MCR Kickman Audio Noise

I been talking to joeyoravec about a scsi issue ( The 50 pin IDC ribbon cable connector ). during that conversation, He sent me the Link about this audio issues.

I do agree that the odd noises that this amplifier section make is most likely due to it's odd design. Something struck a cord with me when he said " I concluded that the design is the problem -- the current through the diode causes this fluttering sound."

One of the things I repaired in the late 70's was a piece of audio equipment using an IC opamp design and not the old fashion tube design of the day. The fix was to replace the typical silicon diodes with a germanium diode because it had different audio characteristics

While trying to fine the audio characteristics of the germanium diode, I ran across this.

Every part matters in sound with diodes being NO exception. The typical run-of-the mill diode found in most audio products typically produce nasty distortion and ringing resulting in treble hardness, grit, image blur, poor resolution,etc... Probably one of the most cost-effective modifications is to replace these with high performance Ultra Soft-recovery diodes. You'll hear much cleaner highs, increased resolution, more palpable mids, and tighter bass! Absolutely a must for any mod due to its low low costs!

From this web site.
http://www.referenceaudiomods.com/M...reen=CTGY&Store_Code=RAM&Category_Code=DIODES

Now while this won't 100% cure the poor audio design in the first place, It might improve the design enough for most people out there.
 
It seemed simpler than that to me.... D102/D106 pull current away from the LM3900 in order to control volume. Notice the 0-12v is divided to 0-1.2v. That means at mid-volume the diode has about 0.6-0.7v across it which is right around the breakdown voltage which is where it's going to behave terrible. That's what I meant by the lousy circuit. Remove that and your fluttering goes away -- except now you need a different way to control volume.

To followup -- that sparkfun STA540 amplifier kit has shutdown problems as described. The amplifier seems to have power issues (bad design?) but no response from their email tech support or user forum for a week (lousy!). An external amplifier with volume control would be a great solution but as far as I've seen the sparkfun STA540 kit is unusable.

So I still have no solution. Until I find a usable external amp with volume control the machine will continue to make a fluttering noise.
 
Germanium diode have a .3 volt drop but If I can find some in my pile of stuff. I would like you to try them in and see it that makes any difference. Just curiosity on my part here.

How many watts are you push out of current amplifier? I still have a few powered computer speakers still kicking around here. If you looking for a one of a kind solution that might work.
 
To followup -- that sparkfun STA540 amplifier kit has shutdown problems as described. The amplifier seems to have power issues (bad design?) but no response from their email tech support or user forum for a week (lousy!). An external amplifier with volume control would be a great solution but as far as I've seen the sparkfun STA540 kit is unusable.


That sucks. Sorry to have suggested it... :/
 
No worries, after searching with a colleague we agreed it looked like the best possible choice. Unfortunately it must have some sort of design flaw since it starts oscillating between running/shutdown even with a perfectly reasonable power supply. It's only drawing 1.5A at the time so I see no reason why it should shutdown (esp before the fuse blows!).

Maybe another amplifier (with volume control) would work, but I am not sure how much longer I will keep beating my head against the wall.
 
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