My Tourbus finally working fine, with clear delay and all knobs working properly after debugging some mistakes.
But I found that when the delay knob is over 70%, high-pitched whine noise comes out.
The pitch of the noise changes when increasing delay time.
It sounds exactly like so-called clock noise or antialiasing noise.
So it cannot be eliminated? I tried to adjust the balance trim pot but no change at all.
Help plz.
The voltage reads are (seems normal except IC3 pin 1 2 3 voltage higher)
IC1 4558
1 -7.59
2 -7.58
3 -7.56
4 -15.07
5 -7.51
6 -7.58
7 -7.59
8 0
IC2 NE570
1 -14.11
2 -13.25
3 -13.25
4 -15.07
5 -13.26
6 -13.24
7 -5.08
8 -13.26
9 -13.26
10 -7.17
11 -8.85
12 -13.26
13 0
14 -13.26
15 -13.25
16 -14.17
IC3 4558
1 -7.58
2 -7.58
3 -7.56
4 -14.98
5 -7.01
6 -7.08
7 -7.08
8 0
| IC4 4558
1 varies
2 -7.19
3 -6.9 to -8
4 -15.16
5 varies
6 -6.9 to -8
7 varies
8 0
IC5 CD4047
1 -7.73
2 -7.34
3 -7.3
4 0
5 0
6 0
7 -15.16
8 -15.16
9 -15.16
10 -7.59
11 -7.59
12 -15.19
13 -7.72
14 0
IC6 4558
1 -6.57
2 -3.35
3 -3.47
4 -14.98
5 -7.56
6 -7.58
7 -7.58
8 0
| IC7 MN3005
1 0
2 -7.6
3 -10.2
4 -10.21
5 -15.16
6 -7.59
7 7.84
8 -14.19
IC8 4558
1 -7.58
2 -7.58
3 -7.55
4 -14.96
5 -8.56
6 -8.58
7 -8.02
8 0
IC9 MN3005
1 0
2 -7.59
3 -10.38
4 -10.34
5 -15.16
6 -7.59
7 -8.6
8 -14.19
|
Just right away, something looks off. Pin 4 of your 4558s should have zero power (its ground)and pin 8 should have the highest power measurement. How sure are you about your measurements?
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This one has the negative power supply. So pin 4 is VD or VC, depending on the IC, and pin 8 is GND.
Some whine is "normal". Can you measure the clock frequency or the delay time?
That would help identify if you are above the common value of 550 ms (as in the DMM).
The tolerances of the components can also affect this, as in the original DMM.
The filters are quite on the limit of the clock frequency, so that variations in components could led to higher cut frequencies, leaving more of the whine in the remaining signal.
Check if you used the right resistors and caps at the filters located after the second MN3005.
Is there any off-board wiring? how good is it?
Is the pedal in a grounded box, or still on your desk?
Depending on how much delay time you are getting, some whine is always expected. Unless you cut a lot of delay time.
The MN3005 are only advertised for 205 ms, aren't they? Two would give you 410 ms without whine. The DMM goes way into whine territory. Without being as dark as other delays, it also lets more noise trough.
I am not sure if changing the calibration (how much signal is amplified where) improves this.
Quote from: thomasha on August 14, 2022, 04:18:44 PM
This one has the negative power supply. So pin 4 is VD or VC, depending on the IC, and pin 8 is GND.
Learned something new, thank you for that!
Thomasha, the max delay time is about 480ms, and no whine from about 360ms.
I will check filter resistors and caps values.
There is no off-board wiring direct from the 18v 1A adapter and the pedal is in a grounded box.
One strange thing to me is when the blend knob turned to 100% (no dry signal) then the whine decreased and disappear completely.
Is what normally happens for clock noise?
I have limited knowledge about electronics, so hard to grasp how the clock noise affects the dry signal and not the delay signal.
Yeah, it is fixed!
I changed the wiring from true-bypass to stock wiring then the noise is completely gone.
I am not sure if the true-bypass wiring is flawed or just me.
Anyway, the noise seems to bleed from the dry signal ground, so suspected the wiring, and bam!
Thanks for the help.
Tourbus was a way harder project for me, but really rewarding. Fantastic delay!
Glad to hear you got it sorted out.
Interesting,
it is probably the external wiring catching up some noise. Positioning is very important. I bet a shielded wire would cure it.
But, glad you found it!