[sdiy] Looking for advice about powered reference monitor problem

[mark verbos]

I have experienced this kind of maddening behavior caused by a scratchy pot. The problem would correspond with pushing on the shaft of the pot. Admittedly, I have seen it in MUCH older devices, but that’s how it looks. 



Mark





> On Nov 19, 2020, at 9:34 PM, The SynthiMuse <synthimuse at gmail.com> wrote:
> 
> If you listen to the monitors with no input signal and check if the small amount of noise is the same for both monitors then that implies that there's a bad connection or solder joint on the input signal. On the other hand, if you hear the backgtound noise profile tracks the previously heard behaviour on the suspect monitor,  that might suggest an issue further up the chain on the power amp end.
> Jimmy Moore's suggestions are good and it helps to have a known good working channel to compare measurements with.
> 
> If there's no conclusion comes from the above, gentle tapping aound the board with an insulated 'prod' might show up where any bad connections might be.
> 
> I have a few old toothbrushes for closing boards and they're useful for this.
> 
> Good luck.
> 
> Gerry Murray
> 
> 
> 
> On Thu, 19 Nov 2020, 19:39 Jimmy Moore, <jamoore84 at gmail.com <mailto:jamoore84 at gmail.com>> wrote:
> It sounds like a cold solder joint that fixes itself after the board warms up, so first step is to check that all the solder joints or connections are good.  Reflow things to be sure.
> 
> If you have a schematic (or can trace things out) start at the power supply and verify that the right voltages exist at all the places they should.
> 
> 
> 
> On Thu, Nov 19, 2020 at 12:24 PM Shawn Rakestraw <shawnrakestraw at gmail.com <mailto:shawnrakestraw at gmail.com>> wrote:
> Hello,
> 
> Sorry, I know this is slightly off-topic, but still relative to music. Hopefully it is not out of line.
> 
> I have a pair of 15+ year old Event 20/20 bas v2 reference monitors. A couple months ago, I began to notice that one of them was operating at a significant difference in volume and it would gradually increase in volume until normal again. So it initially sounds like the audio is panned to the right, but gradually becomes centered again over the period of 5 to 15 minutes.
> 
> I bought a new pair of Adam monitors (one of them had a weird noise problem right out of the box) and I decided to replace the electrolytic capacitors in both of my old Event monitors. I was happy because swapping the capacitors seemed to fix the problem. I returned the Adam monitors and re-employed my old trusty Events.
> 
> After a week or so, now I am noticing the same one having the same issue again. At power up, it takes about 5 minutes to come up to normal volume. It seems odd to me that the problem disappeared after the cap swap and now is returning.
> 
> I know this is a pretty general question, but I thought someone might know exactly what to check.
> 
> I don't have a schematic, but I can tell you there is a giant toroidal transformer that sends power to a single circuit board with 2 amplifiers, one for an 8" speaker and the other for the tweeter. It seems like both speakers suffer from the same volume attenuation problem. The capacitors I replaced were 2 big 10000 uF where the power enters the board and 7 100uF in the amplifier section. There is a bass and treble section, as well as a gain pot.
> 
> Thanks to anyone that may offer some advice.
> 
> - Shawn
> 
> <20201111_153537.jpg>
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