This is a loaner from OJ. Thanks mang!
This came with three tubes: 6J6W, 5844, and Telefunken (E90CC). The layout and presentation of this amp is pretty spectacular IMO. It's all black and I like that. It doesn't get too hot. Seems easy enough to build and comes with plenty of support.
Here is the BOM and info:
http://www.diyforums.org/Torpedo/TORPEDObom.phpThe kit is available at
http://beezar.com/catalog/product_info.php?cPath=42&products_id=153From my impressions (with my HD600s) I felt the 6J6W and the 5844 where a little brighter but perhaps more accurate than the E90CC which I thought was more mellow and forgiving. The E90CC carried IMO a tad more impact and warmth. Still when pushing the volume at Lo-Z things degraded a little with cymbals and detail when using the E90CC. I liked the E90CC better though. Less strident perhaps.
Overall, the amp is pretty involving and dynamic with my HD600s at the volume I usually listen. I think I prefer to listen at Hi-Z w the Torpedo though, at least with the E90CCs.
The following are some impedance measurements:
6J6W: Lo-Z = 21 ohms / Hi-Z = 146 ohms
5844: Lo-Z = 19 ohms / Hi-Z = 119 ohms
E90CC: Lo-Z = 16 ohms / Hi-Z = 96 ohms
The following are some voltage swing measurements (rms):
6J6W (Lo-Z) = 2 V (into 300 ohms) / 2.15 V (open)
5844 (Lo-Z) = 1.7 V (into 300 ohms) / 1.8 V (open)
E90CC (Lo-Z) = 1.43 V (into 300 ohms) / 1.5 V (open)
E90CC (Hi-Z) = 3.48 V (into 300 ohms) / 4.59 V (open)
Lowest distortion was achieved w the 6J6W which was also the tube that yielded highest output impedance, and highest voltage swing... Guess Low-Z does not always correlate to lower non-linear distortion. Highest distortion was present with the E90CCs.
Into 300 ohms and @ 400 mV (rms) the following are THD numbers:
6J6W (Lo-Z) = 0.476%
5844 (Lo-Z) = 0.538%
E90CC (Lo-Z) = 0.602%
E90CC (Hi-Z) = 0.383%
Hi-Z yields lower distortion numbers for all tubes.
IMD SMPTE 60Hz + 7kHz (300 ohms @ 400 mV rms)
6J6W (Lo-Z) = 1.28%
5844 (Lo-Z) = 1.37%
E90CC (Lo-Z) = 1.48%
E90CC (Hi-Z) = 0.935%
IMD DIN 250Hz + 8kHz (300 ohms @ 400 mV rms)
6J6W (Lo-Z) = 1.28%
5844 (Lo-Z) = 1.38%
E90CC (Lo-Z) = 1.52%
E90CC (Hi-Z) = 0.964%
IMD CCIF 19kHz + 20kHz (300 ohms @ 400 mV rms)
6J6W (Lo-Z) = 0.851%
5844 (Lo-Z) = 0.850%
E90CC (Lo-Z) = 0.756%
E90CC (Hi-Z) = 0.434%
My understanding is that < 2% IMD for this class of amps is considered good, but I'm not an expert.
The following are plots for THD with the 6J6W and E90CC at Lo-Z
6J6W
E90CC
The following are plots for IMD (SMPTE) with the 6J6W and E90CC at Lo-Z
6J6W
E90CC
While I felt the E90CCs had more warmth to them, relative to E90CCs there seems to be more upper bass distortion (THD and IMD) with the 6J6W. I did feel the E90CCs where more pleasant though.
However, the 6J6W while lower in THD, does seem to have more harmo
nics up into the treble area. Not sure if this would become significant with complex music and indeed be one of the reasons I felt more stridency with the 6J6Ws, which may or may not explain why I felt the E90CC were more warm and pleasant.
The following are plots for HD600 distortion (@ 96dB SPL) being driven by 2i2, Torpedo E90CC Lo-Z, and Torpedo E90CC Hi-Z:
2i2
Torpedo E90CC Lo-Z
Torpedo E90CC Hi-Z
As can be seen, the amps do seem to impart their distortion characteristics. In terms of linearity, HD600 seems to perform better with Torpedo in Hi-Z mode relative to Lo-Z. However, there will be about 1 dB of bass gain due to output impedance increase.
Subjectively I feel this amp was pretty enjoyable and paired well with my HD600s.