The Workbench

Re: CD4500 Ringing Sound

Dillen — Sun, 25 May 2008 06:05:57 GMT

Did you try to introduce the caps across the power supply physically near the DAC ?

Martin

Re: CD4500 Ringing Sound

camshaft — Sat, 24 May 2008 21:48:05 GMT

Anyone have any ideas about the clock signal? Martin?

Re: CD4500 Ringing Sound

camshaft — Thu, 22 May 2008 22:24:15 GMT

Hmm, wonder if it could be the clock feeding the dac?

Re: CD4500 Ringing Sound

camshaft — Thu, 22 May 2008 22:10:21 GMT

Well I bought a new DAC from that seller. Fortunately got it from him for $20 shipped. Unfortunately it didn't change anything. *cries* stupid cd player!

I did try the digital output awhile back, and that works perfectly, so that would lead me to think the problem had to be at the analog portion. And since I saw the ringing on the analog out pins of the DAC I figured it was the DAC. I'll go look at the schematic again now though and start working from the digital output onward.

Austin

Re: CD4500 Ringing Sound

Dillen — Sun, 18 May 2008 12:13:11 GMT

The price Peter mentions is not that drastic, I think. Worth a try anyways and based on what you describe, it would also be the first thing I'd replace.

Martin

Re: CD4500 Ringing Sound

camshaft — Sat, 17 May 2008 12:07:40 GMT

Yes I'm thinking of trying that Peter, but I still wanted to try to rule out other possibilities before just buying a new chip.

Austin

Re: CD4500 Ringing Sound

Peter — Sat, 17 May 2008 11:51:52 GMT

Buy a new DAC - $39. I have seen TDA1541As advertised as well.

Re: CD4500 Ringing Sound

camshaft — Sat, 17 May 2008 11:24:13 GMT

But Martin, how could the caps help if I can already see on the scope that the supplies to the DAC look clean?

Re: CD4500 Ringing Sound

Dillen — Sat, 17 May 2008 11:14:46 GMT

A digital fault is not very likely but of course it can happen. More likely a faulty DAC (Digital to Analogue Converter).

Try putting a 100uF and a 100nF parallel across the power supply to the DAC, physically close to it.

Martin

Re: CD4500 Ringing Sound

camshaft — Sat, 17 May 2008 10:27:51 GMT

Well the last several posts got deleted during the forum crash, but anyway, I used the scope to look at the 3 power pins on the DAC, and all 3 lines are nice and flat, although one of the voltages 1V high. But I've never seen something like a 1V difference actually cause a problem, so I don't think that's it. So that's where I stand right now, clean power going to the DAC, but still seeing a ringing coming out of its analog outputs. I also put the scope across the 100nF decoupling caps on the DAC, and didn't see any ripple there. Can the DAC chip actually go bad? I suppose there could be an error on the digital side too, but I'd have no clue how to debug a digital error.

Austin

Re: CD4500 Ringing Sound

camshaft — Thu, 15 May 2008 23:04:53 GMT

Hey again Martin, do you know how much voltage ripple is typical on the power supply lines? It was a couple days ago that I checked, but I think I remember it being about +/- 20mV.

Thanks again,

Austin

Re: CD4500 Ringing Sound

camshaft — Wed, 30 Apr 2008 01:16:45 GMT

Ok, I have the scope. On the line level audio pins, there's a 0.3V oscillation that looks to be about 0.2ms wavelength (5kHz). It's an old scope though, and I can't get it to trigger correctly (of course it's probably my fault rather than the scope's), so I'm not positive on the 5kHz as the wave keeps moving around rapidly.

I then looked at the power supply. In my moment of genius I was excited to see a 120Hz oscillation on the power supply lines, before I realized that I was just looking at the doubled power line frequency being output by the full-wave bridge rectifiers. I didn't look at the lines past the outputs of the regulators, which I'll do tomorrow since I need to get to bed.

Austin

Re: CD4500 Ringing Sound

Dillen — Tue, 29 Apr 2008 13:45:26 GMT

The scope will help you, I think. Check for clean power supply voltages, muting circuits etc.

Martin

Re: CD4500 Ringing Sound

camshaft — Tue, 29 Apr 2008 09:52:07 GMT

Well I tried wiggling all the wires and connectors while it was playing, and there was no difference in sound. Martin, are there any specific capacitors you'd suggest replacing, before I go through the trouble of lugging home an oscilloscope from work?

Thanks again,

Austin

Re: CD4500 Ringing Sound

Dillen — Mon, 28 Apr 2008 01:43:18 GMT

It could be a grounding problem, maybe from the chassis to the CD deck. Try re-seating all plugs/connectors.

It could also be that the muting circuit started to oscillate or an unstable power supply, both probably cap problems. I would put an oscilloscope to the signal path and power supply rails to see where it comes from. I agree with the other Martin, this is one fault that is definitely not caused by C2103.

Martin