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Old 18th August 2007, 01:41 PM   #21
sandyK is offline sandyK  Australia
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Default it is a very good amplifier

Giaime
Seeing that Q42 and Q44 have vwery slightly more current available from the current mirror than the loaded side, I would have thought that R77 should have been on the opposite side ?
Seeing that the voltages are so close already, that may be all you need with this particular circuit. I have only tried very well matched differential transistors in more conventional circuits, with, and without current mirrors, so I am only guessing here.

SandyK
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Old 18th August 2007, 01:48 PM   #22
awpagan is offline awpagan  Australia
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Carlos
"But this time, with the same speaker and almost the same parts (supply is different....hummm) i had a very good results."

Is this just "one speaker"?
therefore also one amp module?

If the bass was week or the highs hurt i would measure the module to see why, rather than just dismiss the whole topology.
that is, unless i had calibrated eardrum(s)

allan
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Old 18th August 2007, 01:58 PM   #23
Giaime is offline Giaime  Italy
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Default Re: it is a very good amplifier

Hello SandyK!

Quote:
Originally posted by sandyK
I would say Q41 and Q42 initially.Try and get difference between their collectors closer by a resistor from the unloaded side of the differential pair collector to -VE rail, which gives equivalent to the loading of the BC547. (try something like 22Megohms to see if it makes an audible improvement, and take it from there) I would imagine that you already have a better than average sound stage if those pairs of transistors are well matched .
SandyK
Look at the voltages in my last post: Q41 and Q42 have the same Vce, minus a mere 1mV difference Of course that's SPICE only, but if you cannot make those two Vce equal, with perfectly equal bjts (as in SPICE), that won't be easy to make them equal in reality, with different transistors...

EDIT: I saw your last post after posting mine. Yes, the resistor goes there, because in this design the voltage difference between the collectors is in opposite sign of what you were suggesting me. Maybe, as you say, it's a current mirror trick.

I cannot hear this amp's soundstage, it's still only on SPICE. Maybe I'll build it in the future, it looks promising.

Attached, the full schematic:
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File Type: pdf my_amp.pdf (38.4 KB, 255 views)
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Old 18th August 2007, 02:11 PM   #24
sandyK is offline sandyK  Australia
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Default it is a very good amplifier

Giaime
Don't forget that the unloaded side still has slightly more current, due to the very small bias current on the loaded side, reducing available current to the input side's transistors. This will most likely be more evident in the real world. Try moving that resistor.
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SandyK
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Old 18th August 2007, 03:24 PM   #25
sam9 is offline sam9  United States
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Quote:
I just pointed out that many of his schematics on the net are plainly wrong
From the moment I opened his book it was obvious he would have been better served by a better publisher and editor. Even when the figures are correct, the are often blurry. Of course I don't know the economic circumstances so maybe he did the best he could. Maybe some of this is because the book is really a bunch of individual articles strung together.

I was once pressed in to service to edit a couple of technical publications even though I understood zilch about TWTs and kystrons. I also had never done any editing before. Yet the result was much clearing than what Self's publisher had wrought.
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Old 18th August 2007, 04:26 PM   #26
AndrewT is offline AndrewT  Scotland
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I have Douglas Self, Audio Power Amplifier second edition Newnes Butterworth Heinemann.
There are very few errors in content and all the diagrams are very clear.
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Old 18th August 2007, 09:33 PM   #27
sandyK is offline sandyK  Australia
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Default it is a very good amplifier

I have the same edition as Andrew and haven't noticed any glaring errors. The diagrams are clear too.
I believe that a few of the "errors" mentioned were cleared up in another thread that Sam was involved in.
Andrew do you find the 3rd edition hard to read due to print quality ?

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SandyK
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Old 18th August 2007, 10:41 PM   #28
sam9 is offline sam9  United States
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I was thinking perhaps of figures 5.6, 6.16 and 7.5. Some component names and and vales are not readable. The line thickness is to gread so the merge together. It's always possible I have a bad printing.

As long as I'm justifying my complaints, I would have liked a more extensive index. Sometimes I find myself thinking; "I know it's in here somewhere" but it cvan be a chore to find the exact point I'm looking for.

This is not a complaint directed at Self, these should be addressed by the publisher.
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Old 18th August 2007, 10:51 PM   #29
sandyK is offline sandyK  Australia
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Default Indistinct printing

Sam9
Yes, you are correct about the quality of printing with some of the simple figures. But where it matters most, the printing is quite clear.
SandyK
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Old 18th August 2007, 11:41 PM   #30
fotios is online now fotios  Greece
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Default Re: Re: ....it is a very good amplifier

Quote:
Originally posted by Giaime
Hello fotios,
I absolutely agree, on paper it's a great thing. I was asking myself if it gives too much instability problems, that's why (I thought) people says it's worse sounding. Or maybe they forgot to use high beta devices, and match them
Dear neighbor Giaime
What i said about the usefulness of current mirror it is not only on paper. I have the bad habit to implement in practice what i draw on the paper. After the implementation of circuit i pass the sample from some hard tests in the workbench by injecting square waves of different frequencies in his input with a dummy load in his output and i observe with the scope. I use sinus waves only for the finding of clipping level. If all goes well, then i make audition tests ( as my friend SandyK ) with some other persons. I am in possition to confirm you that what i have seen in the scope it is translated exactly in the quality of music reproduced from the amplifier sample. And the quality of sound it is great. The only improvement that i succedded, according the advice of SandyK, was a further improvement in high frequencies by changing the Miller compensation capacitor from ceramic type in silvered mica. From the D.Self propotitions i am using only the E.F. arrangement instead cascode in VAS stage. What is the beneffit of using CCS in all stages, it is that in practice we can to build bigger and bigger and bigger power amplifiers simply by increasing the voltage and the power level of P.S. changing transistors with higher Vce and multiplying the number of output transistors, with exactly the same circuit each time. Such type amplifiers builded enough years before the edition of D.Self book. And me also i suppose a litle mysterious the CCS arrangement according to D.Self and i reject it. Also i consider that the removing of b-e resistors of the output transistors and its replacing from the shared emiter resistor between the output drivers it is mistake because the output then becames some unstable. These resistors provide local feedback in output transistors and may stay in place in conjuction with the shared resistor. Thus the profit it is doubled.
Fotios
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