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The Kuartlotron - keantoken's simple error-correction superbuffer
The Kuartlotron - keantoken's simple error-correction superbuffer
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Old 20th February 2014, 11:57 AM   #71
baswamin is offline baswamin  India
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Kean,

You are saying that we dont need input filter (220R with 150p C). What about compensation ? In the Mpp thread, we saw a schematic where 22R with 390p cap compensation was shown. When should we use that? In you latest schematic, that is missing.

I am also thinking about the inductor. If you have the input filter, I think the inductor may not be necessary, am I right in saying that? I am planning on building this buffer since it looks simple (need to order some parts though) and hence these questions.

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Old 20th February 2014, 02:00 PM   #72
Joachim Gerhard is offline Joachim Gerhard  Germany
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We made this measurements on my build.
I thermo coupled the transistors.
They are selected for HFE.
I used fixed resistors and did not do a distortion trim.
I can not remember if the TKD pot was in circuit.
I check that today.
Attached Files
File Type: pdf KeanTokenJG_Bode.pdf (11.0 KB, 260 views)
File Type: pdf KeanTokenJG_THD_vs_Ampl.pdf (9.6 KB, 252 views)
File Type: pdf KeanTokenJG_FFT(1).pdf (18.6 KB, 237 views)
File Type: pdf KeanTokenJG_THD_vs_Freq(1).pdf (13.8 KB, 245 views)
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Old 20th February 2014, 07:38 PM   #73
keantoken is offline keantoken  United States
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Thanks for the data Joachim. I based my THD values on the webpage on my experience but your figures are higher. I'm not sure about the drop in THD over 10KHz, that's not normal at all.
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Old 20th February 2014, 07:46 PM   #74
keantoken is offline keantoken  United States
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Quote:
Originally Posted by baswamin View Post
Kean,

You are saying that we dont need input filter (220R with 150p C). What about compensation ? In the Mpp thread, we saw a schematic where 22R with 390p cap compensation was shown. When should we use that? In you latest schematic, that is missing.
The "latest" schematic is on the Kuartlotron webpage in my signature. I posted one special (but not better) schematic for RCruz and Dan exhumed the old schematic with the suboptimal compensation. Build the one on the site; it is the best so far.

Quote:
I am also thinking about the inductor. If you have the input filter, I think the inductor may not be necessary, am I right in saying that? I am planning on building this buffer since it looks simple (need to order some parts though) and hence these questions.
The inductor shouldn't be left out, else you get RF peaking regardless of any input filter. It's not just a filter.
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Old 20th February 2014, 08:05 PM   #75
Joachim Gerhard is offline Joachim Gerhard  Germany
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We will try distortion trimm at 2V 1 kHz next.
Douglas Self found distortion in the TKD pot so we should also measure without.
Notwitstanding the strange step at higher voltage the buffer behaves monotonic, a good sign i think.
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Old 20th February 2014, 08:08 PM   #76
BigE is offline BigE  Canada
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Quote:
Originally Posted by Joachim Gerhard View Post
We will try distortion trimm at 2V 1 kHz next.
Douglas Self found distortion in the TKD pot so we should also measure without.
Notwitstanding the strange step at higher voltage the buffer behaves monotonic, a good sign i think.
Can you elaborate more on the comment that TKD pot has distortion please? How much? why? Should I be worried since I've used one?
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Old 20th February 2014, 08:13 PM   #77
RCruz is offline RCruz  Switzerland
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The Kuartlotron - keantoken's simple error-correction superbuffer
Quote:
Originally Posted by keantoken View Post
Well, you have 10V offset so you'll need a coupling cap no matter what. I would suggest you use the symmetrical supply version with a large input resistor so you can use a small cap and no output cap. The alternative is to use your current supply dropped to 20V with an output cap on the buffer.
Perfect.

Can the buffer be built with a jfet on the input ? That way we could avoid the input cap
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Old 20th February 2014, 08:19 PM   #78
keantoken is offline keantoken  United States
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I've tried putting a Jfet at the input, and it loses most of the good things about this circuit.
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Old 20th February 2014, 08:22 PM   #79
Joachim Gerhard is offline Joachim Gerhard  Germany
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Well, i have to ask Dough but i know he had issues.
You know, bashing TKD right in the open without proof ?
Bad me.
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Old 21st February 2014, 06:44 PM   #80
Calvin is offline Calvin  Germany
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Hi,

@Keantoken
certainly a design I like, as one could use two matched Duals or one matched Quad (That340, though they might generate considerable output offset).
I have difficulties though to follow Your explanations of how its functioning.
For the basic structure (You named it Tringlotron) You claim identical Vbes and Ics.
The only identical Vbes are in fact those for the current mirror.
The Vbes of Q1 and Q2 certainly differ.
Also all 4 Ics differ if You account for the base currents.
Introducing emitter resistors in the CM and their Vbes wonīt be identical too.
What difference could be expected when using a PNP-CM instead?
Iīd expect even slighty lower THD for that one and probabely lower thermal problems!

With the Kuartlotron I basically donīt understand what You call error correction here?
Is it just another term used for positive feedback or for the partial cancellation of the Vbes?
As the Base of Q4 is modulated signal dependent, and hence the base of Q3 there certainly is (positive) feedback, which might have been the source of Joachimīs circuit instability.

What Ya say??

jauu
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