Help me troubleshooting amplifier module

[fosforo]

Hi to all,

some time ago i purchased two subwoofer amplifiers made from the italian RCF. They came from model RCF 600AS.
Yesterday, after a couple of week, i've powerd them.
First of all they works. Second, obviously, they have some probles...
The first one has got the controller board wich has balanced input and outputs, the second one no.
I've connected a cd player to the firs one powering a 12" woofer also from RCF.
Here is the first problem,i've found that the output is quite distorted, even at low levels. (The woofer is in perfect working conditions).
So i tried the second one. As i have said before, this one is without controller board, so i used the one from the first module.
This one is working but even with no signal there is an udible hiss coming out from the speaker. It seems that the filter is not working.
So, here's the questions:

1) anyone could help me troubleshooting the amps? (i can rent an oscilloscope from a friend if it is usefull)

2) I would like to remove the active filter to use an external one, is it possible?

Here's the schematics


Thank you

F.

 

[fosforo]

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[destroyer X]

Fósforo was great Leggionari!

Wonderfull name....i will copy your great idea....i will be fosfori ex in another forum...the X will be used to be recognized by old folks.

Congratulazione fratello Romani...molto buona denominazione.
Bienvenutto al mio core.

Congratulations brother...very good name you choice.

regards,

Carlos

 

[fosforo]

Thank you! 🙂

 

[richie00boy]

What a bizarre design! The driver/gain stage runs 40 volts higher than the output stage - bit excessive, and they regulate the output stage but not the driver/gain stage (which would better benefit from the regulation I think).

 

[fosforo]

What a bizarre design! The driver/gain stage runs 40 volts higher than the output stage - bit excessive, and they regulate the output stage but not the driver/gain stage (which would better benefit from the regulation I think).

Maybe it could be, i'm not so skilled to notice that

Any advice on the problems that i have posted?

Thank you

Fabio

 

[kASD]

Hi Fosforo,

Your amp could be modified, but the Schematic of amp section a little bit wrong as it doesnot have Resistors to bootstrap the Step drivers gate , the resistor should have to be there, unless your amp doesnot work, or they might be a mistake in schematic alone....
Your amp is Class-G 2 Tier....

regards,
K a n w a r

 

[kASD]

What a bizarre design! The driver/gain stage runs 40 volts higher than the output stage - bit excessive, and they regulate the output stage but not the driver/gain stage (which would better benefit from the regulation I think).

Ritchie have a look at the amp...its class-G not Class-AB ....The mosfets are Linear Envelope follower for Step Voltage.....not a regulator

The Design is alright , only you have misunderstood it....

 

[fosforo]

Hi Fosforo,

Your amp could be modified, but the Schematic of amp section a little bit wrong as it doesnot have Resistors to bootstrap the Step drivers gate , the resistor should have to be there, unless your amp doesnot work, or they might be a mistake in schematic alone....
Your amp is Class-G 2 Tier....

They have been created to power bass units so i think that this is a suitable design.
I would like to remove or to modifiy the filter section to have a variable cutoff, do you think that it could be done?
On the other side, any idea on how to troubleshoot the two amps?

Thank you very much

Fabio

 

[richie00boy]

Thanks Kanwar, I did think it a little strange the rails were so high, and the single MOSFET not enough for regulation.

The filter section should be easy enough to modify if it's a normal Sallen-Key type, a matter of taking out two resistors and replacing with a 2-gang pot and two more resistors. There may be a couple of capacitors to change also.

How are you powering the amps? Were they sold to you as fully working?

 

[kASD]

They have been created to power bass units so i think that this is a suitable design.
I would like to remove or to modifiy the filter section to have a variable cutoff, do you think that it could be done?
On the other side, any idea on how to troubleshoot the two amps?

Thank you very much

Fabio

Yes it is possible,

You have to get a scope and fed the input of module with 50Hz sinewave and monitor the waveform through each opamp stage prior to the amp section , this could be help ful to find out which stage is broken....Check for the Waveform integerity....

If you want external filter section, than reroute the XLR Pins by either converting the connection in to unbalanced config and directly connect them to the power amplifer section input and disconnect the previous input from the out put of opamp to that section....

 

[fosforo]

Thanks Kanwar, I did think it a little strange the rails were so high, and the single MOSFET not enough for regulation.

The filter section should be easy enough to modify if it's a normal Sallen-Key type, a matter of taking out two resistors and replacing with a 2-gang pot and two more resistors. There may be a couple of capacitors to change also.

How are you powering the amps? Were they sold to you as fully working?

Great news about the filter section!!!
Could you explain me how to do that modification?
About the amps, i've purchased from a stock, they have been sold as is. I've powered them, attached a cd player and a woofer and raise slowly the volume pot.
They have worked so so as i have explained, now i'm trying to check if i can fix them.

F.

 

[kASD]

In FINAL FILTER page,
remove C53 , C52and join the output of IC3A Pin 1 with a jumper wire to input pin of C3 in FINAL LOW page, then you have bypassed the filter section to use external filter.....

 

[fosforo]

In FINAL FILTER page,
remove C53 , C52and join the output of IC3A Pin 1 with a jumper wire to input pin of C3 in FINAL LOW page, then you have bypassed the filter section to use external filter.....

How about a modified version of the filter with a variable cutoff?