Hi
I have been using this fine Classe Model 20 solid stat pre-amplifier for many years. Recently it encountered a problem:
While I was listening to music, the Pre-amp tends to go to the stand-by mode (green color). I checked whether there were any problems associated with the other connected equipment or the cables. I found none.
This amp drives my Marantz MA500 (pair) power mono block amps.
Also, I switched off the amp for some time and later switched it on and listened to a cd player connected to the pre-amp. After 3-4 minutes of normal play, again the pre-amp goes to the standby mode. Also, I found the green led was blinking continuously without attaining into steady state.
Can anyone help me how to overcome this problem. Unfortunately, Classe has discontinued this model long time ago. So it is difficult to get the service manual of this amp.
I have been using this fine Classe Model 20 solid stat pre-amplifier for many years. Recently it encountered a problem:
While I was listening to music, the Pre-amp tends to go to the stand-by mode (green color). I checked whether there were any problems associated with the other connected equipment or the cables. I found none.
This amp drives my Marantz MA500 (pair) power mono block amps.
Also, I switched off the amp for some time and later switched it on and listened to a cd player connected to the pre-amp. After 3-4 minutes of normal play, again the pre-amp goes to the standby mode. Also, I found the green led was blinking continuously without attaining into steady state.
Can anyone help me how to overcome this problem. Unfortunately, Classe has discontinued this model long time ago. So it is difficult to get the service manual of this amp.
There seems to be very little information at all on this amplifier.
Due to the design being a solid-state discrete design (without op-amps), I'm thinking it might well be a problem with DC offset at the output of the amplifier, causing it to go into standby (or protection) mode. As this is a high end preamp, there might not be a DC blocking capacitor at the output (because of signal quality degradation concerns) so when there is DC offset, the only way to protect the amplifier plugged into the output is to open the output relay (assuming it has one).
Another problem could be overheating however, surely if there was a temperature cut out, it would have triggered even when it was new-the amount of heat produced would stay constant over the working life of the preamp.
These are just a few suggestions as to what it might be.
Due to the design being a solid-state discrete design (without op-amps), I'm thinking it might well be a problem with DC offset at the output of the amplifier, causing it to go into standby (or protection) mode. As this is a high end preamp, there might not be a DC blocking capacitor at the output (because of signal quality degradation concerns) so when there is DC offset, the only way to protect the amplifier plugged into the output is to open the output relay (assuming it has one).
Another problem could be overheating however, surely if there was a temperature cut out, it would have triggered even when it was new-the amount of heat produced would stay constant over the working life of the preamp.
These are just a few suggestions as to what it might be.
classe 20 switching problem
Dear Jack,
Thank you for your kind reply regarding that. According to your reply there can be two possible causes:
1. DC off set at the output of the pre-amplifier
2. The thermal or temperature cut out get activated due to heat generated
The second possibility may be an option, because the player is switched on after a rest, it operates for few minutes ( with red light indicator on) and go to standby mode or protection mode where the amp green light start blinking.
I have to inform you, I am a newbie to DIY, how can I overcome this problem, should I need the schematics. I do not think Classe will be interested in providing that for a discontinued product.
Thanks
Dear Jack,
Thank you for your kind reply regarding that. According to your reply there can be two possible causes:
1. DC off set at the output of the pre-amplifier
2. The thermal or temperature cut out get activated due to heat generated
The second possibility may be an option, because the player is switched on after a rest, it operates for few minutes ( with red light indicator on) and go to standby mode or protection mode where the amp green light start blinking.
I have to inform you, I am a newbie to DIY, how can I overcome this problem, should I need the schematics. I do not think Classe will be interested in providing that for a discontinued product.
Thanks
As you say, the second possibility would be more likely as it it is a solid state design (which probably makes use of heatsinks) and has the possibility to overheat. This is not a problem in designs that use operational amplifiers.
It would also make sense as it takes 3-4 minutes to warm up and then goes over temperature and then back into standby. You then wait for it to cool down and then it will come back on again until it overheats again.
Does the amplifier run hot usually? Also, I wonder why it has only begun to do this recently and not through its whole life.
It would also make sense as it takes 3-4 minutes to warm up and then goes over temperature and then back into standby. You then wait for it to cool down and then it will come back on again until it overheats again.
Does the amplifier run hot usually? Also, I wonder why it has only begun to do this recently and not through its whole life.
Dear Jack,
Thanks for your support. It has never become overheated. After running many hours continuously, it has never get hot. As you asked, it has never had this switching problem.
I have been using this over 15-years without a problem. I drive Marantz MA500 mono-block with this. It has performed flawlessly until this problem. Only problem I have encountered was the Volume Control Pod become scratchy due to dust or wear and tear.
How should I get about.
Cheers
Thanks for your support. It has never become overheated. After running many hours continuously, it has never get hot. As you asked, it has never had this switching problem.
I have been using this over 15-years without a problem. I drive Marantz MA500 mono-block with this. It has performed flawlessly until this problem. Only problem I have encountered was the Volume Control Pod become scratchy due to dust or wear and tear.
How should I get about.
Cheers
How many preamps monitor dc offset or temperature? While certainly not impossible i find this unlikely.
I think it is just the power-on delay system which may also monitor the PS rails. Is it microprocessor based? Remote controlled? If you cannot troubleshoot why don't you post a couple of pics?
I think it is just the power-on delay system which may also monitor the PS rails. Is it microprocessor based? Remote controlled? If you cannot troubleshoot why don't you post a couple of pics?
Classe 20 switching problem
Dear friend,
Thanks for your message. I have attached the schematics of this amp just now from Classe Canada. Classe people are very helpful and without hesitation they sent me the schematics for this discontinued model.
I have uploaded along with my reply for your perusal, so that you can advise me how to troubleshoot or finding the fault of this amp, so that I could get it repaired.
Cheers🙂
Dear friend,
Thanks for your message. I have attached the schematics of this amp just now from Classe Canada. Classe people are very helpful and without hesitation they sent me the schematics for this discontinued model.
I have uploaded along with my reply for your perusal, so that you can advise me how to troubleshoot or finding the fault of this amp, so that I could get it repaired.
Cheers🙂
Classe Model 20 Switching Probelm
Dear friends,
Further to my earlier thread, I give below the opinion given by Classe:
"unfortunately do not have any documents on the troubleshooting guidelines for these earlier units but from the information I could gather from one of our technicians, it certainly look towards a DC offset problem".
If it is the DC offset, how can I get over the problem?
🙂 Mohan
Dear friends,
Further to my earlier thread, I give below the opinion given by Classe:
"unfortunately do not have any documents on the troubleshooting guidelines for these earlier units but from the information I could gather from one of our technicians, it certainly look towards a DC offset problem".
If it is the DC offset, how can I get over the problem?
🙂 Mohan
Hi Mohan
I am quite shocked that Classe came up with such a suggestion. My previous suspicion has been confirmed by the circuit diagram you posted - muting is not in any way connected to either offset or temperature. As it is controlled by a pic i would look for the problem there. You don't mention whether you can unmute from the panel switch or the remote control.
Is the remote control working? If it is, a problem with the pic will be very unlikely. Any possibility the muting switch is faulty? I would also look at the power-on reset of the pic - if CD3 has developed some leakage it could randomly reset the pic which will then enter the muting state. Don't forget to also check the pic PS.
Classe 20 switching problem
Dear Friend,
Thanks for your kind support. Please do not get offended for asking few questions:
1. Can you clarify what do you mean by 'pic"? is it the schematic diagram?
I am a newbie to DIY.
2. I think I can un-mute using the panel switch but after few minutes it goes back to green mode or the protection mode ( from red led indicator under unmute mode).
3. What is power on reset pic- CD3 has developed any leakage
4. What do you mean by checkin pic- 5, does that mean schematic no-5?
Kindly clarify.
Best regards
Mohan
Dear Friend,
Thanks for your kind support. Please do not get offended for asking few questions:
1. Can you clarify what do you mean by 'pic"? is it the schematic diagram?
I am a newbie to DIY.
2. I think I can un-mute using the panel switch but after few minutes it goes back to green mode or the protection mode ( from red led indicator under unmute mode).
3. What is power on reset pic- CD3 has developed any leakage
4. What do you mean by checkin pic- 5, does that mean schematic no-5?
Kindly clarify.
Best regards
Mohan
In that case it may be wise to refer to a technician. Not easy to find a good one though.
The pic is IC1 in the circuit. Apart from replacing CD3 (10uF/any voltage rating above 6.3v) in the reset circuit i have no other easy suggestions.
If all else fails you may wish to disable the muting circuit (very easy) and make sure you power the power amps after the preamp to avoid the thump.
Dear Friend,
Thanks very much, I will get it checked by a Tech friend and come back to you.
I now have a good idea about what you have suggested.
Thank you for your continued support.
Best regards
Mohan
Thanks very much, I will get it checked by a Tech friend and come back to you.
I now have a good idea about what you have suggested.
Thank you for your continued support.
Best regards
Mohan
You are most welcome. Let's hope this helps as replacement of the pic is probably not an option.
Im pretty darn late to this thread! But I just picked up a twenty preamp. Does anyone have any idea on when it came out, what it sold for or anything on turning the unit off??