Hi, I bought Thorens TTA-2000, but I am affraid connect speakers because DC offset between the +/- terminal are 2,5V!!! This is normal value on this "A" class amplifier or is this faulty?
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Thorens TTA-2000 DC offset
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Re: Thorens TTA-2000 DC offset
Hi, schematic on german forum is incorrect. I found one in korean forum and this have only one error, R11 are before R12,R13. Some values are also incorrect, but there are only minimal differences. I measured input voltage: 71V, voltage after trimmer 53V. Voltage between R1 pins: 0,380mV. Heatsin after 30 min 60°C, but this is normal with this amplifier!
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Re: Thorens TTA-2000 DC offset
8 or 16 ohms or around there or even higher ..there won't be any signal therefore little current as vol will be turned down . i guess anything over and including 1 watt should do it .. saying that i believe its class A so idle current will be high . just be quick . you just need to see it drop to 0v .
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Re: Thorens TTA-2000 DC offset
As others have mentioned, this amplifier is not DC-coupled to the loudspeaker. It uses a large coupling capacitor C1 10,000uF
So your DCV reading is likely due to small leakage currents in the big cap. In pictures this amp has a speaker protector relay board? Does it have one?
I did blow up an amp Dynaco ST-120 which also uses huge output-coupling caps. You have to be careful.
When you switch it off, the cap is still charged for a long time, and I was changing speaker wires and shorted them or something heard a thump and it blew the amplifier- even though it was turned OFF.
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Re: Thorens TTA-2000 DC offset
Now that I look closer at the schematic in post 5 I see the output cap. so I guess there is no _____ adjustment.
I don't think the stock unit has speaker protection.
https://old-fidelity-forum.de/thread-41267.html
RIP MeatloafLast edited by R_J; 01-21-2022, 04:30 PM.
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Re: Thorens TTA-2000 DC offset
adjustment for dc balance is done with a scope and set for equal clipping .
one note is when adjusting the idle current can change the dc balance and visa versa vi best to have 2 meters hooked up along with the scope and sine wave input then sort of trade off idle current and dc balance till its right .
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Re: Thorens TTA-2000 DC offset
I think you need a speaker relay to stop the huge thump until the output caps charge up. Not for (shorted output transistor) protection.
There are pics of TTA-2000 with and without one. It might be a mod or add-on. The old Dynaco ST-120 used to make a loud thump with woofer cone lurching out on power up, and slowly sinking back in until output cap charged up.
I don't know what the trimpots are for.
RIP Bat Out of hell, among my first rock LP's bought.Last edited by redwire; 01-22-2022, 12:17 AM.
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