cinemags to those of us with the II who can't afford to upgrade to the III.