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Old 3rd September 2014, 10:47 AM   #1
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Default New Member - Phono to amp distortion

Hello Everybody,

I'm certain that this post will never see the light of day. I have an unusual habit of reading the T&Cs on registrations and this one said I must post intelligently! Please forgive me, whilst climbing this ever-steepening learning curve, my specialised subject is the bleeding obvious!

Btw, my name is Marc but my screen name comes from my long association with the Airstream community. Airstreams are the shape of Twinkies - and the silver speaks for itself.

I recently purchased a Dansette Bermuda II. Now, I love retro but most old valve amps are poor quality and potentially dangerous. Margolin were cabinet makers and it's reflected in their amplifiers!

I decided to upgrade it. It doesn't need very HiFi components. The magic is in the iconic box so I wanted good sound and perhaps it do a few tricks.

The control panel on the Dansette is: Tone - Volume - On/Off and I recreated this unusual arrangement by removing the pots from the new amp and extending them to the original mounting board. It looks quite tidy with stuffing glands where the pots should be and 6 core wire connecting everything. I'm sure many of you have done this but it was new and novel to me!

The control panel also has an input/output with holes which had phonos for external speakers and "Stereo" which must have been a neat trick from a single channel twin contact ceramic cartridge!

I have upgraded it to a Magnetic cartridge, installed a phono preamp and the input/output has been upgraded to 1/4" stereo jacks. One providing an input for an mp3 player. This is really trick on an old set and sounds fantastic! The other I used to export the preamp signal.

I'm sure some of you have seen my error. I routed the "preamp out" through a bridging jack that isolates the signal to the amp when a Jack is plugged in. I also mixed the signal grounds in the process and my research so far tells me this is a no-no! It buzzes like hell!

I have by-passed this arrangement and plugged the preamp straight into the amp and it sounds excellent! I am very lucky that I've put this mass of unrelated stuff together and it seems quite well balanced.

My question is: Can anyone suggest an alternative arrangement so that I can still have the phono output and preserve the good quality signal to the amp?

Many thanks

Marc
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Old 3rd September 2014, 02:57 PM   #2
kevinkr is offline kevinkr  United States
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Posting some pictures of the set up and how it is wired may help other members to advise you on this.

Unfortunate you did not keep the original amplifier, it was probably reparable and not unsafe provided it had an actual power transformer.
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Old 3rd September 2014, 03:08 PM   #3
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Actually, I do have the amplifier and happy to send it to anyone for the cost of postage. I looked into getting it repaired - not many interested - unless they could finance a vacation on the proceeds! ...and I wanted the iconic look of this unit twinned with modern accessibility.

Btw, I'm a photographer so keen to add photos but found they wouldn't load. I assumed this had something to do with new member probation.

Thanks,

Marc
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Old 3rd September 2014, 03:17 PM   #4
kevinkr is offline kevinkr  United States
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Possibly the pictures are too large? I am not aware of any site imposed limitation on newbies posting pictures along with their posts.

Click manage attachments (not shown - you must be in advanced mode for this to show) then click browse, navigate to the picture you want to upload and then click upload.
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Old 3rd September 2014, 03:19 PM   #5
kevinkr is offline kevinkr  United States
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I am sure one of our members in the UK would enjoy tinkering with the old Dansette amplifier.
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Old 3rd September 2014, 03:30 PM   #6
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See below a couple of pics of the unit. The innards shows the arrangement at present. The power supply is in the foreground - and yes I have learned to keep the preamp well away - it will be sited against the wall of the case.

The amp is beyond with the glands sitting where the pots should be and the cable feeding the pots mounted on the original rail.

I've learned alot doing this and I do feel a bit of regret about updating but I remember hearing of an upgrade to old Jags and Astons that improved the performance and braking and thinking that was a good idea - even at 100k a pop! I guess we'll all have an opinion - which is free!

Actually, I think I've worked a solution to this. I also have a Berhinger preamp which includes a 1/4 Jack stereo output - meaning that the ground is already consolidated. I'll feed this into the Jack socket for the output.

Marc



http://www.diyaudio.com/forums/attac...1&d=1409753740
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File Type: jpg photo-Innards.JPG (146.7 KB, 40 views)
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