Left channel distorted after 33 revision.

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06-Mar-2018 03:49 AM

IndeedFergus

IndeedFergus

Posts: 3

I haven't received a reply to my emails for support so I shall try the forum in the meanwhile. 

After I finished the revision of my Quad 33 pre-amplifier the right channel sounded fine but the left channel is distorted when listening through disc, or radio inputs.

Switching the amplifier boards inside the amplifier has no effect.

The Tape input doesn't appear to have any problems and operates fine on both channels. 

Does anyone know the likely problem? Bad solder joints on certain boards? Any help or advice would be greatly appreciated. 

- Fergus

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09-Mar-2018 12:20 AM

EJP

EJP

Posts: 1484

Your excellent detective work has isolated the problem to the input transistor on the Tape Adapter board. Check your soldering around the four 220k resistors, and their values.

EJP
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13-Mar-2018 10:55 PM

IndeedFergus

IndeedFergus

Posts: 3

Thanks for confirming the issue is with the transistors on the tape board. So I checked the tape board and discovered the orientation of the transistors was wrong. I had to find out the original pin-out of the 'Top-hat' type transistors and correct my original orientation as I must have been confused with my issue one board not having an obvious placement for the transistors. Having corrected my mistake everything is working perfectly and sounding great! Thanks for your help. 

When doing my revision I was a little confused by the disc adapter board section and changed the values of the resistors and afterwards realised I shouldn't have done this.  What colours should the original resistors be as I can't figure out which ones to put back to keep the original input gain? 

- Fergus


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14-Mar-2018 12:01 AM

EJP

EJP

Posts: 1484

First locate the two 68k resistors on the edge row: they are 4th from the top and 3rd from the bottom. In between these there are the four resistors that you changed. Original values are:

- next to the 68k resistors: 470R (yellow-violet-black-?)
- in between those two: 220R (red-red-black-?).

EJP
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28-Mar-2018 12:08 AM

IndeedFergus

IndeedFergus

Posts: 3

I managed to get the resistors changed back to original, and seems to work fine. However the colour was different being brown instead of black, but it translated to the same value and seems to work without any problems. Thanks very much for the help. I shall keep using my 33 Pre-amp for a while before I start the revision on my 303 Power-amp to give me a bit of a break! - Fergus. 

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28-Mar-2018 01:53 AM

EJP

EJP

Posts: 1484

Maybe you got 221K resistors? I read the colours off a 1% metal film resistor. If you use a different tolerance the colours from the third onwards are different.
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