Boosting output

I’ve added speakers to my two Shutis as well as my Shruthi-1 CEM and I’ve just hooked them up with by attaching wires to either the output pads or jack posts. This was initially just for testing shrut(h)is with test tone, no amp but liked it so much I installed them in the case. The two Shrutis really kick out the jams but I noticed the CEM Shruthi-1 has a lower gain. I also noticed that the SSM output to the mixer is similar to the CEM output as far as level goes. While the SMR-4 is comparable to the Shrutis.
How can I increase the output of the the CEM and SSM boards? Could I achieve this by lowering the resistance at R12 on the CEM board? I notice the schematics feed the output line back to pin 6 so I don’t think I’d want to mess with R16 or 17 unless the change was logically compensated for and I’m not sure how to figure that out.

CEM3379: increase R16
SSM2044: increase R9, or decrease R25 / R37 (but they should have the same value if you want the HPF to work).

That was the direct answer to the question you asked - how to get a higher voltage at the output. Now, the TL074 is not a power amp and it won’t source/sink much current. Try it, but you won’t go very far if you want to drive those 8 ohm speakers… Why not picking one of those cheap LM386 1W amp kits?

I thought about the kits or using little gem schematics but I just need a little boost I think. I’m using some 5 ohm telephone speakers (the speaker phone speaker). We recycle extensively at work and there were a bunch of these dissected. I grabbed at em. I also used a different pattern for the speaker holes on the CEM and SSM boxes so it might just be a matter of filing out the holes larger.
Thank you so much for your response.

how about increasing the output of the SMR4 board?

(my shruthi-1’s output is quieter than most of my other synths)

Do you have a scope to check the levels on your unit? Because it’s above 2V pp and it’s already too high for some audio interfaces! Actually I have lowered the level a bit on the mkII to make it work on audio interfaces which have less headroom…

Anyway it’s the 68k resistor. Higher value = more gain.

Hi Pichenettes! The output level of my just built Dual SVF Shruthi-1 is noticeably lower than my 2 SMR-4 Shruthi-1. Is it a “normal” behavior ? Is there some resistors to change ?

Thanks for your help.

Hédi K.

The SMR-4 was terribly hot – modular-level hot – and it actually distorted on some soundcard even at minimal gain.

The best would be to scale down the volume on the SMR4, by replacing the 68k resistor on the output amp by a 33k or 22k one. You’ll get the same level as on the dual SVF, which is a more reasonable one.

Thanks for your quick answer. As the output level of the Dual SVF seems to be lower than the SMR4’s one, I will simply adjust the input levels on my soundcard for each of my Shruthis.

Hédi K.