Hello all
Need some help here...
Got this amp last week, good cosmetics, it worked ok. I decided to check bias and DC offset. DC offset in left channel was 8 but it responded well to the pot correction. Right channel was 20, and with pot all the way counterclockwise it went to 10, and that was it. I have to match and replace input transistors I know. I ordered them.
Bias was 16.5 mv at R88 both channels. I adjusted it to specified 33, but other mosfets were all over the place, from 18 to 45, so I turned it down to about 25. Same in left channel. It worked like this for a couple of days, and then - kaboom! Blew both 10A fuses in right channel, and thermal protection LED came on. I found four shorted output IRF244s: Q99, Q92, Q13, Q2. I have no idea what happened...
So, a few questions:
1) I was using outboard turn-on strip, with amp's power switch in ON position - could that do it? Worked fine on all my other amps over the years;
2) Does this amp have a turn-on/turn-off disconnect relay? Because in my case sound comes on as soon as turn it on, and continues for a few seconds after I turn it off;
3) I have located IRF244 mosfets, albeit not cheap. What else should I check for before I plug them in, put the amp on my variac, and pray?
Thank you
Mark
Need some help here...
Got this amp last week, good cosmetics, it worked ok. I decided to check bias and DC offset. DC offset in left channel was 8 but it responded well to the pot correction. Right channel was 20, and with pot all the way counterclockwise it went to 10, and that was it. I have to match and replace input transistors I know. I ordered them.
Bias was 16.5 mv at R88 both channels. I adjusted it to specified 33, but other mosfets were all over the place, from 18 to 45, so I turned it down to about 25. Same in left channel. It worked like this for a couple of days, and then - kaboom! Blew both 10A fuses in right channel, and thermal protection LED came on. I found four shorted output IRF244s: Q99, Q92, Q13, Q2. I have no idea what happened...
So, a few questions:
1) I was using outboard turn-on strip, with amp's power switch in ON position - could that do it? Worked fine on all my other amps over the years;
2) Does this amp have a turn-on/turn-off disconnect relay? Because in my case sound comes on as soon as turn it on, and continues for a few seconds after I turn it off;
3) I have located IRF244 mosfets, albeit not cheap. What else should I check for before I plug them in, put the amp on my variac, and pray?
Thank you
Mark
Last edited:
Unfortunately, the 5802 is not my design. It was apparently a redesign
by the OEM manufacturer for Adcom, Gallien, and does not bear a lot of
resemblance to the 5800 circuit, which was mine.
by the OEM manufacturer for Adcom, Gallien, and does not bear a lot of
resemblance to the 5800 circuit, which was mine.
Thank you very much for clarifying this, and I'm sorry. In this case I would ask moderator to remove my post or move it to regular "sold state" amps, and I will edit it (I don't know how to alert moderator though). Lots of misinfo out there...
Use the !-triangle
Hello marknoir,
I bought my Adcom 5802 in the early 90s. Loved it! The left channel gave out on Dec 2020. She sat in a repair shop for over a year hoping to get input/output transistors. The repair shop said it's impossible to get parts and I'm now heart broken. Just wondering if you were successful in getting transistors for your 5802. If yes, could you help out a senior here?
Regards,
Vic
The very first reply to my very first question here is from 'The ONE and only'. Thank you so much, Mr. Pass, for the effort! The excitement of receiving a message from you this morning created chaos in my house. Babbling to the wife about the creator of Threshold, Pass Labs, and First Watt... just to calm down. If this was a written letter, it wouldn't be legible due to shaky fingers.
Back to business at hand. Just finished chatting with the repair shop tech about my 5802. He said it's the output transistors. But insisted that if one were to only replace the transistors, problem will persist. Only way of fixing this is to get a whole left channel assembly board. I told him that I've tried to do just that at various sites. Adcomparts.com listed part #: 36005818 - Amplifier Assy, but no stock. I've left messages there, but no reply.
I don't know if it's possible to resuscitate my amp, but I'm taking her with me when I go!
Regards,
Vic
Sir, do you think there's any chance of getting the old amp going again?
Regards.
Sorry about delay.
The answer is yes, but I still would like to know what the transistors were. You will appreciate that while I designed the 5800 the 5802 was redesigned by the OEM that Adcom hired to manufacture its successor. It has few similarities to the original, and that presents some challenges. I will look at my files to see if I have the schematic.
The answer is yes, but I still would like to know what the transistors were. You will appreciate that while I designed the 5800 the 5802 was redesigned by the OEM that Adcom hired to manufacture its successor. It has few similarities to the original, and that presents some challenges. I will look at my files to see if I have the schematic.
There seems to be a lot of owners of Adcom products out there claiming it was designed by NP. I too thought the 5802 was your design, wrong for nearly 30 years!
I had plenty of free time these past years. Found some schematics online. Don't know if it'll help.
Thanks for the quick reply!
Regards,
Vic
I had plenty of free time these past years. Found some schematics online. Don't know if it'll help.
Thanks for the quick reply!
Regards,
Vic