Need more volume from my Drum Machine

Thread Starter

apprenticemart2

Joined May 7, 2013
67
Hi All,

I have an old Clef drum machine and I would like it to be louder so I can power it from a 5 volt supply instead of 6 from batteries, and then I can more easily get a PIC in there so I can trigger the sounds over Midi.(it's not particularly loud in its stock configuration anyway)
As the voltage drops the volume drops so I would like to be able to boost it back up again or even better, beyond the original specifications.

I have experimented by changing the values of R116 and R117 but I really need more gains than I'm getting and I would like to know what else I can try.

Thanks.
Martin
 

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#12

Joined Nov 30, 2010
18,224
Try an amplifier.

You are working with a circuit designed to deliver .00021 amps RMS, maximum.
You want to change the voltage supply so it can only deliver 83% of that and not achieve the inevitable results. You are barking up the wrong tree. "Loud" does not come from amplifiers rated in microamps.
 

Thread Starter

apprenticemart2

Joined May 7, 2013
67
Thanks for your reply.

I am firing this into a pre-amp but I have to really crank the gain up to +50dB and beyond and run the accent control on every drum hit to get the volume up.

I have managed to get some gains by changing resistor values in R116 and R117. That gives me about +8db more than it did before. I was just wondering if there can be any more improvements.

The original specification was probably for inputs into a tape recorder which I believe are much more sensitive than modern equipment.

The stronger a signal I can get before amplification the better.

Thanks
Martin
 

tubeguy

Joined Nov 3, 2012
1,157
Exactly what model preamp and type of input are you using?
This unit will work best into a high impedance input, not a low impedance mic input. Do you have a guitar, bass or keyboard amp to try it with?
 

#12

Joined Nov 30, 2010
18,224
One limit is IC13b. What is its part number?
You could change R117 to just enough resistance to keep the chip from smoking if the wires get shorted but you would forfeit the tone control.
I have an amp that I designed for a Rhodes piano that was only producing millivolts of output and Bill Marsden just posted an amplifier that would do the same job in the "Completed Projects" forum.
 

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Thread Starter

apprenticemart2

Joined May 7, 2013
67
That's a thought for now tubeguy, I do have a Mackie onyx 400F which does have a guitar input on the front, I will give it a try.

Thanks #12. IC13b is an LM2904. I will look at R117 again and look over your amp design.

Thanks everyone.
Martin
 

#12

Joined Nov 30, 2010
18,224
The LM2904 can not deliver the bottom one volt or the top 1.5 volts from its supply. With a 5 volt supply, it can deliver about 2.5V peak to peak, if it is properly centered. Then you're going to lose half that in the tone control and the volume control.

The chips' current limit is about 20 milliamps. Theoretically, it could drive a 62 ohm resistor, but it can still only drive 2.5 volts peak to peak. You might lower R117 to 100 ohms and get better results with a low impedance amplifier, but a high impedance pre-amp is a sure thing.

Either one of the pre-amps I presented will work on this, but I think Bill's design is better because it has more head room, and drums have a lot of dynamic range.
 
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