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Incredible quality amplifier by Graham, prepare your ears for it
Incredible quality amplifier by Graham, prepare your ears for it
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Old 28th July 2005, 09:36 PM   #191
MikeB is offline MikeB  Germany
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Hi Barry !
Nice work ! But, shouldn't c13 (feedback) go to signalgnd ?
This way you amplify all differences between signalgnd and pwr-gnd ?

Mike
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Old 28th July 2005, 10:16 PM   #192
destroyer X is offline destroyer X  Brazil
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Default Was good idea to prevent the need of a Cdom

As sometimes it can be needed.

I congratulate you by the beautifull work you have done.

I wish you not need the capacitor, this way, certainly you will have the maximum possible quality of this very good amplifier.

regards,

Carlos
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Old 28th July 2005, 10:21 PM   #193
barryblue is online now barryblue  United Kingdom
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Default Thanks for the fast feedback

Sunrise, Greg and Mike,

Thank you for your fast feedback..much appreciated.

Sunrise : I will look at the default colours and try and change them. As for more groundplane I must admit to being torn on that. I used to think the more copper the better but now consider that it can create as many problems as it solves.....?

Greg, which resisitor on Graham's original schematic have I missed?

Brian, C13 seems to be the same as Graham's schematic...however it is late and my eyes do not work as well as they used too!

Carlos, thank you for the kind words. It seemed prudent to add the questionable capacitor
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Old 28th July 2005, 11:20 PM   #194
Graham Maynard is offline Graham Maynard  United Kingdom
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Hi Barry,

I have just studied you pcb layout and note that you are not using a star earth.
This is a common ground close to input to which all earthy connections should join to.
I have particular concern that the input filter capacitors are at the end of a long track.
The entire input circuit with capacitors could develop rf potential wrt the rest of the circuit.

(Yes sunrise, more grounding needed and should be centered on input area.)

I think the C.dom option is a good idea.

There could be the option of another capacitor to ground from input, as already used by our tutor, Carlos, to filter computer generated noise with direct connection, though I suppose that could also be part of the computer lead.

I always fit two input sockets in parallel per channel. May be used either for looping amplifiers, or for being able to plug in a terminating C or R.

Late for me too, more tomorrow.


Cheers .......... Graham.
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Old 29th July 2005, 05:08 AM   #195
barryblue is online now barryblue  United Kingdom
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Default GEM

Sunrise,

Please see the schematic below which I hope is easier to view.

Graham,

Thank you for your comments. I look forward to hearing more before I start ripping up the layout

Barry
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Old 29th July 2005, 05:08 AM   #196
barryblue is online now barryblue  United Kingdom
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Default GEM

Sunrise,

Please see the schematic below which I hope is easier to view.

Graham,

Thank you for your comments. I look forward to hearing more before I start ripping up the layout

Barry
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Old 29th July 2005, 08:08 AM   #197
Graham Maynard is offline Graham Maynard  United Kingdom
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Hi Barry,

Personally I would keep the noisy rectifiers/psu/line coupled transformer wires away from the pcb.
You do not need snubbers at the fuses when there is a large C either side.
I can assure you that the flash of a blowing fuse with this circuit is wire melting incandescence, and not a spark. (I'm sure Carlos would agree.)
It is also possible that you could parallel a pair of resistor holes with each fuse for 22 ohm then 0.22 ohm resistor fitment to facilitate initial start up testing and biasing; prior to finalising with fuse fitment.
(How will you do this if the outputs devices are all pcb mounted - and - bolted to the heatsink?)
You have the VAS and driver transistors shown as TO92 and not TO126 size, yet I do not know of any TO92 devices that could do this job.
Also the Vbe multiplier should be mounted on the heatsink for thermal feedback.

My suggestion is that everything from the VAS base onwards is mounted and hard wired on the heatsink, with all wires coming to a 4x TO92 pcb.
This should have a substantial central star earth. (I have redrawn the circuit to illustrate my layout, though nothing is drawn out.)
Each rail fuse should first supply rail capacitors and then star out from this separately to components plus heatsink; ie. do not have output device current through track resistance generating a fractional voltage that will modulate supply to the input stage.

My biggest worry with your existing layout is that your input socket is incapable of grounding interference on the screen of the input cable wrt amplifier input.

If you wish to have output devices and drivers pcb mounted then split the circuit and use two pcbs with separation at the VAS base and the positive driver base.

I trust you now understand what is meant by 'star' earth/grounding.
Keep the class-A power device physically closest to the VAS, and keep the inputs 5cm/2" away from output wires/Zobel etc.


Cheers ........... Graham.
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Old 29th July 2005, 08:10 AM   #198
Greg Erskine is offline Greg Erskine  Australia
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Incredible quality amplifier by Graham, prepare your ears for it
Default Re: Thanks for the fast feedback

Quote:
Originally posted by barryblue
Greg, which resisitor on Graham's original schematic have I missed?
You are getting me paranoid now. Hope I'm not going darf.

Notice second 22 ohm resistor R10 in sketch.
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Old 29th July 2005, 10:01 AM   #199
destroyer X is offline destroyer X  Brazil
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Default Well Graham, you calling me tutor, let me really embarrassed.

In my intimate feelings, i am so small in knowledge compared with your that i thank you very much, because of that respect that i really do not deserve.

I am a constructor, and a transistor X - extra destroyer, and to me, polish your shoes can be more than i hope for.

You are great, also Hugh and Mike, and i have enormous respect to all of you...levelled with John lindsey Hood (JLH).

I will copy your message, to show my friends that some respect to me.... well, milacres use to happen.

regards,

Carlos
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Old 29th July 2005, 10:53 AM   #200
sunrise is offline sunrise
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Default Re: GEM

Quote:
Originally posted by barryblue
Sunrise,

Please see the schematic below which I hope is easier to view.

Graham,

Thank you for your comments. I look forward to hearing more before I start ripping up the layout

Barry
Oh boy - this is nice - I like this schematic very much - thank You for the time - this is beutiful


regards and keep up the good work - like carlos said just polishing if I can

to carlos - is this the box where You would put Your amp in ? Is so - are those heatsinks are enough?????
also - nice to see that You put them that way....
regards
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