Tuning the Dandy Horse

[tuckster]

Hi everyone,

I finished this beast but the effects are a bit weak.
The tuning did not went as expected by the manual:

Frequency

C43 empty
C45 22p

Pad 2 with Filter Matrix selected 513KHz
Pad 2 with Slap Back selected 124KHz


pad 3 bias 2 - distortion on beginning and end and very littel in between
pad 4 bias 1 - silence in the beginning, slight distortion then no distortion than again slight distortion then nothing
pad 3 cancel - high pitch all the way
pad 5 6 gain2 - little to no effect
pad 6 gain 1 - little to no effect
FDBK - no oscillation on output possible

Voltage reading
Input: 9,02
15V: 14,94
Pad1: 7,47

IC1
7,48
7,48
7,41
0
7,75
7,75
14,93

IC2
1,08
0
1,8
0
1,85
1,85
0
1,83
1,83
7,09
7,09
1,85
14,92
1,83
1,83
0,75

IC3
14,91
7,43
6,35
0
0
7,43
6,68
6,68

IC4
14,91
0
8,20
0
0
7,40
8,54
8,31

IC5
7,53
7,49
7,41
0
7,53
7,53
7,53
14,93

IC6
7,46
7,44
7,53
7,53
7,53
0
0
0
2,65
0
2,65
8,19
7,39
8,19
7,44
14,93

IC7
7,47
7,4
7,4
7,47
7,47
0
0
0
2,65
13,59
0
7,47
7,47
7,47
7,48
14,93

IC8
7,47
7,47
7,4
14,93
7,47
7,47
7,47
7,48
7,47
7,47
0
7,48
7,48
6,5va

IC9
0
7,47
4,49
0
14,94
14,94
13,54
14,94

IC10
14,94
7,43
7,46
7,42
7,43
7,4
7,46
0
7,44
7,43
7,46
7,4
0
7,46
7,43
0

IC11
14,94
0
17,02

IC12
7,43
7,45
13,53
0
7,44
0
0
0
7,46
0
7,45
7,46
7,46
14,94

IC13
1,38
4,87
0
0
0
2,54
1,4
9,0

The part values have been checked, everything is ok.

Diffrences to the original BOM:
- IC2 is a AS571D smt on a breakout board
- Feedback is a Rev Log type pot

Do you have any suggestions for me to read/do to start another tuning attempt?

[ElectricDruid]

Here's the schematics (we always need a copy of the schematics):

https://lectric-fx.com/wp-content/uploads/2017/03/Dandy-Horse-V.1.0.pdf

The first thing that I'd say is that any circuit that has seven trimmers has a billion incorrect settings. It's asking for trouble!

[aelling]

I've build two of these and I gave up trying to tune it by ear/multimeter, I had to get my dad's sine wave generator and oscilloscope (and help) to do it done, a lot easier.
I had to use a 27p for C45, I also had to use Multi-turn trimpots for the Clock (10K) and Feedback (25K) to get it working properly.

[ElectricDruid]

Did you use MN3207 or MN3007?

[tuckster]

I use MN3007, the jumpers are correct.

[duck_arse]

looking in Druid's build docs, I see a proto/demo/sample built board photo. after much, much, much, much cross referencing, I see that the caps in the C22 and C24 positions are swapped for value. it might be worth checking the board connections with a meter to see whether it is their build error or a silkscreen error, or something else in error. documentation, who needs it.

[aelling]

looking in Druid's build docs, I see a proto/demo/sample built board photo. after much, much, much, much cross referencing, I see that the caps in the C22 and C24 positions are swapped for value. it might be worth checking the board connections with a meter to see whether it is their build error or a silkscreen error, or something else in error. documentation, who needs it.

This is documented in the the BOM sheet. https://docs.google.com/spreadsheets/d/12ozJqCEt-dr_zskvg_MIQ4osyvUtQ0RAFumcial4PoU/edit#gid=943216157

[duck_arse]

documented? really? rather cryptic - I didn't/don't see it. why they spread the needed info over some many places?

[aelling]

Well, "documented" was not the right wording, but at least it was acknowledged mistakes were made.

BTW, tuckster, you can get the frequency down closer to 500kHz on the filter matrix setting, by adding a small cap to C43 (just like C45).

[ElectricDruid]

looking in Druid's build docs

Hey, it's nothing to do with me! I only linked to it!

[antonis]

looking in Druid's build docs

Hey, it's nothing to do with me! I only linked to it!

You should mind out more of what you link Tom or Stephen will slap on your carelessly typing fingers.. 

[tuckster]

First of all:

Thank you guys! It works.

I should have linked the docs in the beginning... And in my opinion the documentation is pretty straight forward.
The capacitors that I use now are the same as before. I tried a few combinations of a lot of different values but the nearest I could get to 500 and was the same as before

c42 22p
C43 empty
c44 68p
C45 22p

Pad 2 with Filter Matrix selected 493KHz was 513KHz
Pad 2 with Slap Back selected 125,3KHz was 124KHz

The only step where I noticed a difference to the adjustment of the trim pots before was this:
pad 5 & 6 gain2 - little to no effect but I noticed that on pad 6 the signal was a bit distorted. Only when turned gain2 almost down it got less distorted (in my opinion...) which seems to be the crucial point.
Even pad 3 cancel has the same behavior as before "high pitch all the way".

Maybe it was the few KHz difference maybe the gain2 trim pot...
I need an oscilloscope :-)

[eh la bas ma]

I managed to calibrate it without oscilloscope, but I spent some time on it and tried new settings several times.

You can get different possibilities according to the trimmers settings. A modulation effect more or less prominent, with various textures.

Even with an oscillo, I am not sure I would be entirely sastisfied with the calibration. Shaping the modulation slowly, untill you really like it, is probably at least just as good, and maybe even better. It requires more time working on the build, but it's supposed to be fun.

I would recommend an oscilloscope if you'd want to build a lot of them fast and all at once.

I remember last time I tried, I noticed the modulation was more discrete, "musical", and less background noises, if I didn't set the volume difference too high with the Gain 1 trimmer. *Almost* the same level i'd say...

"Adjust the Gain1 trimmer until the level at test pad 6 is about 10% higher than at test pad 5."

10% isn't much... unnoticeable i guess.

I also recall that on my build, there was a really narrow sweetspot on Bias1. It was quite important to get it right for a cleaner modulation.

Pad 2 with Filter Matrix selected 493KHz was 513KHz
Pad 2 with Slap Back selected 125,3KHz was 124KHz

Maybe it was the few KHz difference maybe the gain2 trim pot...

I don't think it's important at all to get the exact number. You have a good approximation and it should be perfectly ok.

[tuckster]

I revisited the little fella because I noticed that the modulation sounds like a square wave.
I tuned it again acording to the manual. It's not that bad but in slow settings it's annoying.
What could be the cause of it?