OT odd issue with an amp

[petey twofinger]

so we got a new drum machine . the old drums came from the zoom b2 bass multi effector . the drum sounds go thru this amp hack i made . its a 100 watt 2 x 50 t amp , that runs off 2 12 volt sla batterys .

the new drum machine is making an odd pop noise on some drum sounds when i turn it up . it is notibly quieter than the b2 drums .

i can not figure this out . i will try to collect some data soon . the amp says 48k to 60k for input impedance . i cant find specs on the drum machine , alesis sr18 , so i ohmed it out . is was around 10k or 20k on the headphone output . the b2 is one ohm .

there are gain switches for the amp , it doesnt do this on the low gain setting but it is very quiet . i tried a direct box but it got very quiet . we need the drums loud ! different eq settings on the sr18 effect it . it seems the freq response on the sr18 is a lot higher more hifi than the b2 . whats odd is that it isnt really cutting out , which i have heard the amp do before with the b2 , its making a pop , and it seems to be on the tom toms . i tried different power supply on everything but the amp . the amp led does not get dim when there are peaks .

[GibsonGM]

Can't give you concrete answers without the schema etc., but I would be seriously suspicious of the power supply for the amp.  At least as a first place to look. It could be that it's not capable of delivering the 'burst' of power needed to push out those deep bass notes! 
This may be corrected by getting a higher rated PS, or but improving the quantity of capacitance in the filter section of the PS....can you post the specs for the PS you're using?

I know, sag isn't really associated with "pop" - so maybe the bias is changing around the amp's output transistors, and it jumps into cutoff due to some sag?    That is the next place I'd look!   See how it's doing when the V drops.  Sorry I can't be more informative....post more info as you get into it...there could be 3, 4 things going on, but that's a place to start...

[petey twofinger]

 i tried putting a few booster circuits in between ,  and that did the trick . i think i will install a dual amz mosfett boost in it . i have these on two other amps .

it is a LOT louder , so loud that it can trigger the protection circuit which cuts it out rather than this annoying pop noise . but its a ton louder . and we already are at the point of way too loud . time to start turning down a bit . the camera cant handle the dbs .

what was odd was it wasnt deep bass notes , the kick drum sound wasnt making the pop . it was the high tom sound . also her bass ran fine thru it . thanks though , if i run into any more issues , the power is where i will start monkeying .

[GibsonGM]

Yeah, sometimes there's a workaround like that that will get you by.  Given what you're describing, I'd suspect something is messed up in the 'switchable gain' section, maybe...it's ok til you demand a lot from it, then it pops.  So your booster 'replaces' that section.

I'd hunt in that area, myself, if it mattered to me.   Depends how involved you want to get, I guess!  You might just be exceeding what you can do with the boost in the amp, and clipping, so turning it down, feeding it to a booster - that is actually the right way to deal with multiple boost stages!
Whatever works, I say! 

[petey twofinger]

so i tried building a dual buffer with a tl02 and it didnt do a darned thing , but tomorrow i am going to fully cut in an amz mossfet boost . it says " moderately high impedance " on his site , and the specs on the amp say 48k to 65k input impedance ... not sure , but i did run the amz on it and got it very loud without that pop . the only real test is taking the rig out and running it when we go to jam so ... i am so hoping this works out .

i blew the chip on my kids amp , with the wrong power supply , dont ask ... i knew i was being an idiot , i walked away , then convinced myself i knew what i was doing but it wasnt the amp module i was thinking of , only twelve volts so the 19 volts killed the chip - ow did that not smell pleasant , for a long time !!. i am going to try to remove the old chip tomorrow and install the replacement i ordered . everything was going smooth for a while there , oh well . such is life . and at least i am able to TRY and fix it before replacing it . worst case scenario its like 25 for a whole new board and the chip was 6 bux shipped so .... live and learn i guess . more monkey time with the new drum machine , then i am guessing the weather will turn and its back inside for line in time with a new digital mixing board and a rds3.6 for loops . i have my work cut out for me

thanks for your help man .