Boneyard Question

[CrunchBerry]

Hey all,

I have a question regarding the boneyard.  I have built a boneyard, but now have a higher pitch squealing sound when I turn the gain up much past about 50k.  It seems to sound good with the gain pot lower, then once it is turned up it squeals really badly.  It isn't like a feedback squeal, but more of a constant high pitch, annoying as hell squeal.  I touch around on the vero board and can induce new sounds or squeals, but can't seem to identify the source of this problem.  With the gain pot set low it is working, so that tells me the circuit works ok, right?  Do I need to ground the enclosure?

I have checked the connections about 10 times and everything seems to be ok.  I have checked the resistance that the circuit sees in the feedback loop, from input to output and can see the resistance change when turning the pot, so all the connections seems to be ok.

Any ideas as to what I should be looking for as an issue?  I am pretty much stumped.

Thanks!

[jkokura]

Squealing can be associated with power chips. Can you tell us what chip you're using? Be specific with the numbering as the extra letters can be what tells us what's what.

Jacob

[CrunchBerry]

Looks like a Maxim Max1044   CPA1113.  That is all the information on the chip.

Not sure if this information helps, but I checked the voltage at the Charge Pump outputs and I get + 9VDC and -8.9 VDC.

Thanks for the assistance..

[CrunchBerry]

I was searching the forum a little bit better and stumbled across this old thread...

http://www.madbeanpedals.com/forum/index.php?topic=2290.0

Gonna try some of these things tonight and will re-post any findings.

Thanks.

Jason

[jkokura]

Looks like a Maxim Max1044   CPA1113.  That is all the information on the chip.

Not sure if this information helps, but I checked the voltage at the Charge Pump outputs and I get + 9VDC and -8.9 VDC.

Thanks for the assistance..

Your welcome. I'd suspect that part of the reason may be that your chip is causing the whine. This often happens with Sunking projects as well, and the answer there is to use an SCPA chip instead. The TC1044SCPA is a common one, but the 7660SCPA can work as well. Where did you get your MAX chip?

Jacob

[CrunchBerry]

UPDATE..  I added a 1k resistor in series with the input to the PCB and added shielded wire for the input and output and the whine has decreased.  The gain is able to be turned up higher now before the whine.  I plan on ordering the different charge pumps you mentioned to try and have on hand.  My question is what is the difference between the SCPA and CPA?  I ordered the Max1044CPA from Small Bear and now I am looking at ordering the TC1044SCPA from Mouser, but was just curious of the difference.  After originally posting, I have found a great deal of information regarding this whining sound and it seems like it occurs on a few different pedals that use the Max1044CPA charge pump. 

Thanks again!

Jason

[oldhousescott]

The CPA version has a clock frequency that is in the audible range. This can bleed through on high gain settings causing an audible whine. The SCPA has a connection that doubles the clock frequency, moving it out of the audible range (for mere mortals at least).

[CrunchBerry]

Awesome reply.  That makes a lot of sense...

If only the information I found when I googled that question was that simply stated.

Thanks!!

[bigmufffuzzwizz]

The CPA version has a clock frequency that is in the audible range. This can bleed through on high gain settings causing an audible whine. The SCPA has a connection that doubles the clock frequency, moving it out of the audible range (for mere mortals at least).

Nice explanation! Always learning something around here