Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Solid State => Topic started by: birt on January 19, 2014, 06:27:51 am
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in a dance performance we are using an old "Telectra" portable record player. it fits the set perfectly and works well mechanically.
it has 2 outputs for speakers but the lid of the case only has one speaker. the second one i use as a line-out (added 2K2 series, 270R to ground) so i can also have the sound in the main speakers for the show when needed.
we don't expect a good sound from it, it has to sound old and you have to hear the manipulations of people using it. otherwise we could just fake it and send an external signal to that speaker. the problem we're having now is that in loud parts of the music (especially vocals) the sound distorts too much. i know it's not the speaker because i also hear it on the line-out. it has volume, tone and mic volume controls.
i had a quick peak inside and saw a very small circuit with 1 big cap, maybe 20 components and 2 transistors. (AC180/AC181 combo with square heat sinks. there's 2 seperate AC181's on the board, i guess one for the preamp and one for the mic input) these transistors and the fact that it has the controls labeled in french probably means it's made here in Belgium or at least western europe. there is one trimpot on the board but the sound doesn't really change when i adjust it. all resistors are carbon comp.
so in this stress i'm trying to find out if someone can point me at where to look for the source of this distortion. i suspect these portable players all had very similar circuits...
tonight i will take it home and check the solder joints, replace the caps and maybe some of the resistors if they have drifted. there's not many components anyway.
i know this isn't much information but i haven't had the chance yet to really search. we're in rehearsals right now because our first show is on wednesday already! and we still have to get our record re-made because the needle skits in silent part before the actual music starts.
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The cheap ceramic pickup cartridge would be high on my suspect list.
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maybe i don't have to fix this one. we found another beautiful one that works better and is louder. but it goes just a bit too slow so everything is off key. if i can figure out how to change that this is far superior to the distorting one.
it's a Telefunken Partyset 208. it has a five pin din that is either only input or in and output. but i can't find a manual or schematic. only very small thumbnails
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I agree that the pickup or *needle* can distort.
Replace the needle. (Not easy by Wednesday.)
Run the pickup direct to a guitar amp. The impedance is near-enough. The level may be a bit high. While you might not want to use the guitar amp in performance, this will confirm/deny the onboard amp as a problem.
Bit-too-slow *can* just mean it needs oil. Do NOT get ANY oil on the rubber or where the rubber rolls. I would start with the motor bearings. They are "permanently lubricated" and permanently isn't forever. There's probably still oil in them but it has gummed-up with age.
Clean the rubber and its contact surfaces with high-proof vodka (straight grain alcohol if you can get it).