Classe Audio DR-9

[Ws Audio]

I own a Classe Audio DR-9 and it has buzzing sound. I bought this from a friend of mine and it seems that he’d changed the transistors with the inappropriate ones. I need to change those transistors with the proper ones yet, I don’t know the types.

 

Can someone tell me what is the original type of  transistors used?

[Zaphod Beeblebrox]

Classe' are (or were) notoriously secretive about the devices used in their products. As such, no designation exists on any of their schematics. Output devices had their original part numbers removed. I can't say that I noticed the front end devices. I suggest that you check the other channel and see what part numbers are used.

 

However, there is more.

1) I doubt that replacing the transistors will cure the fault.

2) Classe' employed matching for their transistors, so you will need to fit matched devices.

3) My best GUESS (do not take this as gospel) is that the devices are MPSA42 and MPSA92 transistors, but I am far from certain about this.

[georgehifi]

On 04/02/2019 at 4:29 PM, Zaphod Beeblebrox said:

Classe' are (or were) notoriously secretive about the devices used in their products. As such, no designation exists on any of their schematics.

The DR25 almost identical input stage uses 5 x 2N5619 good bet their the same in the DR9 as both had similar rail volts. 

 

Cheers George

 

 

Edited February 22, 2019 by georgehifi

[Zaphod Beeblebrox]

Not a chance, @georgehifi . A 2N5619 is a TO3, 50 Watt device. The ones fitted to the Classe' amps' front end are TO92, low power devices. In that particular location, I prefer to see much high Voltage devices fitted. The 2N5619 has a maximum Voltage rating of 120 Volts.

[Ws Audio]

3 hours ago, Zaphod Beeblebrox said:

Classe' are (or were) notoriously secretive about the devices used in their products. As such, no designation exists on any of their schematics. Output devices had their original part numbers removed. I can't say that I noticed the front end devices. I suggest that you check the other channel and see what part numbers are used.

 

However, there is more.

1) I doubt that replacing the transistors will cure the fault.

2) Classe' employed matching for their transistors, so you will need to fit matched devices.

3) My best GUESS (do not take this as gospel) is that the devices are MPSA42 and MPSA92 transistors, but I am far from certain about this.

Thank you very much! I’ll take a chance to try it. I can tell it’s the transistors because previously the buzzing sound was quite loud and I tried to change the transistors. The buzzing sound is still exist now yet, it decrease. I’ll let you know the result. Thanks once again.

[Zaphod Beeblebrox]

1 minute ago, Ws Audio said:

Thank you very much! I’ll take a chance to try it. I can tell it’s the transistors because previously the buzzing sound was quite loud and I tried to change the transistors. The buzzing sound is still exist now yet, it decrease. I’ll let you know the result. Thanks once again.

Check the part numbers on the other channel.

 

[Ws Audio]

55 minutes ago, georgehifi said:

The DR25 almost identical input stage uses 5 x 2N5619 good bet their the same in the DR9 as both had similar rail volts. 

 

Cheers George

 

 

Not so sure if it’ll be identically with DR-25, they’re manufactured in different decades..

[Zaphod Beeblebrox]

17 minutes ago, Ws Audio said:

Not so sure if it’ll be identically with DR-25, they’re manufactured in different decades..

The DR-9, DR-10, DR15 and DR25 amps are very similar in design and construction. I have schematics for the DR-10, DR15 and DR-25 amps. The schematics were published in 1991. I can promise you several things:

 

* The 2N5619 is NOT suitable to use in that application.

* The DR-25 will possess an almost identical input stage to the DR-9.

* The nearest likely transistor will be an MPSA92, or similar.

* You will need to match the transistors.

 

[Ws Audio]

On 04/02/2019 at 4:38 PM, Zaphod Beeblebrox said:

The DR-9, DR-10, DR15 and DR25 amps are very similar in design and construction. I have schematics for the DR-10, DR15 and DR-25 amps. The schematics were published in 1991. I can promise you several things:

 

* The 2N5619 is NOT suitable to use in that application.

* The DR-25 will possess an almost identical input stage to the DR-9.

* The nearest likely transistor will be an MPSA92, or similar.

* You will need to match the transistors.

 

Yes, I’m now searching for MPSA92. And by the way I cannot check the part number on the channel because it’s been replaced. Thanks for your input.

[Zaphod Beeblebrox]

3 minutes ago, Ws Audio said:

Yes, I’m now searching for MPSA92. And by the way I cannot check the part number on the channel because it’s been replaced. Thanks for your input.

Why were those devices replaced? I used to service a lot of Classe' power amps. I never had to replace front end transistors.

[Ws Audio]

2 hours ago, Zaphod Beeblebrox said:

Why were those devices replaced? I used to service a lot of Classe' power amps. I never had to replace front end transistors.

Never know, just received it that way and trying to fix it now. Firstly it produce buzzing sound due to broken capacitor. This problem is solved by changing the capacitor but, caused another problem: 500mv dc offset. I need to reduce this to max 1mv dc offset by changing the transistor.

[Ws Audio]

On 06/02/2019 at 8:01 AM, Zaphod Beeblebrox said:

Why were those devices replaced? I used to service a lot of Classe' power amps. I never had to replace front end transistors.

Hi there! Thank you so so much for MPSA92, we made it. It’s now functioning so great. Thanks again.

[Telecine]

Great amp, glad to see you sorted out the problem.

[Ws Audio]

5 hours ago, Telecine said:

Great amp, glad to see you sorted out the problem.

Yeah! I know right. Thanks!