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Tortuga TPB.V1 Tube Preamp Buffer Review

amirm

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This is a review and detailed measurements of the Tortuga TPB.V1 Balanced Tube Preamp Buffer with various set of tubes. It is on kind loan from a member and costs US $1,695 with "Matched Pair Electro-Harmonix 6H30Pi Gold triode tubes."

There is not a whole lot to look at here other than the two tubes sticking out the back:

TPB.V1 Tube Preamp Buffer Review balanced.jpg


There is an internal gain setting which I left alone meaning the unit runs as a buffer (gain of 1). Architecture is tube front-end but back-end is transistor based (I assume to keep impedance low). There is some kind of protection and monitoring circuit that blinks until the tubes have stabilized.

Like the balanced configuration which is rare in tube products:

TPB.V1 Tube Preamp Buffer Review back panel balanced.jpg


The transformer bolt had come loose and I could feel it by shaking it. Tried to tighten it from outside but keeps turning. Likely need to hold the nut inside to keep it from turning.

There are no safety marks on the amplifier.

Tortuga TPB.V1 With Electro-Harmonix 6H30Pi Tubes Measurements
I installed the pair of tube supplied with the amplifier and fired up the dashboard:

TPB.V1 Tube Preamp Buffer Measurements With Electro-Harmonix 6H30Pi.png


I always think something is broken in my instrumentation until I realize this is a tube amp that is made to be a distortion generator (intentionally or not). These are stunningly high levels of distortion but we are driving it at full level. I will show lower levels in a bit. Note that the spectrum shows the dominant component is third harmonic, not second. So even if we assume the common myth that 2nd harmonic is good for you, this box won't deliver that.

Let's sweep the level and see how the distortion varies:

TPB.V1 Tube Preamp Buffer THD+N vs Level Measurements With Electro-Harmonix 6H30Pi.png


The tubes don't seem very "matched to me." That aside, at very low input/output levels, distortion+noise goes down to -60 to -70 dB. In my experience, typical audiophile can't perceive such levels of distortion so it is unlikely any effect you think you are hearing is due to this box.

SNR is better than I expected:

TPB.V1 Tube Preamp Buffer SNR Measurements With Electro-Harmonix 6H30Pi.png


Frequency response is excellent:

TPB.V1 Tube Preamp Buffer Frequency Response Measurements With Electro-Harmonix 6H30Pi.png


As is crosstalk:
TPB.V1 Tube Preamp Buffer Crosstalk Measurements With Electro-Harmonix 6H30Pi.png


What is not so excellent is IMD distortion+noise:

TPB.V1 Tube Preamp Buffer IMD Distortion vs level Measurements With Electro-Harmonix 6H30Pi.png


Ditto for THD+N vs frequency which is off the chart almost:

TPB.V1 Tube Preamp Buffer THD+N vs Frequency Measurements With Electro-Harmonix 6H30Pi.png


Fortunately it is horrible at all frequencies so there is a silver lining there!

Tube Rolling Measurements
I was supplied with three other sets of tubes so let's look at how they do starting with Electro-Harmonix 6922:

TPB.V1 Tube Preamp Buffer Measurements With Electro-Harmonix 6922.png


Man, this makes the supplied tubes look hi-fi! It has so much distortion that you don't need to measure them: just look at how deformed the sine wave has become! People say "trust your ears." No, I say trust your eyes!!! This is horrid. Notice that gain has become negative as well. But maybe these tubes are broken, or the circuit is not optimized for them.

Another set that was supplied is from Russian Reflector factor, the 6H30P-DR:

TPB.V1 Tube Preamp Buffer Measurements With 6H30P-DR Reflector factory.png


We get the same performance as the supplied tubes which I guess is "good."

The wheels fall off again when we switch to Mullard CV2493 tubes:
TPB.V1 Tube Preamp Buffer Measurements With Mullard CV2493.png


The owner tells me these are highest spec'ed tubes of this kind. If they are, something is really, really wrong here.

Conclusions
I am sure everyone who bought these preamps had different ideas than what these measurements show. They thought they were getting second harmonic "tube sound" but instead are getting 3rd harmonic. And with half the tubes tested, the product is just outright broken with severe distortion. I don't care if you want to believe in tube products. Ask for measurements so that you know you are getting what you imagining.

No, I am not going to recommend the Tortuga TPB.V1 Balanced Tube Preamp Buffer. Don't screw up your system with stuff like this. Spend the money on good music, food and fun with the family instead.

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Vict0r

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Thanks for the review, sleep tight and don't let the tube bugs bite. :p
 

YSC

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hum~ but... but don't you think that smooth sloping of the distortion with the main signal looks harmonic and artistic?:cool:
 

anphex

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I am suprised about how the things that should be the main features are the worst performing.

Matched tubes: shows the worst offset I've seen so far
Harmonic tube distortion: 3rd harmonic it is!

Couldn't you just get a really really cheap underpowered no name amp and run it clipping at 5% THD to achieve the same?
 

DSJR

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I seem to recall that many/most tube amp measurements show plenty of third harmonic (memories of many Stereophile tests). I suspect it's how these harmonics are evenly spread that can aid the so-called 'tube sound' in many *domestic* designs...
 

Koeitje

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Well the goal of this product is to add distortion, so they succeeded I guess.
 

Stoutblock

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Might try reversing the tubes from left to right and see if the mismatch problems follow? Would be good to know if the "effects" are at least equal in the component from left to right?

It is interesting that Tortuga designed the buffer for the 6H30 tube but also says the 6922 series can also be used. These tubes are not compatible in most circuits due to heater current. I don't think the 6922 tube is being operated per specification in this circuit but it appears to function (barely).

The 6H30Pi is EH's current TOTL line tube for this series.

The 6H30P-DR are from the Soviet era made by Reflector. Said to be the most liner of triodes. Once quite cheap in the early days of the iron curtain coming down. Now getting very expensive but obvious of no benefit in this circuit.

The EH6922 is a standard inexpensive tube readily available.

The Mullard CV2493 is a rare tube from the 70s that can be used in 6922 applications. Said to be one of the highest performing tubes of this family and popular in tube phono stages. Obviously of little benefit in this circuit.
 
Last edited:

charleski

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The idea that tube amps predominantly offer low even-order distortion is a complete myth, as shown here. It's all about the circuit design, and it just happens that some of the classic tube designs end up that way ... but you can easily change that if you fiddle the circuit without having a clue. No volume control, no input selector, what is this expensive box supposed to do? Is it really just being sold as a way to bolt on some 'tube sound'? The mind boggles.

These are Russian tubes, so the 'H' is actually an 'N' ;)

Impressive frequency response for a tube design, though the rest is junk.
 

Veri

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Maybe I am missing something: with no gain and no function knob, what is the purpose of this box? Impedance matching? Or rather distortion generator?
Tube buffer distortion generator...?
 

Stoutblock

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Maybe I am missing something: with no gain and no function knob, what is the purpose of this box? Impedance matching? Or rather distortion generator?

From the website:
  1. Improve the sound quality of your existing preamp
  2. Sand some of that hard digital edge off your DAC’s output
  3. Add some tube euphonics to your solid state system
  4. Allows you to use long cable runs between your passive preamp and amp.
  5. Resolves most impedance mismatches between components
  6. Drive a subwoofer amp from your passive preamp
  7. Put more authority and punch into your system’s dynamics
 

3125b

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Sure, 1700$ might seem a lot, but you're not only getting 2nd order harmonics, but all the harmonics, IMD, noise and power supply hum. Not a bad deal now, is it?
 

Jimbob54

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