Boss - PN-2 Tremolo/Pan  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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raindog
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Post by raindog »

guts only...
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Warpeggio
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Post by Warpeggio »

I recently came upon this and wanted to share with the group. If anyone can suggest replacements for the hard-to-find transistors and ICs, I'd love to hear them.
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lolbou
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Post by lolbou »

Which one do you need to change, and why?
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

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roseblood11
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Post by roseblood11 »

That pedal never got much attention, as it's "just another Boss pedal", but it sounds really great and has a wide range of sounds. It's really worth cloning it.

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Warpeggio
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Post by Warpeggio »

I'm pretty new to this, other than some previous training with amateur radio, and *barely* making a working soldering project in Basic Electronics 101. I'm starting with some other projects, but i'm also researching tremolo design, and wanted to compare the PN-2 with the TR-2, vs the old Univibe LDR style trems. I see a PN-2 on Noel Gallagher's board, although i'm not convinced he's picked it for it's unique tone.

That said, i'm at the point where i'm looking at this design, and trying to really understand the transistors and ICs. I think i've found some candidates, but just wanted to discuss with the group to see if there's any lessons from the TR-2 that can be carried over to the PN-2, especially regarding the transistors. I'm not sure which of these are being used because they WERE common at the time, and which are being used in an explicit way for specific characteristics.

2SC3378GR, or 2SC2240GR, NPN Transistor
Looks like the 2SC2240 still has decent availability through some suppliers.

2SC2458GR, Small Signal NPN Transistor
I'm having a hard time finding this one - some other projects suggested possibly substituting a BC549.

2SA1048GR, PNP Transistor
Seems to be generally available.

2SK184GR, or 2SK117GR, JFET
184 and 117 both seem to be out of production, but an old post in another forum suggested LSK170. I suppose other *170 FETs from other manufacturers would be close in equivalence?

1SK118Y, JFET
Can't find this one. I assume i simply need to find a JFET with similar performance profile?

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Warpeggio
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Post by Warpeggio »

Okay, the 2SC2458 NPN, that's being used as a flip-flop right? So if i substitute it, i just need to keep the performance of the flip-flop in mind. (I'm kind of just keeping notes on this as I go through the research, I hope that's OK.)

The next thing i'm looking at is the pair of 2SC3378 that's next to the output jacks. What's going on here? The TR-2 uses, coincidentally, a 2SC2458 in this position. Is this just a little boost?

And then 2SK184GR next to the input jack, that circuit is your standard boss buffer, right?

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Warpeggio
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Post by Warpeggio »

Slowly realizing that i've just figured out the most boring parts of the circuit. :slap:

I wanted to just link to this other thread that talks about alternatives for the M5207L01 VCA: http://www.edaboard.com/thread261853.html

As far as I can tell, the VCA is the real moneymaker in this chip. 0v on lin1 is completely attenuated out1, 1v on lin1 is near unity. Seems like it should be fairly easy to find a modern equivalent, maybe THAT 2181 or 2002 (haven't looked that closely yet).

BA728N and M5238L make up the LFO. BA728N also gets used for the 5.5v supply - i think that's what 2SA1048GR is up to as well.

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Warpeggio
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Post by Warpeggio »

Spent more time learning about this schem today. I'll continue to make assertions, in the spirit of Cunningham's Law.

I previously mentioned BA728N, it's actually doing 4.5v supply, where 2SA1048GR does 5.5v.

M5218P is the peanut butter to M5207L01's jelly: The VCA output is current signal, so an op amp is used as a "transimpedance amplifier" to convert back to usable voltage signal. Signal hits the 2SK118Y switching FET, then the final output boost on 2SC3378GR (i still don't know what this is called, it's always engaged with the buffer), and on to the jack from there.

I'm going to take a look at the LFO next, although i don't think i'll learn anything there that will surprise this group. I see 4 op-amps, with a 5th involved in wave shaping, which reminds me of the Craig Anderton Tremolo, but i don't know if the network is the same.

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Nocentelli
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Post by Nocentelli »

Bit of a bump - I'd be really interested in making a modern/available parts workalike
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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jayrope
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Post by jayrope »

Using a PN-2 since 25 years. The same pedal. It's literally indestructable.
However, in 2019 i am wondering if there is a much simpler way just to build an autopan?
Any hints appreciated.

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madscijrjr
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Post by madscijrjr »

I'd also be interested in plans for an auto-pan pedal.
Did you ever find one?

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Nocentelli
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Post by Nocentelli »

madscijrjr wrote: 24 Jan 2024, 18:23 I'd also be interested in plans for an auto-pan pedal.
Did you ever find one?
This is the only DIY-friendly schematic i've found: It's the 4ms stereo panneur
schematic (1).pdf
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modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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madscijrjr
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Post by madscijrjr »

Thanks!

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