Thanks Michael
Sorry for the delayed reply, have been rather busy. Got some old Amigas and an Atari to look at, and had almost given up
The capacitor you mentioned, mate, is fine. I have tested the drive transistor and this appears to be working correctly, removed the relay and tested it and it does indeed also seem to work.
Would be very grateful if you could send me the schematics for the amplifier to my previously posted GMail account, as i am having difficulty finding where to re-connect the speaker outputs' earth, as the amplifier has apparently been modified by someone, previously, so my friend says, to bypass all the tone controls. I'm sure there's something missing! Some of this circuit doesn't make much sense, mostly the final output stage, unless there are hidden connections on another layer, that i can't see, hence the need for the schematic.
For now i've re-attached the speaker earths where they were when it came to me. However, one of those E connectors is linked straight to the negative trace that runs the relay! The other, like i said, through a resistor that goes also to the headphone jack's ground...and to the other side of the relay! When i removed it to test, i opened it up to see if the insides were fine. They seemed to be, and indeed learned that the output from the amp stages is connected to these resistors when the relay is inactive. As you can understand, this irritating amplifier has left me rather stumped!
If you still require pictures, i will be happy to take some for you.
Regards, and thankyou so much for replying,
Lee
Sorry for the delayed reply, have been rather busy. Got some old Amigas and an Atari to look at, and had almost given up
The capacitor you mentioned, mate, is fine. I have tested the drive transistor and this appears to be working correctly, removed the relay and tested it and it does indeed also seem to work.
Would be very grateful if you could send me the schematics for the amplifier to my previously posted GMail account, as i am having difficulty finding where to re-connect the speaker outputs' earth, as the amplifier has apparently been modified by someone, previously, so my friend says, to bypass all the tone controls. I'm sure there's something missing! Some of this circuit doesn't make much sense, mostly the final output stage, unless there are hidden connections on another layer, that i can't see, hence the need for the schematic.
For now i've re-attached the speaker earths where they were when it came to me. However, one of those E connectors is linked straight to the negative trace that runs the relay! The other, like i said, through a resistor that goes also to the headphone jack's ground...and to the other side of the relay! When i removed it to test, i opened it up to see if the insides were fine. They seemed to be, and indeed learned that the output from the amp stages is connected to these resistors when the relay is inactive. As you can understand, this irritating amplifier has left me rather stumped!
If you still require pictures, i will be happy to take some for you.
Regards, and thankyou so much for replying,
Lee
Apologies for another post...
But i just took a look at the picture that other guy posted, hijacking my question
It looks totally different to the one i'm repairing, inside! Transformer looks slightly different, and the transistors are not connected by wires and attached upside down on the heatsinks, they are connected straight to the PCB and are joined to the heatsink on a flat plate.
And i should point out, this amp does not appear to have had that much usage, or "hammer", as some of you lot seem to have given it. All the capacitors are fine, there is no heat related discolouration and all the transistors read the same values on my multimeter. Pretty sure it should work once i get this damn problem figured out.
This used to be used, years ago, to drive some huge old 14" Leak speakers, so the owner tells me. Do indeed want lol
Many thanks for your help.
Lee
But i just took a look at the picture that other guy posted, hijacking my question
It looks totally different to the one i'm repairing, inside! Transformer looks slightly different, and the transistors are not connected by wires and attached upside down on the heatsinks, they are connected straight to the PCB and are joined to the heatsink on a flat plate.
And i should point out, this amp does not appear to have had that much usage, or "hammer", as some of you lot seem to have given it. All the capacitors are fine, there is no heat related discolouration and all the transistors read the same values on my multimeter. Pretty sure it should work once i get this damn problem figured out.
This used to be used, years ago, to drive some huge old 14" Leak speakers, so the owner tells me. Do indeed want
lolMany thanks for your help.
Lee
Thierry,
You did not need to pay Sugden for the schematic as I could send it for free. Sometimes it takes a couple days before I send it, especially if it is requested during the wekkend, but I always do.
Lee,
You say the A28 is not like the one shown in the post from Thierry. This is probably because you have an earlier A28. Without a picture, it is very hard to tell. It would definitely help the thread if you posted a couple images from your A28. I wish I could post images of the various A28 incarnations but I do not have any. All I have are schematics, drawings of pcb parts placement and notes. I mainly work from memory. If it is an earlier version I do have a lot of schematics and drawings but the problem is that they are large enough to cover a kitchen table. It is a real pain to scan a schematic in parts and put it back together digitally. Very labour intensive. I will see what I can do but don't hold your breath...
I am not sure but I think the firsts A28 had EI transformers versus toroidal for later units. It could be a way to distinguish them easily...
Regards all,
Michel
You did not need to pay Sugden for the schematic as I could send it for free. Sometimes it takes a couple days before I send it, especially if it is requested during the wekkend, but I always do.
Lee,
You say the A28 is not like the one shown in the post from Thierry. This is probably because you have an earlier A28. Without a picture, it is very hard to tell. It would definitely help the thread if you posted a couple images from your A28. I wish I could post images of the various A28 incarnations but I do not have any. All I have are schematics, drawings of pcb parts placement and notes. I mainly work from memory. If it is an earlier version I do have a lot of schematics and drawings but the problem is that they are large enough to cover a kitchen table. It is a real pain to scan a schematic in parts and put it back together digitally. Very labour intensive. I will see what I can do but don't hold your breath...
I am not sure but I think the firsts A28 had EI transformers versus toroidal for later units. It could be a way to distinguish them easily...
Regards all,
Michel
Lee,
By chance an A28 serial 2226 has been brought in today for service.
It looks a lot like the one in Thierry post. I looked at where the negative speaker wires go and they are, as in your amplifier, where they should be. Don't be fooled by the fact that they connect to the 47 ohm resistor, in fact, if you look at the component side, you will see both the wire and resistor connect to ground. This resistor is there so the speaker side of the output capacitor is not floating. This way it does not accumulate a charge that would produce an unwanted "thump" when the relay is switching the speaker on.
I found time to scan parts of the schematics of the older A28. Let me know if you want them. Be aware the file size is 7 MB. Make sure your mail box can receive a file that size or that there is enough space left...
Regards,
Michel
By chance an A28 serial 2226 has been brought in today for service.
It looks a lot like the one in Thierry post. I looked at where the negative speaker wires go and they are, as in your amplifier, where they should be. Don't be fooled by the fact that they connect to the 47 ohm resistor, in fact, if you look at the component side, you will see both the wire and resistor connect to ground. This resistor is there so the speaker side of the output capacitor is not floating. This way it does not accumulate a charge that would produce an unwanted "thump" when the relay is switching the speaker on.
I found time to scan parts of the schematics of the older A28. Let me know if you want them. Be aware the file size is 7 MB. Make sure your mail box can receive a file that size or that there is enough space left...
Regards,
Michel
Hi Michel
would you mind to send the schematics to me ??
Thanks in advance
/Peter
peter.langgaard.jensen@gmail.com
would you mind to send the schematics to me ??
Thanks in advance
/Peter
peter.langgaard.jensen@gmail.com
Hi Michel
I thought this post was long dead.
I manged to get one of my P28's working, but the other not.
I'd stuck them in the loft thinking I wasn't going to get anywhere with fixing the duff one.
I would be most grateful if you could send me a copy of the schematics, mine are P28's with a rear heatsink, didn't know there were another type.
I think if I remeber correctly the faulty one does produce audio, but is hardly drawing any bias current compared to the working one.
I'll have to go up the loft and get them down, (and brush the dust of my scope).
Thanks in advance.
Dave C.
david.chapman66@googlemail.com
I thought this post was long dead.
I manged to get one of my P28's working, but the other not.
I'd stuck them in the loft thinking I wasn't going to get anywhere with fixing the duff one.
I would be most grateful if you could send me a copy of the schematics, mine are P28's with a rear heatsink, didn't know there were another type.
I think if I remeber correctly the faulty one does produce audio, but is hardly drawing any bias current compared to the working one.
I'll have to go up the loft and get them down, (and brush the dust of my scope).
Thanks in advance.
Dave C.
david.chapman66@googlemail.com
Thanks again Michel for the schematics.
One channel on my P28 is dead. My fault. Long story short, I shorted the output while the unit was on, heard a 'bizz', and now the amp keeps blowing fuses for that channel.
I measure a short between the collector and emitter of 2SB776, so I believe this is my broken component.
2SD896 test OK, but I would buy two of them as a precaution if I could find any.
I tried to find a place to buy those power transistors. This is not an easy job.
Anyone has suggestions on where to buy 2SB776 and 2SD896 ? (Michel, if you know local places near Montreal, that would be awesome).
Also, where do you find replacement for the 4700uF capacitors ?
One channel on my P28 is dead. My fault. Long story short, I shorted the output while the unit was on, heard a 'bizz', and now the amp keeps blowing fuses for that channel.
I measure a short between the collector and emitter of 2SB776, so I believe this is my broken component.
2SD896 test OK, but I would buy two of them as a precaution if I could find any.
I tried to find a place to buy those power transistors. This is not an easy job.
Anyone has suggestions on where to buy 2SB776 and 2SD896 ? (Michel, if you know local places near Montreal, that would be awesome).
Also, where do you find replacement for the 4700uF capacitors ?
Bonjour Ghyslain,
One of the only places you can find replacement transistors in Montréal is www.raybel.com. The best way to work with Raybel is to give them a call. If they do not have what you need my second choice would be www.globalsemi.com but they are in Ontario.
As for the 4700 µF 80 V my first choice is always www.digikey.ca.
I usually order the Panasonic P7372-ND as replacement for the P28.
Bonne chance,
Michel
One of the only places you can find replacement transistors in Montréal is www.raybel.com. The best way to work with Raybel is to give them a call. If they do not have what you need my second choice would be www.globalsemi.com but they are in Ontario.
As for the 4700 µF 80 V my first choice is always www.digikey.ca.
I usually order the Panasonic P7372-ND as replacement for the P28.
Bonne chance,
Michel
Sugden P28 bridged mode
Hi everybody,
I have two Sugden P28, which I want to use in bridged mode.
Both amps have their heatsink at the rear. One amp has an Output-
relais, two jumpers per channel and a toggle switch. The other amp
has one jumper per channel, a toggle switch, but no relais. This amp also has three input sockets: one left, one right, one bridged.
What do I have to do to get both amps working in bridged mode?
To which output-terminal is the speaker connected in bridged mode? Tried to receive these informations from Sugden, but no reply.
Regards,
B.
Hi everybody,
I have two Sugden P28, which I want to use in bridged mode.
Both amps have their heatsink at the rear. One amp has an Output-
relais, two jumpers per channel and a toggle switch. The other amp
has one jumper per channel, a toggle switch, but no relais. This amp also has three input sockets: one left, one right, one bridged.
What do I have to do to get both amps working in bridged mode?
To which output-terminal is the speaker connected in bridged mode? Tried to receive these informations from Sugden, but no reply.
Regards,
B.
Hi all
I 've just got an A28II. There is a minor problem that the bias current of the R chanel is higher than the left chanel. I measured the voltage across the power resistor near the output transistors and adjust the pot to reduce the bias current of right channel to be equal left channel but not sure if this is correct setting. The heat sink is only slighly warm, clearly not much in class A.
Can Michel or anyone help me with this? I would appreciate if any of you can email me the schematic (quan_ta at yahoo dot com).
thanks
I 've just got an A28II. There is a minor problem that the bias current of the R chanel is higher than the left chanel. I measured the voltage across the power resistor near the output transistors and adjust the pot to reduce the bias current of right channel to be equal left channel but not sure if this is correct setting. The heat sink is only slighly warm, clearly not much in class A.
Can Michel or anyone help me with this? I would appreciate if any of you can email me the schematic (quan_ta at yahoo dot com).
thanks
Michel,
I have an old A28 (black unit, white lettering, heatsink on the back) that needs service. One channel is very noisy/distorted.
Can you please send me the schematic and/or any other service information you have?
Best regards,
Jan
jan.sten@gurba.com
I have an old A28 (black unit, white lettering, heatsink on the back) that needs service. One channel is very noisy/distorted.
Can you please send me the schematic and/or any other service information you have?
Best regards,
Jan
jan.sten@gurba.com
A28ii
Michel
I have an A28II that has a lot of DC on the outptu for about 20 seconds, it then fades away. It works normally after that - any suggestions as to what may be causing it ?
It looks like I need to replace the 4700 µF 80 V caps in the psu, a higher mF value will be ok ?
If you can email me the schematic for this amp I would really appreciate it.
graham@appley.plus.com
Thanks a lot
Graham
Michel
I have an A28II that has a lot of DC on the outptu for about 20 seconds, it then fades away. It works normally after that - any suggestions as to what may be causing it ?
It looks like I need to replace the 4700 µF 80 V caps in the psu, a higher mF value will be ok ?
If you can email me the schematic for this amp I would really appreciate it.
graham@appley.plus.com
Thanks a lot
Graham