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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 22nd Mar 2019, 12:26 pm   #1
Dazmond
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Join Date: Mar 2015
Location: York, North Yorkshire, UK.
Posts: 254
Default Decca Gram Mid / High Frequency Distortion

Hi Folks,

I have a Decca gram (Deccalian 12) that's giving me some grief - it has distortion issues on one channel at the top end of the frequency spectrum, very noticeable on percussion sounds such as cymbals etc.

So far I've ruled out the cartridge and stylus, the speakers, and the crossovers.

I've substituted the cartridge and stylus for a known good one, both caps on each crossover tested leaky on my Heathkit IT28, replaced but still the same issues. I've substituted the speakers with some hifi ones I had kicking about but still issues in the one channel. I've tried bypassing the crossovers but the output is too harsh in the ears to really tell what's happening. (although after the capacitor change there's nothing in the crossovers that could be failing anyway)

I've also gone through the other inputs with a different source still the same issues.

Both channels are as they should be bias wise as per the service sheet. All voltages check out, there's a few electrolytics in the signal path but they all seem to check out ok.

I did have a high pitched motor boating issue coming out of the faulty channel when ever I tapped the main amp board, however I've been over a few joints and cleaned the trim pots for the bias and this has now gone away.

I appreciate faults like this can be difficult to trace but any help would be appreciated.

Many thanks,

Darren.
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