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Old 4th December 2006, 06:48 PM   #31
AndrewT is offline AndrewT  Scotland
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Hi Lineup,
you're still wrong.

It is not constant current. Except for that one single-ended topology.

ClassA supply rails vary their current draw as the output draws current.

While the ClassA amp is idling the supply is constant current. Send some current to the load and the supply rail current changes.
If it's dual polarity with a push pull topology then both supply rails change current to allow the output to be driven.
Quote:
If it ain't a very constant loading for Power supply - it ain't Class A.
and that's wrong as well.
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Old 4th December 2006, 07:15 PM   #32
Floric is offline Floric  Europe
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Boys stop this PLEASE! Not that way!

Holger, you have been listening to a lot of phono amps, a lot more than I did for shure. Do you have any exeriences with schematics like this one. Except for the trick with the parallel transistors, it is a quite simple schematic which has a lot of charme. But is it really capable to compete with a midrange opamp (opa2132 e.g.) in a "state of the art" schematic, like the one Thorsten presented with the Analogue Addicts?

I'm not shure.

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Old 4th December 2006, 07:25 PM   #33
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Hi Floric,
to be honest: I have no clue if this one can cope with a good OP circuit. I never listened to this circuit.
This is a nearly 25 year old Elektor project and I like it for it's simplicity, and simple things sometimes just sound better.
It has even been marketed in Germany (without the author's permission, I am sure) and many people report it sounds good.
You can build this one for 20, and that's a quality of it's own.
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Old 4th December 2006, 07:27 PM   #34
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Forgot to say: Andrew's of course right on the Class A current draw thing, but that's indeed another story and doesn't belong here.
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Old 4th December 2006, 08:53 PM   #35
Floric is offline Floric  Europe
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O.k. for 20 we should give it a try.

Thanks for your reply.
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Old 5th December 2006, 05:02 PM   #36
Nordic is offline Nordic  South Africa
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Ok so what is the verdict?
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Old 15th December 2006, 05:36 AM   #37
lineup is offline lineup  Sweden
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Default so much for saying something is constant

Quote:
Originally posted by HBarske
Forgot to say: Andrew's of course right on the Class A current draw thing, but that's indeed another story and doesn't belong here.

Yes, as I told and even changed to expression average power supply loading,
I did agree, too.


Back to this circuit and the suggested clever power supply
using LM317 for CCS and feeding a precise shunt regulation.

I did some estimation of my actually circuit
with expected output voltage
(1mV rms from average pickup??? gives 100mV rms out)
into a normal average load (10kohm ??).

The output current variations (modulation)
is only a few uA by my Low Noise BC550C circuit.
( 14uA out = 7uA variation in each push pull output transistor )
gives a modulation dept of our shunt regulator of what ..
...... fractions of a % !!!

So, in this very case, which I had in mind, when posting,
and if we also would add some suitable power supply rails bypass capacitors,
we do not have to feel bad saying the power supply see a 'constant load'.


In fact what we call constant
in an audio amplifier at work
is only constant by our definition.

Even most advanced CCS we can think of, as well as more simple ones,
can and WILL HAVE slight variations in current delivered to rest of circuit.
When audio amplifier is processing, even small voltages/currents.


lineup
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Old 28th December 2006, 10:37 AM   #38
lineup is offline lineup  Sweden
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Default Re: RIAA phono riaa preamplifier MM BC550C BC560C Version 2

Quote:
Originally posted by lineup


Great layout!
As far as I can see.
It is not the most simple circuit to design a PCB for.
With all them transistors .....

Now, this was Version 1, from my first post.

If you could update to my Version 2.
In this post:
http://www.diyaudio.com/forums/showt...54#post1072254

... and as you see from my comments,
has been a new feature with two 1N4148 diodes
and one small Multi Turn trim potentiometer
for offset adjustment.

And if you read my comments further R17 has been removed.

HBarske
The PCB for version 2
you said you would do - have you done this layout?

See my Post #16 for schematic.

Regards & Christmas
lineup
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Old 6th January 2007, 05:33 PM   #39
lineup is offline lineup  Sweden
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Quote:
Originally posted by HBarske
Just a quick shot to see how this might turn out.
We have:
- two channels
- board size: 109 x 63 mm
- seperate regs as shown above for each channel
- added pass transistors to the tl431 for more dissipation

This is how it looks right now:
Quote:
Originally posted by HBarske
Okay, I will add those modifications.

Some PSU dimensioning thoughts:

The amplifier is normally rum at +/- 15 Volts, IIRC.
Let's assume the output stage is run at, as you said, 5 mA. So I think we won't have more than 10 mA overall current consumption.

Holger, HBarske
you said you would make new layout of version 2:
Okay, I will add those modifications.

I am waiting ..
This low noise riaa
is easy to build - opamp style with common transistors
and will have very great performance - if my sims are somewhat correct.

I think a good PCB prototype silksheet
would be of interest and use for many 'Analogue people'.
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Old 6th January 2007, 09:05 PM   #40
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Give me another week. Not much time ATM.
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