r21 old question

aaronboumans · 18th October 2004, 09:39 AM

I am in the process of building 2 A3's and an A5 for an active system
The A5 is working correctly but the A3 (all 4!!) have an occillation of about 650Khz. Removing R21 reduce the voltage across R120-123 from 1V to 0.35V
I saw a message by GRollins (or was it Peter Daniels?) saying he removed R21 (and R124-127) permanently? What will be the effect if I did this also? Will there be a need to adjust anything else(yes, adjust R19 so 0.5V will be across R120-R123) and will this help the overall sound of the Aleph?

GRollins · 18th October 2004, 09:34 PM

I'm not sure which resistor you're referring to when you say R21--I don't see one on the schematic for the Aleph 3.
If you remove R124-127, you're removing part of the Aleph current source. Those resistors are the current sensing array. Once you start down that path, forever will the Dark Side dominate your destiny...
Er, sorry, got carried away.
If you disable the Aleph current source, you'll no longer have an Aleph, you'll have a Zen on steroids. Whether the sound suits you or not is up to you.

Grey

aaronboumans · 19th October 2004, 08:10 AM

hahahaha!!
Thanks Grey
I made a mistake, i was reffering to R114/C103
So no further adjustments needed?
Did you notice any significant difference with and without the currentfeedbackloop? I cannot judge this yet because my old speakers are sold and the new ones are not ready yet.

raincheck · 1st November 2004, 11:29 PM

Thanks for all the info,
Does all this mean that I can use a 6.3 V rated cap for all THREE 220uf locations on each channel of the aleph amp. How did you guys calculate this?
Thanks,
Tom

raincheck · 1st November 2004, 11:33 PM

Im sorry, I replied to the wrong thread,
I'm referring to the 220uF coupling caps on the Aleph amps.....I was trying to figure out the max voltage rating,
Thanks,
Tom

wuffwaff · 2nd November 2004, 07:15 AM

Hi Aaron,

removing the cap plus resistor maens you don´t have an active current source anymore. Peak current will be halved and power will be quartered (when current limited).

Why don´t you try changing the small cap near the ZTX450/BC550? Make it a bit larger and see if the oscillation disappears.

William

Nelson Pass · 2nd November 2004, 06:25 PM

If that doesn't work, try the lag compensation on the D-G
of the Mosfet on the (-) side.

aaronboumans · 2nd November 2004, 08:05 PM

Thanks everyone, specially mr. Pass not so much for his answer but for making some of his designs available to us.
Ok I now have a stable current source (on all amps)with AC feedback, placed an 1nF cap over CE of Q105. Absoulutly clean scope-image.

Today I completely finished one monoblock, picture will follow on
active system, first pictures

18th October 2004, 09:39 AM	#1
aaronboumans diyAudio Member Join Date: Feb 2003 Location: deventer	r21 old question I am in the process of building 2 A3's and an A5 for an active system The A5 is working correctly but the A3 (all 4!!) have an occillation of about 650Khz. Removing R21 reduce the voltage across R120-123 from 1V to 0.35V I saw a message by GRollins (or was it Peter Daniels?) saying he removed R21 (and R124-127) permanently? What will be the effect if I did this also? Will there be a need to adjust anything else(yes, adjust R19 so 0.5V will be across R120-R123) and will this help the overall sound of the Aleph?

1st November 2004, 11:29 PM	#4
raincheck diyAudio Member Join Date: Dec 2001 Location: Avalon	Can I use a 6.3 v cap at all three locations Thanks for all the info, Does all this mean that I can use a 6.3 V rated cap for all THREE 220uf locations on each channel of the aleph amp. How did you guys calculate this? Thanks, Tom __________________ In The Days Before Rock 'n ' Roll

1st November 2004, 11:33 PM	#5
raincheck diyAudio Member Join Date: Dec 2001 Location: Avalon	wrong thread Im sorry, I replied to the wrong thread, I'm referring to the 220uF coupling caps on the Aleph amps.....I was trying to figure out the max voltage rating, Thanks, Tom __________________ In The Days Before Rock 'n ' Roll

2nd November 2004, 07:15 AM	#6
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	Hi Aaron, removing the cap plus resistor maens you don´t have an active current source anymore. Peak current will be halved and power will be quartered (when current limited). Why don´t you try changing the small cap near the ZTX450/BC550? Make it a bit larger and see if the oscillation disappears. William __________________ een ooievaar is geen konijn want zijn oren zijn te klein!

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18th October 2004, 09:34 PM	#2
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	I'm not sure which resistor you're referring to when you say R21--I don't see one on the schematic for the Aleph 3. If you remove R124-127, you're removing part of the Aleph current source. Those resistors are the current sensing array. Once you start down that path, forever will the Dark Side dominate your destiny... Er, sorry, got carried away. If you disable the Aleph current source, you'll no longer have an Aleph, you'll have a Zen on steroids. Whether the sound suits you or not is up to you. Grey

19th October 2004, 08:10 AM	#3
aaronboumans diyAudio Member Join Date: Feb 2003 Location: deventer	hahahaha!! Thanks Grey I made a mistake, i was reffering to R114/C103 So no further adjustments needed? Did you notice any significant difference with and without the currentfeedbackloop? I cannot judge this yet because my old speakers are sold and the new ones are not ready yet.

2nd November 2004, 06:25 PM	#7
Nelson Pass The one and only Join Date: Mar 2001	If that doesn't work, try the lag compensation on the D-G of the Mosfet on the (-) side.

2nd November 2004, 08:05 PM	#8
aaronboumans diyAudio Member Join Date: Feb 2003 Location: deventer	Thanks everyone, specially mr. Pass not so much for his answer but for making some of his designs available to us. Ok I now have a stable current source (on all amps)with AC feedback, placed an 1nF cap over CE of Q105. Absoulutly clean scope-image. Today I completely finished one monoblock, picture will follow on active system, first pictures

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