Boss TR-2 and M5207L01

[Mark Hammer]

A buddy in my language class loaned me his TR-2 Tremolo pedal this afternoon.  I'm pretty much set for tremolos, but was curious and thought I'd take a peek inside and see what made it tick (well, throb is more like it; we don't really *like* ticking in our tremolos, do we?).

The construction inside is rather atypical in some ways.  I haven't taken apart a lot of Boss pedals, but was surprised to see small plastic chassis-mount pots instead of PC-mount ones.  The more typical row-of-wires at the far end of the board was largely absent, with a couple of clusters of connecting wires instead.

Op-amps were a trio of BA15218N SIPs.  These are Rohm equivalents for the Mitsubishi M5218L dual op-amps that Roland/Boss seems to like a lot.  The "brains" behind the pedal would seem to be the M5207L01 chip, though.  I dug around for info, but couldn't find datasheets anywhere.  The most I can find out so far is that it is a dual VCA chip.  There is another chip numbered M5207 but the L01 version is the one we want.  The non-L01 version is some sort of digital melody chip which obviously isn't the one we want, plus it doesn't have nearly enough pins.  

Whether the M5207L01 is an equivalent for another better-known chip or something wholly unique, I can't tell.   Initially, I thought the dual VCA might have been used in a Small Stone or Ross Phaser-like LFO circuit, but then it dawned on me that the VCA was the control element and the LFO was likely your standard dual op-amp LFO, or some more exotic version thereof.

In any event, if anyone has a better way to find out more about this particular chip (M5207), I'd be appreciative.  In view of the possibility of CA3080's (and possibly variants) disappearing from shelves, finding another candidate to work) with would be nice.  Certainly something that subs directly for a 13600 or 13700, but in SIP form, would be terrific for making layouts easier.  Most folks here work with either DIPs or transistors, and probably have little experience with the way that SIPs let you choose between sticking the passive components on this side of the chip or the other.  Dual-VCAs in SIP form, "greenie" caps, and vertically mounted resistors would let you stick 8 stages of phase shift in a 1590B with little difficulty.  Now THERE's an idea.

[Arno van der Heijden]

Here's the schematic:

http://img71.exs.cx/img71/8981/boss-TR2-tremolo.jpg

[Mark Hammer]

Thanks.

Oddly enough, the schematic suggests the chip is an electronic attenuator.  I wonder if that's true.

[puretube]

...never trust a schematic on the web...
it does look trustworthy to me, though.

have you seen the way Dr. Moog used resistor arrays (vertical)
in his Moogerfooger?
the topology of phase-shifters cry for the use of them!

[Mark Hammer]

Yup.  I've seen some inside shots.  A real work of art.  Now try and imagine that same circuit using SIPs for the dual OTAs.  A thing of beauty.

[Nick123]

It (just) a very linear VCA.
L01 version is for 1Vmax and L05 for 5Vmax.
Send me your e-mail address and I can send you a
factory pdf file.

[puretube]

free information block:

[Mark Hammer]

Thanks to both Ton and Nick for directing me to the relevant files.  Actually, both chips seems very interesting, and seem to lend themselves to guitar/instrument-related stuff quite readily.

For instance, the M5207L *is*, essentially, a dual voltage-controlled attenuator.  If you had a single control linked o the two gain/attenuation cells, you could simultaneously vary the amount of drive in two different clipping circuits, either for cascaded gain stages or for panning between two qualitatively different clippers.  For that matter, use a panning control for a dual input mixer, and the other pot to adjust drive for the two clippers and you could have a bit of channel A driven heavily, mixed with lightly-driven channel B in larger proportion, and other sorts of combos.  Other possibilities abound.

Thanks guys.

[puretube]

thanks f.t. mail, Nick:

that`s an interesting IC (a pity, those M*tsub*shi chips arent available, and all those datasheets are next to impossible to find...).

the circuit could probably be re-designed with discretes,
but then the fun of having it readily at hand in a SIL-pack is gone...

[analogguru]

This chip also was used in many DJ-mixing consoles for the talkover function.
If you need a datasheet, I can send by mail...>300k

analogguru

[mrsage]

It's super easy to mod them for a volume pot, too. Some settings have a perceived volume drop, and if you add a volume pot in place of one of the resistors, you can counteract that.

And if you upgrade some of the signal path components, you can reduce noise and have a halfway decent clean boost.

http://tinypic.com/23vehu

It's essentially what Keeley does, except I used a separate alpha pot instead of a dual pot. And I didn't change the caps to metal film.