Tone ctrl bypass reduces volume?

DragonMaster · 4th September 2005, 12:03 AM

In my cheapo-vintage-Toshiba-integrated-amplifier, I decided to bypass the tone control board. I removed the ground wire and connected Lin with Lout and Rin with Rout together.

Since I've done this, the gain turned lower than before : I have to put volume pot on 2 instead of ½. Also, now, the gain and tone greatly depends of the source. The tuner sounds crappy with tons of bass, and the CD player is clear, loud and practically bass free.

Does someone knows how can this happen? Impedance?

Leolabs · 4th September 2005, 01:55 AM

Did u actually bypass the tone-control,ie leave the board no connection at all or just loop the I/Os???

DragonMaster · 4th September 2005, 02:06 AM

I've connected the source selector directly to the preamp instead of source selector ->tone control ->preamp

Leolabs · 4th September 2005, 02:09 AM

Is your tone control active or passive???

DragonMaster · 4th September 2005, 02:32 AM

Passive, that's what I find strange.

anatech · 5th September 2005, 01:57 AM

Hi DragonMaster,
Is it possible that your tone control circuit is in the feedback loop of the amplifer stage?. To test, put a 22K resistor between the in and out. If the tone controls were in the feedback network the gain will go up. Install an equivalent resistance to the impedance of the tone control circuit. Trial and error with on channel will get you there.
-Chris

DragonMaster · 5th September 2005, 03:46 AM

I'll try. I'll post you the results.

Enzo · 7th September 2005, 03:42 AM

But like leo asks, did you DISconnect the tone circuit or just leave it in place with the bypass installed?

DragonMaster · 7th September 2005, 03:28 PM

I've disconnected it and connected the inputs and outputs together.

Should I try disconnecting them?

anatech · 7th September 2005, 08:45 PM

Don't do that. If it's part of the feedback network you will breal the loop partially. Normally there is a DC path of very high resistance.

Connect a resistor between those points as I suggested to see if the gain goes up.

-Chris

4th September 2005, 12:03 AM	#1
DragonMaster diyAudio Member Join Date: Dec 2003 Location: Montreal	Tone ctrl bypass reduces volume? In my cheapo-vintage-Toshiba-integrated-amplifier, I decided to bypass the tone control board. I removed the ground wire and connected Lin with Lout and Rin with Rout together. Since I've done this, the gain turned lower than before : I have to put volume pot on 2 instead of ½. Also, now, the gain and tone greatly depends of the source. The tuner sounds crappy with tons of bass, and the CD player is clear, loud and practically bass free. Does someone knows how can this happen? Impedance? __________________ Antoine http://dmsaudio.ca/

4th September 2005, 02:06 AM	#3
DragonMaster diyAudio Member Join Date: Dec 2003 Location: Montreal	I've connected the source selector directly to the preamp instead of source selector ->tone control ->preamp __________________ Antoine http://dmsaudio.ca/

4th September 2005, 02:32 AM	#5
DragonMaster diyAudio Member Join Date: Dec 2003 Location: Montreal	Passive, that's what I find strange. __________________ Antoine http://dmsaudio.ca/

5th September 2005, 03:46 AM	#7
DragonMaster diyAudio Member Join Date: Dec 2003 Location: Montreal	I'll try. I'll post you the results. __________________ Antoine http://dmsaudio.ca/

7th September 2005, 03:28 PM	#9
DragonMaster diyAudio Member Join Date: Dec 2003 Location: Montreal	I've disconnected it and connected the inputs and outputs together. Should I try disconnecting them? __________________ Antoine http://dmsaudio.ca/


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4th September 2005, 01:55 AM	#2
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Did u actually bypass the tone-control,ie leave the board no connection at all or just loop the I/Os???

4th September 2005, 02:09 AM	#4
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Is your tone control active or passive???

5th September 2005, 01:57 AM	#6
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi DragonMaster, Is it possible that your tone control circuit is in the feedback loop of the amplifer stage?. To test, put a 22K resistor between the in and out. If the tone controls were in the feedback network the gain will go up. Install an equivalent resistance to the impedance of the tone control circuit. Trial and error with on channel will get you there. -Chris

7th September 2005, 03:42 AM	#8
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	But like leo asks, did you DISconnect the tone circuit or just leave it in place with the bypass installed?

7th September 2005, 08:45 PM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Don't do that. If it's part of the feedback network you will breal the loop partially. Normally there is a DC path of very high resistance. Connect a resistor between those points as I suggested to see if the gain goes up. -Chris

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