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Old 19th September 2008, 08:28 PM   #1
Stefanoo is offline Stefanoo  Italy
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Default pro-ject tube box

Hi guys,

i have a tube box first version with a problem.
I track a huge distortion a the output.
I am testing it with a sine wave of 10mV pk-pk.

I was wondering if anybody can point out a service manual/ schematic for this phono stage.
I have never fixed a valves circuit and therefore i am a little bit concerned.

Any hints is of course welcome.


Thank you very much for the attention.


Best,
Stefano.
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Old 20th September 2008, 08:42 PM   #2
Stefanoo is offline Stefanoo  Italy
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nobody?
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Old 20th September 2008, 08:51 PM   #3
Alastair E is offline Alastair E  Wales
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Any more details, or model-number/picture etc would help others identify it.

The name is meaningless to me, --but then again I stay away from 'audiophool' places!
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Old 20th September 2008, 09:05 PM   #4
Stefanoo is offline Stefanoo  Italy
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Alastair thanks for your reply.
Sorry i put the model of the pre phono as a subject of this 3d.
Anyways, the phono in object is the Tube Box by Pro-Ject.
Is the first version, the black phono with these little 2 windows on the front that are showing the 2 valves.

Here is a link to the phono
http://images.google.com/imgres?imgu...icial%26sa%3DG


I don't know if you also meant to attach picture of the distortion as well by that.
If so, i will attach them tomorrow.
I would just like to have a schematic for this phono.
Plus i never had dealt with valves before so i am a little bit concerned.


thank you anyways for the attention.
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Old 20th September 2008, 09:32 PM   #5
kmaier is offline kmaier  United States
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That's the Sumiko unit... here's links for some manuals:

http://www.sumikoaudio.net/project/m...eboxmanual.pdf
http://www.sumikoaudio.net/project/m..._tubeboxII.pdf

No schematics however... not sure if they ever published outside of Sumiko.

They've made quite a few variations. They all appear to use a 16V AC supply. This usually means very low DC voltage via a tripler or quadrupler, i,e., about 50 volts DC. Most of these designs date back 10+ years, are mainly op-amps used for the bulk of the circuitry with a twin-triode stuffed in the middle configured for unity gain. They push the signal thru this "stage" with the "logic" that you get "tube sound". I'd be surprised if it's something other than this.

Chances are you have a power supply problem or a bad op-amp. They usually drive the tube filament via a bridge rectifier and regulator and then a series string of diodes for the tripler/quadrupler for plate supply. I suggest checking for voltages at the tube socket as a starting point. Good luck.

Regards, KM
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