MN3005 Dirtbag: huge earpercing hiss and huge distortion

[gtr2]

I can get you some of my chip voltages later tonight.

Josh

[gtr2]

I just saw you are using a road rage to power.  What IC are you using for the charge pump?

Josh

[djaaz]

LT1054
Pin 1 is off the board.

LT1054SCP

No "A".

[madbean]

The distortion makes me think the problem resides with R11 and R12. This sets the compression level out of the NE570, and the video sounds like it is amplifying it too much. While I've never had this happen using two 68k's at 15v, it might be worth trying a lower value here such as 47k or 33k. It's a pain, but I would try socekting those two to test this out. Keep in mind though that the signal will be quite loud out of the compressor portion anyway---one other thing to try is a larger value for R42, such as 20k.

I don't suggest doing the mods from the v3205....those are not tested with the MN3005, and in reality they should not be necessary.

[gtr2]

Ok the charge pump was worth a try.    I was thinking maybe you were not getting enough mA for the circuit but you should have no problem with the LT1054.

Here are my voltages in an effort to help you and those in the future.  The input voltage is 14.75V.  I omitted IC7 since thats the modulation section.

Josh

IC1
1) 7.14
2) 7.14
3) 7.12
4) 0
5) 7.07
6) 7.14
7) 7.14
8 ) 14.74

IC2
1) 1.18
2) 1.78
3) 1.78
4) 0
5) 1.78
6) 1.78
7) 10.12
8 ) 1.78
9) 1.78
10) 7.73
11) 6.02
12) 1.78
13) 14.74
14) 1.78
15) 1.78
16) 0

IC3
1) 7.14
2) 7.14
3) 7.12
4) 0
5) 7.12
6) 7.14
7) 7.14
8 ) 14.74

IC4
1) 14.7
2) 7.29
3) 6.28
4) 6.27
5) 0
6) 7.29
7) 7.82
8 ) 0

IC5
1) 14.7
2) 7.29
3) 7.33
4) 7.33
5) 0
6) 7.29
7) 8.94
8 ) 0

IC6
1) 8.95
2) 8.83
3) 8.8
4) 0
5) 6.96
6) 6.98
7) 6.83
8 ) 14.74

IC8
1) 7.14
2) 7.14
3) 7.12
4) 0
5) 7.66
6) 7.73
7) 7.73
8 ) 14.74

[djaaz]

Thanks Josh!

There's not so much difference with my IC2's voltage except maybe for pin 16.

From there i will first wait for the ne570 i ordered to arrive, just in case.
And then, if nothing changes, as Brian suggested, socket R11&R12 to try different values.
Thanks for the help guys, i'll let you know how it goes.

Brian, is there any interest to put the voltages in the build documentation?

[djaaz]

Almost done!
Changed the compander and that was it.

Remaining issues are:

A bit of distortion when the level pot is above the unity gain (not a big deal at all but i would like to increase the level just a tiny bit). I don't know if the TL082 that still is in the circuit for IC8 could be responsible. Will replace it with a TL072.

I still have some bit of distortion on the repeat when i hit the string stronger than my daughter would. I should maybe play with R11 & R12 as Brian suggested?

The delay is definitely shorter than my memory toy:
I will change the delay pot that measured 97k to a bigger value.
Maybe try to socket C41 and try to increase it a bit. I measured a perfect 240pf, i could test with 250pf?

But the thing sounds incredibly promising. Thanks for your help guys!

[madbean]

Remember: some distortion is part of the character of the vintage DMM. That level pot is a huge boost, so naturally if you start cranking it up, it's going to start breaking up.

Glad the compander issue was resolved.

Try a larger value for the 240pF as you mentioned. 270pF would be the most common value above 240.

[djaaz]

Thanks Brian.
I have some 250pf capacitors lying around, will try them first.
I don't mind having dirt in there, it's exactly what i'm seeking.
I'll have a real DMM to compare tomorrow and will recheck how the original behave, but if i want to improve this distortion, tweaking R11 & R12 values are the way to go?

I will also build the V3205 version now that i'm done with this one and if you still have some boards.

[gtr2]

Excellent news!

Josh

[djaaz]

Yes, i'm quite happy and i'm going to start working on the enclosure.
I'm gonna try to etch this one.

Still have some thing to enhance, still have some hiss for instance.

But i'll shoot a better video before boxing it.

Thanks for your help, guys.

[gtr2]

I'd be willing to bet it will be quiet once you box it.  I look forward to the build report!

Josh