New Preamp

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DaveC113

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Re: New Preamp
« Reply #40 on: 29 Nov 2015, 08:31 pm »
Yeah, I think it would be best to not add resistance to the output. The buffer should be capable of driving a whole bunch amps at the same time. If you calculate the current required operating at 2V RMS with a 50k (or whatever) impedance using Ohm's Law you'll find it's a tiny bit of current. I do think the available current should be many multiples of what's required, but in any case the 6SN7 outputs are running around 8mA with an output impedance of 500-600 ohms which should be fine for a great majority of implementations. Subjectively, the buffer sounds a lot better to me, it adds nice tone and body, improves dynamics and dimensionality. It makes the music more engaging and fun to listen to.  :D


rollo

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Re: New Preamp
« Reply #41 on: 30 Nov 2015, 07:28 pm »
 Sorry late to the party. This is such a wonder to look at oh my !! Gorgeous just gorgeous.


charles

rajacat

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Re: New Preamp
« Reply #42 on: 30 Nov 2015, 07:54 pm »
Yeah, I think it would be best to not add resistance to the output. The buffer should be capable of driving a whole bunch amps at the same time. If you calculate the current required operating at 2V RMS with a 50k (or whatever) impedance using Ohm's Law you'll find it's a tiny bit of current. I do think the available current should be many multiples of what's required, but in any case the 6SN7 outputs are running around 8mA with an output impedance of 500-600 ohms which should be fine for a great majority of implementations. Subjectively, the buffer sounds a lot better to me, it adds nice tone and body, improves dynamics and dimensionality. It makes the music more engaging and fun to listen to.  :D
Thanks for the detailed reply.
I'll go ahead and build the buffer and try it first on the output for my waveguides' compression tweeters. If I like it, I'll wire the Tortuga so that the it can be used on all the outputs via a couple sets of RCAs'. I've already built the Torts' case so it would be awkward installing the buffer due to space limitations. 

Odal3

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Re: New Preamp
« Reply #43 on: 1 Dec 2015, 04:40 pm »
Many thanks for the info!

DaveC113

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Re: New Preamp
« Reply #44 on: 1 Dec 2015, 05:10 pm »
Thanks for the detailed reply.
I'll go ahead and build the buffer and try it first on the output for my waveguides' compression tweeters. If I like it, I'll wire the Tortuga so that the it can be used on all the outputs via a couple sets of RCAs'. I've already built the Torts' case so it would be awkward installing the buffer due to space limitations.

I'm pretty sure you'll be happy with it... A few things are worth upgrading from the kit imo:

- Last stage power supply caps to Clarity TC, those are the big blue caps that are mounted to the chassis....

- Cathode and last stage PS resistors to Mills

- Grid stoppers and grid leak to Amtrans carbon (stay far away from Kiwame)

- Output caps to Jupiter Copper and use the supplied ones for 1st stage power supply bypass, C17 I believe.

If you want to do 6V/12V switching for the heaters you need a 3PDT switch, the board is already setup for it with jumpers for series/parallel operation so this is pretty easy to implement.


rpf

Re: New Preamp
« Reply #45 on: 13 Dec 2015, 05:20 pm »
Beautiful pieces! Congrats, guys.

Freo-1

Re: New Preamp
« Reply #46 on: 13 Dec 2015, 05:27 pm »
Looks awesome.  Bet it sounds great.

Looking forward to a evaluation of the sound.

Salectric

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Re: New Preamp
« Reply #47 on: 17 Dec 2015, 06:25 pm »
Very nice looking! 

I am curious about the breakin requirements of the Silver/Gold wires used in the chassis wiring.  They seem to use Teflon insulation or something similar so don't they need several hundred hours of use to break in fully?  Is there any way to simplify that process with chassis wiring or do you just have to use the preamp for a few months?

DaveC113

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Re: New Preamp
« Reply #48 on: 17 Dec 2015, 08:17 pm »
Hi Saleectric, I have a cable cooker so I could have used that but lots of other stuff needs to burn-in anyways. The burn-in on the silver/gold wire isn't that bad... it's there but it's more subtle than other kinds of wire like my copper litz wire. That stuff makes your system sound broken for the first few hours, very dramatic burn-in. Overall burn-in on new components like this is pretty dramatic with the forst few hours sounding really bad compared to later and this is no exception. By now it's sounding amazing though, which leads to Freo's question about sound...

Freo, the sound is awesome. We sprang for top of the line parts like Furutech FP-901(R) RCA jacks, Jupiter copper caps, Clarity TC power supply caps, Mills resistors, my D4 cable for internal wiring, etc... I tried the Tortuga LDR by itsself and it's a spectacular attenuator, very clear and seems to have no effect on the signal at all. The tube buffer improves dynamics, tone, and dimensionality as well as buffering the signal, the same things most people comment on wrt tube buffers but in this case the buffer design and parts are as good as it gets. The rest of the system is currently a optioned-out Odyssey Stratos and Pioneer S-1EX speakers, I couldn't be happier with how it all turned out! I still love my Omegas and have projects planned for them but this system is spectacular.


Salectric

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Re: New Preamp
« Reply #49 on: 22 Dec 2015, 01:16 pm »
Dave, thanks for the reply.  I am going to order some Silver/Gold from you to try as input signal wiring in my linestage.  Presently I have Neotech 20g Silver for both signal and ground wiring, so the Silver/Gold should make a nice comparison.  I am curious why you continue to use the solid silver wires for ground connections (for example in the D4) if the Silver/Gold sounds better.  Do the two cables perhaps have complementary colorations that make the combination better sounding than either wire by itself?

DaveC113

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Re: New Preamp
« Reply #50 on: 16 Jan 2016, 05:42 pm »
Dave, thanks for the reply.  I am going to order some Silver/Gold from you to try as input signal wiring in my linestage.  Presently I have Neotech 20g Silver for both signal and ground wiring, so the Silver/Gold should make a nice comparison.  I am curious why you continue to use the solid silver wires for ground connections (for example in the D4) if the Silver/Gold sounds better.  Do the two cables perhaps have complementary colorations that make the combination better sounding than either wire by itself?

At this point it's more a question of how much cream do you like in your coffee? :)

The silver/gold alloy removes the main disadvantages of pure UPOCC silver, it makes for a more realistic timbre and more weight to the images. Some cable companies use a LOT of UPOCC silver to reduce this issue, both Wireworld and Siltech use 17g of UPOCC silver in their top end IC cables. I use a more normal amount of wire for my IC cables but go with the gold alloy instead of just using twice as much pure silver wire. The difference between the pure silver and silver/gold alloy isn't huge, but it's really what makes my cables special, unique and higher performing than my competition.

Salectric

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Re: New Preamp
« Reply #51 on: 18 Jan 2016, 02:13 pm »
Very interesting!  Your shipment of some Silver/Gold arrived Friday so I will be trying it soon. 

DaveC113

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Re: New Preamp
« Reply #52 on: 18 Jan 2016, 03:45 pm »
Very interesting!  Your shipment of some Silver/Gold arrived Friday so I will be trying it soon.

Oh, good!   :thumb:  Let me know what you think.

Tomy2Tone

Re: New Preamp
« Reply #53 on: 1 Apr 2016, 12:35 am »
So Dave, have you guys been making anymore of these amps? I'm hoping to try a Tortuga again and see how it performs with my Lampi dac pushing it to my Odyssey Kismet amps but I'm really intrigued about your version here with the 6sn7 tubes.

Never heard a 6sn7 tube before, my current preamp uses 6922's. Anybody know what differences there are between these two?

RPM123

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Re: New Preamp
« Reply #54 on: 1 Apr 2016, 01:46 am »
So Dave, have you guys been making anymore of these amps? I'm hoping to try a Tortuga again and see how it performs with my Lampi dac pushing it to my Odyssey Kismet amps but I'm really intrigued about your version here with the 6sn7 tubes.

Never heard a 6sn7 tube before, my current preamp uses 6922's. Anybody know what differences there are between these two?

Well, here is something from Dehavilland Electronics: "The octal tubes we employ give you what in "Tube Lore" is described as "BIG TONE", something you just can't get with nine pin miniature tubes found in most preamps. 12AX7’s or 6922’s just can't get there. While many companies say that the simplest circuit is the best, they don’t practice what they preach -- they have miles of circuitry and solid state regulation everywhere."  http://www.dehavillandhifi.com/UltraVerve-Preamplifier.htm

And having had both types of preamps, I would have to agree with the above statement. They (6Sn7) do tend towards a more "robust" sound, which I like...a lot!

Tomy2Tone

Re: New Preamp
« Reply #55 on: 1 Apr 2016, 02:09 pm »
Well, here is something from Dehavilland Electronics: "The octal tubes we employ give you what in "Tube Lore" is described as "BIG TONE", something you just can't get with nine pin miniature tubes found in most preamps. 12AX7’s or 6922’s just can't get there. While many companies say that the simplest circuit is the best, they don’t practice what they preach -- they have miles of circuitry and solid state regulation everywhere."  http://www.dehavillandhifi.com/UltraVerve-Preamplifier.htm

And having had both types of preamps, I would have to agree with the above statement. They (6Sn7) do tend towards a more "robust" sound, which I like...a lot!

Thanks for that link. Amazing what tubes can do and it sounds like the 6sn7 gives what some would say is a more traditional tube sound. Can you say what preamp you had that used 6922's?

jriggy

Re: New Preamp
« Reply #56 on: 1 Apr 2016, 03:22 pm »
6SN7's tend to have microphonic issues more often than the smaller 9pin tubes do, so it can be a lil laborious to fit a quiet pair that you also like a lot. Doesn't mean it can't be done, just that it 6SN7's can be a lil more prone to it.

With that said...

Tony2Tone,

I love to hear from ya if you do that test, since we have the same pre and same DAC  :thumb:

I contacted Dave about this preamp late last year but I was unable to continue at the time... It is a beautiful looking unit and the parts combination is very intriguing.

Jason

RPM123

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Re: New Preamp
« Reply #57 on: 1 Apr 2016, 03:38 pm »
Thanks for that link. Amazing what tubes can do and it sounds like the 6sn7 gives what some would say is a more traditional tube sound. Can you say what preamp you had that used 6922's?

I have had Audio Horizon and Dodd Audio preamps. I currently have a MW LS100 pre with some East German 6SN7s, which sound great in this unit!

Here is what Brent Jesse has to say about the tubes in question:

"The 6SN7 tube is a medium-mu twin triode in an octal based package, usually glass, although some metal envelope types were made. In normal use it operates as a class A amplifier. It was widely used in the early days of television as the vertical amplifier, and it's use was so common in most TV chassis designs that vintage 6SN7 tubes are still fairly easy to find today. Audio designers soon found it made a great audio preamp with it's large plates, ample power reserve, and low microphonic octal package. The GTA and GTB types, having been fine tuned for demands in television chassis vertical sweep circuits, can handle up to 7 watts maximum plate power!

The demands for these tubes today are primarily in vintage and recent design audio amplifiers and preamplifiers of the high-fidelity type, up to and including the most expensive and esoteric. It seems there is a 6SN7 tube for every taste and budget, and some of the vintage versions are being hunted to extinction, especially those made for the military. I will try to explain the differences between some of these tubes, and list specifically what I have in stock. I expect some of these tubes will skyrocket in price worldwide as more and more audio designers find out that this preamp tube is a design that really can't be improved upon....and that the fine vintage tubes just cannot (and probably will not) ever be duplicated by a current production tube.

Three envelope sizes are common in the full octal base version: SHORT, glass is 1.5 inches high; MEDIUM, glass is 1 3/4 inches high; TALL or "TALL BOY", glass is 2 inches high."

"The 6DJ8 is a twin triode in a small 9-pin miniature glass package, with a very high transconductance for each triode unit. Well made vintage versions of this tube are quite low noise and can be found in many tube preamplifiers, phono preamps, and headphone amplifiers. This tube was also widely used in Tektronix oscilloscopes and other industrial test equipment needing wideband signal amplification. These tubes can tend to be microphonic, so careful selection needs to be considered if using them in high gain stages. This is a frame grid tube, meaning the grid wire is wound around a tiny framework. The grid wire itself is vanishingly thin....thinner than human hair. These tubes were not originally designed for audio use, but more so for test equipment. Therefore, not alot of attention was paid to making this tube as quiet microphonically as possible, and the fine grid wire on the frame can tend to exaggerate the problem, if it exists in the particular tube. The better Western Europe vintage tubes seem to be the best with regards to low microphonics and low noise. Matching these closer than 5 percent is often difficult, as is the case with most vintage tubes, since quantities are rarely found from the same batch or date code. This should not pose a problem for any well-designed preamp circuit." 

DaveC113

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Re: New Preamp
« Reply #58 on: 1 Apr 2016, 10:37 pm »
So Dave, have you guys been making anymore of these amps? I'm hoping to try a Tortuga again and see how it performs with my Lampi dac pushing it to my Odyssey Kismet amps but I'm really intrigued about your version here with the 6sn7 tubes.

Never heard a 6sn7 tube before, my current preamp uses 6922's. Anybody know what differences there are between these two?

I haven't offered the pre for sale as the costs are pretty high. I'm very happy with the performance though, it's an amazing sounding preamp.

I'm not sure the tube buffer or any tube preamp is going to be a good idea with a Lampi DAC with DHT output tubes, but it's hard to say... the buffer has an output impedance less than the Lampi, about 500 ohms where the Lampi is going to depend on plate resistance of the tube in use, but that'll always be a good bit more than a cathode follower buffer. I'm more thinking in terms of tone, which is a good part of the appeal of the Lampi DACs having that DHT output section. You might want to consider trying the Lampi without a pre or just a passive pre like the Tortuga, my guess is it will be better overall that way. In my system I prefer the buffer over the Tortuga straight, but the tube output section does add a tiny bit of noise... moreso than a preamp with gain as the signal isn't amplified, it's actually reduced by 3-4 dB. With the Lampi DAC I can't see the additional noise and complexity of a tube buffer being worthwhile.

On the tubes, the 6922/6DJ8 are great tubes as well. The circuit design and parts quality will make a much bigger difference than 6922 vs 6SN7. The tube buffer I used in my preamp is Broski's ACF circuit, which uses a triode as a plate load and has a bipolar power supply to cancel some of the PS noise at the output. It's a very low distortion circuit that does not sound tubey at all, you get some of the 6SN7 sound from the buffer but not too much "tubiness".

genjamon

Re: New Preamp
« Reply #59 on: 1 Apr 2016, 10:50 pm »
So Dave, have you guys been making anymore of these amps? I'm hoping to try a Tortuga again and see how it performs with my Lampi dac pushing it to my Odyssey Kismet amps but I'm really intrigued about your version here with the 6sn7 tubes.

Never heard a 6sn7 tube before, my current preamp uses 6922's. Anybody know what differences there are between these two?

The Dude preamp that you heard at my place last summer was a 6sn7 preamp - so technically you HAVE heard one before.  Though who knows how much that was contributing to the overall sound, and how much you even remember of the overall sound with all the other variables going that day.  Also, I found out from the guy I sold it to that it was WAY out of spec.  It wasn't sounding nearly as good as his buddy's that he had heard in his system that led him to buy mine.  So, he brought it to a shop, who found some of the caps were off spec, which they were able to make some adjustments to fix.  He says it now sounds magnificent.  So, you didn't hear it in its prime either...