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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Re: Thorens TTA-2000 DC offset
Seems a bit high, does the amp have a DC offset adjustment inside? Are both channels the same? -
Re: Thorens TTA-2000 DC offset
looks like cap coupled output so will read some dc unloaded ..try a load on it ..Comment
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Re: Thorens TTA-2000 DC offset
zoldi, can you download the schematic from that forum and post here?
Do both R, L channels have the same offset of 2.5V?Comment
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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!Attached FilesComment
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Re: Thorens TTA-2000 DC offset
Yes, both channels are same. DC adjustment maybe not...Comment
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Re: Thorens TTA-2000 DC offset
if you haven't got a resistor to load the output use a crappy speaker .. that dc will go away .Comment
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Re: Thorens TTA-2000 DC offset
I haven't tried load on it, because I don't want to destroy the speakers...Comment
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Re: Thorens TTA-2000 DC offset
its capacitor coupled output so unless the caps are leaking its normal to see some dc without speaker loads .Comment
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Re: Thorens TTA-2000 DC offset
so do you think, i can use it normally with speakers?Comment
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Re: Thorens TTA-2000 DC offset
you should test it with speakers you don't care about first . or a suitable resistor .Comment
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Re: Thorens TTA-2000 DC offset
OK, thanks. What type of resistor is suitable for this test (value in ohms, wattage)?Comment
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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 .Comment
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Re: Thorens TTA-2000 DC offset
2.5vdc is not that much voltage, but you can place about a 1 amp fuse in series with your speaker just to be safe. Do not have a source connected and playing music etc. as that would blow the fuse for sure. just use this setup to check the dc offsetComment
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Re: Thorens TTA-2000 DC offset
one thing it isnt dc offset on this amp .. its called dc balance .. one output is at rail and the other about half that . that's why it has a capacitor to block the dc ..Comment
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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.Comment
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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.Comment
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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 .Comment
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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.Attached FilesLast edited by redwire; 01-22-2022, 12:17 AM.Comment
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Re: Thorens TTA-2000 DC offset
The test is done. With old speakers and 1A fuse, because I dont have suitable resistor. After turning on, the current disappeared. I measured only 0,04 or 0 mA.
A have a version with protection board with relay (1. photo in post #19).Comment
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Hi guys, this is general query really
So I have a Hill DX3000 3KW audio amplifier here.
It has a topology/design like a class A/B but all the banks of output transistors (10 transistors in each 'side' of the channel) are NPN.
I was wondering what class this is. It doesn't fit the description of class A.
It also doesn't match class A/B or B amplifiers as all the examples I see have a complimentary output stage desigs (NPN/PNP) and clearly is not G, H or D
I looked for 'class A push pull' but that didn't tell me anything either
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TV Model: Hitachi 40HYC42
Power Supply: 17IPS71
MainBoard: 17MB95M
Panel: VES400UNDS-2D-NO3
When the set came in it was dead. Fuse was open primary side and the power mosfet was shorted. So I ordered a new power supply. Now it turns on, only displays "Hitachi" and then power off red and blue led flashing.
I had to modify the 0ohm resistors in the led backlight of the new PS like the original power supply.
Is there any variants on 17IPS71 power supply's?
UART output pins 10 and 12 on scart connector:
...Code:12:24:04.595
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My childhood best friend was killed about 9 years ago. His parents are finally letting go of his things, and they offered me his Polk RTi100 tower speakers. The Polk RTi100 towers are one of a handful of designs from the early 2000s that is a full range 3-way tower with a built-in self-powered subwoofer. This is accomplished with a plate amp integrated into the speaker input panel.
I think they used them for a while, but they've been sitting for at least a few years now. After about 40 hours of driving to their house and back (both they and I have moved in the last 9 years) I got... -
Hi Folks
Need some advice on how to test a subwoofer amplifier if i have access to only a multimeter.
Problem
I have a Boston Acoustics active Subwoofer (soundware S). Its rated output is 200W. But the output i am getting is very low i can barely hear/feel it even if put the gain at max. I replaced all the capacitors in the Subwoofer amplifier but still no change.
Is there anyway to test this without getting an oscilloscope/Function generator to see if the fault is with amplifier, driver or the source??
Any advice would be appreciated... -
Hi, people.
I've got an amplifier assembly from Mackie CR4 parts. It's just an amplifier, there was no speaker housing, so I used my set of CR4s to test it.
Anyway, upon connecting everything and hooking the "new" amplifier to an audio source, the sound played clearly and strongly for the first ten seconds. I was happy it was working. Then the sound started to fade out during the playback until it was no more. After it had "dropped to zero", there were two very short intervals of sound playing at the normal volume, as if the amplifier was trying to...
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