Aleph A30 - troubleshooting tips

fcel · 26th August 2005, 07:37 PM

I have successfully built Aleph 2 in the past but I did not have much luck with the Aleph A30 amp that I have built recently. I'm soliciting for some help from this forum - troubleshooting tips.

Board used:
BrianGT (the lastest GP which I'm sure quite a few folks here have already built successfully).

Parts used:
Except for the output transistors and the front end transistors, all parts are based entirely on Brian's part list from his web site. Matched transistors was obtained from a forum member.

Issues:
1) On one channel, starting up using a variac, 10mv on both output, heatsink heated up nicely, sound is 'muffled", and after about 5 to 10 minutes, smoke comes of one of the output transistors (connected to + power supply side).
2) On the other channel, I see smoke coming out of one of the output transistors (also connected to the + power supply side) as the variac voltage reaches 90VAC.
3) No smoke coming out form either signal boards. Thanks for that.
4) Power supply boards measure +24.5V and -24.5V. So, I know power supply is okay.

Questions:
Before I dive in and tear everything apart to start troubleshooting, is there something obvious that I have overlooked? Some troubleshooting tips?

Nelson Pass · 26th August 2005, 07:42 PM

At least you have a variac. I would start by measuring output
DC offset, and the DC values across the Source resistors on the
output transistors to find out who's drawing the current. Then
I would look to see what the drive voltage is on that transistor
and/or the voltage across its Gate stopping resistor (221 ohm).

jleaman · 27th August 2005, 03:43 AM

Maybe i should follow this.. you got your parts did you ?

fcel · 27th August 2005, 04:11 AM

No, I still have not received the parts from the group buy. Is it 10 weeks already?

I purchase the parts from digikey last week.

jleaman · 27th August 2005, 04:12 AM

Quote:

Originally posted by fcel
No, I still have not received the parts from the group buy. Is it 10 weeks already?

Mmmm no.

fcel · 27th August 2005, 04:22 AM

There were more than 70 individual sign up for the PCB GP and more than 50 individual sign up for the component GP. Has anybody built the A30 yet - the subject of this thread? I haven't seen any pictures in this forum but I know quite a few have built the mini-A.

mpmarino · 27th August 2005, 05:16 AM

Quote:

Except for the output transistors and the front end transistors, all parts are based entirely on Brian's part list from his web site. Matched transistors was obtained from a forum member.

What parts are you using exactly?

I will be powering my A 30/3 probably in a week or so and am interested in avoiding the troubles you are having.

Thanks,
Marc

jleaman · 27th August 2005, 05:20 AM

I must warn people i hope you guys have big heat sinks. I have just powered up Brentw's mini a's on a 8x8" heat sink and they get pretty hot.

id think that a a 30 will get hotter too.

fcel · 27th August 2005, 05:27 AM

Marc,
I used parts from the parts list that Brian had provided from his web site http://www.diyamps.com/aleph/aleph.shtml

Stones · 27th August 2005, 08:03 AM

Quote:

Originally posted by fcel
There were more than 70 individual sign up for the PCB GP and more than 50 individual sign up for the component GP. Has anybody built the A30 yet - the subject of this thread? I haven't seen any pictures in this forum but I know quite a few have built the mini-A.

I built A5's with brians PCB's link
No problems worked 1st go.

26th August 2005, 07:37 PM	#1
fcel diyAudio Member Join Date: Sep 2001 Location: LA County	Aleph A30 - troubleshooting tips I have successfully built Aleph 2 in the past but I did not have much luck with the Aleph A30 amp that I have built recently. I'm soliciting for some help from this forum - troubleshooting tips. Board used: BrianGT (the lastest GP which I'm sure quite a few folks here have already built successfully). Parts used: Except for the output transistors and the front end transistors, all parts are based entirely on Brian's part list from his web site. Matched transistors was obtained from a forum member. Issues: 1) On one channel, starting up using a variac, 10mv on both output, heatsink heated up nicely, sound is 'muffled", and after about 5 to 10 minutes, smoke comes of one of the output transistors (connected to + power supply side). 2) On the other channel, I see smoke coming out of one of the output transistors (also connected to the + power supply side) as the variac voltage reaches 90VAC. 3) No smoke coming out form either signal boards. Thanks for that. 4) Power supply boards measure +24.5V and -24.5V. So, I know power supply is okay. Questions: Before I dive in and tear everything apart to start troubleshooting, is there something obvious that I have overlooked? Some troubleshooting tips?

27th August 2005, 03:43 AM	#3
jleaman diyAudio Member Join Date: Apr 2002 Location: Nanaimo	Maybe i should follow this.. you got your parts did you ? __________________ Baby Danika, Born January 20th 1:54am.. http://itsparks.dyndns.orgMix a LittleUntangle&Opendns.org Perfect..

27th August 2005, 05:20 AM	#8
jleaman diyAudio Member Join Date: Apr 2002 Location: Nanaimo	I must warn people i hope you guys have big heat sinks. I have just powered up Brentw's mini a's on a 8x8" heat sink and they get pretty hot. id think that a a 30 will get hotter too. __________________ Baby Danika, Born January 20th 1:54am.. http://itsparks.dyndns.orgMix a LittleUntangle&Opendns.org Perfect..

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26th August 2005, 07:42 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	At least you have a variac. I would start by measuring output DC offset, and the DC values across the Source resistors on the output transistors to find out who's drawing the current. Then I would look to see what the drive voltage is on that transistor and/or the voltage across its Gate stopping resistor (221 ohm).

27th August 2005, 04:11 AM	#4
fcel diyAudio Member Join Date: Sep 2001 Location: LA County	No, I still have not received the parts from the group buy. Is it 10 weeks already? I purchase the parts from digikey last week.

27th August 2005, 04:22 AM	#6
fcel diyAudio Member Join Date: Sep 2001 Location: LA County	There were more than 70 individual sign up for the PCB GP and more than 50 individual sign up for the component GP. Has anybody built the A30 yet - the subject of this thread? I haven't seen any pictures in this forum but I know quite a few have built the mini-A.

27th August 2005, 05:27 AM	#9
fcel diyAudio Member Join Date: Sep 2001 Location: LA County	Marc, I used parts from the parts list that Brian had provided from his web site http://www.diyamps.com/aleph/aleph.shtml

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