Carver tfm-25 turn off noise

The Fuxtor

The Fuxtor

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I have a post in the The Carver Site about this issue, but I figured maybe I could get some help from here ?? The issue is when the amp is powered off with no signal , a buzz/thump noise is occurring but only when the amp is in bridge mono mode. I replaced the main filter caps and both speaker protect relays ( right channel & left ). In stereo 2 channel operation there is hardly any noise. It would seem as if the relay/s are not closing signal quick enough at power off? I got a vid..

 

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That noise is a long time after power off.

C310 33u/25V (and R327) performs the power on muting. For some reason it's not discharging at power off. Not clear what the discharge path should be.

Check solder on C310 but wont be the issue, something in the power supply(?) is supposed to run down the cap, will try and find schematic.

Noted the datasheet suggests a 22uf cap, the 33uf probably reqiuired for power on transients...

edit C503 (3300uf/63V) is on the same rail, did you increase this cap?
 
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mbz said:
That noise is a long time after power off.

C310 33u/25V (and R327) performs the power on muting. For some reason it's not discharging at power off. Not clear what the discharge path should be.

Check solder on C310 but wont be the issue, something in the power supply(?) is supposed to run down the cap, will try and find schematic.

Noted the datasheet suggests a 22uf cap, the 33uf probably reqiuired for power on transients...

edit C503 (3300uf/63V) is on the same rail, did you increase this cap?
Click to expand...
C503 was replaced, same size. The amp was noisy still with the original
 
In 2 channel mode does the relay de-engergize immediately when the power switch is turned off? Pin 1 of the TA7317P detects the power switch.

Craig
 
llwhtt said:
Input a signal to each channel and confirm the signal dies instantly when the power switch is turned off.
Click to expand...
Ok, checking in stereo 2 channel each signal collapses on the scope almost immediately after power switch is turned off. I'm not sure but it sounds like the relays do not click again for a few more seconds tho?
 
What I think you are hearing are the circuit voltages collapsing before the relay de-energizes, the relay should de-energize instantly so you can't hear what the circuit is doing during shut down. Check to see what the -17 volts on R323 is doing when you turn it off.
 
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llwhtt said:
What I think you are hearing is the circuit voltages collapsing before the relay de-energizes, the relay should de-energized instantly so you can't hear what the circuit is doing during shut down. Check to see what the -17 volts on R323 is doing when you turn it off.
Click to expand...
The voltage drops immediately at turn off. Again this is in 2 channel mode.
 
Any problem in 2 channel mode will be exacerbated in mono/bridged mode because it's 4x the power.
 
Ok, I'm getting something to change? I replaced C310 and the noise is quite a bit shorter now. Still there tho?
 
Looking at SW151, in the stereo position there appears to be a path from the +15V opamp rails to GND through R167(4k7), in mono this path is not provided, however this does not appear significant, it's more about controlling Q151, Q102 (audio mute?) Still digging
 
There's a bit of info about this on this thread.
It explains the importance of q102's 2sc2878 transistor

Carver TFM 35 DC on the output - PLEASE HELP!

Weird, but ok... Here is a run down of all transistors Transistor E C B Q102 -0.67 0 -9.22 Q103 1.97 87.7 2.56 Q104 2.03 88.4 2.6 Q105 -2.05 -88.2 -2.6 Q106 -2.09 -88.3 -2.64 Q151 0 -9.23 0 IC 101 1 = 0.02 2 = 0.005 3 = 0.005 4 = -15.82 5 = -0.67 6 = -0.67 7 = 0.009 8 = 15.63...
www.diyaudio.com www.diyaudio.com

Edit: I just realized the explanation is from Craig! @llwhtt
 
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I have another unit here that I installed the same relays into and I checked it. It discharges the relay immediately after power off ?
I also checked IC301 and found pin#6 voltage is off? Expected -0.5v and I'm getting +1.1v. I think this pin goes high when in protection? I'm not sure this reading means anything..
 
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Just to keep on here, I disconnected the meter board as it is connected to speaker output directly and there was no change there..
I get the same right meter only deflection at power off in stereo mode as well.
 
Take a check on the TA7317 pin 1. It is a task-specific IC used to drive the mute relays, and similar (if not identical) that that used in a lot of other amps. Pin one takes a signal from the power supply pre-rectifier, so it should see the power switch open instantly, and drop the relays with zero delay.

Check voltage there, and parts in that section of the circuit. The "burp" you are getting may actually not be a problem - it may be there in all of these, but not noted elsewhere because they mute correctly.

www.alldatasheet.com

TA7317P Datasheet(PDF)

Part #: TA7317P. Download. File Size: 176Kbytes. Page: 3 Pages. Description: PROTECTION CIRCUIT FOR OCL POWER AMPLIFIER AND SPEAKER. Manufacturer: Toshiba Semiconductor.
www.alldatasheet.com
 
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tadawson said:
Take a check on the TA7317 pin 1. It is a task-specific IC used to drive the mute relays, and similar (if not identical) that that used in a lot of other amps. Pin ooe takes a signal from the power supply pre-rectifier, so it should see the power switch open instantly, and drop the relays with zero delay.

Check voltage there, and parts in that section of the circuit. The "burp" you are getting may actually not be a problem - it may be there in all of these, but not noted elsewhere because they mute correctly.

www.alldatasheet.com

TA7317P Datasheet(PDF)

Part #: TA7317P. Download. File Size: 176Kbytes. Page: 3 Pages. Description: PROTECTION CIRCUIT FOR OCL POWER AMPLIFIER AND SPEAKER. Manufacturer: Toshiba Semiconductor.
www.alldatasheet.com
Click to expand...
I have another tfm-25 here , buddy has 2 for bridging, and the other unit received the same relays and new filter caps. The noise doesn't occur in the other amp. Monitoring the relays show instant relay voltage drain. Not so on this one??
I'll check this out!! Thanks
Edit: I checked these voltages out earlier. They all check out as normal
 
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