noise floor problem

johndiy · 29th August 2006, 11:35 PM

I have built this zen circuit as a headphone amp, all works
well except for its noise floor i use sensitive headphones and
these make the problem worse

in the power supply i have used a total of 10000uf capacitance
to tame the ripple but noise floor is still too high

whats the problem?

can you help

john

MikeB · 30th August 2006, 08:00 AM

You might try a resistor to the gate. Eventually the mosfet oscillates.
Shouldn't the mosfet have a small resistor at the source ?

Mike

AndrewT · 30th August 2006, 08:12 AM

Hi,
just guessing, but, have you snubbered the PSU rectifier?

How about RCRC type smoothing after the recifier?

Headphones are very critical of noise and demand a very good PSRR of the amp and/or very low noise from the PSU.

johndiy · 30th August 2006, 09:26 AM

Quote:

Originally posted by AndrewT
Hi,
just guessing, but, have you snubbered the PSU rectifier?

How about RCRC type smoothing after the recifier?

Headphones are very critical of noise and demand a very good PSRR of the amp and/or very low noise from the PSU.

"snubbered the PSU rectifier" yes

rcrc no i dont want voltage drop at the filter

i have use 10000uf should i go higher?

john

johndiy · 30th August 2006, 09:29 AM

Quote:

Originally posted by MikeB
You might try a resistor to the gate. Eventually the mosfet oscillates.
Shouldn't the mosfet have a small resistor at the source ?

Mike

it is not oscillation, small resistor at the source? why?

john

parsecaudio · 30th August 2006, 09:45 AM

The source resistor is in order to put a feedback for bias current control and stabilization.
Your amp has the problems of all too much simples circuits.
A low noise circuit is suggested for headphone amp.

richie00boy · 30th August 2006, 09:51 AM

What is your actual problem? Is it actually noise (which is broadband) or is it hum? If it's hum then it may simply be a grounding issue and nothing is wrong with your circuit or PSU. I know headphones can be sensitive but 10000uF should be more than enough by a long way.

gmphadte · 30th August 2006, 10:22 AM

The voltage used is not known but still...

Use an LM317 circuit with cap at adj pin or use a capacitance multiplier with a darlington.

Gajanan Phadte

parsecaudio · 30th August 2006, 10:49 AM

The philosophy of this circuits is the employ of the minimal count of the components that they are in series with the audio signal.
A voltage stabilizer integrated circuit it is not adapted to this philosophy.
This amp have a very low PSRR and the supply noise
(above all without any circuit of ripple rejection) it must to be tolerate....

AndrewT · 30th August 2006, 11:06 AM

Hi,
poor PSRR, simple C PSU (snubbered), and headphones are a conflicting set of requirements.

Something has to give.

30th August 2006, 08:12 AM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, just guessing, but, have you snubbered the PSU rectifier? How about RCRC type smoothing after the recifier? Headphones are very critical of noise and demand a very good PSRR of the amp and/or very low noise from the PSU. __________________ regards Andrew T.

30th August 2006, 09:45 AM	#6
parsecaudio diyAudio Member Join Date: Apr 2004 Location: ventimiglia	. The source resistor is in order to put a feedback for bias current control and stabilization. Your amp has the problems of all too much simples circuits. A low noise circuit is suggested for headphone amp.

30th August 2006, 09:51 AM	#7
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	What is your actual problem? Is it actually noise (which is broadband) or is it hum? If it's hum then it may simply be a grounding issue and nothing is wrong with your circuit or PSU. I know headphones can be sensitive but 10000uF should be more than enough by a long way. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

30th August 2006, 11:06 AM	#10
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, poor PSRR, simple C PSU (snubbered), and headphones are a conflicting set of requirements. Something has to give. __________________ regards Andrew T.

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30th August 2006, 08:00 AM	#2
MikeB diyAudio Member Join Date: Apr 2004 Location: Gütersloh	You might try a resistor to the gate. Eventually the mosfet oscillates. Shouldn't the mosfet have a small resistor at the source ? Mike

30th August 2006, 10:22 AM	#8
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	The voltage used is not known but still... Use an LM317 circuit with cap at adj pin or use a capacitance multiplier with a darlington. Gajanan Phadte

30th August 2006, 10:49 AM	#9
parsecaudio diyAudio Member Join Date: Apr 2004 Location: ventimiglia	The philosophy of this circuits is the employ of the minimal count of the components that they are in series with the audio signal. A voltage stabilizer integrated circuit it is not adapted to this philosophy. This amp have a very low PSRR and the supply noise (above all without any circuit of ripple rejection) it must to be tolerate....

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