Aquaboy Deluxe, fluctuating supply voltage 3PRR @15v and modulation LFO Noise

[timbo_93631]

So I am wrapping up an ABDLX and having a problem with the modulation.  You can hear some faint motorboating with the modulation switched off that corresponds to the rate control and depth makes no difference.  I have a 3PRR using a LT1054, the only subs on it are 1n5819's instead of 1n5817's which seems okay according to the datasheet, and with an 78L15 it puts out about 14v.  What I have observed is that the supply voltage to the ABDLX board fluctuates about .5vdc with IC6 in, and remains steady with it pulled, and obviously the motorboating goes away.  Any ideas?  I have check all solder joints and values in the area.

Also I'd like to have the modulation switched with a footswitch, but as is I am getting some nasty switch pop when I make and break the connection between pad 2 of the wave switch, something that I don't remember from the previous ABDLX I built when using a on/off/on SPDT toggle.

[timbo_93631]

So, I hooked it up with 9v supply and everything is hunky dory, makes me think the 3PRR can't supply the current the ABDLX needs as configured.  I am wondering if replacing the regulator with a 12v or 15v Zener might be wiser to save a smidge of current supply, and also if it would be necessary to have 1n5817's (or even 1n4001's) rather than the 1n5819's I subbed.

[Scruffie]

Do not use a zener, you'll cause your self all kinds of hassle.

Your regulator should not be putting out only 14V, that's too low, it is likely the 1N5819 subs you made, they have too higher fV.

[timbo_93631]

yeah, I think the fv for 5819's is 600mv vs. 450mv for the 5817's, but I also didn't think that would matter in terms of operation as the circuit works fine, delay is good, but using either a 12v or 15v regulator and LT1054 the voltage is not stable and fluctuating with the swing of the LFO which I think is because trying to draw too much current.

[Scruffie]

The regulator not functioning correctly in the case of a 15V regulator due to not getting enough voltage from the charge pump will cause issues, so let's do this with the 12V regulator until you get the 1N5817 diodes.

First, what opamp are you using for the LFO? You may find either an LM1458 or LM358 works better.

Second, LEDs, what are you using for the vactrol and rate LED? Some Ultra-brights in the LFO will pull more current, you could try disconnecting the rate LED and see if the issue is resolved.

Third, try jumping R52 and see if that helps any.

[timbo_93631]

Using TL062, and VTL5C3, will try disconnecting the rate LED.

[timbo_93631]

I found another 1n5817, so I put a 1n5819 that had a low forward drop in D1, and used the 17's in D3 and D4, looks better now, 14.98v coming from the regulator.

[Scruffie]

So did that solve the issue?

[timbo_93631]

No bench time today, we completed one of those 40 week builds over at the hospital, build report forthcoming.

[wgc]

Congrats!

[timbo_93631]

So did that solve the issue?

No, so I tried building a second 3PRR with 1n5817's only (thanks again Cody!) and there was the same issue, 18v and 15v taps fluctuating +/-.5v and voltages a little low.  Both boards stabilized using 12v regulators, maybe the 15v's I have are faulty?  Maybe my pedalboard power supply couldn't supply enough current?  I think it is rated at 250mA per tap so I don't think that would be the problem. 

In the end I found I was having two separate issues, one was the supply voltage jumping up and down which was solved with the 12v regulator.  One I got that issue sorted it became apparent that the motorboating of the modulation circuit while switched to off was unrelated as it still persisted.  I searched here and at FSB and read about similar problems people had with the original Aquaboy modulation daughterboards, some people having success with the values used in the Aquaboy 2012 build doc in dealing with it and some suggestions of killing power to the modulation circuit as the best fix.  I made the following changes which resolved all the problems I was having:
Changed R47 from 4k7 to 10k to limit the upper range of the speed/rate control
Changed R50 and R51 from the suggested-for-15v-operation 5k to 7k5
Changed R56 to 100k
Put R43 on the modulation footswitch so I could kill the +9v supply to the modulation circuit and end the motorboating by brute force.

[flanagan0718]

Nice glad the issue was resolved and the ABDX went to a good home!