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300B OTL Preamp/Headphone Amp

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#3
FullRangeMan said:
Comments on this 300B OTL headphone amp wanted.
Velvetizer

Could it be better than the 6N1P from Decware (CSP3):
Audiophile Tube Preamplifier / OTL Headphone amp by DECWARE
Thanks
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I don't see how the Velvetizer could fail to be better than the Audiophool Preamp: it's Decware -- 'nuff said.

"Purist SRPP design Zero negative feedback"

They obviously don't know how to use an SRPP. This design remains balanced for just the one load impedance where the Isource= Isink. This was not a prob for its intended purpose: a line driver working into the characteristic impedance of a low SWR T-line.

For other loads, it quickly goes out of balance. Speeks and headphones represent anything but a constant load. Fail to include corrective NFB, and the performance of the SRPP degrades even faster and farther. The Decware Audiophool Preamp/Headphone amp goes for just $124,900 😱 😱 😱 😱

The Transcendent Sound offering might include audiophool marketing nonsense, but at least they show specs and distortion profiles that look quite clean, which, of course, means it can't really be the FX box the ad copy says it is.
 
#4
How much feedback on the Transcendent? He uses a lot of feedback on his other OTL designs. All that bragging about low output impedance and low distortion, that's all made possible with tons of feedback. Feedback done right sounds good, but it is not an easy design task and there are very few high feedback amps in this world that sound as good as non-feedback amps. With OTL you need a lot of negative feedback, and yes, you hear it. That's why decware advertises no feedback. Does dec mean no global feedback or none at all?

Another thing to consider about the 300B is there are plenty of OK sounding 300B tubes available for reasonable money, but the really good ones are pretty expensive. Shuguang Black Treasure are the best I've tried, $330/pair.

Make sure the Transcendent's output caps are small enough that you can afford to upgrade them to decent quality film caps. My Transcendent Grounded Grid Preamp kit came with Solen caps (yuk.) The advantage of using a lot of feedback is the output cap should be small in size, but check to make sure. You don't want to need 100uF and have to use electrolytic.
 
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#6
jazbo8 said:
Even funk's Lego OTL looks better than the Velvetizer, might even sound better...😛
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Thanks! I appreciate it 😀. And costs a sh#tload less too.

I seriously doubt decware can achieve less than 60 ohm output impedance with a SRPP with the claimed ZERO feedback. Second, as miles pointed out, a SRPP needs to be optimized for a certain load for max performance. What's more, you'll only get 30V output into a very high load. BS upon BS.

And what about a SRPP is 'purist' 😕. Not impressed by decware.
 
#8
Richidoo said:
How much feedback on the Transcendent? He uses a lot of feedback on his other OTL designs. All that bragging about low output impedance and low distortion, that's all made possible with tons of feedback. Feedback done right sounds good, but it is not an easy design task and there are very few high feedback amps in this world that sound as good as non-feedback amps. With OTL you need a lot of negative feedback, and yes, you hear it. That's why decware advertises no feedback. Does dec mean no global feedback or none at all?
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That's the halibut right there. With an OTL, you lose the OPT and its associated nonlinearities. You gain many paralleled VTs all operating into near vertical loadlines that aren't linear. Is that really an improvement? You will be needing gNFB to compensate regardless of whether you include an OPT or not. I think you'd be better off going solid state with the OTL back end: no need for lots of amps for heaters, no need to massively parallel to get bigamps for speeks, and devices that are naturally high current, low voltage (therefore Lo-Z) are probably less bothered by nasty, vertical loadlines.

Decware means no gNFB. They still use triodes, and triodes have an internal NFB mechanism built into it as Vgk and Vpk are pulling Ip in opposite directions, which is NFB by definition, and triodes display all the consequences of NFB: the reduced voltage gains, and lower rp's as compared to pentodes and transistors that avoid that inherent NFB.

Another thing to consider about the 300B is there are plenty of OK sounding 300B tubes available for reasonable money, but the really good ones are pretty expensive. Shuguang Black Treasure are the best I've tried, $330/pair.
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Which is why I don't use them. Why pay that audiophool premium if you don't have to? Lots of really decent audio finals available by repurposing TV HD and VD power finals. Some, like the 6AV5, can be made into pseudotriodes that sound every bit as good as 300Bs and 2A3s for a whole lot less. Probably other types will work that way too, if their screens will stand the voltage spec busting.
 
#9
funk1980 said:
Thanks! I appreciate it 😀. And costs a sh#tload less too.

I seriously doubt decware can achieve less than 60 ohm output impedance with a SRPP with the claimed ZERO feedback. Second, as miles pointed out, a SRPP needs to be optimized for a certain load for max performance. What's more, you'll only get 30V output into a very high load. BS upon BS.

And what about a SRPP is 'purist' 😕. Not impressed by decware.
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Whar I find strange in the Decware CSP2/3 is they use pots in the input and output.
Would it be hiding anything??
 
#10
FullRangeMan said:
Whar I find strange in the Decware CSP2/3 is they use pots in the input and output.
Would it be hiding anything??
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Yeah, I agree. Reminds me of several bass amps I owned. 'Gain' control to set the input level and master volume for the output. It's the ultimate compromise to accommodate for the variety of input signals and sensitivity levels of the next stage. But a compromise non the less. In the CSP2/3's case for example, a 6922 will distort like crazy when presented with a 5V input signal, yet that's what they've designed for. I don't really dig it for what's supposed to be a high-end headphone/pre amp, as it will also alter the amount of distortion depending on the ratio between the two controls and your able te set them to put out the same signallevel with totally different THD+N.
 
#14
Wow. Tough crowd.
I use a CSP2, so far only in front of SS power amps and it's never failed to sweeten whatever I drive with it (at this very moment an ACA). Headphone use is a distant second place. I listen with my ears, not my formulas and for my purposes, it is also what I believe to be the perfect pre for something like a FirstWatt F4 (not yet, but soon to be, built), which will need the voltage the CSP can supply.
 
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