[walkern]

I want to start a 'New Topic' to sing the praises of the SainSmart 6N3 tube preamp that Poultrygeist recommended a while back here in the C&C area.  I was considering buying an Aikido buffer kit and giving it a try to replace my current volume control (an older LDR kit which has served me very well ahead of my Class D Audio SDS amp).  I've tried a couple of buffers (one tube model from Grant Fidelity and a solid state Pass B1) and a MapleTree audio tube preamp in the past, but found that I preferred the sound with my source (Oppo) playing directly to the LDR and then into the amp.  When I saw the comment from Poultrygeist I figured this was a really cheap and easy way to try a tube front end again. 

The stock unit is only $38 from Amazon (also available on ebay) and includes most of what you'd need to get it up and running.  I ordered mine with an IEC AC inlet/power switch so it would be easy to plug in and turn on and off (note it does not come with an AC power cord, so you'll need to dig up one of those).  Total spent was less than $50, including a small cigar box I ordered from Ebay to enclose the little bugger.  You could just lay out the unit and it's transformer on a board, but I was reluctant to leave high voltage wiring exposed (input to the trafo is 120V, and outputs from the trafo are as high as 170 V).

The unit arrived fairly promptly, and was well packed in a box (previous feedback on Amazon had complaints about the packaging, which the seller apparently took to heart). After wiring up the AC inlet/switch and the transformer (instructions at Amazon are helpful as the labels on the unit for what wire goes where are in Chinese) I inserted the stock Chinese 6N3 tubes and fired it up.  Not only did it work, but it sounded quite promising  The overall sound was dynamic, detailed, and yet offered a decent bit of 'tube magic'.  The stock tubes were a bit forward in the midrange, which pulled the whole soundstage toward the listening seat.  Bass and treble were clean and clear but a little lower in overall level than the midrange. The imaging was quite diffuse, and after a little experimenting (and a little break-in time) I concluded that (IMHO) the unit inverts absolute phase... so I reversed the speaker lead hookups on my amp. 

I set about researching other tube options and I have tried a few alternatives with some interesting and very positive results.  Russian (NOS) 6N3 tubes (got 5 on e-bay from a U.S. seller for $15) offer up a more traditional tube sound, with a little extra warmth in the midbass, a bit less deep bass extension and control, more relaxed but less extended treble, and a very even overall tonal balance.  The imaging with these tubes is more precise yet still is very holographic.  I also tried a pair of NOS RCA 5670 tubes (physically shorter but otherwise a perfect plug in replacement) that were a bit more expensive ($20 pair), and they sound VERY much like the NOS Russian 6N3s.  The only really notable differences were that the imaging lost some precision, and the overall sound became a little more polite (a bit more refined, but a bit less dynamic or less energetic?). Lastly, I picked up a pair of NOS JAN GE 5670s on ebay ($4 each) from a seller in Fresno CA.  These are an absolute 'must try' tube in this preamp.  Bass extension and control took several notches up, and the extra midbass warmth disappeared.  The midrange is to-die-for with extraordinary detail and refinement, and the treble sounds extremely clean, clear and extended with no sense of grit or spit or sizzle.  The soundstage developed greater width and depth, however it did become a little less precise than with the Russian 6N3 tubes.  The dynamics are incredible, from micro to macro, and the unit is dead quiet in use... no transformer hum, and no noise or hiss through my speakers. Overall I would describe the sound with the GE 5670s as every bit of what many modern tube preamp designs shoot for.

At this point I am done experimenting with tubes, and am thrilled with the unit exactly as it is (no mods or upgrades being considered).  If you've been curious about what it would be like to add a tube front end to your system, and you want to keep things really C & C, I can't imagine a better bargain than the SainSmart.  To use an automotive analogy... it's like paying for a used Nissan Versa or Toyota Yaris and getting a shiny new BMW M2.

Some operational 'things to know'... (1) there is only one set of inputs and outputs (both single ended RCA), so if you have multiple sources you'll need to buy/add a switcher or shut the unit off and switch connections.  (2) On my unit the colors for the RCA connectors were not as pictured, and not the standard I've become accustomed to over the years... however they are labeled correctly and in English.  On all previous equipment I've owned the red colored RCA input or output was assigned to the right channel, and the white colored RCA input or output was assigned to the left channel.  On my unit of the 6N3 this was reversed.  (3) Although one might presume that each tube would drive 1 channel (one for the left and one for the right) this is not the case.  One tube is an input or driver tube, and the other is an output tube.  The circuit uses 1/2 of each tube for each channel (6N3s and 5670s are dual triodes).  SO, if you get a drastic channel imbalance (was noted once in the feedback at Amazon) switching the tube from one socket to the other will not make the problem switch channels.  I got a bad tube from Tube Depot (which they promptly replace for free), yet the preamp still worked in stereo, but with way less gain / volume.

[Markvdv]

Obviously the Aikido or Pass B1 don't change the signal as much as this chinese amplifier. The schematic is supposed to be of the chinese amp and to some it might show why this amp has sound of its own or if output is inverted:

[walkern]

Thanks for the schematic Markvdv.  I guess I should have included in my original post that this preamp circuit is supposed to be a copy of a Matisse Fantasy Preamp.  I've looked over the Matisse circuit diagrams (as best I can... I'm no E.E.) and it appears to me that this isn't a very close copy.  None the less, I am still quite pleased with the sound.

Neil

[ClefChef]

Obviously the Aikido or Pass B1 don't change the signal as much as this chinese amplifier. The schematic is supposed to be of the chinese amp and to some it might show why this amp has sound of its own or if output is inverted:

It's one of the worst schematics for the tube preamp.

[Markvdv]

Very poor for a tubepreamp or very poor because not the circuit of this chinese tubeamp ? I think people can check easily, from ampboard photo's it certainly looks like this and person that drew it had the amp. But componentvalues change by the day probably. If r1 is 10k there might be problem running these tubes the way they do for that half and to solve it a very low value was needed ? Volumecontrol at the other side is the other part I understand to be poor choice. So first component at input and first befor output seem poor to me, why and what happens in between is mystery to me.

[Poultrygeist]

ClefChef,

Next time you're in town please stop by for a listen. I think you'll be impressed when you hear it paired with a TPA3116.

[walkern]

I'm not sure who put together the drawing of the schematic, but after looking at it and the unit I have, I can see some errors.  First off, there are no SMD resistors.  All the resistors are 'through hole' full sized resistors.  Secondly, the heater voltage listed in the drawing is 200V, but the actual heater voltage of the unit is 170V.  It does appear to me though that the volume control pot is following the gain stages and immediately before the output, which doesn't make much sense to me either.

The circuit design may be lousy or questionable (again, not being an E.E. or having done any circuit design myself, I am in no position to judge), and that may be one part of the explanation for why it is so cheap.  None the less, in my system it sounds very good... perhaps despite it's circuit design issues.

[Markvdv]

So maybe there are different/multiple ones on Amazon (pic=amazon) ? Btw heater isn't in schematic.

[walkern]

That's what I get for just looking at the board from the top.

[Markvdv]

They can hide anywhere and they want to escape whenever they can, I think I have some colonies under my desk.

[rongon]

Obviously the Aikido or Pass B1 don't change the signal as much as this chinese amplifier. The schematic is supposed to be of the chinese amp and to some it might show why this amp has sound of its own or if output is inverted:

The output is non-inverted (2 inverting stages = non-inverting from in to out).

I think there are some problems with this circuit. It looks like a version of the Dyna PAS type line stage, but with the volume control on the output.

The volume control VR1 is on the output of the circuit. That means it will load down the feedback loop from the plate of the second stage to the cathode of the first stage. The preamp will change level of distortion, tonal quality, and frequency response as you change the setting of the volume control. That's just bad design, imo.

Another problem with the volume control being on the output is that the first stage will always see full blast output from the source (player). Let's say you're feeding the output from a DAC to this preamp. If that DAC is playing loud pop music, there will likely be long-duration signal peaks up near 2V RMS (2.83V peak). Those peaks could very well draw grid current from the first stage 6N3, which will reduce the input impedance of the first stage and cause the source's output stage to distort. This distortion cannot be fixed by the feedback loop in the preamp (R5 and C3 going to the first stage cathode).

R1, the input 'grid leak' resistor, is only 10k, so will present a heavy load on tube phono preamps like the RCA circuit that use ECC83/12AX7/6N2P with no output buffer. If you do use a phono preamp like this with this line stage, it'll sound like poop, I assure you. You could try fixing this by changing R1 to something like 470k, but that would make the first stage's grid current problem much worse, defeating the purpose of the larger value R1.

It may be that the extra harmonic distortion from this preamp is euphonic and pleasing to hear, and could be adding some 'body' to the sound from the TPA3116. The end result could be pleasing, but I don't think adjectives like 'detailed' and 'transparent' would be accurate.

I'll put this circuit into a spice simulation program and see what that says. Could be interesting...

--

[wushuliu]

The output is non-inverted (2 inverting stages = non-inverting from in to out).

I think there are some problems with this circuit. It looks like a version of the Dyna PAS type line stage, but with the volume control on the output.

The volume control VR1 is on the output of the circuit. That means it will load down the feedback loop from the plate of the second stage to the cathode of the first stage. The preamp will change level of distortion, tonal quality, and frequency response as you change the setting of the volume control. That's just bad design, imo.

Another problem with the volume control being on the output is that the first stage will always see full blast output from the source (player). Let's say you're feeding the output from a DAC to this preamp. If that DAC is playing loud pop music, there will likely be long-duration signal peaks up near 2V RMS (2.83V peak). Those peaks could very well draw grid current from the first stage 6N3, which will reduce the input impedance of the first stage and cause the source's output stage to distort. This distortion cannot be fixed by the feedback loop in the preamp (R5 and C3 going to the first stage cathode).

R1, the input 'grid leak' resistor, is only 10k, so will present a heavy load on tube phono preamps like the RCA circuit that use ECC83/12AX7/6N2P with no output buffer. If you do use a phono preamp like this with this line stage, it'll sound like poop, I assure you. You could try fixing this by changing R1 to something like 470k, but that would make the first stage's grid current problem much worse, defeating the purpose of the larger value R1.

It may be that the extra harmonic distortion from this preamp is euphonic and pleasing to hear, and could be adding some 'body' to the sound from the TPA3116. The end result could be pleasing, but I don't think adjectives like 'detailed' and 'transparent' would be accurate.

I'll put this circuit into a spice simulation program and see what that says. Could be interesting...

--

That's assuming the schematic is accurate, which in the case of some of these chinese audio components is doubtful.

[walkern]

Rather than analyzing the circuit design and judging the sound based on theory or conjecture, it might be useful to give the unit a listen.  I've got a modest assortment of amps and preamps and one SS buffer (the aforementioned B1) in house, and this little puppy (with the tubes previously mentioned) sounds quite good to me.  And not 'good' like old fashioned tubed good (rolled off highs, slow transients, vague imaging, emphasized midbass and indistinct low bass).  Given it's dirt cheap price, I just figured some folks here with a very modest budget might wanna give it a listen.  So far mine has been reliable, quiet (no hum), and in general an absolute delight.

[wushuliu]

Rather than analyzing the circuit design and judging the sound based on theory or conjecture, it might be useful to give the unit a listen.  I've got a modest assortment of amps and preamps and one SS buffer (the aforementioned B1) in house, and this little puppy (with the tubes previously mentioned) sounds quite good to me.  And not 'good' like old fashioned tubed good (rolled off highs, slow transients, vague imaging, emphasized midbass and indistinct low bass).  Given it's dirt cheap price, I just figured some folks here with a very modest budget might wanna give it a listen.  So far mine has been reliable, quiet (no hum), and in general an absolute delight.

Thanks Neil. I may get one. Especially since Amazon carries them now, so easy return.

[Higherground]

Can anyone confirm 100% that is in fact the schematic for the 6N3 preamp sold on Amazon and Ebay.

Just want to know what I`m buying, it`s part of the enjoyment knowing how it works....

[walkern]

Sorry I can't.  I know diddly squat about reading schematics, and I'm clearly not skilled at spotting all the goodies on the board I've got.

N

[Markvdv]

Old topic but I did see one at a friend now, schematic is ok, high voltage is 2k resistor 180uF 2k resistor 180uF and then the 4 (2channels) load resistors. Measured AC voltage at board input was 175V, the 180uF are 200V dc rated.... too low to last very long. Feedback capacitor value is 1000nF or 1uF. Voltage over 4k7 cathoderesistors first stage 3.2V, over 510 ohm second stage 1.4 V.

[pinkfloyd4ever]

I'd be interested to hear comparisons between this and a Schiit Saga.  I wish this one had a remote and 4-5 inputs though

[I.Greyhound Fan]

It might be fun to tinker with the little preamp with different caps and resistors along with a Blue Alps volume pot.

[Poultrygeist]

I'd be interested to hear comparisons between this and a Schiit Saga.  I wish this one had a remote and 4-5 inputs though

If it had those features it wouldn't cost $35 but a cheap switch box will give you plenty of inputs.