100m-ish Audio Delay with V3205SD - step by step (5 to 8V)

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ixtern
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100m-ish Audio Delay with V3205SD - step by step (5 to 8V)

Post by ixtern » Thu Nov 07, 2019 3:16 am

Recently I've built two 100m-ish Audio Delay Modules from Mark Graves. One with pretty standard MN3007, one with Coolaudio's V3205SD. The second one was little harder so I want to document it here.
Supply voltage was chosen 5V (-5V to the chip GND, 0V to the chip Vdd) as it was recommended by the datasheet and many other modules using this BBD.

Changes in the PCB (from build doc) needed to use V3205 chip in 100m-ish module was little unclear to me so I had to draw my own diagram for part of schematic with BBD chip.
Image
Also BBD output resistors (R53 and R54) were showed incorrectly to be connected to the ground while they should be connected to the lowest potential (BBD chip GND = -5V).
Correct connection for the R53 and R54 is showed on the photo:
Image

Here are the signals taken from the oscilloscope in the different module points.

LFO output, max frequency:
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LFO output, min frequency:
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Clock output, max frequency, no BBD chip (clock signal is deformed with BBD chip due to large input capacitance):
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Clock output, min frequency, no BBD chip:
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Input signal (sine 1 kHz from TH Maximus VCO):
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Signal at U2a pin1 (Op Amp output):
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Signal at Q3 emitter:
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Signal at Q4 emitter (BBD in, without chip):
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BBD chip was installed at this point.
Signal at BBD input (chip's pin 7):
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Signal at BBD output 1(chip's pin 3):
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Signal at BBD output 2(chip's pin 4):
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TP1 signal before regulation:
Image
TP1 signal after regulation with PR2:
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Next input signal was changed to the low frequency (100Hz) saw to better see the delay.
BBD input (yellow) and output (blue) signals at minimum delay. Delay is visible as a phase difference. Signals may be distorted due to oscilloscope AC coupling here and oscilloscope input capacitance.
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Module input and output signals without delay effect:
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Module input and output signals with delay effect:
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Photos of the assembled modules with MN3007 and V3205 (BC550 and BC560 transistors with different pin allocation than original ones were used):
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Image

V3205SD was bought from the supplier claiming to have it directly from the Coolaudio.
Last edited by ixtern on Fri Nov 08, 2019 1:23 pm, edited 1 time in total.

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fitzgreyve
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Post by fitzgreyve » Thu Nov 07, 2019 4:27 am

Many thanks for posting this! I'm glad that you got it working.

I did make some initial tests with a couple of (supposed) V3205D's, but both failed. I tried to run them at just below the maximum CololAudio specified supply of 8V. I suspect that they may have been chinese copies, and only OK running at the more common stompbox 5V supply.

Would you object if I added your diagram etc. to the end of the build doc (with credit)?

How are noise levels with the V3205 ?
Under developement:
- "Muse"
---------------------------------------
https://fitzgreyve2.blogspot.com/

ixtern
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Posts: 203
Joined: Mon Jan 22, 2018 4:34 am

Post by ixtern » Thu Nov 07, 2019 4:34 am

fitzgreyve wrote:Many thanks for posting this! I'm glad that you got it working.

I did make some initial tests with a couple of (supposed) V3205D's, but both failed. I tried to run them at just below the maximum CololAudio specified supply of 8V. I suspect that they may have been chinese copies, and only OK running at the more common stompbox 5V supply.

Would you object if I added your diagram etc. to the end of the build doc (with credit)?

How are noise levels with the V3205 ?
No problem with adding my diagrams to the build doc.
As for noise I didn't checked it yet (I've ended all this work late night yesterday). One thing to be fixed, I think, is that output level is too low (but it is for V3205 and MN3007 also) and may be amplified a little.

ixtern
Common Wiggler
Posts: 203
Joined: Mon Jan 22, 2018 4:34 am

Post by ixtern » Fri Nov 08, 2019 1:22 pm

Today I have tested how V3205SD works with different supply voltages. No problems with voltages up to 8V (max usable supply voltage by datasheet).
Here are the oscilloscope screenshots taken at TP1 (blue: input signal, yellow: TP1).
5V:
Image
6V:
Image
7V:
Image
8V:
Image

Closer look at TP1 signal (8V supply).
Max delay:
Image
Min delay:
Image

Additionally I have take difference in TP1 between good and bad PR3 setting.
Bad PR3 setting:
Image
Good PR3 setting:
Image

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fitzgreyve
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Post by fitzgreyve » Sat Nov 09, 2019 7:21 am

ixtern wrote: One thing to be fixed, I think, is that output level is too low (but it is for V3205 and MN3007 also) and may be amplified a little.
I've used the Roland values (for the MN30xx based circuit).
With 10V p-p input, I'm getting about 15V p-p output.

The output level is determined by R31 - increase it for greater output level.
Ideally C17 then needs to be decreased proportionally.
Under developement:
- "Muse"
---------------------------------------
https://fitzgreyve2.blogspot.com/

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