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Author Topic: Zenith record player amp conversion  (Read 8930 times)

MCM1910

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Re: Zenith record player amp conversion
« Reply #15 on: June 13, 2015, 03:16:11 PM »
Well so here is the update.  I decided that I wanted to unhook this from the record player because as it was set up I had to turn on the old record player motor to turn on the amp.  So I disconnected it from all of that stuff and wired up a switch and added a terminal strip to this scrap of MDF to make solid connections while I was testing.  Wouldn't you know it in the process both sides of the amp started to work!  I have an idea of my error and its embarrassing but anyway it is fully functional now.  With an MP3 player feeding it, it gets reasonably loud too!

So now I am a little stuck because I'm not sure if I want to use this for a home stereo or continue with converting it into a guitar amp.  If I am to use it for guitar it will need some sort of preamp feeding it or something to boost the output.  Anyone have any thoughts or opinions on what I should do next?

Thank you for all the help!


LateDev

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Re: Zenith record player amp conversion
« Reply #16 on: June 30, 2015, 06:29:03 AM »
I must have time slipped there, which is easy these days.

I saw Enzo had said for you to check all the Voltages and compare between the channels, which is good advice as Voltages can vary from the ideal on the circuit diagram.

The first thing you do with any repair job is to make sure that there is a supply and the Voltages around the circuit are correct, or at least within 10%. Having 2 channels allows you to compare these Voltages with relative ease.
No PSU on to any part of the circuit, no output.

Once you have done this, then you can start on signal tracing.

As far as the pre-amp is concerned you could of course modify the input or you can just bypass the whole front section up to point 14 and 35, but more about that later if you decide to go down that route.

The main thing is to get it working first :)

DrGonz78

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Re: Zenith record player amp conversion
« Reply #17 on: June 30, 2015, 06:51:54 AM »
As far as I can tell the OP had fixed the amp. Intermittent problem or user error I am not sure but the amp was working. I can't recommend turning it into a guitar amp unless that is what MCM1910 wants to do. Modifying circuit board layouts and changing the preamp to work with guitar will take some doing. Still sounds like some fun tinkering to be done too.
“A person who never made a mistake never tried anything new.” -Albert Einstein

J M Fahey

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Re: Zenith record player amp conversion
« Reply #18 on: June 30, 2015, 07:20:53 AM »
  Anyone have any thoughts or opinions on what I should do next?
It's your choice :)

That said, for a music player you'd need a couple reasonably efficient speakers because availoable power is not much.
Frequency response might not be that flat either, specially on lowest frequencies, but it depends on your program material too.

FWIW it might be fun to use it to listen to some old ... *vinyl* (gasp !!)

MCM1910

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Re: Zenith record player amp conversion
« Reply #19 on: July 05, 2015, 09:48:33 PM »
Sorry I missed the last few responses. It has been crazy here recently. The amp currently functions completely as designed except for some slightly scratchy pots. I'm in the process of designing a new enclosure for it now. I still haven't decided what exactly to do with it. I currently have a stereo jack wired to the input and have been listening to my iPod through it in the shop. It sounds decent...has a cool Lofi vinyl vibe...I found a really nice record player that needs some work but should be able to get up and running and I'm considering using this amp for that...

I still like the idea of using it as a guitar amp. If I do does anyone have any suggestions? ROG preamp? P27 preamp?

MCM1910

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Re: Zenith record player amp conversion
« Reply #20 on: August 10, 2015, 02:58:07 PM »
I just thought I would update everyone on this thing, as I am still working it out...

I repaired a record player and put it into the amp.  Very low output so I took the plunge and ordered a phono preamp to see if that would help.  It did and I was able to get decent output out of it.

I'm preparing to make the enclosure.  I started by obtaining an aluminum bar which I am drilling to be a "faceplate."  I plan to make the enclosure to look similar to a guitar head and will be using pine. 

One new problem I am trying to work out is how to add an on/off lamp.  Looking at the schematic it appears the power coming off the rectifier is 22V?  Should I tap into that and then try to drop voltage (with a resistor?) to a more manageable level?  It looks like there are some points in the schematic that are labeled as around 12V, could I just tap into those spots?

As always thanks again for all your help...

Stay tuned, if I make any progress in putting it together I will post pics