ARP 1601 clone Build Thread

[oscarthesquirrel]

Hi..quick question about the new 1601 clone I've just received (fully built) from Synthcube. For some reason, the clock out voltage appears to be approx 6.4V and won't drive my ARP2600 (which needs +10v or higher)...I'd assumed that a 1601 clone would pump out enough volts to drive the thing it was designed to work with. It works fine with my modular gear (Doepfer ADSRs).

I can use a CV.OCD gate booster to get it trigger the ADSR via S/H gate in on the 2600 (which is the way the 1601 should connect with the 2600 originally to send the gat signal to trigger the 2600 envelope). And just to say my 2600 gate S/H works fine via internal hard patch and when patched from the outputs of VCOs 1,2,3 (in LFO mode so that I can actually hear it trigger).

I've checked the clock output on my 'scope and it responds OK to the PWM, the clock FM also works as it should.

Puzzled really - should the 1601 clock out signal be 10V or higher ? None of the gate buses appear to output anything over 6.4V either.

Appreciate any guidance

Thx

[Jim the Oldbie]

Hmm... my 1601 clone was putting out close to 14V on those outputs last I checked. Have you measured your power supply rail voltages?

[oscarthesquirrel]

Hi Jim - I've received this one fully assembled and haven't disassembled it yet to check..it came from the US and I'm here in Malaysia hooked up to good ol' 240V. I'm using the 100V-240V switching PSU that was supplied with the 1601 (and which outputs 15.13V - I've just checked).

[Jim the Oldbie]

If you do pop the hood to check the rails, remember to measure the wall wart voltage coming in again, with the unit turned on. It might measure differently under load. I think it should be 12 VDC, although a bit higher is no problem.

[Kipling]

If you have one of the latest Rev 6a PCBs then all the gate and clock outputs have individual trimmers along the top of the board to set the output voltage. They are all labelled so you should be able to adjust them all to suit. For ARP gear including the TTSH you will need to adjust these to maximum for the full 14V output.

[oscarthesquirrel]

Thanks Kipling - that may well be the issue....perhaps it was set for Eurorack rather than an original 2600....

Really appreciate the prompt advice.

THX !

[oscarthesquirrel]

@Kipling just looked at some pics of the board and I can see 6 trimmers for R222, R226, R206, R207, R217, R218

I've also got a copy of the original 1601 service manual and these trimmers would be for Quantiser CV V/oct, A&B offset and A&B Mod adjustment Where would the gate and clock output trimers be located / or what is their board designation pls ?

Sorry if I'm being clueless, but I can't locate any gate/clock trimmers in the original service manual

[Kipling]

Thanks Kipling - that may well be the issue....perhaps it was set for Eurorack rather than an original 2600....

Really appreciate the prompt advice.

THX !

More likely those trimmers were left mid-position as they generally are from the factory.

[oscarthesquirrel]

Is there a pic or diagram of the Rev 6a board so that I can identify the relevant trimmers pls ?

[Kipling]

There are six of them along to top edge of the PCB. Each is marked with its function. I’ll sort out a picture ASAP.

[oscarthesquirrel]

Thanks - appreciate it !

[elmegil]

Hi..quick question about the new 1601 clone I've just received (fully built) from Synthcube. For some reason, the clock out voltage appears to be approx 6.4V and won't drive my ARP2600 (which needs +10v or higher)...I'd assumed that a 1601 clone would pump out enough volts to drive the thing it was designed to work with. It works fine with my modular gear (Doepfer ADSRs).

I can use a CV.OCD gate booster to get it trigger the ADSR via S/H gate in on the 2600 (which is the way the 1601 should connect with the 2600 originally to send the gat signal to trigger the 2600 envelope). And just to say my 2600 gate S/H works fine via internal hard patch and when patched from the outputs of VCOs 1,2,3 (in LFO mode so that I can actually hear it trigger).

I've checked the clock output on my 'scope and it responds OK to the PWM, the clock FM also works as it should.

Puzzled really - should the 1601 clock out signal be 10V or higher ? None of the gate buses appear to output anything over 6.4V either.

Appreciate any guidance

Thx

Hi Steve, I'm Pete, and I'm the guy who built that one. First let me apologize that you don't have the right gate output levels. I have discussed this with Synthcube already and I will commit to you here as well I will do whatever I can to help resolve this.

I've built a few different ones for them in recent months, of two different PCB versions.

If you have the version with the trimmers, that is very likely the issue, as John pointed out, I believe I left them set at the trimmer's default mid position.

Here's a photo of the area of the PCB in question, though it's not a populated one:

edit (wrong photo first time)

IMG_3277.JPG

If you don't have that version, instead of the trimmers, there will be 3 resistors next to each of those transistors along the top edge. A high resolution, well-lit photo of that area of the PCB would let me confirm the resistors at least appear to be correct.

Again, I apologize that this isn't working for you "out of the box". Let me know what you see about which version you have, and we'll take it from there.

Pete

[Kipling]

An enlargement of the PCB layout for the Rev 6a board with the six trimmers highlighted

V-out trimmers.JPG

[oscarthesquirrel]

Hi Steve, I'm Pete, and I'm the guy who built that one. First let me apologize that you don't have the right gate output levels. I have discussed this with Synthcube already and I will commit to you here as well I will do whatever I can to help resolve this.

HI Pete...thanks for your help....

I'll peek under the lid after my morning coffee and shower to see what lurks there...trimmers (I'm hoping), otherwise I'll break out the Nikon D700 and 105mm macro and peer at the resistors... I've built a fair few modules in my time (incl a Klee), so I'm pretty OK with calibrating things (and desoldering if and when necessary). If I've got the trimmer version I'll hook the 1601 up to the 'scope and adjust the levels accordingly.

I'll post an update later this am.

Cheers
Steve

[Jim the Oldbie]

Aha! It's all about them version #s, heh. (Mine's a V5.)

Sorry for lowering the S/N ratio here.

[oscarthesquirrel]

Tada...V6a board and a few trimmer twists later I'm a happy boy...

Gates 1,2,3 Pos 1, Clocked gate out and Clock out all doing what they do best...

Thanks to everyone for their prompt and courteous guidance.

Steve

[elmegil]

Tada...V6a board and a few trimmer twists later I'm a happy boy...

Gates 1,2,3 Pos 1, Clocked gate out and Clock out all doing what they do best...

Thanks to everyone for their prompt and courteous guidance.

Steve

I'm glad you were able to sort it

[Kipling]

[Kipling]

Note that these six trimmers are not in the original ARP design so do not appear in the service manual. I added them to make the 1601 clone more eurorack-friendly where gate/clock voltages of 14V could be damaging.

[oscarthesquirrel]

Note that these six trimmers are not in the original ARP design so do not appear in the service manual. I added them to make the 1601 clone more eurorack-friendly where gate/clock voltages of 14V could be damaging.

Its super-helpful to have those trimmers ! I'm sure there are Eurorack modules out there that wouldn't like a 14V thump and its makes the clone 1601 totally Eurorack friendly to have them. However, I've already got 3xA-155s and a Klee in my system, so the 1601 stays paired with the 2600.

[uwe]

i'm building this to go with my ttsh. thanks for all the hard work you guys poured into this! i finally sourced all the ICs and finished the build.

the quantizer is giving me some trouble. i have the sequencer stopped and step 1 active. the quantizer A output range is 0-2V, but bounces around quite a bit when i move the slider. it looks like it dips to 0V and then comes back to where the slider is set. it also changes notes without slider movement irregularly every 20 clock cycles or so. the note change seems to happen only when the slider is set <50%. the unquantized output goes from 0-10V.

quantizer output B has a different issue. the slider at 100% gives me 2V and approaches 1V when i lower it, but it suddenly drops to 0V when i reach 50%.

i'm still struggling with those issues. the only fault i can find is that I have no output on TP17, which should be one of the counters (Q5) from the Z25 CD4024. When I scope this it looks like Q4 lines up with the reset cycle so it makes sense that Q5 would never trigger. Does this mean I have issues with the reset circuit or the clock? The clock cycle is also twice as long while the reset is happening.
I replaced the CD4024 anyway (twice), but no luck.

here are the scope shots:
clock (purple) and RESET (yellow)
clock (purple) and Q4 (yellow)

[elmegil]

i'm still struggling with those issues. the only fault i can find is that I have no output on TP17, which should be one of the counters (Q5) from the Z25 CD4024. When I scope this it looks like Q4 lines up with the reset cycle so it makes sense that Q5 would never trigger. Does this mean I have issues with the reset circuit or the clock? The clock cycle is also twice as long while the reset is happening.
I replaced the CD4024 anyway (twice), but no luck.

here are the scope shots:
clock (purple) and RESET (yellow)
clock (purple) and Q4 (yellow)

It's not clear to me which thing you're calling the clock. The behavior you're showing/describing looks like the inverse of TP13?

[elmegil]

BTW have you walked through the service manual test points? It would be helpful to know what each of the test points 11 through 21 look like.

[KSS]

i'm still struggling with those issues.

Sounds like your staircase is missing a few steps. Check the matched resistors for good soldering and a clean PCB. The current shift is probably okay since you're reporting "20 clock" and that shifts every 2.
But check Z25 as its the clk for the staircase
Get a scope on that staircase!

The next place to look is the comparator reading the staircase.
After that, the input and output switches alternating AB into the comparator and out of the quantizer.

But it sounds most ike the staircase is wonky. Or the reading of it, if the staircase itself looks solid on the scope.

[uwe]

It's not clear to me which thing you're calling the clock. The behavior you're showing/describing looks like the inverse of TP13?

Sorry - I'm talking about the clock input (pin 1) to Z25 (CD4024).

BTW have you walked through the service manual test points? It would be helpful to know what each of the test points 11 through 21 look like.

Yes I've done that. All good except TP17 where I have no output at all, and TP19 where the negative pulse from the comparator isn't a square.

TP19 (yellow)

Sounds like your staircase is missing a few steps. Check the matched resistors for good soldering and a clean PCB. The current shift is probably okay since you're reporting "20 clock" and that shifts every 2.
But check Z25 as its the clk for the staircase
Get a scope on that staircase!

The next place to look is the comparator reading the staircase.
After that, the input and output switches alternating AB into the comparator and out of the quantizer.

But it sounds most ike the staircase is wonky. Or the reading of it, if the staircase itself looks solid on the scope.

Are you talking about the scanner output on TP18? It looks fine on the scope I believe.
TP18 (yellow)

I did replace Z25 twice already, although they were from the same batch. I think that Q5/TP17 should be firing but isn't.

As I mentioned above the comparator pulse looks a bit wonky. Looks like that is coming from the Z23 opamp. Could that be faulty? I didn't see anything else of that shape on any of the pins.