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Old 10th October 2009, 05:23 PM   #431
Nico Ras is offline Nico Ras  South Africa
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If you tie the capacitors all through 10 ohm to ground then you forcing the caps to have ESR = 10 ohms, this is not good.
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Old 10th October 2009, 05:26 PM   #432
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by Nico Ras View Post
What is the purpose of mute if R21 is present? I was under the impression that mute was for headphone protection during cap charge-up.

Gareth, which coils are you using, where can I see a footprint.

Furthermore I see a number of ground signals, where is ground? It is floating somewhere in space.

Nico
I'm half-expecting some further discussion on R21 as to whether it should be smaller, adjustable or swithable, but you are right, if we leave it as is we might be able to simplify further.

Coils - I haven't looked at all the suggestions yet, sorry no footprint

Ground - This needs some discussion to avoid 'hum' etc. I had envisaged both channels floating above the chasis, the 'lower rail' connected to the chasis through a bridge rectifier, which further separates the channels from each other. I saw this somewhere on one of Nelson's designs - should I draw a diagram ?
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Old 10th October 2009, 05:29 PM   #433
Bigun is offline Bigun  Canada
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If you tie the capacitors all through 10 ohm to ground then you forcing the caps to have ESR = 10 ohms, this is not good.
I don't think I've understood my error yet ? - I'm looking at caps as being between rails or between 'a' and 'b'. I don't worry about where ground is at all, I only look where currents flow. The idea is, I can put ground anywhere on the circuit - it's just a point of reference ?
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Old 10th October 2009, 05:47 PM   #434
Nico Ras is offline Nico Ras  South Africa
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Hi Gareth, because of the single supply, the "ground" is effectively the negative supply. Now looking at C11, C13 they are tied through R19 forcing their ESR=10 ohms.

Also have a look at the signal current, if the signal swings negative (in other words Q4 turns on) how does the current flow?

Don't get me wrong, I am not directing these questions at you personally Gareth it is to anyone out there.

Nico
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Old 10th October 2009, 05:51 PM   #435
Nico Ras is offline Nico Ras  South Africa
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One final question. This is regarding the headphone impedance, I know of some having a low impedance around 32 ohms, most decent headphones have a much higher impedance around 200 - 500 ohms, why did we select 23 Ohms and why a 1000 uF pass capacitor, anyone though about that? As it stands the frequency is 7Hz, anybody listen to this?
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Old 10th October 2009, 05:56 PM   #436
Nico Ras is offline Nico Ras  South Africa
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What is the purpose of a zobel network and for what load is it designed or is its purpose just to shunt some oscillation and at what frequency seeing that we have headphones varying in impedance from 23 ohms to 500 ohms. Nobody questions these things and take it for granted.
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Old 10th October 2009, 06:59 PM   #437
Nico Ras is offline Nico Ras  South Africa
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I believe one of Hugh's objectives are for you guys to learn something as well as come up with the final design collectively. Some have added good ideas others seem to accept their fate like an animal led to slaughter.

Ask questions someone will respond and everyone will benefit greatly. Besides you will be proud to have a part in this when it is complete.

Kind regards

Nico
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Old 10th October 2009, 08:27 PM   #438
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by Nico Ras View Post
Hi Gareth, because of the single supply, the "ground" is effectively the negative supply. Now looking at C11, C13 they are tied through R19 forcing their ESR=10 ohms.

Also have a look at the signal current, if the signal swings negative (in other words Q4 turns on) how does the current flow?

Don't get me wrong, I am not directing these questions at you personally Gareth it is to anyone out there.

Nico
Ask away, I'm not a shy person

OK, here's how I see it. C11 and C13 are there to decouple the 'upper rail' with respect to the lower rail and NOT with respect to the chasis. So R19 is no hindrance ?
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Old 10th October 2009, 08:50 PM   #439
Sheldon is offline Sheldon  United States
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Ask away, I'm not a shy person

OK, here's how I see it. C11 and C13 are there to decouple the 'upper rail' with respect to the lower rail and NOT with respect to the chasis. So R19 is no hindrance ?
But that's not what you have drawn. C11 and C13 are shown as connected to "earth" and R19 connects the negative rail to earth. If you connect C11,13 to the negative rail instead, then R19 is not in series with the caps.

Do you need an earth connection with a 25V rail? It's already isolated in the power supply. Also, if a wall wart is used, it won't be earthed anyway.

Sheldon

Last edited by Sheldon; 10th October 2009 at 08:58 PM.
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Old 10th October 2009, 09:09 PM   #440
Bigun is offline Bigun  Canada
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Yes - you're right. I said the right thing but didn't draw it that way.


Here's an updated drawing - I've remove the mute switch - we'll put it back if the 120R resistor is questioned and removed before we finalize.

Note that the "Rcorssfeed" is supposed to represent a potentiometer for user adjustment.
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Last edited by Bigun; 10th October 2009 at 09:14 PM.
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