© Don Sachs, 2015

Custom 6SN7 Line Stage

This is the finest preamp that I have ever heard!

NOTE:  I have modified the preamp to take a 6BY5 rectifier because it sounds better and you can source 6BY5 tubes for $12 or less.  If you own one of my preamps and pay the return shipping I will modify it for you and provide a 6BY5 tube for $75.   If you own an SP14 kit or any other version of this preamp please DO NOT JUST PLUG A 6BY5 TUBE INTO YOUR PREAMP AS YOU WILL DAMAGE IT AND IT WILL NOT WORK!   This modification is something I developed for my customers only.  I will NOT share the details and I will NOT modify any preamp that I did not build.  Sorry, but this is what sets my gear apart from the kit versions. Latest:  New version with OLED display and relay input switching.  This is the only version I am building because it is the best. My latest and greatest version features OLED display and relay input switching.  It can only be built in the cherry or walnut case.  The special model has every option.  (photo with large display at right) 64 step remote Khozmo attenuator relay input switching, one xlr input and 3 rca inputs Cryo treated copper signal path wiring (better than Duelund to my ear) all film cap power supply Polish oil caps on output 4 WE6SN7 tubes included In cherry $2699 and in walnut it is $2739 It can be built with just 4 rca inputs and no xlr for $200 less.  It cannot be built in the black alumininum case.  The base capacitor value is 0.47uF for the Polish oil caps, plus the second set of outputs has a 3 uF film cap suitable for subwoofers.   The 0.47 uF cap will drive any amp >=80K input impedance.  If you have a lower impedance power amp, then I can use a larger value of the Polish oil cap: price increase for 1 uF cap (47K or higher input impedance) $100 price increase for 1.5 uF cap (20K or higher input impedance) $125 The signal path is considerably shorter.  I have eliminiated the channel level attenuators.  If your system is balanced with a vocal dead center, then you don’t need them.   This is the best sounding version of my preamp. Note: one pair of XLR inputs using excellent Cinemag line transformers for the conversion is always an option, but I cannot do XLR outputs, so please don’t ask.  Also, I no longer wish to build preamps with HT switches, so please don’t ask for that either. i All preamp builds use the all film cap power supply.  The only electrolyic capacitors are in the filtering for the regulated 6 volt DC filament supply for the tubes.  The entire signal path now has only quality film capacitors.  Also, all my preamps have my new mod that allows you to use the 6BY5 rectifier types as well as the 6X5GT.  Sounds better and I give you one of each with the preamp. I am not alone in my opinion of this preamp.  I have gotten two very nice reviews lately from customers who have them.  They are too long to post at the bottom of the page so I have created a customer review page where I post feedback.  There is also a thread going on Audio Circle about the preamp.  This is the old back story (I have improved things considerably since this was written): When I built the first one of these preamps, it was the first thing I had ever heard that I thought was every bit as good a piece of gear as a fully restored Citation II amplifier.  Really, this preamp is so good that it is scary.  You can read my initial listening impressions from a few years ago here.  The preamp is based on the 6SN7 tube, which has always been one of my favorites.  The bigger octal tubes like the 6SN7 have a much more relaxed, fuller, and richer sound than the smaller tubes like the 12AX7, 12AU7 or 12AT7 tubes used in many other preamps.  You get all of the detail with no brightness.  The preamp is based on the SP14 board from Roy Mottram.  Here is a link to Roy’s SP14 page: http://www.tubes4hifi.com/pre11.htm#SP14 I looked at Roy’s page and decided to build my version because his basic design is absolutely fantastic.  This is essentially a $3000-$4000+ commercial preamp built for $2000-2500.  My price has risen because I have kept improving the parts and design and made all the options standard.   It is a cost no object design without all the ridiculous markup and hype of the high end industry.   I have spent numerous hours experimenting with parts choices based on my many years of experience restoring vintage tube gear.  I know what parts sound very good in various positions in the circuit.  This preamp is incredibly good for a number of reasons.  First, the audio circuit itself is a wonderful, but simple design that has a very short signal path and really only one coupling capacitor per channel at the output.  The tubes are direct coupled.  The 6SN7 is a fantastic audio tube as noted above.  If you are used to the sound of small tubes you are in for a treat, and you most likely will never go back.  Small tubes just aren’t going to cut it for you!  Second, the power supply is a fully dual-mono design.  Each channel has its own B+ (high voltage) and filament supplies.  This gives amazing stereo separation because each channel is independent.  The B+ power supplies are tube rectified (the BEST way to go in a tube preamp, none of that solid-state hash) which gives a soft-start and simplifies the design compared to a solid-state design, and it also sounds better! Then the B+ is fed to a separate voltage regulator for each channel that eliminates all variation in the supply, and reduces the noise by at least 20 dB, making for a deep, totally dark background.  The two filament supplies (one for each channel) use ultra-fast schottky diodes, and then the filament voltage is regulated by a low-noise, low-impedance device that is completely isolated from the audio signals by floating the 6 volt supply about 70 volts above ground so there is no hum whatsoever.  The 6 volt DC regulated filament supplies are driven by completely separate transformer windings for each channel.  In fact there are separate filament and high voltage transformers.  The power supply and filament supply design gives stunning channel separation and the blackest background that I have ever heard in ANY preamp, tube or SS. My version uses a wooden case with the tubes on top.  That helps it run very cool and it will be reliable for many years.  Plus you can easily swap tubes.  I use full aluminum front and rear panels to allow easy mounting of controls and jacks, and also to keep the signal path parts well separated from the AC.  All signal wiring is done with Duelund tinned copper stranded wire.  The B+ and filament runs are done with mil-spec stranded OFC copper Teflon insulated wire.  This preamp is very quiet and the wire will NEVER become brittle with age.  It is the same wire I use in all of the Citation II amps.  All the signal path resistors have been chosen for the best sound.  There are Takman REX carbon film resistors on the grids and cathodes and 1% metal film resistors on the B+ and in the power supply, and a nice pair of Kiwame resistors in a key spot.  It is dead quiet and incredibly dynamic.  The first B+ filtering before the regulators is done using a large film cap, not electrolytic capacitors.  The other electrolytic caps are all very high quality Nichicon or Panasonic 10,000 hour 105 degree rated capacitors.  The volume control is a 64 step Khozmo remote controlled attenuator.  It is built with very low noise resistors and there are only two in the signal path, one per channel, at any one time. I have used Gold Point attenuators and they sound very good.  The Khozmo is much better. The preamp has two sets of output jacks, each can be driven by their own pair of output capacitors, or the two can be in parallel and driven by one set of caps.  The basic version of the preamp will come with a very nice 0.47 uF film and foil cap with a small bypass cap and the jacks in parallel.  This cap combo rivals most anything you will hear at any price.  I really don’t want to build them with lesser capacitors anymore.  The base cap combo will easily drive any amplifier with an input impedance of > 80K.  Most every tube power amp around is 100K or higher.  If you need to drive a solid state power amp with a lower input impedance I can use larger output capacitors.  For example, the 1.0 uF caps will drive most any amp with >= 47K input impedance (any tube amp and almost all SS amps).  I have sent over 80 units out to customers and these are their comments from the first three: Mark from Sacramento: Moment by moment, the sound of this preamp is revealing its magic with absolutely zero detractions.  Among its attributes, I am stunned at the black background on silent passages in music.  I prefer this preamp to the Citation I preamp you modified for me in the past and and the C-I is a fantastic preamp. A SS preamp could not be more quiet. The dynamic extention is breathtaking.  I am eager to have my fellow Bay Area Audio Society members give a listen to this fine preamp as I think the members will not fail to appreciate the accuracy and sonic attributes of this modestly-priced preamp.  No question, this is a stunning preamp as I hear it more.  I think that like fine preamps, it is ruthlessly revealing. The ability to use balanced inputs from a DAC raises the performance of this preamp to a higher level. I think there is some magic in the 6SN7 tubes that almost no other preamp designer uses.  Don has listened to a variety to 6SN7 tubes, the result of which he has optimized the sonic signature of this preamp with the tubes he supplies — no need for expensive tube rolling with this preamp. I have had a dozen tube and SS preamps in my system over the past 45 years and this is the most pleasing preamp I have ever heard.  One could spend 5X-10X the price of this preamp and I suspect would not find their performance exceeding what what Don has created.              Bill from Anaheim: It’s been running 24 / 7 mostly since I got back here on Tuesday.  I turned it off one night.  All other nights I just turned off the amp and let the pre cook.  It continues to improve (or my ability to listen to it appropriately improves).  The improvement is not subtle. Overall, the system is now presenting with extraordinary fidelity … breathtaking dynamics and transparency … combined with a rich and colorful tone. So easy to listen to and so easy to be drawn into whatever performance is playing.  Currently listening to John Williams playing Rodrigo Guitar Concerto … a 70’s recording well done and well transferred to CD … and my rip to a HD and playing back through the Wavelength … Wow! I’m really glad to have this pre-amp! Thank you Don. Jose L. from Oakland: My quest in searching for tube preamp done when I saw this preamp it  was love at first sight without  knowing how it sound.  After contacting Don, very friendly and he knows  his stuff.  He answered all my questions and fears  about  tube amplifier.     This preamp produces the  finest  and incredible  audio   and I cannot imagine getting this quality sound for the price. Thank you  for giving new life for an old hobby Warranty: This preamp should be totally reliable.  So I will guarantee it for one full year.  If anything goes wrong (exept for a tube) I will pay shipping both ways, fix it, and return it for free.  If a tube that I supply fails in 90 days I will replace it.  Now if you have a party and someone spills beer on it then I will fix it for you as cheaply as possible, but the cost is on you.  Realistically I would expect this unit to be trouble-free for many years.  If you get a problem more than two years down the line and you pay the shipping I will fix it for only the cost of parts, forever. Options: 12 gauge cryo treated fantastic power cord $89 This cord makes a 10% difference over any other $50-100 cord I have tried.  I am not into snake oil super expensive boutique parts, but this cord has won me over.  Richer, deeper sounding.  Let’s put it this way.  Once you have one of these attached to this preamp you won’t want to swap it out.  Really.  I won’t part with mine! Other options are possible.  I can use any output capacitors you wish.    Just contact me to discuss your needs.
Vintage Tube Audio  Restoration and Repair
rear view New OLED display version inside view