That was exactly what I thought I was going to find when I first saw the PCB shot. It just got weird after that.
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Tortuga TPB.V1 Tube Preamp Buffer Review
- Thread starter amirm
- Start date
solderdude
Grand Contributor
The guy is not after creating a high quality low distortion tube buffer.
I suspect he wanted as much harmonics.
Gain selection appears to just be 3 different cathode resistors.
This seems to be what's in the product:
on the tube side there also seems to be a current source.
https://tortugaaudio.com/docs/tpb-v1-service-manual/
I suspect he wanted as much harmonics.
Gain selection appears to just be 3 different cathode resistors.
This seems to be what's in the product:
on the tube side there also seems to be a current source.
https://tortugaaudio.com/docs/tpb-v1-service-manual/
KSTR
Major Contributor
Tortuga show a basic circuit diagram for the single-ended version:
Anode and (switchable) degeneration resistors not shown, but of course those are essential to make the first stage a (low-gain) inverter. In the balanced version I would guess they use a degenerated LTP with CCS bias and hopefully they got the polarity right (SE version inverts). Anyway, the tube will run with strong local feedback to reduce gain and total distortion, at the cost of introducing the full spray of upper harmonics.
Anode and (switchable) degeneration resistors not shown, but of course those are essential to make the first stage a (low-gain) inverter. In the balanced version I would guess they use a degenerated LTP with CCS bias and hopefully they got the polarity right (SE version inverts). Anyway, the tube will run with strong local feedback to reduce gain and total distortion, at the cost of introducing the full spray of upper harmonics.
KSTR
Major Contributor
I don't think so. He just didn't anticipate that someone would throw 4Vrms at it. ;-)
Up to 2Vrms I think the perfomance (THD -65dBc, 0.05%) is pretty acceptable with the stock tubes (at least with the left channel). I'd love to see a 1kHz spectrum at 1Vrms and several kOhm of input series resistance, mimicking a pot's worst case impedance (@amirm).
So the cost is justified by using stupidly expensive V Caps.
At voltages up to 2Vrms, especially for the right channel, this thing is approaching transparency for listening to music. Seems like a lot of parts and expense to in essence "do nothing" (except make things worse that you can't hear). I guess if you put the wrong tubes in it at least it "does something" you can hear.
solderdude
Grand Contributor
Alas
The buffer is meant to be used after the LDR volume control. So when set to -20dB or so (what could be normal listening level) the THD of the volume control will be even higher than that of the buffer.
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No sane audiophile in the 1960s would have used a SET amplifier. They were relegated to jukeboxes and radios. The adoption of this primitive technology by modern enthusiasts is simply perverse.
No, in my case using a SET solves a specific problem. Sweeping generalities are generally not accurate.
Robin L
Major Contributor
I'd be curious to find out what problem got ironed out by a paleolithic design. I will confess to having heard that special SET magick a couple of times. It's all about the midrange.No, in my case using a SET solves a specific problem. Sweeping generalities are generally not accurate.
OP
- Thread Starter
- #212
What?
My speakers (horns - active crossovers) are 107db/w efficient from 500Hz up, and this is the driver which uses the SET. I use the SET to eliminate any potential for crossover distortion - the audibility of this form of distortion has been a problem in the past. These drivers, coupled to the large horns, are so sensitive that any low level grunge or noise upstream is audible. A PP class "A/B" tube amplifier or ultralinear amp would also be devoid of crossover distortion, but this topology would suppress even order harmonic distortion which then leaves the odd orders to irritate. The SET is heavily modified and uses feedback, so the harmonic distortion is typically <= .02% at most at the levels I listen at.
Also, since the SET is only capable of 2.5 watts, potential accidental damage to the diaphragms of the drivers is lessened.
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magicscreen
Active Member
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- May 21, 2019
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Sorry, I have not seen any successful double blind test in audio.
OP
- Thread Starter
- #215
I have post countless ones that I have passed (search for my alias and foobar). No way one can claim transparency for all people with such high levels of distortion.
dasdoing
Major Contributor
I can understand that some like the warmer sound of saturation.....
BUT, why not use something like this where you actualy have control over the saturation? https://www.thermionicculture.com/i...ure-vulture-1-17-192012-03-20-11-02-02-detail
BUT, why not use something like this where you actualy have control over the saturation? https://www.thermionicculture.com/i...ure-vulture-1-17-192012-03-20-11-02-02-detail
Way too little audiophile lingo. It is as if that product was designed by, *gasp*, actual engineers.
It would have been interesting to see an ASR review of that part.
dasdoing
Major Contributor
here it is on a full track. he uses a more advanced version but in the T mode which is also available in the basic version
That sounded sweet in the mastering part of the video. I’ll bet this device can push the harmonics way over the fundamental when it is cranked to full tilt?
Distortion that doesn’t suck FTW.
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