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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

noisy pre amp, audio transformer noisy?
noisy pre amp, audio transformer noisy?
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Old 12th August 2015, 06:12 PM   #1
Salomon102 is offline Salomon102  Canada
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Join Date: Jun 2011
Location: montreal
Default noisy pre amp, audio transformer noisy?

Hi guys,
i normaly hang out in the solid state amplifier forum, this is my first post in here!

i have a BAE 1073MP pre amp with a noise problem and i think i have narrowed it down to a noisy audio transformer.

the transformer itself is a carnhill transformers vtb9045.
it makes noise regardless of if theres a input device or not
it seems to be too sensible to outside disturbance.
if i tap the transformer with a pen, i can hear it on the output.
if i tap the transformer with my finger i can hear it on the output.
and of course its sensible to electric interference if i bring the power supply next to it.

im wondering if its normal for an audio transformer to be so succeptible to outside disturbance?
it seems a transformer is around 120$ for me to aquire. would it be worth it to replace it with the same thing?

thank you for your input guys.
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Old 12th August 2015, 06:52 PM   #2
sreten is offline sreten  United Kingdom
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Location: Brighton UK
Hi,

Swap transformers between the two channels.
What happens ?

rgds, sreten.
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Old 12th August 2015, 06:53 PM   #3
simon7000 is offline simon7000  United States
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Join Date: Nov 2008
Location: Oakmont PA
Quote:
Originally Posted by Salomon102 View Post
Hi guys,
i normaly hang out in the solid state amplifier forum, this is my first post in here!

i have a BAE 1073MP pre amp with a noise problem and i think i have narrowed it down to a noisy audio transformer.

the transformer itself is a carnhill transformers vtb9045.
it makes noise regardless of if theres a input device or not
it seems to be too sensible to outside disturbance.
if i tap the transformer with a pen, i can hear it on the output.
if i tap the transformer with my finger i can hear it on the output.
and of course its sensible to electric interference if i bring the power supply next to it.

im wondering if its normal for an audio transformer to be so succeptible to outside disturbance?
it seems a transformer is around 120$ for me to aquire. would it be worth it to replace it with the same thing?

thank you for your input guys.

These are the classic signs of a low level audio transformer someone checked for continuity with an ohmmeter. Remove the transformer from the circuit and run an AC current through it. Use a 47 ohm resistor and a signal generator set for about 25 hertz. Start at around 5 volts and over the course of an hour reduce this to zero volts. That should mostly fix the transformer. Either that or blow it open! If you think it is too small to take 100 mA start with 1 volt. Try it out and if it isn't healed try a bit more voltage.

Now that should cover mechanical noise, electrical pick up requires a shielded enclosure. So be sure you have a decent case for the gizmo.
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Old 12th August 2015, 07:00 PM   #4
Salomon102 is offline Salomon102  Canada
diyAudio Member
 
Join Date: Jun 2011
Location: montreal
Quote:
Originally Posted by simon7000 View Post
These are the classic signs of a low level audio transformer someone checked for continuity with an ohmmeter. Remove the transformer from the circuit and run an AC current through it. Use a 47 ohm resistor and a signal generator set for about 25 hertz. Start at around 5 volts and over the course of an hour reduce this to zero volts. That should mostly fix the transformer. Either that or blow it open! If you think it is too small to take 100 mA start with 1 volt. Try it out and if it isn't healed try a bit more voltage.

Now that should cover mechanical noise, electrical pick up requires a shielded enclosure. So be sure you have a decent case for the gizmo.
id be curious to know how passing ac will fix it.
is it because the winding moves around and sets itself?

Sent from my SM-G920W8 using Tapatalk
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Old 12th August 2015, 07:05 PM   #5
Salomon102 is offline Salomon102  Canada
diyAudio Member
 
Join Date: Jun 2011
Location: montreal
Quote:
Originally Posted by sreten View Post
Hi,

Swap transformers between the two channels.
What happens ?

rgds, sreten.
this unit only has a single channel

Sent from my SM-G920W8 using Tapatalk
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Old 12th August 2015, 07:53 PM   #6
simon7000 is offline simon7000  United States
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Join Date: Nov 2008
Location: Oakmont PA
Quote:
Originally Posted by Salomon102 View Post
id be curious to know how passing ac will fix it.
is it because the winding moves around and sets itself?

Sent from my SM-G920W8 using Tapatalk
No it demagnetizes the core.
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