The ASV is AWESOME (Was: ASV filter problem)

[Synthbuilder]

Q5 looks fine. I'm not so sure about Q6. I wouldn't expect the voltage difference between gate and source to be so different. Maybe try another J201 in Q6?

Tony

[Pav]

Ill try that tomorrow ..thanks.

[Pav]

Well I couldn't bring myself to change th j201 until I did a few more tests...and I found that with the main board powered on on its own, the j201 behaved and I can tune pin 7 u10 to 0.0v.
Reassembled I got the garbage random voltages suggesting bad solder joint .again. I will have to change to rule it out but wanted to ask if that was a valid test on the main board alone..or not indicative without pot and Osc boards?

[Synthbuilder]

Well I couldn't bring myself to change th j201 until I did a few more tests...and I found that with the main board powered on on its own, the j201 behaved and I can tune pin 7 u10 to 0.0v.

Without the pot board in place the filter sits at around two octaves lower than it would do with the pot board connected. So it should be fine to calibrate the filter in this way.

This is odd though - this suggests that Q6 is fine but the pot board is putting out some weird control voltage which prevents the filter from being fully calibrated. But if the other offset trimmer calibrates OK that suggests the pot board is working correctly...

Maybe it is just a bad joint somewhere on the main board and connecting the two boards disturbs that joint and it fails. In this case gently flexing and/or wiggling some components on the main board without the pot board in place should also reveal this problem.

A scope is the best tool to measure these sorts of flip-flop behaviours on a board. Just probe the source of Q6 and see if its stable when you flex/wiggle stuff.

Tony

[Pav]

I am pleased to say i have got F_OFF1 & FOFF_2 calibrated with all boards in place . I re-flowed all the joints on the pot board I could see without removing the panel. I re-flowed CN7 and CN8 SILs on the main board just in case as they deal with filter signals.
I then refitted all together - and hey presto they calibrate to 0.0v

I can continue with rest of calibration now.

Heres a video test

[Purveyor2]

Finished my ASV this weekend and think I have a problem with the filter/main out. The main out seems band passed and significantly lower volume than the mixer out. The filter works, HP swept to HP and BP via switch. Res is nice and squelchy. Individual outs for both Osc and mix out are loud and clear. Sub out is very faint, ground noise overtakes. The main out again is super low volume, lots of ground noise. Volume improved when I cranked the 50k A level trimmer but no sub osc perceptible. Triangle out works fine.

I’ve checked voltages throughout, no issues noted. I’ve scoped the signals and all good into the mixer IC. Oscilloscope ran out of juice, didn’t get to the filter section.

Thought maybe my ribbon on hdr 3 was bad so I tested just the pins connected to a jack. Same results.

Thoughts?
Thanks

[Synthbuilder]

Finished my ASV this weekend and think I have a problem with the filter/main out.

My first thought was that the panel ground is not connected properly. If you are using the four way power headers make sure both pins 2 and 3 on each connector, PSU1 and PSU2, have a connection back to the power supply's 0V. If using the MU connectors then make sure that pins 2 and 3 on the PSU2 header on the main board are linked together with a bit of wire.

Next thing to try is to make sure the ENV2 output is working. Make sure that when there is no jack inserted into the gate socket, the LED is on, and the voltage on ENV2 output is roughly 5V with the ENV2's sustain pot at full. If not, you have a problem with ENV2 circuitry based around U24. This wouldn't explain why the sub out is quiet though - which sounds as though it could be another problem.

Tony

[Purveyor2]

I hadn’t linked the pads on PSU2. All ground noise resolved. Clear and loud sub at individual out. Main out is corrected as well. Sub still seems a little low in the main, though I suspect by design. For instance, if I take either osc to 50% in the mixer with the sub on full can’t really hear anymore although I can tell if I turn the sub off. Probably my aging ears.

Anyway it sounds great. Thank you!

[Synthbuilder]

I hadn’t linked the pads on PSU2. All ground noise resolved.

Sub still seems a little low in the main, though I suspect by design.

The sub is a triangle wave of around 6V peak, so is actually a bigger signal than the other waveforms. However, being a triangle it has few harmonics so is often drowned out by the sawtooths.

It might be worth a check though that it is 6V peak (12V peak to peak) and not something lower. Just measure the output voltage from the sub out.

Tony

[Purveyor2]

Just priced a panel with front panel express using Tony’s fpd file and sending them a Dotcom blank panel. $150 - That can’t be right?!?
Just starting my 5U system, thinking I should just go MOTM...

[Synthbuilder]

Just priced a panel with front panel express using Tony’s fpd file and sending them a Dotcom blank panel. $150 - That can’t be right?!?

Probably is. I think if you send them a blank panel it has to be engraved rather than printed so it'll be twice what the standard printed panel costs. The printed panel works out to be around 78Euros.

Just starting my 5U system, thinking I should just go MOTM...

If you're only planning to make Oakley stuff, then MOTM is the best way to do it. The panels are designed around the MOTM format. While direct conversion to MU looks OK for single width panels, the double width ones look somewhat stretched out.

I have been thinking about making some MU only modules - MU panels with PCBs parallel to the panel like the ASV. But the market is quite small these days so I'm not sure when I'll get on to it.

Tony

[Pav]

Hi,
I have finally realized after a session with eljay listening to his shiney new well calibrated ASV (including the spectral analysis on the filter in Ableton) that i have a problem with my ASV LFO . checking with scope ..its not a +/- 4v sinewave but a +/- 14v toblarone like square wave.
Max Frequency is calibrated ok. Rate is ok.

Looking at schematic - do the diodes in the transistors do the shaping or the LM 1300 ..? just trying to narrow down search for dodgy soldering

[Synthbuilder]

but a +/- 14v toblarone like square wave.
Max Frequency is calibrated ok.

Check that that R86, R87 and R107 are the correct values. (390R, 22K & 15K respectively)

If soldering is at fault then one of the solder pads around R86 or R107 could be the problem.

It's the transistors in the input stage of the LM13700 that do the shaping.

Tony

[Pav]

Actually turned out to be R84 was 4.7k and not 47k. Thats the second 4.7k i had mistakenly put in fro a 47k Better check me bags of each .
That said I now have a beautiful sine wave from LFO OUT

I have to put the vco board back now - to see if the rest still works after pulling it apart twice.

[Purveyor2]

Now that I finally have my panel and racked my system it is apparent that my asv filter is quite ‘weedy’ and cutting. With the filter wide open in LP mode, no res, all modulation off, drone mode - the final out is lower in volume than mix out (normal per manual) but it seems ‘band passed’ with no low end. sub is imperceptible from final out and strong from sub out and mix out. BP/shape switch is working, filter shape knob clearly changes from LP to HP as it should and BP setting sounds like a BP filter.

I get strong full outputs from individual osc outs and sub out. Same with mix out. But when sent through the wide open filter sound quality is lost, not just volume.

I recalibrated per manual, checked a bunch of components around mixer, filter, env2 and all ok except 2.2u caps on pot board where schematic says 1u. I switched them, no change. Reflowed some sections, nothing.

Should I just swap the j201s? Pretty sure I got them from mouser but honestly don’t remember.

[Synthbuilder]

Now that I finally have my panel and racked my system it is apparent that my asv filter is quite ‘weedy’ and cutting.

Is C15 on the main board definitely correct? It should be 680nF but it it's something like 6n8, that could indeed give you the sort of results you're getting.

Tony

[Purveyor2]

Yeah I looked at that one, it’s a wima 680. I’ll swap it out today and see if there’s any change.

[Synthbuilder]

Yeah I looked at that one, it’s a wima 680.

Probably OK then.

What does the VCO 1 to VCA triangle wave sound like? This bypasses the filter entirely and goes direct from the VCO to the VCA circuitry. Turn down all the other waveforms going into the filter and listen only to the triangle wave. Do you lose bass with the triangle wave when you play low notes?

Tony

[Purveyor2]

Tony
The triangle sounds good when played low.
I think I’ll switch out the 680nf and the j201s and see what happens.

[Purveyor2]

It was a 680p
Dropped in an appropriate cap and it’s all good.

Thanks
Stuart