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Author Topic: The Torpedo  (Read 3467 times)

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ultrabike

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The Torpedo
« on: September 03, 2014, 09:25:03 AM »

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.php

The kit is available at http://beezar.com/catalog/product_info.php?cPath=42&products_id=153

From 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.
« Last Edit: September 03, 2014, 10:03:24 AM by ultrabike »
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firev1

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Re: The Torpedo
« Reply #1 on: September 03, 2014, 01:32:51 PM »

Wow thanks for posting this Ultra, this is rather interesting! Both the amps and the effects they impart on the headphones.
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OJneg

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Re: The Torpedo
« Reply #2 on: September 03, 2014, 02:43:43 PM »

My comments from the Shoutbox:

Quote (selected)
The tube with the highest mu should yield the best measurements. Not because high mu tubes are inherent more linear, but rather because feeding the input a hot source (anywhere near 2Vpp) will create distortion

Therefore, a tube with higher mu can achieve an equivalent voltage on the output whie having the loweswt voltage at the gate, hence lowest distortion

It took a bit of poking around with my DMM to figure that out; fortuntely my D/A's output can be set for 0dBV which avoids the problem

It's also worth keeping in mind that 2V into an HD600 is 110dB   :-0 And the HD600 is one of the harder to drive hi Z phones out there in terms of sensitivity.

If you're looking to drive lo Z planars, this isn't the amp for you. It failed to drive the HE560 to any effect at the meet.
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ultrabike

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Re: The Torpedo
« Reply #3 on: September 03, 2014, 03:26:00 PM »

Yup. Tubes voltage swing correlated to non-linear performance. All the non-linear distortion tests were done at 0.4 Vrms into 300 ohms (output voltage), except the ones where HD600 SPL was measured (96 dB @ 1kHz).
« Last Edit: September 03, 2014, 04:04:55 PM by ultrabike »
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Clemmaster

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Re: The Torpedo
« Reply #4 on: September 03, 2014, 09:15:01 PM »

Did anybody try to drive the HD-800 with it?

Would this be considered a good amp for it?
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ultrabike

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Re: The Torpedo
« Reply #5 on: September 03, 2014, 09:31:56 PM »

Possible. The HD800 is around 300 ohms and fairly sensitive so large amounts of current may not be needed. On Hi-Z it might bring up more warmth to the 800s + good voltage swing headroom. Furthermore Hi-Z seems to give better linear results.

On Hi-Z this amp is proly close to the IEC Standard:
http://www.changstar.com/index.php/topic,90.msg403.html#msg403
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OJneg

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Re: The Torpedo
« Reply #6 on: September 03, 2014, 11:46:37 PM »

Clem, I have an HD800 incoming. I'll let you know. I did give a brief listen to the combo at the SF meet and I thought it was pretty solid. Marv and Anax agreed unless I'm mistaken. There are a few other good cheap-ish tube amps around the Torpedo's price though. Valhalla2 and BH Crack + SB come to mind. A more in-depth comparison would be needed to eek out the champion.

BTW ultra, love the new avatar  :)p12
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ultrabike

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Re: The Torpedo
« Reply #7 on: September 03, 2014, 11:58:49 PM »

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Marvey

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Re: The Torpedo
« Reply #8 on: September 04, 2014, 12:07:17 AM »

Yes. Works with HD800 very well. It's a really good amp for the price + effort of putting it together. I pretty much like all of Doug's designs.
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MisterRogers

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Re: The Torpedo
« Reply #9 on: September 04, 2014, 12:46:08 AM »

Agreed. I enjoyed a Torpedo for a good 6 months. I was continually impressed by the performance level of this little amp. Torpedo being a 'Parafeed' had much to do with me trying the Mainline.
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