Boss PH-2 IR3109 Chips removed. Worth repair?

[broomhandle]

while ago I purchased 2 PH-2 from Japan. One working, one needing repair. The 2nd PH-2 had the IR3109 chips removed and 2 LM13700N chips installed. The pedal when plugged in just has a buzz. Engaged or not. I have looked at the board, and I can not see any issues. I do not know where to start to troubleshoot. Or with these chips installed, is it even worth it for a repair? I would like to see it live on..

Or, is there a mod i can do since the original chips are gone. And this 1997 pedal has had a hard life.

[ElectricDruid]

I'd say, "yes, definitely". That didn't used to be the case, but these days Alfa Rpar in Latvia make a clone of the IR3109, the AS3109. It's available in various places:

https://www.ericasynths.lv/shop/ics/voltage-controlled-filter-3109/

https://www.exploding-shed.com/alfa-rpar-as3109-voltage-controlled-filter-vcf/103114PD16

There are other places too - and (full disclosure) I personally have a load of Alfa chips for sale, but not that one.

If you want a direct drop-in replacement for the missing chip, make sure you get the DIP version, not the SOIC. If the board has been mucked about with to make it work with LM13700's, you might still need to alter stuff back to original to get it working.

HTH,
Tom

[broomhandle]

So will the LM13700N chips no way work? What are these chips? And could they possible create the buzz?

I think I need just the 2 chips. Everything else looks exactly like my other PH-2.

[tootsMcgee]

It's hard to tell from the photo but some of the soldering on those chips looks kinda questionable. Are you sure nothing is bridging? That it is buzzing when bypassed implies something else is wrong. Got an audio probe/scope handy to poke around?

I found this schem in another thread...https://lh3.googleusercontent.com/pw/ACtC-3cMQx9_U3qwCyf4KL0os4jJcPt7_AggABv6zCPZuDbfgKVb-FeTBT289mdG4A3KW9OB9eg6LYjimVw29i4N1uWUMA_p6F6l9RrYeyYVR7pVMjvpJLTd5Bz-O3xHxYRWRm80AHfsTquffFYDh-pI4b9Xtg=w1442-h994-no

It looks like bypassed signal chain goes straight down from the tip of IC1, horizontal, then down a bit more to Q2 and then into the other half of IC1. (Both stages are inverting, interesting, dunno why.) So checking after Q1/C4, at the IC2 pins 1-2-3, after Q2, IC1 pins 5-6-7 in bypass mode would be interesting.

Is there any signal at all or is it just like, humming constantly?

[broomhandle]

I would like to know if it works before I buy chips. I do have a audio probe. And yes, buzz/hum constantly effect engaged or not. If I can figure that part out 1st.

agreed: "So checking after Q1/C4, at the IC2 pins 1-2-3, after Q2, IC1 pins 5-6-7 in bypass mode would be interesting."

and attached is a photo of my working "good" 1995 PH-2

[ElectricDruid]

So will the LM13700N chips no way work? What are these chips? And could they possible create the buzz?

No, the '13700 is a dual OTA, whereas the '3109 is a quad OTA, so they're not remotely compatible. You *could* design something very similar using *two* LM13700s to replace each IR3109, but you definitely can't stick a 13700 in a socket designed for a 3109 and expect it to work. It won't.
Might it create a buzz? Possibly.

I think I need just the 2 chips. Everything else looks exactly like my other PH-2.

That sounds pretty promising. It's likely that at some point in its life, someone sold or used the IR3109's to repair something else. For quite a while, these old phasers were the cheapest source of these chips, so if you had a broken SH-101, MC-202, Juno 60, MKS-30 etc synth, you basically had to find one to keep it running.
After that, someone who clearly had no idea what they were doing thought to put 13700's in it instead because they'd read somewhere on the interwebz that the 3109 was an OTA chip.
That's my guess as to its history, anyway!

[broomhandle]

So will the LM13700N chips no way work? What are these chips? And could they possible create the buzz?

No, the '13700 is a dual OTA, whereas the '3109 is a quad OTA, so they're not remotely compatible. You *could* design something very similar using *two* LM13700s to replace each IR3109, but you definitely can't stick a 13700 in a socket designed for a 3109 and expect it to work. It won't.
Might it create a buzz? Possibly.

I think I need just the 2 chips. Everything else looks exactly like my other PH-2.

That sounds pretty promising. It's likely that at some point in its life, someone sold or used the IR3109's to repair something else. For quite a while, these old phasers were the cheapest source of these chips, so if you had a broken SH-101, MC-202, Juno 60, MKS-30 etc synth, you basically had to find one to keep it running.
After that, someone who clearly had no idea what they were doing thought to put 13700's in it instead because they'd read somewhere on the interwebz that the 3109 was an OTA chip.
That's my guess as to its history, anyway!

Sounds good, I think I want to work on the buzz, pass though 1st then replace the chips. I think I will start by checking where the chips were replaced to see if any points are touching. Other than that I am not sure.

[Mark Hammer]

Tom is spot on.  Sounds like whoever tried to install the 13700s still had a lot to learn.

The PH-2 is a kind of general-purpose phaser.  It has 8 swept allpass stages (using a pair of 3109s, and 4 fixed allpass stages to add more phase shift to what is being produced in the OTAs.  It seems to be arranged in two banks of 6 stages (i.e., 4 swept, plus 2 fixed, times 2). My own personal bias is that the sweet spot for guitar seems to be at 6 stages (with 8 stages as the runner-up).  So 12 stages may be great for running a string synth through, but won't do more for a guitar than 6 will.

What that suggests is that it might be possible to install ONE 3109, and just use the "mode" for that particular set of 6 stages. The schematic is a wee bit hard to follow, and there's no iron-clad guarantees, but it kind of looks like this may be possible.

The other thing I wonder is how difficult it would be to simply toggle-bypass the fixed stages.  That could provide 4 or 6 stages for one mode, and 8, 10, or 12 for the other mode.

[broomhandle]

Update: I am dumb. I cleaned the AC jack and I have bypass. So, LED is off. I engaged the pedal. No effect. But the LED stays on. (even if I disengage the effect)

To me it sounds like everything should be good if I swap the chips to the correct ones. I compared the board to my good PH-2. Everything looks the same.

[broomhandle]

Update: Still dumb. I can not believe it. Last pin. Pad was barely on. Maybe previous owner. Can anybody verify, I think a wire from this pin to this pin of the chip. Ugh.. it was all good until the last pin.

[tootsMcgee]

I would like to know if it works before I buy chips. I do have a audio probe. And yes, buzz/hum constantly effect engaged or not. If I can figure that part out 1st.

agreed: "So checking after Q1/C4, at the IC2 pins 1-2-3, after Q2, IC1 pins 5-6-7 in bypass mode would be interesting."

and attached is a photo of my working "good" 1995 PH-2

Looking at these pics, it looks like that is the correct place to run a jumper.

I don't know if there's space but I'd almost be tempted to put in a socket to avoid having to solder/unsolder big DIP packages...then again you shouldn't need to be swapping things out once it's all in place...

Good luck, fingers crossed!

[broomhandle]

I would like to know if it works before I buy chips. I do have a audio probe. And yes, buzz/hum constantly effect engaged or not. If I can figure that part out 1st.

agreed: "So checking after Q1/C4, at the IC2 pins 1-2-3, after Q2, IC1 pins 5-6-7 in bypass mode would be interesting."

and attached is a photo of my working "good" 1995 PH-2

Looking at these pics, it looks like that is the correct place to run a jumper.

I don't know if there's space but I'd almost be tempted to put in a socket to avoid having to solder/unsolder big DIP packages...then again you shouldn't need to be swapping things out once it's all in place...

Good luck, fingers crossed!

I might do that if there is space. I just want to make sure that is the correct place to jump a wire.

[tootsMcgee]

It looks right to me, but hopefully someone else can chime in.

Dry-check the sockets if you do go that route: put them in the board with the chips in them and make sure the thing goes together. Don't be like me and put in a socket and then find out it's too tall for the pedal lol

[ElectricDruid]

It looks right to me, but hopefully someone else can chime in.

Yes, it looks right to me too. The pad has peeled up/off. It happens on old boards all the time if you're not *extremely* careful, and sometimes even when you are, which is a bit frustrating!

If you're going to fit sockets, *defintely* do a dry fit to make sure there's space before soldering anything.

[broomhandle]

Update: new chips in, the pedal is back. I did use a socket for the chips. The only issue is I feel the volume is lower than my original PH-2. Its is a quiet signal. Still usable, but I can tell a difference. Any thoughts?

[ElectricDruid]

Hey, good work! That's great news.

Is it only quieter when the effect is on, or is it quieter all the time? How's the balance between the effect off level and the effect on level?

[Mark Hammer]

The dilemma faced by effects that use passing/blocking of a 2nd signal path to produce or cancel an "effect" is that anything which results in notches or momentary/varying drops in amplitude, can reduce the apparent overall volume of the output, resulting in effect/bypass volume differences.  It's a whole lot easier to fix at the mixer stage when using true bypass.

Just out of curiosity, is the problematic volume drop evident in BOTH modes, and/or when the resonance is turned up?

[broomhandle]

Hey, good work! That's great news.

Is it only quieter when the effect is on, or is it quieter all the time? How's the balance between the effect off level and the effect on level?

No, standard volume though. It feels lower volume, and it is less bass. It also feels that the original, the phase lasts longer. The new chips it fades faster. "Same settings"

[crane]

I can't comment on your problem BUT - I am from Latvia and I have studied EE in Latvia about 15 years ago. Most of the professors were still from the soviet times and told us how ICs were "copied" from western ones at those times - usually it was not a 1 to 1 clone and involved some cost cutting which made the IC worse than the original part. Not saying this is the case - could as well be. Could as well be just an entertaining story for you all.

Hey, good work! That's great news.

Is it only quieter when the effect is on, or is it quieter all the time? How's the balance between the effect off level and the effect on level?

No, standard volume though. It feels lower volume, and it is less bass. It also feels that the original, the phase lasts longer. The new chips it fades faster. "Same settings"

[ElectricDruid]

I can't comment on your problem BUT - I am from Latvia and I have studied EE in Latvia about 15 years ago. Most of the professors were still from the soviet times and told us how ICs were "copied" from western ones at those times - usually it was not a 1 to 1 clone and involved some cost cutting which made the IC worse than the original part. Not saying this is the case - could as well be. Could as well be just an entertaining story for you all.

While this is possible, I think it's fairly unlikely. That was necessary during the soviet era because no-one was sharing the information, but the situation is different today. The reason we suddenly have so many synth chips available again is because the patents have lapsed, so the information on how the originals were created is available for anyone with the know-how and facilities. You don't have to reverse-engineer it any longer.
Some of Alfa's chips are actually *better* than the originals. Their CA3080 clone, the AS3080, is as good as the CA3080A "selected" variant in all respects, and better than it in several other parameters. That's the benefit of modern processes over what they were using in the 70s.