noise problems with an OptiMOS

sinigersky · 24th October 2006, 09:28 AM

Hi,

I have built a Slone's OptiMOS with SMD implementation of the low-power part on a double layer PCB 160 mm x 50 mm. Input transistors are BC850C / BC860C, the SMD version of 2N5551 is MMBT5551, driver transistors are 2SC3421 / 2SA1358, output is "standard" 2SK1058 / 2SJ160. Powered by +/- 50V. The output transistors are biased to approx. 40 mA without signal.

It sounds great - very good detail, powerful bass.

The problem with it is I get an audible noise when listening at lower signal levels. If the CD player is not playing, nothing is to be heard, but when it starts, at low volume levels, noise is to be heard as high as the signal. I am afraid my amp is ringing... but unfortunatelly I don't have an oscilloscope.

I would be glad to hear some ideas what could cause such a noise, and what could I try in order to find out what is happening.

Thanx!

pinkmouse · 24th October 2006, 09:31 AM

What kind of noise? Buzzing, whistling, white noise?

sinigersky · 24th October 2006, 09:33 AM

I would call it white noise, like the noise of a casette.

pinkmouse · 24th October 2006, 09:54 AM

Short the amp inputs, and see if the noise is still there. I suspect however that the problem is with your CD player...

HiFiNutNut · 12th December 2006, 01:00 AM

I have built 3 dual monoblocks of the Optimos and they are all dead quiet. The only noise is the mechanical vibration of the big transformers. They hum from time to time.

Regards,
Bill

Leolabs · 12th December 2006, 01:37 AM

Check grounding/wiring.

taj · 21st December 2006, 05:39 AM

Which book did G.R.S. publish the OptiMOS design in? I have his Tab Electronics book and his High Power Amplifiers book, and he doesn't give names to the amps, though in the final design of the latter book, he refers to it as an optimized MOSFET design. Is this one, or is it published in the book I don't have?

..Todd

CHRIS DIAMONDS · 16th August 2011, 08:18 PM

As all the friends suggested check all of that, plus you could lift your inputs ground by connecting a 10 Ω resistor from inputs ground to ground. Also instead of the resistor you can put the same way a thermistor like a keystone CL 60. It has exactly the same resistance and is for 6A. Thermistors also can be used as surge supressors if you connect it on the primary of the transformer.That is from the great Nelson Pass. Check also your wiring if it passes close to the transformer it picks up noise.I hope gave you an answer.

gmphadte · 17th August 2011, 04:08 AM

Have u connected the shield on both sides of the interconnecting cable...

Gajanan Phadte

CHRIS DIAMONDS · 17th August 2011, 10:56 AM

Yes absolutely , otherwise there is no connection.

24th October 2006, 09:28 AM	#1
sinigersky diyAudio Member Join Date: Sep 2004 Location: Germany	noise problems with an OptiMOS Hi, I have built a Slone's OptiMOS with SMD implementation of the low-power part on a double layer PCB 160 mm x 50 mm. Input transistors are BC850C / BC860C, the SMD version of 2N5551 is MMBT5551, driver transistors are 2SC3421 / 2SA1358, output is "standard" 2SK1058 / 2SJ160. Powered by +/- 50V. The output transistors are biased to approx. 40 mA without signal. It sounds great - very good detail, powerful bass. The problem with it is I get an audible noise when listening at lower signal levels. If the CD player is not playing, nothing is to be heard, but when it starts, at low volume levels, noise is to be heard as high as the signal. I am afraid my amp is ringing... but unfortunatelly I don't have an oscilloscope. I would be glad to hear some ideas what could cause such a noise, and what could I try in order to find out what is happening. Thanx! __________________ GeleTheMaster / SINIGERSKY AUDIO

24th October 2006, 09:31 AM	#2
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	What kind of noise? Buzzing, whistling, white noise? __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

24th October 2006, 09:33 AM	#3
sinigersky diyAudio Member Join Date: Sep 2004 Location: Germany	I would call it white noise, like the noise of a casette. __________________ GeleTheMaster / SINIGERSKY AUDIO

24th October 2006, 09:54 AM	#4
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Short the amp inputs, and see if the noise is still there. I suspect however that the problem is with your CD player... __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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12th December 2006, 01:00 AM	#5
HiFiNutNut diyAudio Member Join Date: May 2004 Location: Sydney	I have built 3 dual monoblocks of the Optimos and they are all dead quiet. The only noise is the mechanical vibration of the big transformers. They hum from time to time. Regards, Bill

12th December 2006, 01:37 AM	#6
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Check grounding/wiring.

21st December 2006, 05:39 AM	#7
taj diyAudio Member Join Date: Feb 2005	Which book did G.R.S. publish the OptiMOS design in? I have his Tab Electronics book and his High Power Amplifiers book, and he doesn't give names to the amps, though in the final design of the latter book, he refers to it as an optimized MOSFET design. Is this one, or is it published in the book I don't have? ..Todd

16th August 2011, 08:18 PM	#8
CHRIS DIAMONDS diyAudio Member Join Date: Sep 2010	As all the friends suggested check all of that, plus you could lift your inputs ground by connecting a 10 Ω resistor from inputs ground to ground. Also instead of the resistor you can put the same way a thermistor like a keystone CL 60. It has exactly the same resistance and is for 6A. Thermistors also can be used as surge supressors if you connect it on the primary of the transformer.That is from the great Nelson Pass. Check also your wiring if it passes close to the transformer it picks up noise.I hope gave you an answer.

17th August 2011, 04:08 AM	#9
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	Have u connected the shield on both sides of the interconnecting cable... Gajanan Phadte

17th August 2011, 10:56 AM	#10
CHRIS DIAMONDS diyAudio Member Join Date: Sep 2010	Yes absolutely , otherwise there is no connection.

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