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Super Triode Connected (STC) chip amp
Super Triode Connected (STC) chip amp
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Old 21st September 2018, 03:01 PM   #61
hpeter is offline hpeter  Slovakia
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your point ?

i bet you will not feel it at -60dB
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Old 7th September 2019, 12:37 PM   #62
jfetter is offline jfetter  Costa Rica
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Super Triode Connected (STC) chip amp
Any more updates here?
Stc is very interesting. I've read all of jp early work.
seems like the perfect balance of 2h/3h can be obtained.
Too looks like a more elaborate local feedback arrangement.
A good thing...

Doing a prototype now, can't wait to hear.
But now puts more pressure on my test eqpt ie oscillators and analyzers.
Wish I had noticed Stc three years ago.

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Old 12th September 2019, 09:53 PM   #63
jfetter is offline jfetter  Costa Rica
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Took one of my previous boards and re-configured as a real STC, yep this is what I've been looking for. In fact can tone it down. Plenty of range to play with.
This plot is 1khz, with 2khz dominant harmonic, a 4th is there but no dirty 5ths. So STC is real. 6SN7-SA5532 used here. Mid level drive.

What is nice , you can tap the high fidelity output or STC output or pan mix both.

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Old 14th September 2019, 07:25 PM   #64
jfetter is offline jfetter  Costa Rica
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Verification from totally different set of test eqpt.
This is same identical untouched line amp, testing with UR22mk2 on pc based software.

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Old 18th September 2019, 09:13 PM   #65
jfetter is offline jfetter  Costa Rica
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Super Triode Connected (STC) chip amp
i do not think H2 is a magic pill , just want the ability to inject (without pots) an H2 level that is a known constant percentage of the signal.
That is ability to throttle up-down .05% to 2% and bypass.

So far with the limited time on it, as of today ,selecting hi-med-lo gain tubes is only method. Of course thats fun too.

It can be done solid state but just not sounding the same to me. Not sure why.

This is a JJ 12AX7 plot shown with identical signal levels, one is STC mode and other is normal mode which mirrors the generator signal. SA5532 op-amp. The vertical scale is uncalibrated. Voltage 250mv RMS. Unity gain and +-15VDC supply. No high voltage.

If you want to know what STC super triode mode is , look at some of the published data on it. Very simple thesis, a triode vacuum tube is placed in feedback of amplifier to flavor entire signal. Thats it.

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Old 18th September 2019, 10:41 PM   #66
Bigun is offline Bigun  Canada
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Super Triode Connected (STC) chip amp
try the 6as7, lowest mu tubes allow more influence from signal on the anode ?
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Old 18th September 2019, 11:13 PM   #67
jfetter is offline jfetter  Costa Rica
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Good info , I have three tube caddy but no 6as7.
Have to get some.
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Old 19th September 2019, 01:27 AM   #68
PRR is offline PRR  United States
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> H2 level that is a known constant percentage of the signal.

"Natural" H2 varies with signal level. Your ear "knows" this.

"Constant" H2 can be computed with frequency doubling. Which is typically also level dependent and not pure H2. And full of intermodulation when used with multi-tone signal (speech/music).
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Old 19th September 2019, 02:06 AM   #69
jfetter is offline jfetter  Costa Rica
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Quote:
Originally Posted by PRR View Post
> H2 level that is a known constant percentage of the signal.

"Natural" H2 varies with signal level. Your ear "knows" this.

"Constant" H2 can be computed with frequency doubling. Which is typically also level dependent and not pure H2. And full of intermodulation when used with multi-tone signal (speech/music).
It may indeed do variable level 2H, I have not fully characterized. Maybe specific to some tube type don't know. Going to listen for a few weeks and see.

I'm not understanding why the 3H disappeared. It definitely was on input, and re-appears on normal output. Normal meaning the op-amp outer closed loop vs the pre-distortion output.
But on the 2H tap the 3H is gone.

Doing it all analog, the processor route has real limitations and assumes we know everything to be modeled. Plus analog way more fun.

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Old 9th October 2019, 09:47 PM   #70
jfetter is offline jfetter  Costa Rica
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Had some time to look for variable h2-h3 ratio.
This is still using a 6SN7/SA5532 . Large anodes seem to make a difference on low-voltage vs B9 style glass. Lower noise and fewer surprises.

I put a bypass across the triode so it can be varied 0-100% which equates to 0-5% THD.

These plots show the 0.1 % THD selected, then a one percent THD selected showing a variation in the h2-h3 ratio based on amplitude. (So it does vary the ratios.)
Last is zero % THD which displays the op-amp and sound card distortion.( tube is bypassed )

No 'tits' are observed until about 5 Vrms in highest triode mode.

Now doing a stereo board / line-buffer based on this info. The switching supply mounted on pcb did not work out well. So going back to dedicated analog supply.
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File Type: png zero-point-one-selected.png (5.6 KB, 10 views)
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File Type: png full-triode-bypass-gen-third.png (7.9 KB, 9 views)
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