Interesting that it was so sensitive to filament voltage. That is one thing I have not tried varying. I guess Rp much be significantly higher at 0.64V vs. 0.72V.
This makes me wonder if the parameters can be further improved by running at the high limit of 0.8V...
Thanks for posting your results!
Pete
This evening there was time for some listening tests.
My first tube amp was a EL34 PP with 6SN7 and 5751 electro harmonics tubes.
This amp was so different from what i was used to listen(Hypex ucd) to, that it was love at first site(hearing). Blues and female vocals sounded performed in a smokey bar as i was there.
My first setup with the harmonizer was source Shanling Cd-t100se and Thorens recordplayer to passive volume/source control to SE 813 tube amp with dynaudio audience 52se speakers. The harmonizer was inbetween the passive control and SE 813 amp. The sound was mixed up, everthing was one blur. Not as without the harmonizer, then the music becomes one with the room and placement is as real i can touch the musicians. So my setup does not need the harmonizer.
Then i changed the SE 813 tube amp for a Ncore500 amp. With the harmonizer as before between passive control and amp. Now was the sound also complete different as without the harmonizer. But this sound was as my first tube amp. And i was back in that smokey bar where Eva Cassidy performs like never before.
I think when bias adjusted so that harmonic distorsion is minimal, the nutube 6p1 a great add on is for people who searching for this great warm sound and do not want to buy big tube amps and disarm they class-d amps.
I have tried a lot of tube buffers for this purpose but this one i like most.
My first tube amp was a EL34 PP with 6SN7 and 5751 electro harmonics tubes.
This amp was so different from what i was used to listen(Hypex ucd) to, that it was love at first site(hearing). Blues and female vocals sounded performed in a smokey bar as i was there.
My first setup with the harmonizer was source Shanling Cd-t100se and Thorens recordplayer to passive volume/source control to SE 813 tube amp with dynaudio audience 52se speakers. The harmonizer was inbetween the passive control and SE 813 amp. The sound was mixed up, everthing was one blur. Not as without the harmonizer, then the music becomes one with the room and placement is as real i can touch the musicians. So my setup does not need the harmonizer.
Then i changed the SE 813 tube amp for a Ncore500 amp. With the harmonizer as before between passive control and amp. Now was the sound also complete different as without the harmonizer. But this sound was as my first tube amp. And i was back in that smokey bar where Eva Cassidy performs like never before.
I think when bias adjusted so that harmonic distorsion is minimal, the nutube 6p1 a great add on is for people who searching for this great warm sound and do not want to buy big tube amps and disarm they class-d amps.
I have tried a lot of tube buffers for this purpose but this one i like most.
Attachments
I am a little surprised by the limited interest. Maybe it is not well known enough. And the price is a bit high for many DIYers, a lot more than an NOS battery tube.
In Japan, I believe that they sold a couple thousand to DIYers within the first two months...
Pete
Then i changed the SE 813 tube amp for a Ncore500 amp. With the harmonizer as before between passive control and amp. Now was the sound also complete different as without the harmonizer. But this sound was as my first tube amp. And i was back in that smokey bar where Eva Cassidy performs like never before.
I think when bias adjusted so that harmonic distorsion is minimal, the nutube 6p1 a great add on is for people who searching for this great warm sound and do not want to buy big tube amps and disarm they class-d amps.
I have tried a lot of tube buffers for this purpose but this one i like most.
Thanks. I agree with you - when I built a class-D amp with the Nutube as a front end, to me, the result sounded a lot like a big single-ended triode amplifier. It seems you have the same experience...
Pete
Are there any published schematics for a simple buffer or class-d amplifier front end, that don't include opamps? I don't have the ability to design these circuits myself, and the inclusion of opamps makes other circuits less attractive to me (I fully understand these are required for driving tricky loads). If there was the equivalent of the B1 buffer circuit - something simple and easy for people to replicate - I'm sure that would increase interest and demand. I've got two nutubes from Pete ready to go 
Are there any published schematics for a simple buffer or class-d amplifier front end, that don't include opamps? I don't have the ability to design these circuits myself, and the inclusion of opamps makes other circuits less attractive to me (I fully understand these are required for driving tricky loads). If there was the equivalent of the B1 buffer circuit - something simple and easy for people to replicate - I'm sure that would increase interest and demand. I've got two nutubes from Pete ready to go
I am working on a few reference schematics. Also an article is upcoming in audioXpress. It's pretty simple.
You typically need some kind of buffer on the input to drive the grid. I have used both a JFET buffer, and a small MOSFET follower. Either works well. If the input impedance of the class D amp is low (10's of K) you also need an output buffer - same idea, JFET or MOSFET.
I am attaching the schematic of the entire class-D hybrid amp I built (shown below). I used dual JFETs to buffer in and out, and a JFET phase splitter to drive complementary inputs to the class D. This preformed better than driving it single-ended.
Pete
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I did not need much gain, so there is some NFB around the tube - R4. So there is less distortion. At 1V RMS in, though, the amp is getting close to clipping at 50W.
I thought I had measurements of the whole amp, but can't locate them. I may have to run them again.
Pete
At your service.Are there any published schematics for a simple buffer or class-d amplifier front end, that don't include opamps? I don't have the ability to design these circuits myself, and the inclusion of opamps makes other circuits less attractive to me (I fully understand these are required for driving tricky loads). If there was the equivalent of the B1 buffer circuit - something simple and easy for people to replicate - I'm sure that would increase interest and demand. I've got two nutubes from Pete ready to go
You can leave the switches and potmeter for only buffer.
Ronny
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Below schematic i now use.
Differences to origenal:
- R3/R13 from 330k to 100k, Other working point, a little bit hotter
- Ad R25/R26 behind output capacitor C2/C10 to ground to lower DC.
- Changed C2/C10 from 100uf to 10uf. They did not needed so big.
- Remove C3/C11 because they where not there in the first place.
Differences to origenal:
- R3/R13 from 330k to 100k, Other working point, a little bit hotter
- Ad R25/R26 behind output capacitor C2/C10 to ground to lower DC.
- Changed C2/C10 from 100uf to 10uf. They did not needed so big.
- Remove C3/C11 because they where not there in the first place.
Attachments
Using the halves for stereo now, I see. 
That MP7770 is an interesting amp chip, haven't seen it before. I suppose if you had a differential (balanced) input signal you could use the nuTube on each half of that signal, and no need for the phase splitter. That's a bit OT, so no need to pursue it.
That MP7770 is an interesting amp chip, haven't seen it before. I suppose if you had a differential (balanced) input signal you could use the nuTube on each half of that signal, and no need for the phase splitter. That's a bit OT, so no need to pursue it.
Using the halves for stereo now, I see.
That MP7770 is an interesting amp chip, haven't seen it before. I suppose if you had a differential (balanced) input signal you could use the nuTube on each half of that signal, and no need for the phase splitter. That's a bit OT, so no need to pursue it.
The MP7770 is actually a pretty decent class-D part. It is self-oscillating. Architecturally a little like the the Hypex amplifiers. But this one is monolithic, and cheap.
If you use good external filter components the performance is quite good.
Pete
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