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Old 29th January 2007, 07:41 PM   #391
cviller is offline cviller  Denmark
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Default Good and bad news

I built my version of this fishing project this weekend, but the results are mixed. The sound is incredible - the first channel I tested had some dc on the output 80mV, but I tried it with my speakers anyways. I was astonished the clean sound and all the details!

Now the problem is the ripple on my supply and output. I only have one psu for both channels. The crc for each rail looks like this:

2x15mF -> 5x 1R -> 4x15mF

The ripple with both channels running is just below 100mV on each rail (measured with my scope).

The ripple with only one channel running seems to be approx 80% of one rail ripple. I have looked around with a probe and the only place that seems to be without ripple is the grounded input and source on jfets.

Any suggestions to what I should look for? Shouldn't it be possible to reject 100mV ripple?

I have attached a picture of my boards so Choky can give his usual comment. And I will post my schematics in few minutes.
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Old 29th January 2007, 07:49 PM   #392
cviller is offline cviller  Denmark
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The schematics with the values I have used.

The first time I tried it with only one channel, I couldn't hear any hum, but I can't make it go away now...
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Old 29th January 2007, 08:13 PM   #393
Zen Mod is offline Zen Mod  Serbia
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first thing first: ugly!

second - where are heatsinks?


third- on first sight,schm looks good ; for later-try to vary 22 ohms source degeneration resistors, down and up,just to see (hear) can you spot any difference

next- you have hum now even with one channel only,and you have nada hum in first test?

if yes- you definitely have gnd loop somewhere ;

tell me - xformer,graetz,caps,res,caps ........?

have you some sisy xformer here

play little with PSUd if you have time

and-try with 3x15mF-0R2-3x15mF

and-what's Iq?
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Old 29th January 2007, 08:34 PM   #394
cviller is offline cviller  Denmark
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I have uploaded a few pics here:
http://viller.org/audio/2007jan_jfish/hum/

Quote:
next- you have hum now even with one channel only,and you have nada hum in first test?

if yes- you definitely have gnd loop somewhere ;
Yes, there was no hum before, but I used a water boiler in series with mains so it might have done some strange tricks.


Quote:
tell me - xformer,graetz,caps,res,caps ........?
I have used zalman grease and mica. The transformers are two of the 10x17V 1.5A I have been talking about a few times. They don't make any bad noises and doesn't get hot at all.
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Old 29th January 2007, 08:49 PM   #395
Zen Mod is offline Zen Mod  Serbia
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star ground-make it fat and precise

everything goes to star ground ,separately :

spk minus wire
pcb ground
input connector ground (not connected on pcb,just on connector side!)

and-that's probably "everything" ; 3 ground wires for each channel

if you make like this,you probably will not have any gnd loop

clear or you need sketch?

if you already know this,hehe- I hope that some noob will read this somewhere in time....

you didn't answer - what's Iq?

EDIT:

now,looking at first picture,I can see that you have 3 gnd connections to each pcb............power ground wire (from PS),speaker ground wire (from pcb to spk (scope probe gnd connected to it) ) and shielded and input cable..

as I say (often to my self ) ......no-no...........ya really need just one gnd wire to pcb.......(from PS central gnd point to pcb)

try it
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Old 30th January 2007, 05:39 AM   #396
cviller is offline cviller  Denmark
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Quote:
star ground-make it fat and precise

everything goes to star ground ,separately :

spk minus wire
pcb ground
input connector ground (not connected on pcb,just on connector side!)

and-that's probably "everything" ; 3 ground wires for each channel

if you make like this,you probably will not have any gnd loop

clear or you need sketch?
What about rectifier bridge? Can I make the psu pcb starground?

I don't really like the idea of ditching the shield on input connectors, but I guess I might have to....

Quote:
you didn't answer - what's Iq?
Sorry about that. I didn't answer cos I was not sure if you just meant the current through my transistors or something else. I have close to 1A through each transistor.


Quote:
try it
I will.
Thanks for your suggestions!
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Old 30th January 2007, 11:32 AM   #397
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by cviller


What about rectifier bridge? Can I make the psu pcb starground?

I don't really like the idea of ditching the shield on input connectors, but I guess I might have to....



Sorry about that. I didn't answer cos I was not sure if you just meant the current through my transistors or something else. I have close to 1A through each transistor.




gimme pic of copper side of PSU pcb and I'll point you to adequate point .............center between cap's grounds...

ditching the shield.........think and re-think........do you really need g-loop?

grounding shield just at connector side is 100% effective...........shield is still shield and not conductor for g-loop

got it,regarding Iq
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Old 30th January 2007, 11:50 AM   #398
cviller is offline cviller  Denmark
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Quote:
Originally posted by Zen Mod


gimme pic of copper side of PSU pcb and I'll point you to adequate point .............center between cap's grounds...

ditching the shield.........think and re-think........do you really need g-loop?

grounding shield just at connector side is 100% effective...........shield is still shield and not conductor for g-loop
I think shield only works effectively if it is return-path for signal...

I have attached the underside of my psu. The left side is output and right side is input. The two grounded leads just to the right of the middle are from the rectifier bridges. Should I place starground in the middle to the left?
I have tried to measure hum on ground nodes, but haven't found anything. I will however still try the starground, although I think the root cause is somewhere else.
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Old 30th January 2007, 11:57 AM   #399
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by cviller


I think shield only works effectively if it is return-path for signal...




yes-if input connector is isolated from case and not grounded to star ground


Quote:
...... The two grounded leads just to the right of the middle are from the rectifier bridges. ......
place good enough for all ground wires
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Old 30th January 2007, 12:42 PM   #400
cviller is offline cviller  Denmark
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Thanks Choky for helping me with this!

I tried to move all ground wires to gnd terminal on my psu board and only running one channel but I didn't see any noticeable improvements, but I discovered something else. There is a very large difference in my CCS transistors source resistor voltages. One reads 450mV whilst the other is 200mV (across a 0.47 resistor).

I did match all my transistors to within 0.01V at 1A and 20sek. Could it be my resistors or should I try with some different transistors? The gate voltages were the same in reference to ground.
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