Rowe Ri3 Amplifier

[nigelr2000]

Hi All

My first post so bear with me.

I had this Ri3come in for repair and although I have done all the record playing bits and that side is working fine the amplifier is giving me a headache. Firstly it is a completely different design to the one in the manual being Mono instead of Stereo.

The original fault with it was one of the smoothing caps had blown out so blowing up the ILP output module (AL248) which didn't like running on unbalanced supplies. I replaced the amp with the Mosfet version MOS 248. The preamp board all looked OK.


The + & - 15 volt supplies are OK but when you put a signal through it it is really unstable with 100Hz hum, the volume control is inactive and makes very little difference, the tone controls affect the volume? and when you try to scope any of the pins it just introduces noise wiping out the music. I have replaced all the op amps and remote volume chip with no effect. Does anyone know what amp this is and can point me to the schematic as it would be a lot easier than tracing out the circuit especially as it's a double sided board. 

Pics of it are here photos.app.goo.gl/3PASPi6zhqZ896pXA

[jukenorman]

Hi Nigel,
Is that a (dreaded!) Rainbow amp - you haven't said where you are located in the world? If so, there's a little bit of background info in this thread
jukeboxaddicts.proboards.com/thread/2960/r87-golden-woe?page=2

Norman.

[nigelr2000]

I am located in sunny Norfolk in the UK. I think you have cracked it. I have got the amp to run but the pre-amp is really unstable, seems from what I am reading they were from new. I improved it a lot by strapping a couple of 10 mf caps across the power lines as they had no de-coupling eeek.

[nigelr2000]

Just to put this one to bed I ended up Junking the pre-amp as it was just so bad and unstable it didn't even have riaa tone correction on the pre amp stage.
I used a Cambridge phono pre amp I had lying around and built a simple one transistor Baxandall tone control panel, all I had to do then was rob the old mute relay off the original board and mount it on a bit of veroboard and jobs a goodun. Sounds really nice, a whole lot better than the original would have sounded.
Pics of the build stages and final build here photos.app.goo.gl/rBDn6yLQoPqEiMNp8

[wdln]

Nice work!

[jukenorman]

By an amazing coincidence, I have just taken a Seeburg DS160 in for repair - I've just looked inside it and it's got one of these amplifiers cobbled up! How pleased am I?

Norman.

[Ron Rich]

Hi Norman,
Must be your lucky Day ! Is the amp stereo,, or mono-- ?? LOL
Ron Rich

[jukenorman]

Hi Ron,
The amp is mono, so only half the trouble! It also actually works apart from the mute relay not being hooked up - which I hope wouldn't be beyond me lol! I don't think I'll spend a lot of time on it but I might try Nigel's tip of a couple of electrolytics in the power supply lines.

Norman.

[nigelr2000]

Good luck with it Norman

[Ron Rich]

Hi Norman,g
"Mute" should be no problem-- hook it up to the AVC/Mute/Ground, plug-- will have a ground (earth), on it any time it should be muted. Ron Rich