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[IN STOCK] L-1 Quad VC EQ. Eurorack. (Mouser cart p.4)
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page Previous  1, 2, 3, 4, 5, 6 [all]
Author [IN STOCK] L-1 Quad VC EQ. Eurorack. (Mouser cart p.4)
Revok
resynthesize wrote:
anyone have a good source for axial 4.7n polystyrene caps in the U.S.? trying to avoid the overseas waiting game...


smallbear
L-1
https://eu.mouser.com/ProductDetail/Xicon/23PW247?qs=LLoUvApQnRSgj8Kqc cfvGA%3d%3d
resynthesize
L-1 wrote:
https://eu.mouser.com/ProductDetail/Xicon/23PW247?qs=LLoUvApQnRSgj8Kqc cfvGA%3d%3d


I saw these before, but they have radial leads. can i squeeze them or should I continue the hunt for axial?
resynthesize
Revok wrote:
resynthesize wrote:
anyone have a good source for axial 4.7n polystyrene caps in the U.S.? trying to avoid the overseas waiting game...


smallbear


unfortunately no 4.7n at small bear d'oh!
Revok
The 0.0047uF are the same as 4.7nF.

Here's a site you can reference for switching from uF to nF or pF: http://www.justradios.com/uFnFpF.html

Or you can multiply or divide by 1000.
uF*1000=nF
nF*1000=pF

pF/1000=nF
nF/1000=uF

edit:had the math backwards
resynthesize
Revok wrote:
The 0.0047uF are the same as 4.7nF.

Here's a site you can reference for switching from uF to nF or pF: http://www.justradios.com/uFnFpF.html

Or you can multiply or divide by 1000.
uF*1000=nF
nF*1000=pF

pF/1000=nF
nF/1000=uF

edit:had the math backwards


ah, thanks! just ordered some from smallbear.
resynthesize
would appreciate some help with this build. channels 1 and 2 are not affecting the audio at all, e.g. what I patch to the input is what I hear on the output. channel 3 and channel 4 have a sort of resonancy effect, but they sound like they're oscillating at a barely audible high frequency.

things i have done so far:

* checked orientation of all polarized components and IC
* checked for shorts from +12/-12 to ground
* inspected and touched up a few suspicious solder joints
* took a bunch of high-res pics for inspection (attached)

I don't see any obvious issues, so I have a few questions:

1) I substituted 1n4001 diodes instead of 1n4004 since that's what I had around. Is this OK?
2) The partslist for PCB2[1] lists 2 more 1n4004 diodes, but I don't see any place for them on the PCB. Is this a documentation error or did I overlook placement?
3) I bought OPA2604s from this reverb store[2], any chance they are fake or bad? I have some TL072s lying around, I was thinking of swapping them out to test.

Any other ideas? Any/all help much appreciated! very frustrating


[1]: http://l-1.su/images/VCEQ/L-1_QUAD_VC_EQ_PCB2_Parts_list.pdf
[2]: https://reverb.com/item/2412187-10-x-burr-brown-opa2604ap-opa2604-free -shipping-new-authentic-usa-seller
L-1
resynthesize

At first - all installed OPA2604 are fake.

Solve this at first. You can try another dual opamps if don't have OPA2604.

These are original OPA2604 in new (bigger logo) and old designs. As you can see - the circle must be not flat but 3D, and the logo must be drawn dual lines.

resynthesize
L-1 wrote:
resynthesize

At first - all installed OPA2604 are fake.

Solve this at first. You can try another dual opamps if don't have OPA2604.


I just tried swapping the OPA2604s out for TL072s. Same problem Dead Banana

Here's a quick video showing what I'm hearing: https://youtu.be/5QgItxuOvlA . it's just cellphone audio so you may have to turn up the volume to hear the high-pitched oscillation at the beginning. What else could be wrong?

edit: also swapped out all the TL074s, same behavior.
L-1
resynthesize

You didn't installed standoffs. They are needed for ground connection between boards (no ground pins at the connectors).

Build looks very clean! Good job!
resynthesize
L-1 wrote:
resynthesize

You didn't installed standoffs. They are needed for ground connection between boards (no ground pins at the connectors).

Build looks very clean! Good job!


duh! I thought I was being smart by testing everything before final assembly.

With the standoffs installed, channels 3 and 4 are working great, but channels 1 and 2 are still dead. By "dead", I mean that with no input, setting the self-osc dipswitches produce no output, and if I patch something to the input, I hear it at the output but the sound isn't affected by the channels at all.

What can I check? Is it possible some of the ICs were destroyed by having no ground path?

thanks for your guidance as always Alex.
Addam
You can always try the ol' IC switcheroo (put the op amps for channel 3 into channel 1, for instance). If you're worried about things getting fried you can check the voltages at the IC sockets with the ICs removed (being careful not to short anything). Having 2 working channels makes troubleshooting "nice" (not really) because you can compare the working side vs the non-working (with a multimeter or by probing with an oscilloscope if you have one).

A bit of a longshot but you can try doing a simple continuity test between the connectors bridging PCBs 1 and 2 when they're connected (with power off, of course)
L-1
resynthesize

Common for cannels 1 and 2 are THAT300, DG412 on this side. Check them and everything around. Try to swap them with another side.

If no selfoscillation when switches are on, or oscillation too quiet, possiple to reduce resistors values in resonance loops. There are 24K99. Installing 24K usually helps. I marked them red.

NS4W
the opamps are out of stock at mouser, could you point to another source? help
resynthesize
L-1 wrote:
resynthesize

Common for cannels 1 and 2 are THAT300, DG412 on this side. Check them and everything around. Try to swap them with another side.



Swapped the THAT300 and DG412s and reflowed all IC pins, no difference :(

I got out the scope and started probing around. I see a sine at the bottom pin of every 4.7n cap, so I assume that the 24.99k resistors are fine and oscillation is starting somewhere.

Here's the difference I noticed between the two pairs of channels:

For the working pair of channels, the DG412 pins 2 and 15 are outputting a sine, while on the non-working channels there is no/minimal voltage.

For the middle and top row of OPAs, I have a sine out at pin 1 of all ICs. For the bottom row,
for the bottom row, sine out of pin 7 of channel 4, pin 1 of channel 3, and no sines out of any pin for channels 1/2.

Does this help narrow down what else I could check?
L-1
NS4W

Buy from Banzai https://www.banzaimusic.com/OPA2604.html

or use another dual opamps.

resynthesize

If you have a sine at 1-st pin of 2-nd channel middle row OPA. That means you have it at pins 11 and 14 of the DG412 switch because they connected direct. But you have no signal at switch output (15 or 10 pins for 2-nd channel). Something around the switch then.
resynthesize
L-1 wrote:


If you have a sine at 1-st pin of 2-nd channel middle row OPA. That means you have it at pins 11 and 14 of the DG412 switch because they connected direct. But you have no signal at switch output (15 or 10 pins for 2-nd channel). Something around the switch then.


Thanks. I spent about 30 minutes going over everything around the switch. Finally, I pulled out the switch IC and happened to notice this:



The eagle-eyed among you will observe that the pin 5 socket is missing the little gold ring that makes contact with the IC leg. I replaced the IC and soldered that leg in and now everything is working. This was a first for me, will check sockets in the future before installing!
L-1
resynthesize

Good you solved that all !
NS4W
Under the THAT300P socket there are two areas with pads that looks like spots for smd-chips, shall I ignore those?
hmmm.....

Just want to make sure before I solder the socket and cover the area.
Multi Grooves
I think I'll get into building this but I'd like to know about upgrades/options.

1) Aside from the mica caps, are there any other upgrades/alternatives for this build?

2) Is there any discernible difference between the op amps (OPA2604 & TL072) or is there anything else recommended?
Multi Grooves
Gentle bump*
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