Guys,
My dirtbag is still on my test rig. While biasing and playing with the gain trimmer, i have so much hiss coming out of it that i don't think boxing it is not a good idea.
Any idea on how to troubleshoot on this one? I haven't probed it yet. Will do that as a next step.
In the meanwhile, if any of you have a brilliant idea...
I spent a lot of time trying to bias as well as possible. In the end, i have an awful delay:
1. The pedal distort the dry part.
2. The repeats distorts and are very dirty after the second repeat.
3. The delay is short (i measured 480 ms but somehow it sounds shorter, don't ask me). It's definitely way shorter than my memory toy.
Any idea what i should look at first?
Would a video or sound sample help?
At which point does the hiss get introduced? Have you tried checking it out with an audio probe?
It's not about just the hiss anymore.
I built some kind of ugly fuzz / delay pedal. I will send some sound sample, that will be worth a thousand words.
And i will use the audio probe.
As the repeats during the bias did not sound as bad as the pedal output, i'm guessing the distortion comes after.
I spent an hour toying with the audio probe.
I have hiss very early in the circuit going out of IC1 & increasing.
The mod pot varies the frequencies of the hiss from pot full counter clockwise: "grave", full clock "treble".
Now the distortion:
Clean almost all along the circuit and then out of the NE570 everything distorts.
Faulty chip or should i check & post the voltage?
Check the components around the compander...
So some more probing & some more finding. But no changes yet:
VC= 15,1 V regulated with a road rage.
Blend pot, full clock.
Level pot: i have distortion on the delay as soon as the level exceed the first third of its course.
IC8A: I have some distortion at Pin1 (not the same), replaced it with TL082 (less noise & no more distortion)
NE570: Signal enters clean at pins 5, 6, 14 & 15. Distortion on pin 10&11.
Here's the voltage for NE570:
1: 1 16: 1,7
2: 1,8 15: 2,45
3: 1,8 14: 2,43
4: 0 13: 15,1
5: 1,8 12: 1,43
6: 1,8 11: 6,6
7: 9,94 10: 8,5
8: 1,83 9: 1,8
Kind of lost here. Looks like the thing distorts from a lot of different places. With the level pot at a low level, i can pinpoint the main source of distortion on the ne570, but i feel like it's not the only issue i have.
Any help is welcome!
Two videos:
First one if in & out of the circuit & the output of the second mn3005.
Second is delay in & out of ne570
Anyone with a working circuit willing to share its voltage?
No one?
C27 is a bit more than 3,9n (around 4,1). i'll change that if i can find another one in my cap stash.
(http://djaaz.free.fr/DSC00039.JPG)
The ear piercing hiss is the sound you get when you audio probe BBD's. The distorted dry signal is certainly a problem.
C27 at 3n9 is fine, don't change it.
What are pickups are you running in to the delay to test it?
Josh
Thanks for your answer! I was feeling a bit lonely.
The hiss is present at output as well. Of course, not as loud but certainly enough to be a showstopper.
I use humbuckers. The signal when the blend pot is at zero does not distorts easily. Clean does not break until the level pot is way up the clock.
I changed C27 to a value closer to 3,9n without change as expected.
I played a bit with R42 (11k). R42 connects PIN 12 to the ground on the schematic.
I removed R42 & moved a bit R62. I thought there could be a bridge there cause the layout is tight.
I tried the circuit without R42 and i had just the delay without distortion. I socketed the side of 42 that is connected to the compander & hooked a 100k pot from there to ground.
I had very different behavior. I could not find a suitable value but i could get rid of some distortion. At least on the delay. Nothing pretty though, nothing usable.
Running out of idea..
Anyone have any idea on where to go from there?
I'm thinking of trying another ne570 and from there socket all components around the compander and try different values, but i can't help thinking there must something more obvious to check first.
It's early and I've got to get the family off for the day but I will take a look at this a little later this morning and try to offer some help.
Thanks Brian, I ordered a new ne570 just in case but i'm pretty sure there's more problem there than the compander.
I took a look at the mods for the V3205 versions. I was wondering if some of these changes could help.
But then again, why my build is acting so weird when there are so many working ones out there.
I'm pretty sure, there's something messed up with my build, i just can't find it by myself.
What about the chip voltage?
I can get you some of my chip voltages later tonight.
Josh
I just saw you are using a road rage to power. What IC are you using for the charge pump?
Josh
LT1054
Pin 1 is off the board.
LT1054SCP
No "A".
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.
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
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?
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!
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.
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.
Excellent news!
Josh
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.
I'd be willing to bet it will be quiet once you box it. I look forward to the build report!
Josh