AudioCircle
Industry Circles => ZenWave Audio => Topic started by: DaveC113 on 25 Nov 2015, 09:46 pm
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I'm happy to be finishing up my next project, a zero-gain preamp using Tortuga's LDR and Broski's Aikido tube buffer.
RDavidson helped with design and is getting one of them, his is made with spalted maple and natural aluminum metal parts, mine is maple burl with brushed copper front and top panels.
I needed a buffer preamp and this one turned out great, I'm super happy with the way it sounds. I can't imagine a better way to build it or I would have. :D
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09004_zps6rpw9p98.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09004_zps6rpw9p98.jpg.html)
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09006_zpsskrbq4ew.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09006_zpsskrbq4ew.jpg.html)
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09011_zpsc7rzoiae.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09011_zpsc7rzoiae.jpg.html)
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09013_zps1qu77rcz.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09013_zps1qu77rcz.jpg.html)
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09018_zpsc1wupcfb.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09018_zpsc1wupcfb.jpg.html)
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09021_zpsn9apgiob.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09021_zpsn9apgiob.jpg.html)
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09023_zps6vsekaon.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09023_zps6vsekaon.jpg.html)
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09029_zpswvw3a0bj.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09029_zpswvw3a0bj.jpg.html)
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Here's the spalted maple chassis:
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09032_zpsshudoac5.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09032_zpsshudoac5.jpg.html)
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09033_zpsyrp8qpl7.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09033_zpsyrp8qpl7.jpg.html)
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09039_zpsg4knttm0.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09039_zpsg4knttm0.jpg.html)
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09042_zpspdbi4kt3.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09042_zpspdbi4kt3.jpg.html)
(http://i99.photobucket.com/albums/l318/davec113/MNT%20Preamp/DSC09046_zpshpbhk4pb.jpg) (http://s99.photobucket.com/user/davec113/media/MNT%20Preamp/DSC09046_zpshpbhk4pb.jpg.html)
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Sweet, very nice, Dave! Enjoy!
Happy Thanksgiving,
Pete
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Great machine, congratulations.
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Beautiful work!
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Looks snazzy :thumb:
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:thumb:
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Awesome!
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State of the ART! You fu*k*n ROCK!!!
Love it. Send me big detailed pics to my email!
Best,
Anand.
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Very nice! :thumb:
What is all the compressed wool padding for, especially the interior?
Could you give me your source for the controller knob?
Thanks,
Roy
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AWESOME! This is actually my first time seeing these in their completed state. Can't wait to receive mine!
Beautiful craftsmanship, Dave. Great working with you and I learned a lot along the way. Looking forward to our next endeavor. :wink:
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Daaaaang!
(http://www.audiocircle.com/image.php?id=132437)
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WOW! Beautiful work, very impressive. :thumb: :thumb: :thumb: :thumb:
Best,
Ed
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Lol, Tom... and thanks everyone! RDavidson is a talented designer, it looks good without being too complicated to build. This was my first project using the CNC mill, what an amazing tool... CAD>Reality quickly and accurately. As an engineer I always handed off my work to mechanical designers who handed off their work to fabricators, doing it myself is a lot of work but it's fun and satisfying. At least I have Ryan doing Solidworks. :thumb:
A few details:
- The felt padding is a gasket/vibration pad for the three power trafos mounted on the top sheet. The wood boxes are meant to resemble potted trafos, but they aren't potted because I wanted to use a passive convection cooling system for them since wood is an insulator. The trafo boxes are painted with a heavy coat of carbon conductive grouding paint and attached to ground via the wood screws holding them to the topsheet. There is a hole for wires and another for ventilation, then three holes on the top/back of the covers for an exit. The boxes stay cool to the touch after the preamp was on for 8 hours and the filament trafo (EI trafo between the 2 wood boxes) only gets mildly warm, it's hugely oversized which is mostly for looks. And if I want to add another 10 6SN7s I'm all set. :lol: The felt on the interior is used to damp capacitors mostly. I just siliconed a little felt to them. Ceramic caps are microphonic so it''s a good idea to damp them imo... and while electrolytics are debatable it takes 5 min and $1 worth of materials to damp them.
- The interiors of the chassis and trafo boxes are painted with a couple heavy coats of carbon conductive grounding paint and a metal bottom plate will be used so it effectively has an enclosure. It doesn't make much of a difference in most homes but I figured I'd go the extra length for this one. I've watched distortion readings go down when a metal lid is placed on an open preamp.
- It can use 6SN7, 12SN7 or 12SX7 tubes, there is a heater voltage switch in the back panel. John Broski recommended 12SX7 so I have a pair to try out...
- The big blue caps are for the last stage of the power supply filter, which is split into separate RC filters for each channel. Each tube has it's own Clarity TC 175 uF ultra-low impedance film cap. The caps right after the rectifier are electrolytic but they have a film cap bypass and make only a very subtle, fairly insignificant difference in that position. The Clarity TCs make a massive difference where they are used in this preamp. The caps are hugely oversized but they aren't much more expensive and ESR goes down as size goes up.
- The big white rectangle near the IEC is a time delay relay for the B+ supply, it allows the heaters to warm up for 30 sec before high voltage is turned on.
- Now that all the CAD/CAM work is done it's possible I could make chassis for other folks using the same design without it costing a small fortune. It's not really my preamp as it's a collection of 3 kits, but it's a combination I think is as close to ideal as possible while staying in a reasonable budget and other folks could build their own if they wanted.
Oh yeah, Roy... this is the ebay seller I got the knobs from:
http://www.ebay.com/sch/m.html?_odkw=&_ssn=along1986090&_osacat=0&_from=R40&_trksid=p2046732.m570.l1313.TR12.TRC2.A0.H0.Xknob.TRS0&_nkw=knob&_sacat=0
I had to specify whether I wanted indicators in the notes, so make sure you specify no indicators for encoder knobs. I'm happy with the fit and finish of the knobs, they are solid aluminum.
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So what's the price on these?
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Stunning man. Very nicely done. You done your homework, in to out I see :thumb:
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Good job Dave
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Dave, when you get the chance, you ought to post some pics with the displays turned on and the tubes burning. :D
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So what's the price on these?
I could only really sell the chassis to DIYers, and/or help with assembly as a build service like many folks are offering for the NCore NC400 amps. You have to order the parts and send them in to get assembled. I don't intend for this to be a stand alone product for ZenWave as the design of the controller and buffer are not my own, just to be clear, but a build service and bare chassis is possible. If anyone is interested send me a PM please. Pricing would be case-by-case depending on the details. This was not an inexpensive project but it is an amazing preamp. I love remote control...
Now I gotta get to work and finish Ryan's up, it's not quite done yet... :green: I'll try a pic with the light out soon... good idea.
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Link for the knob seller doesn't work.
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Link for the knob seller doesn't work.
It worked for me
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It took me right to here - http://www.ebay.com/sch/m.html?_odkw=&_ssn=along1986090&_osacat=0&_from=R40&_trksid=p2046732.m570.l1313.TR12.TRC2.A0.H0.Xknob.TRS0&_nkw=knob&_sacat=0&afsrc=1&rmvSB=true
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Gorgeous pieces Dave.
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Beautiful work, Dave and RDavidson. Really beautiful statement pieces. :bowdown:
Where's the one for your next Tour? :wink:
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Link for the knob seller doesn't work.
strange, it works for me... try searching for seller along198 in ebay.
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Using my phone, the link takes me to a string of several listings, but not directly to the specific knob we selected.
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6/12 volt switch.... that's sweet.... 8)
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Beautiful work, Dave and RDavidson. Really beautiful statement pieces. :bowdown:
Thank you, JerryM. It took a lot of "behind the scenes" work to get to the result you see. MAJOR attention to detail was paid inside and out, down to every screw location with the idea that these may easily be the last preamps Dave or I will ever want/need. Everything had to be right. I'm proud to say these were built without a prototype chassis or circuit layout first....which is a testament to the foundational work and parts by Tortuga and Glassware Audio Designs. What you see, is our first go. I think we were pretty successful. :D
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Using my phone, the link takes me to a string of several listings, but not directly to the specific knob we selected.
Right, I'm not sure that exact knob is still available but it looks like he has a bunch of them. I think the 44x22s are the same ones:
http://www.ebay.com/itm/1pcs-D-44mm-x-H-22mm-aluminum-volume-knob-amplifier-knob-silver-color-sn-/141412688599?hash=item20ecda62d7:g:LbUAAOSwDk5UG-wu
http://www.ebay.com/itm/1pcs-D-44mm-H-22mm-full-aluminum-volume-knob-amplifier-knob-black-color-sn-/141795665132?hash=item2103ae24ec:g:ERoAAOSw5VFWFfKy
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Thank you, JerryM. It took a lot of "behind the scenes" work to get to the result you see. MAJOR attention to detail was paid inside and out, down to every screw location with the idea that these may easily be the last preamp we'll ever want/need. Everything had to be right. I'm proud to say these were built without a prototype chassis or circuit layout first. What you see, is our first go. I think we were pretty successful. :D
I sure look forward to reading your impressions. :thumb:
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Making the decision to move forward with this (sort of unproven) project took a bit of a leap of faith, considering the time and monetary investment. I already had an excellent preamp (2 for awhile, actually), but decided to sell them to help fund this endeavor. Given the base circuitry and Dave's know-how, I came to the realization that it was a unique opportunity to not only obtain a state-of-the-art preamp at a reasonable price, but also have a chance to design something I'm personally interested in. I think I'm going to be completely blown away.
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Ryan,any class-a ss preamp/pwramp in the works?
great built this one mate... :thumb:
cheers
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Dave,
Thanks for the link; it worked for me.
Compressed wool is certainly handy to have around for various DIY projects. I have used it for footers and for diffusion on baffles. It's also useful under fairly heavy gear, such as speakers, to function as a slider on wood floors.
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GG, sorry, but the answer is no. I'll leave the Class A SS amp designs to Nelson Pass. :thumb:
Note, when I say I "designed" the preamp, I'm speaking about the esthetic design and tactile / functional aspects only. Dave did everything else. It was a team effort, though Dave was the one who put the rubber to the road.
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Wow - absolutely amazing looking. Congratulations to both of you. You must be beyond excited! The brushed cupper with the color scheme is super nice
Dave - would you mind detailing out hook up wire choices and connectors to someone like me who is trying to learn.
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I see a USB port.
Do you have a block diagram of the pre-amp?
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Wow - absolutely amazing looking. Congratulations to both of you. You must be beyond excited! The brushed cupper with the color scheme is super nice
Dave - would you mind detailing out hook up wire choices and connectors to someone like me who is trying to learn.
Thanks!
For power and ground wiring I used surplus mil-spec wire, stranded silver plated copper in teflon insulation. At the IEC I used Furutech push-connectors and at the power switch and relay I used ring terminals. Mostly 18g but for ground I doubled it and used 12g for the IEC>ground and for IEC > Power switch. Used 18g and ring terminals for the 6V/12V switch.
For signal wiring I used scraps of my OCC silver/gold wire and UPOCC silver for input #1. For #2 and #3 I used UPOCC copper scraps. Out to the LDR used more OCC silver/gold/UPOCC silver scraps and for LDR>Buffer and Buffer>Outs I used lengths of my D4 interconnect cable which use the same wire... OCC silver/gold and UPOCC silver.
Lots of folks would use more stuff to organize wire like terminal strips to hook up the power trafos. I just connected most of the leads directly, for me it really doesn't take much more effort to solder/unsolder wires from the PCBs if needed, it's quick and easy but I've done a lot of soldering.
SS, the USB port is only for potential firmware updates for the Tortuga LDR board, there is no DAC or anything. I don't have a diagram, it's too simple to require one... The signal goes from RCA In > Input switching board > LDR board > Tube Buffer > RCA Outs.
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I just spent a good ten minutes going back and forth between the two different woods. [Of course, that was after I had oohed and aahed at the preamps.] :thumb:
I'm still not totally sure which I prefer, but I have a couple questions about them. What was used to finish them? Were any dyes or tints added to bring out the grain? Where did you find the wood?
Thanks!
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I just spent a good ten minutes going back and forth between the two different woods. [Of course, that was after I had oohed and aahed at the preamps.] :thumb:
I'm still not totally sure which I prefer, but I have a couple questions about them. What was used to finish them? Were any dyes or tints added to bring out the grain? Where did you find the wood?
Thanks!
Me too! They both look really cool. I was going to for a vintage/retro look while Ryan's preamp is more modern looking imo.
The finish is sanding sealer > clear gloss lacquer. The spalted wood absorbed a ton of both sealer and lacquer, it took many, many coats to get it to look how it does. The burl absorbed a lot of finish too but nowhere near the spalted maple. The spalted maple is the nicest I've ever seen but pretty far along in the spalting process so there are some soft spots that were very hard to finish. No dies or tints used. The wood was sourced from ebay, there's a lot of amazing wood listed there.
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. The signal goes from RCA In > Input switching board > LDR board > Tube Buffer > RCA Outs.
Dave,
Could you place the buffer in front of the input side instead at the output so you wouldn't need a buffer for each output? This would be for a bi-amp setup.
On second thought, I suppose I wouldn't be gaining anything by installing it on the input because I'd need a separate buffer for each input or one buffer before the input RCAs' relay board. :duh:
Alternatively, I'll need a buffer for each output or wire one buffer just in front of the output RCAs'.
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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
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Sorry late to the party. This is such a wonder to look at oh my !! Gorgeous just gorgeous.
charles
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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.
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Many thanks for the info!
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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.
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Beautiful pieces! Congrats, guys.
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Looks awesome. Bet it sounds great.
Looking forward to a evaluation of the sound.
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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?
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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.
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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?
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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.
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Very interesting! Your shipment of some Silver/Gold arrived Friday so I will be trying it soon.
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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.
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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?
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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!
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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?
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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
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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."
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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".
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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...
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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...
Yeah, I guess I should have stated I hadn't heard a 6sn7 in my setup. I do remember that day at your place but like you said there were a lot of variables. That was my first time hearing a Line Magnetic amp the Dude was hooked up to as well.
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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".
Thanks Dave. I believe the dht tubes are on the L7 version and up if I remember right. I have a L4 with 12au7 and 12at7 tubes. I had tried a Tortuga pre a while back when I was using a dspeaker am 2.0 as a dac and thought it was ok but the Rogue Perseus I had at the time had more detail and better sound stage which was the opposite of another forum member here who used to have a Perseus before he got a Tortuga. But he was using a Eastern Electric dac in front of the Tortuga.
I think Morten might have another tour coming up so I may get another chance to see how it goes. I feel at this point I'm just tinkering as what I got now really sounds phenomenal. I guess it's a case of always wondering "hey, what if...."
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Nice design, the wood gives it a nice look.
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Thanks zermatt! And welcome to AudioCircle! :thumb:
Tommy, it's kinda hard to say what'll be ideal for your system and tastes... even though your Lampi doesn't use the big DHT ouput tubes I'm not sure following it with another tube section will be ideal. Some of it depends on what the output impedance of the Lampi is and the input impedance of your amps. If there aren't any impedance mismatches keeping it simple with a passive volume control is likely the best idea. I'd love to send a preamp to try out but for now I simply can't get into making preamps commercially. My speaker needs to be my main focus right now. I hope you can make it to RMAF again this year to hear it! :green:
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I was able to follow most of this design for the signal wiring. Which transformers did you use? I was interested in doing something similar.
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Hi Dave,
Just saw this post and what you have achieved is really amazing. Your definitely gifted. Hope you really enjoy the preamplifier in your system.
Cheers Rod
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I was able to follow most of this design for the signal wiring. Which transformers did you use? I was interested in doing something similar.
Hi WC, I used toroids that are enclosed in the wood boxes, they are also wrapped in mu-metal to reduce noise. If I remember right they are 120V in 240V out for the tube B+ and 120V in 12V out for the Tortuga LDRs.
Rod, thanks much!