Hi. Don't know why I'm messing with this. It's a fixation right now. It's all apart on my bench and is time consuming to work on, so want to do everything to it at once.
It's a GE 3-5266B 5 watt per channel cassette stereo boombox. The issue is very high noise level, even with no tape playing. It plays normally, but it's crazy to me that this level of noise was acceptable, if normal. Are most GEs like this with noise? Select "tape" function with no tape in it, and you hear SHHHHHH even at half volume? I don't remember it. Have had several GE boomboxes in my life. Btw, I'm not talking about motor noise. With nothing running, the hiss is loud.
It uses an LA3220 14 pin DIP, "low noise" preamp with ALC. Have ruled out (I believe) everything external to the chip. The 5 volts Vcc is clean, replaced all the 40 yr-old caps (though none tested bad) in that circuit. Resistors are fine.
The first thing I did was float the input pins. Floating the + inputs caused no change (hiss/roar still there). Floated the - inputs, and silence. But, after tracing it out, the only reason I lost my noise is because I broke the feedback loop (from the output). The chip is generating the noise internally. No change when I disconnected the head wiring (from the board), floated the ALC pins, etc. No change. Replaced the chip with a new NTE1634, and it's no better at all.
There does not appear to be any newer, compatible I.C. available with lower noise. So, my thought is to make a replacement circuit, using OPA2134 op amps, or find a very low noise preamp w/ALC chip to adapt into the circuit.
Feel stupid messing with this or getting this involved with it. It's a 37-38 yr old tape recorder and who knows why I care about it, but would like to improve this circuit.
Did electronics repair for a living for about 18 years, and did warranty work (audio) at a dealer for Pioneer and Fisher in the 90's. After leaving that shop, I went to a "we fix everything" shop for ten years. So, I've worked on my share of every brand.
If anyone else has done any mods pertaining to this and has a recommendation, I'd like to hear it. Thanks.
It's a GE 3-5266B 5 watt per channel cassette stereo boombox. The issue is very high noise level, even with no tape playing. It plays normally, but it's crazy to me that this level of noise was acceptable, if normal. Are most GEs like this with noise? Select "tape" function with no tape in it, and you hear SHHHHHH even at half volume? I don't remember it. Have had several GE boomboxes in my life. Btw, I'm not talking about motor noise. With nothing running, the hiss is loud.
It uses an LA3220 14 pin DIP, "low noise" preamp with ALC. Have ruled out (I believe) everything external to the chip. The 5 volts Vcc is clean, replaced all the 40 yr-old caps (though none tested bad) in that circuit. Resistors are fine.
The first thing I did was float the input pins. Floating the + inputs caused no change (hiss/roar still there). Floated the - inputs, and silence. But, after tracing it out, the only reason I lost my noise is because I broke the feedback loop (from the output). The chip is generating the noise internally. No change when I disconnected the head wiring (from the board), floated the ALC pins, etc. No change. Replaced the chip with a new NTE1634, and it's no better at all.
There does not appear to be any newer, compatible I.C. available with lower noise. So, my thought is to make a replacement circuit, using OPA2134 op amps, or find a very low noise preamp w/ALC chip to adapt into the circuit.
Feel stupid messing with this or getting this involved with it. It's a 37-38 yr old tape recorder and who knows why I care about it, but would like to improve this circuit.
Did electronics repair for a living for about 18 years, and did warranty work (audio) at a dealer for Pioneer and Fisher in the 90's. After leaving that shop, I went to a "we fix everything" shop for ten years. So, I've worked on my share of every brand.
If anyone else has done any mods pertaining to this and has a recommendation, I'd like to hear it. Thanks.
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I would find the exact faulty component and replace it with the correct part. Sounds like the LA3220 was not faulty ... put it back and find the faulty part.
Degausing the playback head can improve signal to noise levels.
Degausing the playback head can improve signal to noise levels.
Agree the LA3220 wasn't faulty. It's just the way it is, so the option remains to either like it, or replace the circuit with something else.
No, it's definitely coming from the preamp. No other source has noise. Even the magnetic phono stage is quiet, surprisingly. Aux in is quiet, also. Did notice that the unit has 100kohm feedback resistors, while the sample circuit shown for the LA3220 had 51k. I shunted each one to drop their resistance down to 50k, and the noise dropped very marginally. But so did the gain of my tape playback, so nothing really gained there.