Problems with Crescendo ME

[RickIvo]

Anyone has already build the Crescendo ME amplifier from Elektor.
Any problems with 4 ohm loudspeaker?

I have built the Crescendo ME, just like the one in the maganize.
I am having problems with 4 ohms load, the protect circuit disconect the amplifier from the load at mid sound nivel
(Output 10Veff for a 4 ohm)

Does anyone have the same problem?

Best Regards and thanks.

 

[Helix]

there are some threads here about crescendo ME amps

http://www.diyaudio.com/forums/showthread.php?threadid=890

http://www.diyaudio.com/forums/showthread.php?threadid=5381

http://www.diyaudio.com/forums/showthread.php?threadid=4838

http://www.diyaudio.com/forums/showthread.php?threadid=2633

http://www.diyaudio.com/forums/showthread.php?threadid=3690

http://www.diyaudio.com/forums/showthread.php?threadid=2077

http://www.diyaudio.com/forums/showthread.php?threadid=3444

Check using a multimeter the DC voltage level at the speaker terminals of your amp when you turn the music power up. At switch on my CME starts with about 2 volts ('hidden' because the anti-thump speaker protection relays are still de-energized) and settles in a second or so and then the relays energize when the DC is well below 100mV. DC output level on mine then stands at 20mV or so.

I have tested my CME and it seems fine supplying full power in to a 5 ohm resistive dummy load, when you drive it in to clipping the SOA protection de-energises the output relays, until the input is reduced to small level.

 

[RickIvo]

Helix, thanks by the reply.

have you tested your CME with sin wave generator and an a oscilloscope?

That what i did, the signal is undistorced by at a output of +/- 12Vrms with a load of 4 ohm, the relays disct the amplifier.

The DC component at the output with no signal is around 10mV.

Best Regards.

 

[Helix]

i did and i get 100v pk-pk then the relay clicks out as you drive it into heavy distortion

 

[RickIvo]

Helix, i found out today, with the help of a signal gen, that the amplifier with a dummy load of 4 ohm work very well with a signal of 1 kHz, but if you put a signal of for ex. of 30kHz at a output of 13Vrms, to relays disc. the amplifier.

In the caracteriscts it says that the Freq. Resp is 1,5 Hz - 300kHz.

Could you try to test your amp to full power with a signal of ex. 30kHz - 35kHz.

Best Regards.

 

[Helix]

i think i have found similar problems, but my sig gen will only go to 25Khz, i will try this tommorow

 

[RickIvo]

Ok, them tell me the results.

 

[RickIvo]

Helix, did u already tried?

 

[Helix]

Under a 10 ohm resistive load i get 80v pk-pk out for 3.5v pk-pk input from 3 Hz to 25kHz
With a 5 ohm reistive load i only get 76v pk-pk befour distortion

Once distortion is noticable the protection will kick in.

25khz is the highest my signal gen. will go

however at around 20 to 10khz the amp will quite happly be driven deep in to distortion without the protection kicking in, but at 25kHz as soon as there is a little visable distortion the protection kicks in very rapidly. maybe this is signs of what you are seeing?



i previously said 100v pk-pk and i was wrong i meant 80v pkpk (my amp isn't 100% efficent)

sorry i too so long to do this, i have been busy.

 

[Helix]

CM amp problems

Hello,

Check the following:
1)The DC output at the speaker terminals, if this is above 500mV or so then there is a problem with the DC servo, and speaker protection will cut in.
2) The input source is free of high freq. power.
4) The bias point of the amp, measured by the voltage drop across the ouput FET drain resistors as per elektor instuctions. This is also how the SOA protection circuitry measures the speaker current. If these resistors arn't quite the right value, that maybe the problem.