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Old 26th April 2007, 08:12 PM   #11
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Quote:
I have made simulations Lumanauw....interesting.
Hi, Carlos, what did you find in simulation? Does it behaves like JLH or different?
Quote:
As a remember it was a nice sounding amp
Thanks Latala for the info
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Old 26th April 2007, 09:20 PM   #12
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Default Those schematics came from the time AD149 was a special transistor.

Chromium finish...TO-3...enormous and heavy unit (weigth).

Was a 10 watts transistor, used for Voltage amplifiers and also for automobile radios push pull output...hehe.

Nice old days...people used to listen music those days...and now a days Scopes, Spectrum analisers, Simulators, Distortion Analisers seem to be the target for the industry.

regards,

Carlos

.................................................. ................................................
Lumanauw.

Was not good in simulations.... i am already making modifications...if something finishes with a nice result, then i will inform you some.

Well...simulator cannot tell me how it will sound...we really need to construct..will you do that?... i cannot till Nov/Dec

regards,

Carlos
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Old 26th April 2007, 11:16 PM   #13
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Here you go! Nothing special but might sound good!
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File Type: gif mullard-spice.gif (28.3 KB, 2160 views)
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Old 27th April 2007, 12:02 AM   #14
AKSA is offline AKSA  Australia
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Choco,

Even if you eliminate the output coupler, the driver earth return currents will still have to pass through the power supply caps.

I can see the appeal of no output coupler, but I have built amps with this configuration using composite caps and really, they sound just fine..... AND, if the amp fails, the speaker is safe!

Cheers,

Hugh
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Old 27th April 2007, 12:17 AM   #15
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AKSA: I can see the appeal of no output coupler, but I have built amps with this configuration using composite caps and really, they sound just fine..... AND, if the amp fails, the speaker is safe!

EXACTLY!
Anyone suspicious should build or listen to old QUAD-303!
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Old 27th April 2007, 04:22 AM   #16
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Carlos,

If I built the amp, I will write here how it sounds.

So, the output cap is OK. There are many 160uF bootstraps, I think it's OK too. I'm thinking of putting 2xdiode back-to-back accross bases of 2xBC147B (differential) to advoid overdrive/clipping. Is this OK?
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Old 27th April 2007, 08:27 AM   #17
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Default I also think that the output condenser will not disturb sound quality.


The amplifier may sound good....Bora's simulations is showing a very good result.

Very good Lumanauw...if you construct, please, let us know the details.

regards,

Carlos
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Old 27th April 2007, 01:32 PM   #18
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Quote:
Originally posted by AKSA
Choco,

Even if you eliminate the output coupler, the driver earth return currents will still have to pass through the power supply caps.

I can see the appeal of no output coupler, but I have built amps with this configuration using composite caps and really, they sound just fine..... AND, if the amp fails, the speaker is safe!

Cheers,

Hugh
Hi Hugh,
of course always the signal current must pass somehow through the supply caps. But from my understanding their influence is much less, because their nonlinearities will not fully be reflected in the output signal. Their influence should be greatly reduced by the closed loop PSRR of the amp, or not ?

Regarding e-caps itself... I am also not fanatic in this regard. During my Rookie games I also played around with cheap noname e-caps in the line signal area. Some 6.3V/1500uF types and I gave them a 1.5V DC voltage bias. In the beginning I could not measure and not hear any difference. Later I noticed that they caused slightly unstable distorsion results, but even after these measurements my ears did not notice a difference between the signal path with or without the caps.
But I did not feel really comfortable and decided to go for a design that does not need e-caps in the signal path. ...yes, it was more about the appeal of 'no e-cap'..
It might also depend on the ratio of Zc vs Zload.
If Zc is always very low vs Zload, then nonlinearities of Zc are probably quite uncritical. While in filter applications where Zc is similar like Zload or even dominant then the cap might be much more critical.
What are your experiences in this regard?

And speaker protection... come on.. who cares about real life advantages ?!!

Read you soon
Markus
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Old 27th April 2007, 11:55 PM   #19
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This is one of many similar 1960s amplifier circuits published by P Tharma of Mullard Laboratories in his book -
Transistor Audio Amplifiers.
I have a copy in the roofspace (somewhere) but have not seen it for 30 years.
Initially these were all PNP except for the input transistor being a newly developed germanium NPN. BC107>9 types later became the input device. The polarities reversed when silicon power became available, and I think a germanium OC44 became the input device before PNP silicon prices fell.

I checked at Amazon, and a few copies of the book can still be found.

They were better than many tube amplifiers of their day, but would need components to be re-chosen to match today's standards.

Cheers ......... Graham.
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Old 28th April 2007, 01:37 AM   #20
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This is an odd circuit, it is interesting that what looks like the VAS bootstrap capacitor is not that at all, it is in fact negative feedback. I believe that this is required to set the gain of the
lower half of the output stage, or it could be an error. Were the schematics redrawn?

The first diff transistor, essentially the VAS, is not bootstrapped, instead it is fed from a higher voltage supply and power out is wasted in the 4R7 in the supply line.

I'd try bootstrapping the VAS and removing the 4R7 to the output stage.

This is an odd circuit and I believe it could use some refinement.

It is interesting from a food for thought perspective.

Pete B.
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