Tube Preamp Buffer - TOUR!

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Shakeydeal

Re: Tube Preamp Buffer - TOUR!
« Reply #20 on: 21 Feb 2017, 01:52 pm »
I would like to add my name to the list for standby.

Shakey

tortugaranger

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Re: Tube Preamp Buffer - TOUR!
« Reply #21 on: 21 Feb 2017, 02:20 pm »
Hi All - Just a update to the standby list

1) golfrod - CA
2) 33na3rd - WA
3) konut - WA (moved to end of tour due to DAC being unavailable)
4) dracule1 - TX
5) glynnw - LA
6) ozarktom - MO
7) dburna - IL
8 ) tjhub - WI
9) mitch2 - MI
10) wirenut - OH
11) rklein - OH
12) rustyjefferson - MD
13a) konut - WA  13b) slefley - WA

Standby folks in case someone drops out:
1) keven1031
2) skakeydeal
4) JerryM
5)
« Last Edit: 17 Mar 2017, 07:47 pm by tortugaranger »

tortugaranger

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Re: Tube Preamp Buffer - TOUR!
« Reply #22 on: 22 Feb 2017, 09:40 pm »
I just realized I forgot to mention that the buffer unit out on the tour has its gain set at +3 dB and not at the default 0 dB level.

Gain is set via a cathode resistor that we had guessed would yield 0 dB at 11.5k ohms. After the tour unit went out we did the actual final gain measurements  and it turns out 11.5k is perfect for 3 dB. Since the tour unit only has one of three gain resistors installed there's no way to adjust the tour unit gain up or down. Shouldn't be a problem. I ran that tour unit for many hours coupled with an LDR3.V2 passive and I did notice there was more volume headroom so no big surprise.

golfrod will be forwarding the buffer to one other participant in LA (existing customer I shoe-horned in) over the weekend who will give it a vey quick listen before sending it off to 33na3rd next week.

golfrod sent me a very brief note saying "you may be on to something here". More to follow I'm sure. :thumb:

33na3rd

Re: Tube Preamp Buffer - TOUR!
« Reply #23 on: 24 Feb 2017, 05:54 pm »
 I'm really looking forward to hear how that 3 dB gain affects the vinyl side of my system!

Thank you Morten!

golfrod

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Re: Tube Preamp Buffer - TOUR!
« Reply #24 on: 26 Feb 2017, 10:23 pm »
   I've had the new Tortuga Tube Buffer in the system for three days before handing it off to another local user of the Tortuga preamp yesterday. This will really be more of an impression that the buffer left on me than a real detailed review as I only had it for this limited time. The basic system I used it in had the following pieces: Antipodes DX music server>Sonore USB converter>Chord Qute Dac>Tortuga Tube Buffer>Tortuga Preamp or Wyred4sound STP SE modded Preamp>Wells Innamorta Amp> Audience Clairaudient 4+4 Speakers.
   How would you describe the sound of the buffer and it's effect on the system? I think those of you who have experience with both solid state and tube components would understand best. With just one of the two preamps in the system you get a very clear resolved transparent picture with excellent extension top to bottom and very good soundstage in both depth and width. By adding the tube buffer the images get "meatier" with the transients getting slightly softer while retaining very good transparency. This was not a slowing and muddying effect but rather adding a bit of more dimensionality if you will. Another comparison might be a gloss photograph versus a matt finish one. I have a well reviewed Dodd tube buffer which I felt was already quite transparent with a sweet sound. Where I think the Tortuga Tube Buffer has bettered it is the two slight weak points of the Dodd buffer, bass extension and slight smaller scale in soundstage size. With the Tortuga buffer in the chain neither characteristic was reduced in comparison to just the preamps in the system. In fact a friend who came over to listen thought it was more open and layered. One last observation would be that the buffer is very quiet as I could hear no added noise even with your ear at the speaker.
   So what would be my final assessment of the buffer? I think it's a success in that with it you will be able to add a "tube flavor" without really compromising the strong points of the Tortuga preamp. I didn't really get to observe the impedance matching properties of the buffer as the system is fairly well matched already.
   Thanks Morten for the opportunity to try the buffer, great job!

kernelbob

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Re: Tube Preamp Buffer - TOUR!
« Reply #25 on: 26 Feb 2017, 11:30 pm »
Hi Golfrod, I thought the normal position for the tube buffer was after the Tortuga controller, not before it.  The input impedance of the buffer is, if I remember correctly, 100k ohms.  The Tortuga single ended controller is capable of any input impedance from 1k to 99k, so I don't understand the benefit inserting the tube buffer ahead of the controller.

On the other hand, the output impedance of the Tortuga controller can be fairly high with (again if I remember correctly) values as high as 1600 ohms.  The tube buffer specs indicate the output impedance of the tube buffer is around 40 ohms.  That low output impedance of the buffer makes a better match for a power amp, especially if it has lowish input impedance.

I could be completely off track, but I'm curious as to where the buffer would normally be used in the component chain.

Best,
Robert

golfrod

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Re: Tube Preamp Buffer - TOUR!
« Reply #26 on: 27 Feb 2017, 05:34 am »
Hi Robert, I don't believe that there is a "normal position" for a buffer but is rather determined by how you want to use it in your system. Morton has an article on his site ( Is a Preamp Buffer Right for You? ) which talks about various uses for a buffer. I've used several buffers including the well known Burson Buffer. They suggest you try a buffer before and after your preamp. My Wyred4sound SE preamp is buffered on the input and the output..... I only had the buffer for a few days so I mainly wanted to see how the buffer would work as Morten put it in his buffer article as a "sonic coloring agent". I'm very familiar with the sound of the system with the Tortuga preamp right in front of the amp and have no impedance matching problems as the amp has a high enough input impedance. That way I could better assess any changes or effects the buffer had on the sound as that would be the only variable..... I'm sure other participants will use it as you outlined and will report. Thanks, Rod

tortugaranger

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Re: Tube Preamp Buffer - TOUR!
« Reply #27 on: 27 Feb 2017, 11:56 pm »
Hi Robert, I don't believe that there is a "normal position" for a buffer but is rather determined by how you want to use it in your system. Morton has an article on his site ( Is a Preamp Buffer Right for You? ) which talks about various uses for a buffer. I've used several buffers including the well known Burson Buffer. They suggest you try a buffer before and after your preamp. My Wyred4sound SE preamp is buffered on the input and the output..... I only had the buffer for a few days so I mainly wanted to see how the buffer would work as Morten put it in his buffer article as a "sonic coloring agent". I'm very familiar with the sound of the system with the Tortuga preamp right in front of the amp and have no impedance matching problems as the amp has a high enough input impedance. That way I could better assess any changes or effects the buffer had on the sound as that would be the only variable..... I'm sure other participants will use it as you outlined and will report. Thanks, Rod

Rod makes an interesting point that frankly I hadn't spent much time considering. That point being that where you position the buffer - upstream or downstream of an existing preamp - may not matter provided you aren't dealing with an impedance matching issue. As Robert mentioned in his post below the presumption is you put the buffer downstream of a passive attenuator. The logic being this isolates (i.e. buffers) the source/attenuator/preamp from the downstream amp. On the other hand, notwithstanding that the output impedance of our LDR passive preamp (or any pot-in-a-box for that matter) varies with attenuation setting, as long as the preamp output impedance is low enough relative to the amp's higher input impedance, lowering/fixing the impedance into the amp by inserting a buffer might not buy you anything - impedance-wise. Said differently, when the bridging ratio between source and amp are sufficient, making it bigger yet yields little or no incremental benefit. The tube preamp buffer provides a very muscular output signal and whether that's upstream or downstream of a passive attenuator I suspect that characteristic will be evident either way. Same with the whatever euphonics are imparted by the tube stage of the buffer. I will be interesting to hear feedback from others on this. In fact now I have to go try it myself!!  :thumb:

ponger

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Re: Tube Preamp Buffer - TOUR!
« Reply #28 on: 4 Mar 2017, 06:36 am »
Hello all.  I'm the guy that Morten squeezed into the tour, and sort of split time with golfrod.

I really don't have too much to add to golfrod's comments.  Happily, I don't think that any transparency was lost, which I think is one of the Tortugas' biggest strengths.  In my system, the soundstage width was about the same, but the image was a bit larger.  The tone was richer, without losing dynamics.  I think a nice change especially if your system tends to the neutral to slightly thin, detailed side.  My system is comprised of a prototype Well Tempered Turntable > Coda 06x phono stage > Tortuga pre > electronic crossover > 2 Music Reference RM-9 >DIY open baffle 15" and AMT.  Quite different from golfrod's, but much the same impression it seems.

Thank you Morten for the listen, and off to the next tour participant.

Mas

33na3rd

Re: Tube Preamp Buffer - TOUR!
« Reply #29 on: 8 Mar 2017, 12:47 am »
Hi Folks, I had the pleasure of listening to the Tortuga Buffer after ponger.

My system consists of three sources.
Michell Gyro Dec SE/Rega RB-600/Grace F9E>Avid Pellar Phono
Pioneer PLX-1000/Paradox Bodied Shure SC35C>Muse Model One Phono
Marantz CD6004>Rega DAC

Preamp is the Tortuga LDR3.V2 feeding either my modified Moscode 300, or Muse Model 100. Speakers are Audio Physic Virgo 2 and KEF R400b subwoofer.

I first tried the Buffer with my Modified Moscode 300. This amp has an usually high input impedance of 274 kilohm, making it an ideal candidate for use with a passive pre. Unfortunately, adding the buffer in front of the Moscode did not provide any meaningful improvement.

Now when I put the Buffer in front of my Muse Model 100 (Zin 50 kilohm), the buffer added dynamics and better bass!

50 kilohm is still pretty high, so I'm hoping we'll hear from some folks who try the Buffer with amps that have a Zin between 10-35 kilohm.
 
With my Muse in the system The Buffer added a bit of heft to the lower registers that was greatly appreciated on rock/pop tracks. The buffer was largely transparent, rivaling comparably priced preamps, but not as transparent as the LDR3.V2 by itself. I thought the buffer would really help the vinyl side of my system, so I was surprised that it was the digital side of my system sounded so dramatically better with the buffer. My Rega DAC has a Zout of 600 ohms, which is a little high, and the buffer really showed what impedance matching can do. The Buffer did indeed give LP's a firmer foundation, especially the Michell/Avid set up. I liked the tonal balance that the Buffer provided. I did not notice a change in the width or depth of the soundstage in my system.

I enjoyed my time with the Buffer and would like to thank Morten for having me on the tour. It was very educational. I feel like I have a better practical understanding of the relationship between gain, impedance, and current!

Jeff

RDavidson

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Re: Tube Preamp Buffer - TOUR!
« Reply #30 on: 8 Mar 2017, 02:27 am »
Hi Robert, I don't believe that there is a "normal position" for a buffer but is rather determined by how you want to use it in your system. Morton has an article on his site ( Is a Preamp Buffer Right for You? ) which talks about various uses for a buffer. I've used several buffers including the well known Burson Buffer. They suggest you try a buffer before and after your preamp. My Wyred4sound SE preamp is buffered on the input and the output..... I only had the buffer for a few days so I mainly wanted to see how the buffer would work as Morten put it in his buffer article as a "sonic coloring agent". I'm very familiar with the sound of the system with the Tortuga preamp right in front of the amp and have no impedance matching problems as the amp has a high enough input impedance. That way I could better assess any changes or effects the buffer had on the sound as that would be the only variable..... I'm sure other participants will use it as you outlined and will report. Thanks, Rod

I owned the STP-SE for several years. Very good piece of gear. I don't believe it is buffered both on input and output. That wouldn't make sense as only one buffer is needed to do what a buffer is supposed to do (with respect to impedance issues and providing a little bit of a boost in output voltage). Pretty positive the buffer is only on the output as the input stage is purely passive. It's the same setup as Morten's buffered preamp, but with a resistor ladder attenuator and solid state buffer. Sorry. Don't mean to derail. I have a custom built Tortuga based buffered preamp and have been following the thread here and there.

tortugaranger

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Re: Tube Preamp Buffer - TOUR!
« Reply #31 on: 10 Mar 2017, 02:32 pm »
We are having a brief pause in the tour. I've called the tour buffer back home for a very quick tweak to the output stage cap/resistor which provided noticeably improved sound in our testing. It will take less than 24 hours to make the change and send on its way.  :thumb:

golfrod

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Re: Tube Preamp Buffer - TOUR!
« Reply #32 on: 10 Mar 2017, 07:03 pm »
Hi Mr Davidson, While I respect that you owned the Wyred4sound STP I beg to differ as I do believe the preamp is buffered both on the input and output. If you read the literature carefully as well as many of the reviews you'll see that it's even mentioned in the articles. In Srajan's latest review on 6moons of the STP SE stage2 (Jan 2017) you'll see in the first paragraph quote "the STP runs discrete buffers on either side of it's 0.5 dB-stepped attenuator matrix". As far as the reason why this would make sense is the impedance matching on the input and output is just as important on both the amp and preamp. A good buffer will have a high input impedance and a low output impedance which would allow this. I mentioned earlier the well known Burson buffer which I have used with great success and they also suggest you try a buffer in both positions. This is the best explanation I can offer as I'm actually very technically challenged :). Thanks, Rod

RDavidson

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Re: Tube Preamp Buffer - TOUR!
« Reply #33 on: 11 Mar 2017, 04:04 am »
Where we're getting mixed up is in semantics. A buffer consists of an input stage and an output stage. This equals 1 buffer total. The STP-SE doesn't have two buffers. The buffer's input stage and output stage are merely separated (by the attenuator), probably because it is solid state which affords this type of circuit design. Tubes inherently do the impedance conversion / matching (their input stage and output stage are built together in the tube), which is why a tube buffer stage is either entirely before or after the volume control (in a buffered preamp)....but it'd be kinda cool if one could design an "input" tube an "output" tube to make a buffer design like the STP-SE. :thumb:

tortugaranger

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Re: Tube Preamp Buffer - TOUR!
« Reply #34 on: 11 Mar 2017, 03:43 pm »
Where we're getting mixed up is in semantics. A buffer consists of an input stage and an output stage. This equals 1 buffer total. The STP-SE doesn't have two buffers. The buffer's input stage and output stage are merely separated (by the attenuator), probably because it is solid state which affords this type of circuit design. Tubes inherently do the impedance conversion / matching (their input stage and output stage are built together in the tube), which is why a tube buffer stage is either entirely before or after the volume control (in a buffered preamp)....but it'd be kinda cool if one could design an "input" tube an "output" tube to make a buffer design like the STP-SE. :thumb:

I agree this is partially a semantics issue. The confusion is compounded by the fact that there are buffers and then there are buffers. In circuit design it's very common to put a simple high impedance buffer at the input of say a preamp for isolation. Typical of such a buffer is a simple unity gain op amp as shown below.

 

A consumer reading a manufacturer's product description reads that the buffer product has a buffer on the input and the output. Wow, a buffer with a buffer at both ends. Technically true but the meat & potatoes high performance end of most audio buffer products is the output stage.

In the case of our 2 stage tube buffer you would be correct in describing the tube itself as an input buffer (with optional gain). The output stage is a solid state buffer. Taken as a whole, it's an audio buffer.

RDavidson

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Re: Tube Preamp Buffer - TOUR!
« Reply #35 on: 11 Mar 2017, 06:49 pm »
Interesting stuff Morten and thanks for further clarification. What you're doing seems pretty unique. I'm not sure I've seen another buffer that uses a tube as only the input stage....unless most tube buffer's are designed this way? I don't think they are.

tortugaranger

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Re: Tube Preamp Buffer - TOUR!
« Reply #36 on: 11 Mar 2017, 07:02 pm »
Interesting stuff Morten and thanks for further clarification. What you're doing seems pretty unique. I'm not sure I've seen another buffer that uses a tube as only the input stage....unless most tube buffer's are designed this way? I don't think they are.

This is the conceptual design but like most things the devil's in the details. You can call it a 2-stage hybrid buffer or you can call it a 0 to +6 dB  gain preamp without a volume control - both are correct.


sfox7076

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Re: Tube Preamp Buffer - TOUR!
« Reply #37 on: 14 Mar 2017, 02:35 pm »
It's a gyrator concept.  I used a similar concept to build my preamp that uses DHTs (I have 16-18db of gain though).  Mine was based on the work of Ale of Bartola Valves.  I won't discuss more than that here, because here is not the place, but it is the best sounding design I have ever heard and mates very well with a passive attenuator.   I am sure the Tortuga version is amazing.

tortugaranger

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Re: Tube Preamp Buffer - TOUR!
« Reply #38 on: 17 Mar 2017, 06:38 pm »
The tour unit is back on the road after a longer stay in the barn than I'd planned. The changes only took a couple of hours plus some testing to confirm but it was finding the time to get it done.

The tour unit now has the upgraded VCap OIMP output caps. Both the output cap and resistor size was changed to optimize performance. To my ears the buffer now has even more coherent output than before. I also popped in a Belleson SuperRegulator which powers both the tube plate and the output FET. Sounds great on my rigs. Looking forward to everyone's feedback.

If anyone on the tour happens to have a pair of 6CG7 tubes sitting around feel free to substitute them for the 6H30's and let us know what you think. I tried this recently and the buffer is quite happy with 6CG7s.

Enjoy!
Morten

JerryM

Re: Tube Preamp Buffer - TOUR!
« Reply #39 on: 17 Mar 2017, 06:49 pm »
I volunteer to be the very last AC member on the Tour.  8)

And yes, I have several different pairs of NOS 6CG7s here.  :D

Have fun,

Jerry