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?
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?
Did u actually bypass the tone-control,ie leave the board no connection at all or just loop the I/Os???
I've connected the source selector directly to the preamp instead of source selector ->tone control ->preamp
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
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
But like leo asks, did you DISconnect the tone circuit or just leave it in place with the bypass installed?
I've disconnected it and connected the inputs and outputs together.
Should I try disconnecting them?
Should I try disconnecting them?
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
Connect a resistor between those points as I suggested to see if the gain goes up.
-Chris
Tomorrow I might go get some 22Ks if I don't already have some. (Or measure the resistance of the board)
Hi DragonMaster,
The value is not important. 10K, 22K, 33K - whatever you have lying around. Insert in one channel and leave the other shorted. This makes it easier to compare.
-Chris
The value is not important. 10K, 22K, 33K - whatever you have lying around. Insert in one channel and leave the other shorted. This makes it easier to compare.
-Chris
It's really easy to compare even without trying one channel at the time. The step between 1/2 and 2 on this amplifier is enormous.
You can make the difference between normal and really loud easily without doing it 1 chan @ the time.
I've got PAs, so 2 is way too much, even with a 40w/chan amp.
You can make the difference between normal and really loud easily without doing it 1 chan @ the time.
I've got PAs, so 2 is way too much, even with a 40w/chan amp.
Tomorrow I'll have the amp under hand and I'll be near the local shop, so I can get some resistors.
Putting resistors will be helpful to make the volume more stable, but I'll be stuck with pot tracking problems. Between 0 and 1, the tracking is really unstable, there are bumps in the volume that are different between both channels. The problem is that it's not really easy to find 4-pin/channel pots.
Also, when the tone board was connected, the balance was working worse than now(It still is) : It was not working until -8/+8. The only effect it had was that it would trigger the channels on and off.
Putting resistors will be helpful to make the volume more stable, but I'll be stuck with pot tracking problems. Between 0 and 1, the tracking is really unstable, there are bumps in the volume that are different between both channels. The problem is that it's not really easy to find 4-pin/channel pots.
Also, when the tone board was connected, the balance was working worse than now(It still is) : It was not working until -8/+8. The only effect it had was that it would trigger the channels on and off.
You may be further ahead to reconnect things as they were. If the controls were in the feedback path, then there is no additional distortion to worry about. Any small deviation from flat response pales in comparison to your room and speakers.
-Chris
-Chris
I had only 56ks and it seems that the tone board resistance is higher than that. Now, I need to put it to 1 instead of 2.
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