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Old 12th February 2011, 10:19 PM   #11
ontoaba is offline ontoaba  Indonesia
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May I ask about he volume pot? Sorry for asking too much. Did this amp sounds best at specific volume or just flat?

Thanks,
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Old 14th February 2011, 12:42 AM   #12
hbc is offline hbc  United Kingdom
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Hi Ontoaba, Yes initially I used a transistor, Q5 on circuit above, with adjustment to base voltage, I had the digital circuit on the -ve rail. it was OK but I just don't quite trust tranies in this kind of roll with no feedback. have not conclusively proved to my self yet, but still.

now have a set up "like" the one here, with the signal going to the cathode, RF style. used this circuit initially because it looked like it would do what I wanted it to do, No Over-Sampling DACs and tubes but it really doesn't work very well. so I have now just fixed bias. will post cct when I get one drawn.

I am a bit confused about the sound at the moment, because it is so different to anything else I have done. basically if you turn up the volume you just get more, louder is better, because you can hear more!


I need to do some more listening in other systems to get a proper opinion. I have done some measurement, and frequency response is flat, and distortion is 2nd -56dB, 3rd -39dB, relative to -4 dB fundamental IIRC @ 1k.


The -ve rail of the sounds tech has gone down, it doesn't look to complicated so hopefully can fix.


h
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Old 14th February 2011, 10:46 PM   #13
ontoaba is offline ontoaba  Indonesia
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It is better to not modify your first success, until you built another. Sometimes our ears feel everything worse. And if you want to find "truth", use only your eyes to measuring sound quality will not help. Scope based(ARTA) measurement only help to show any voltage waveform based, not sound waves that we heard.

That probably hearing fatigue or something else, like bad situation that you feel.
I am sure, the pot did change speaker driving composition. If you need more power up 20W or more, may be I could help with my linearized emitter follower classAB that will do almost same with classA EF.

Any comparison of two or more amplifiers, are very helpful. Of course, you need to fix -ve first.

Last edited by ontoaba; 14th February 2011 at 11:05 PM.
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Old 15th February 2011, 01:37 PM   #14
hbc is offline hbc  United Kingdom
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Default Current to voltage stage

This circuit hangs 50 volts below GND on a little switching regulator, the SPDIF is AC coupled.
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File Type: png feb spdif iv.PNG (72.9 KB, 214 views)
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Old 16th February 2011, 04:00 AM   #15
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It seems that the distortion coming from the tubes not the output stages. The configuration added the tube current to DAC source current. The result is it more linear, but still distorted most at H3.

Hi, hbc, did that 470ohm and double TDA1543 is the best value or just placed there by calculation?
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Old 17th February 2011, 07:36 AM   #16
ontoaba is offline ontoaba  Indonesia
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Hi, h

I am simulating bjt version replacing the tubes. It also has higher H3 distortion. This one is linearized EF in classB with 1/10 current gain of normal EF, ready for 50Watts with (modified)higher Vref of current sources.

The input should be in positive side, to get it the similar. May be just fine, it is only reversed loudspeaker polarity differences.
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File Type: png BJT classB buffering BJT SE classA.PNG (23.3 KB, 199 views)
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Old 17th February 2011, 02:39 PM   #17
hbc is offline hbc  United Kingdom
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Have been / am a bit ill at the moment, (writing this in bed!!) in occasional burst of energy have been able to progress a bit. Fixed sounds tech distortion analyser. A Tantalum cap added to help noise (wasn't me) had gone short.


Re not changing things and listening fatigue, yes I agree, there are many variables. I have been curious about these things and have some of the variable pinned down I feel. See:


http://www.artandmusic.netfirms.com/...ear/weird.html


note: this link doesn't work today, will try and fix when I have time, (sorry)


It is quite easy to put a transistor back in to the circuit, I also want de-construct the circuit quite soon and measure the different elements.


Anyway, have been able to make some measurements, and these come in a about 1%THD at full output of 10 Watts in to 8R. The ARTA does do measurement of distortion and all sorts of things, I am learning to love it more all the time.


http://www.fesb.hr/~mateljan/arta/


using the curves from mr klausmobile:


Tube Tester Files - 6N23P - 6H23P
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Old 17th February 2011, 04:48 PM   #18
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As a reference see picture above for approx operating point. Yes it will run positive grid occasionally but still quite linear, and have low z drive to grid anyways.


Have also removed cathode resistors and replaced with current sources, they were a short term fix to get the current up, but they were robbing me of gain, so the amp can now clip as intended.


Here is a plot of the today's distortion, for what its worth, running at about 2.5 watts




Hi Ontoaba,


re your interesting circuit, looks quite like Complementary Feedback Pair arrangement which has been my output stage of choice for last 20 years. I am using Darlingtons in this amp to avoid feedback, which is one of the aims of this project. I am quite interested in making linear output stage, and /or keeping output transistors turned on in standby, to reduce class b switching glitch during the alternate cycle. But as yet have not come up with the “circuit” good luck with you efforts.
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Old 17th February 2011, 11:24 PM   #19
ontoaba is offline ontoaba  Indonesia
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Thanks for these software h,
Hope you getting fine,

I am simulating this last night, will try it after my current project finished. It is now tripple EF(it should have thermal compensator with it), and simulated distortion is almost flat at 20Hz-20kHz

What happen with the feedback? umm, did you find something on your 20years output stage or is that really do something bad?
I do find worse thing with BJT differential input usage in loudspeaker driving.
This one has very weak feedback but may be effective to take classA BJT functionality for classAB operation.
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File Type: png 60W tripleEF.PNG (28.8 KB, 89 views)

Last edited by ontoaba; 17th February 2011 at 11:31 PM.
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Old 18th February 2011, 12:47 AM   #20
ontoaba is offline ontoaba  Indonesia
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Too late to edit, That was "three stage", not "triple EF"

Hi, h

It is now less than 10k pot position than before, there may be little different. But you cant compare its sound differences with only one.
Anyway, better stay to take good rest, and not too hard in work. I have another time playing with this kind input resistor, may be I'll play with it again when built this circuit.
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