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Old 17 October 2009, 03:50   #1
8bitbubsy
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Quiet/Low sound on A600

A600 (A300 rev 1)...
Mobo is super clean, no signs of leaks from the caps and so on...
Still, the volume is quite low! I have to turn my amp a bit higher than usual to hear the sound. Well, the sound is normal sounding, no crack/clipping/noise, it's just quiet...

What do you think is the issue? Bad caps under the RCAs?
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Old 17 October 2009, 05:19   #2
Zetr0
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@8bitbubsy

This is somewhat of a two fold problem

Lets talk Power and Impedence

Firstly the Audio Circuit is Highly effected by -12v power, IF you PSU is poping out not enough -12v then you will experience a range of probems.

Most notibly you will have a crackling effect, however this can be smoothed out and you are left with a LOW volume.

Its possible that somewhere in your Audio circuit you have a HIGH impedence on the line, or perhaps even your cables, although the latter I do doubt.

So what todo ?

well you need to do some more investigation I am afraid to say... you must get a multimeter to check the -12v to the system when in opperation, so PLEASE be EXTRA carfull, more so to yourself, so take precautions =)

when testing your power in situe, and remember on load of the amiga powered up, the -12v must read higher than -11.5 (on load), any lower than that and you are likely to notice problems.

Initially it will reduce the volume, any lower still crackles will begin to happen as the voltages spike


My initial thoughts lead me to believe a -12v issue (to low) and as such the resistors are causing more impedence than the circuit is designed for.

I dont blame the resistors, its crappy voltage that utlimately to blame.

*Remember

Electricity is like water, it has mass (energy) it has a current (amps) and it has a flow (-ie to +ie)

within this analogy with poor power you dont have smooth currents, this can cause eddies and reflections within the current. The harder the PSU has to chuck out power the more distubed the current and as such you begin to introduce "Dirty" power, and this will begin to damage components.

hmm, I think I can show you kinda what I mean...
[ Show youtube player ]

A pity I cannot find now the water filter system that produces an even clean flow in one direction, they use this method to shine lights through the columns of "Smoothed water" water jets, as the water is traveling in uniform direction it acts like fiber optic cable.

Last edited by Zetr0; 17 October 2009 at 05:36.
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Old 17 October 2009, 07:18   #3
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I use an ATX PSU, and I'm sure the -12v line is fine.. All the lines are measured under load, and ranges very good.
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Old 22 October 2009, 09:05   #4
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Update:
The two caps under the RCAs are now exchanged for two new and non-polarized ones..
The volume is still a bit low, and the right channels is more quiet than the left.. And more noise in the right one... The right one seems to be very 'unstable'.. The noise comes and goes, but it's always quieter then the left.
I thought only these two were the audio circuit caps..? Which of the rest of the A600 caps are used in the audio circuit?
The PSU is fine, checked.

Last edited by 8bitbubsy; 22 October 2009 at 09:56.
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Old 22 October 2009, 17:12   #5
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No other electrolytic capacitor directly involved on the audio circuit, but you'll find that one of the remaining capacitors is the -12V filter (a 100uF x 25V, IIRC) near the power connector area.
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Old 22 October 2009, 23:05   #6
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The right channel is dying - it's 90% lower than the left one.

Using an A600 PSU, measured it now on load (Amiga 600 on):

-12v measures: -12.27v
12v measures: 11.53v
5v measures: 5.03v

Last edited by 8bitbubsy; 23 October 2009 at 07:49.
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Old 23 October 2009, 07:44   #7
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Both channels started to make noises now, so I exchanged the -12v cap (22f) for a new one.. Didn't help at all.. Also, I resoldered stuff that seemed to have dried solder joints.. This is getting on my nerves
Bass sounds like noise/bad speakers playing on max. Also, all the high frequencies are clipped. Sounds like treble is all gone... Also, it comes and goes. Sometimes, the "nice and clean" sound comes back.

Last edited by 8bitbubsy; 23 October 2009 at 07:59.
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Old 24 October 2009, 05:46   #8
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Check the operational amplifier behind the audio decoupling capacitors.
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Old 24 October 2009, 07:09   #9
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Quote:
Originally Posted by rkauer View Post
Check the operational amplifier behind the audio decoupling capacitors.
How does it look like? What is its number?
A300 Rev 1...

EDIT:
Quote:
Originally Posted by AUDIO PROBLEMS
Problems with left, right or both channels:
- 8364 U3 Paula
- LF347/TL084 OP-amp U14
- Q331 or Q321 F.E.T.
- CN3 or CN4 (cold solder connection)
- EMI 1303 or 1302 (R243-R233 1k ohm A2000)
I'll be giving those a look soon.




The trace broke, so I had to bridge it... Also, I'll be getting a 470 000 ohm resistor to bridge with instead...
Well, I doubt that's the issue, but it sure had bad solder joint !

Last edited by 8bitbubsy; 24 October 2009 at 09:21.
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Old 24 October 2009, 11:00   #10
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Ok, spent an hour giving all the SMD components fresh and new solder tin. Well, now the sound is MUCH better. It's stable in both channels, and it doesn't come and go. Also, the volume is normal.
BUT! The sound clips. Bass (only the deep basses) = noisy and clipped.

EDIT: Solved! The issue was the PSU... So a mixture of the PSU and bad solder joint it was.

Last edited by 8bitbubsy; 24 October 2009 at 12:32.
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