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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 18th February 2014, 10:35 PM   #61
keantoken is offline keantoken  United States
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Well, everyone has different design objectives. CFA's can use plain miller compensation, TMC, TPC, double EF, triple EF, beta-enhanced VAS, and so on, and all these probably have a different optimal input stage designs. So really you can't ask "which is the best input stage for a CFA".

It's not as if we can think in universal terms for a bunch of completely different amps, just because they were all thrown into the CFA bin. Each amp needs its own treatment.
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Last edited by keantoken; 18th February 2014 at 10:38 PM.
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Old 18th February 2014, 11:32 PM   #62
audiostar is offline audiostar  United States
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keantoken,

I asked you before and I will ask you again. When will we see your DIY Amplifier?
Also, when do you graduate from college?
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Old 19th February 2014, 01:59 AM   #63
danielwritesbac is offline danielwritesbac  United States
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Quote:
Originally Posted by RCruz View Post
I am planning to use the Kuartlotron just after a jfet common source high gain amp stage. It outputs 10v DC offset modulated by signal. Maybe I can build the stock buffer with symmetrical psu (so I will loose output cap) but would like to increase it's input impedance to 1mega so I can use a small cap in the input.
1 mega input load is a sure fire way to get DC offset out of anything. Therefore, you can try it if you also install an output cap.

On split rail power, Kuartlotron supports input loads from 10k (and lower) to 100k without an output cap. I'm using 56k so that my sound card won't be dull in tone, but this need depends on the source.
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Old 19th February 2014, 02:46 PM   #64
Zero D is offline Zero D  United Kingdom
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Quote:
Originally Posted by keantoken

That works great with low source impedance, and a source that's willing to drive the entire buffer at 1GHz. But it causes negative input resistance which turns your input cable into an RF transmitter, or at the least cancels the loss of the preceeding wiring and boosts RFI reception.
Negative resistance ! Well that lead to some Very interesting stuff indeed, & not just audio.

The RF transmitter aspect could be good for Phone etc Jammimg puropses

The wiring cancellation is intriguing ! Maybe the RFI could be eliminated with a simple R/C filter, and/or inductor ?

Thanx for your observations etc
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Old 19th February 2014, 06:51 PM   #65
RCruz is offline RCruz  Switzerland
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The Kuartlotron - keantoken's simple error-correction superbuffer
Quote:
Originally Posted by keantoken View Post
What is signal ground referenced to? If it's on the same supply, I need to know where the reference is. If isolated supply, then I can make a single-rail version without coupling caps. It may be that you will end up needing caps in the signal path if you want to power it from the same supply as your Jfet circuit.
Well, the jfet common source high gain stage is powered from a single rail 35v psu and the signal gnd is the same as the psu. There is an output offset around 10vdc.

I would like to use the buffer after that so if I build the stock version with simetric psu, I will need a coupling cap and would like to minimize it ... that is why I wanted a very high input imp on the buffer.

Off course if you can come up with a single rail version without coupling caps, that would be even better.
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Old 19th February 2014, 10:14 PM   #66
keantoken is offline keantoken  United States
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Someone asked, so here is a simulation. This zip file contains all the files needed and the simulation should run out of the box.
Attached Files
File Type: zip KuartlotronDC.zip (14.2 KB, 183 views)
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Old 19th February 2014, 10:28 PM   #67
keantoken is offline keantoken  United States
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Quote:
Originally Posted by RCruz View Post
Well, the jfet common source high gain stage is powered from a single rail 35v psu and the signal gnd is the same as the psu. There is an output offset around 10vdc.

I would like to use the buffer after that so if I build the stock version with simetric psu, I will need a coupling cap and would like to minimize it ... that is why I wanted a very high input imp on the buffer.

Off course if you can come up with a single rail version without coupling caps, that would be even better.
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.
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Old 19th February 2014, 10:37 PM   #68
keantoken is offline keantoken  United States
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Quote:
Originally Posted by Zero D View Post
The wiring cancellation is intriguing ! Maybe the RFI could be eliminated with a simple R/C filter, and/or inductor ?
You could do that, but the RC is not just a filter, but an RF load on the preceeding circuit. If an opamp has noisy output, and you increase the output load, you may reduce the noise, but you worsen the performance of the opamp by forcing it to drive an RC. This is one reason I chose the tiny input RC snubber instead. This is all that is necessary for a stable circuit; the builder can add RC filtering IF it is necessary or advantageous. In this way I am not adding "unnecessary features with side-effects" to the circuit. This is appropriate for a buffer which is meant to reduce the load on the preceeding circuit.
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Last edited by keantoken; 19th February 2014 at 10:41 PM.
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Old 20th February 2014, 03:51 AM   #69
Zero D is offline Zero D  United Kingdom
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@ keantoken

Points taken I only posted my Cap idea as i was surprised/impressed by the increase in BW it's able to achieve, & therefore felt it "might" be worth persuing in some way/s.
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Old 20th February 2014, 04:12 AM   #70
keantoken is offline keantoken  United States
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Well, there is good and bad and the circumstances which determine which is which. I decided that for my circumstances, it wasn't viable. I can't speak for other circumstances however, and it would be interesting see if it's useful for other applications.

This circuit does seem like it could be useful for instrumentation. It reminds me of the kind of circuits you find in analog oscilloscope schematics.
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