Explendid amplifier designed by Michael Bittner, our MikeB - Page 423 - diyAudio
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Old 16th June 2017, 08:34 AM   #4221
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
Mooly,
can the Forum add an instruction somewhere where Members can find it easily?
Still a work in progress but is now located in Forum Problems where it can be linked to whenever needed.

How to attach images to your posts.
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Old 16th June 2017, 08:47 AM   #4222
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I got it, problem it was be solved, like thimios says, i make secon zobel xonstructio with 10 ohm and 100 nf, and now it can be setting bias at 24 mv. In fact the problem is 4.7 ohm its not same colour with value , that resistor value is 1 ohm , no i uses 10 ohm, thank everybody ... its really good sound cool ampli....regard
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Old 16th June 2017, 08:53 AM   #4223
Mooly is offline Mooly  United Kingdom
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Pleased to hear you got it sorted
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Old 16th June 2017, 09:01 AM   #4224
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Ok thankyou very much for all of your suggestion its good forum, and i follow this forum for learn everything about elektronik
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Old 16th June 2017, 03:08 PM   #4225
AndrewT is offline AndrewT  Scotland
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Originally Posted by janpaeusman View Post
I was checking all resistor and i find no one of their value was right, like 150 ohm read 144 ohm, is that normally?,
6ohms error could be from an ohmeter error and/or from a resistor error.
6ohms in 150ohms is 4%. That is a big error, far beyond what a 1% resistor tolerance and a 0.5% DMM tolerance would add up to.
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Old 16th June 2017, 07:35 PM   #4226
mjona is offline mjona  New Zealand
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I have attached my simulation file with a link to the Cordell models I used.

Running this will show how well it copes with a reactive load. Various load capacitor values and signal input levels should be tried.

The small overshoots with 100n deteriorate when higher values are substituted.

Looking at the Vas section the benefits of pole-splitting are conferred by the Miller capacitor stabilizing Q5 in the other half of the differential pair there are 47k resistors with 330pF which load the collectors of Q6 and Q9 to ground.

Since there is a signal transfer between the circuit halves via the emitters of Q4 and Q5 there is a cross feed in phase opposition.

Since Miller capacitance in transistors varies with collector voltage (which is not constant) there is a question of equality of capacitance in either arm.

A 1uF capacitor in parallel with 8R with a square wave input will show how close the relationship is. The amount of ripple at high signal inputs shows this to be a troubled one.

The capacitors in the simulation are notionally perfect in terms of value matching and transparency to signals and stray circuit capacitance has not been allowed for.
Attached Files
File Type: asc Explendid .asc (10.6 KB, 26 views)

Last edited by mjona; 16th June 2017 at 07:46 PM.
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Old 17th June 2017, 12:48 AM   #4227
mjona is offline mjona  New Zealand
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I posted my .asc to help investigation of Mike Bittner's circuit by whoever may be interested.

This bears some resemblance to a project amplifier that appeared in the Australian Silicon Chip magazine in 2003 as SC480 which Altronics in that country as a kit is still available.

The circuit for this is attached.

Silicon Chip published a replacement for the SC480 earlier this year - this has better specs.

The LTP Vas has been dispensed with - in IC manufacture where settling time is quoted as an important parameter it is worth looking at the circuit representation to see what that indicates about the preferred Vas structure.
Attached Files
File Type: pdf IMG_20170617_0003_NEW.pdf (96.1 KB, 58 views)
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Old 18th June 2017, 07:08 AM   #4228
mjona is offline mjona  New Zealand
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Quite a few views - I have felt a heel for not having any form of solution to the snags I pointed out. I have now had a bit of time to look at the circuit more closely over the weekend and made some basic changes that might be of interest.

Normally I would run simulations with a range of capacitor values from 4nF up to 2uF over a range of signal input levels - The amended circuit can cope with 2uF and some other values however it could still do with further refinement. I am leaving that as a digest for others.
Attached Files
File Type: asc Explendid-plus basicmods .asc (9.1 KB, 15 views)
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Old 18th June 2017, 09:09 PM   #4229
mjona is offline mjona  New Zealand
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For those who prefer lead compensation, C4 in the latest simulation could be moved to that position in parallel with R29.

Running the simulation for a variety of capacitor values and signal levels should be investigated for satisfaction.

If the values of R12 or R15 are altered, the value of R11 needs to be altered to be identical in value.

Hopefully most will have already seen from viewing the SC480 circuit that equal values are necessary to set Q5 and Q6 emitter balance point.
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