Boss - PN-2 Tremolo/Pan  [schematic]

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

Boss - PN-2 Tremolo/Pan  [schematic]

Postby Warpeggio » 27 Sep 2016, 02:46

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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Re: Boss - PN-2 Tremolo/Pan

Postby lolbou » 27 Sep 2016, 10:54

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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Re: Boss - PN-2 Tremolo/Pan

Postby roseblood11 » 27 Sep 2016, 14:17

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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Re: Boss - PN-2 Tremolo/Pan

Postby Warpeggio » 27 Sep 2016, 18:15

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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Re: Boss - PN-2 Tremolo/Pan

Postby Warpeggio » 28 Sep 2016, 01:37

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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Re: Boss - PN-2 Tremolo/Pan

Postby Warpeggio » 28 Sep 2016, 14:56

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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Re: Boss - PN-2 Tremolo/Pan

Postby Warpeggio » 29 Sep 2016, 02:51

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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Re: Boss - PN-2 Tremolo/Pan

Postby Nocentelli » 09 Nov 2017, 21:47

Bit of a bump - I'd be really interested in making a modern/available parts workalike
mmolteratx wrote:absolutely zero commercial use allowed. If I find anyone selling these, I'll fly to your house and kick you in the nads. And you may or may not find yourself in trouble.
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