Are you looking for a buffer or a preamp?
The item in the first link is described as a preamp. They don't even mention the word "buffer". Not that it matters because almost all of the listings that use the term "buffer" in the description are actually preamps, with gain, not buffers, which have no gain.
The description does say, "Allows you to enjoy high-pressure tube at a low supply of charm". So you can be confident that they know their stuff.
Unless you can compare schematics, relying on sellers to be honest and accurate when they say their device is "based on" some well known circuit amounts to wishful thinking.
A well known example are boards and kits that claim to be Marantz 7 preamp clones. Those who have compared them say the only thing they have in common is that they both use 12AX7s. The circuits are not the same, so it's just marketing BS.
The second link shows another kit that's supposedly based on the Musical Fidelity X-10D. It does have a schematic posted. It is not a buffer, it's a two stage preamp.
A quick search for Musical Fidelity X-10D schematics indicates that it is also not a buffer. It's a two stage preamp, similar to the schematic posted in the second link.
One important difference I noticed between the Musical Fidelity X-10D and the device in your first link is that they use totally different tubes. So even if the circuit is the same I would not expect them to sound the same.
The link I posted above (post #73) is a buffer. There is a schematic posted under Product Description.
The advantage of a buffer is that it allows you to use long interconnects and, usually more importantly, creates a better impedance match with SS or chip amps.
You may like the sound of the other kits just fine but they are not buffers and don't offer any of the advantages of a buffer.
Some gain won't go amiss as it's fitting between my dac's I/V transformer and Krell KSA50 clone.
Yes, the Chinese sellers are experts at BS, laughable in many cases but often their products can be improved by replacing components with higher quality.
For the money, I decided it was worth a go.
Yes, the Chinese sellers are experts at BS, laughable in many cases but often their products can be improved by replacing components with higher quality.
For the money, I decided it was worth a go.
Chinese preamp has arrived so will do some testing today.
I found the schematic but there are some differences...
One mistake is that the grid stoppers are on the input side of the coupling capacitor, where presumably, they are a waste of time?
The output capacitors have a low, 12k resistor to ground rather than the 100k shown in the schematic so may need to change it.
(schematic shows it connected to -28v but it is connected to gnd)
I found the schematic but there are some differences...
One mistake is that the grid stoppers are on the input side of the coupling capacitor, where presumably, they are a waste of time?
The output capacitors have a low, 12k resistor to ground rather than the 100k shown in the schematic so may need to change it.
(schematic shows it connected to -28v but it is connected to gnd)
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Found more issues - surprise, surprise!
The heaters were running on 8.4V so a resistor had to be changed.
Changing the 12k resistor on the outputs to 150K improved the LF response so it's flat to below 20hz.
The gain is about 7 times (17db).
B+ 36v, Anode/plate +20v, Cathode -35.6v, grid -34.8, HT 72v, Ia ~3.5ma
Fitted a 1K grid stopper in the correct position - before the input capacitor.
This preamp is certainly going to add 'colour' to the sound of any source.
The heaters were running on 8.4V so a resistor had to be changed.
Changing the 12k resistor on the outputs to 150K improved the LF response so it's flat to below 20hz.
The gain is about 7 times (17db).
B+ 36v, Anode/plate +20v, Cathode -35.6v, grid -34.8, HT 72v, Ia ~3.5ma
Fitted a 1K grid stopper in the correct position - before the input capacitor.
This preamp is certainly going to add 'colour' to the sound of any source.
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We have an old saying (probably inherited from Spain):
"My horse died *just* when it was learning to go without food"
Now connected and sounding respectable but more listening needed and I will fit a bypass switch to the preamp for easier comparison. No hiss or hum.
I believe the output impedance will not be particularly low so the input impedance of the the amp will affect the sq?
(source: Technics mash dac or LG Oled TV, via optical cable to SU8 ESS9038sqm dac and Pioneer A/v amp (until the tube and Krell clone are completed), ML Aeon speakers)
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Albert Einstein: “Insanity is doing the same thing over and over again and expecting different results.”
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