MT-2 Opamp swap

[the recluse]

I am getting ready to mod a Boss MT-2 with some of the indyguitarist mods, and was planning on socketing the opamp to allow for some experimentation.  The problem is I cant figure out which opamp to socket as there are four of them.  Looking at the schematic in the the indyguitarist book I am guessing it would be IC3 as that seems to be the input section. Does anyone know offhand which one will have the best effect?

[nico21]

i've just bought the indyguitarist mod book and he does not mention opamp swap 

anyway, have a look at the monte allums mods page, you will see that he changes only one opamp, the IC4 one
you could change them all... for me i'm think i'm goind to swap 1, 2, 4 for opa2134 and IC3 for ne5532

BTW indyguitarist circles the R25 resistor in the picture of the mt-2 pcb but he does not mention R25 in the text any idea ?

[5thumbs]

I've discussed this very topic with Monte after I swapped two of the op amps in my Monte-modded MT-2.  Op amps IC3 and IC4 are in the main signal path (IC3 being the pre-clipping op amp and IC4 being the op amp for boosting specific frequencies to get the "high gain" tone), so he and I agreed those would be the op amps to replace with OPA2134PA op amps.

Op amps IC1 and IC2 are part of the "fancy" tone section on the MT-2, so we thought there might be less impact in swapping those for the BB op amps.  (I didn't try replacing IC1 and IC2, so I can't give you an opinion on those.)

One potential point of interest is that IC3 in my MT-2 was a JRC4558L (in-line version of the JRC4558D), not an MT5218AL like all the schematics on the Internet indicate.  IC1, IC2 and IC4 were all MT5218AL chips, as indicated in the schematics.

Both Monte and I have done the swap of IC3 and IC4 for the OPA2134PA chips.  Monte indicated to me that he liked that combination the best.  I tried a few different op amps in those positions myself (RC4558D, TL072IP) and found that the OPA2134PA really smoothed out the tone and was the best of the lot.  Monte might be able to tell you how other op amps sounded, but I left the OPA2134PA chips in IC3 and IC4 because they were a marked improvement over the JRC4558L and MT5218AL chips they replaced.

I guess I should also mention that my MT-2 was modded using Monte's MT-2 Sustainiac mod prior to the op amp swaps.  I bet the OPA2134PA chips will improve even a stock MT-2 though.

Good luck!

[soulsonic]

BTW indyguitarist circles the R25 resistor in the picture of the mt-2 pcb but he does not mention R25 in the text any idea ?

R25 isn't circled in the copy I'm currently looking at.

And about the opamps... are you guys going to get SIP versions of the ones you've mentioned, or are you going to rig up a DIP to fit in the SIP's space?

[nico21]

my copy is the 607 one charged yesterday...

for opa2134, only dip package existing, so...second solution

[5thumbs]

for opa2134, only dip package existing, so...second solution

Cimarron Technology sells DIP8 to SIL adapter boards (http://www.cimarrontechnology.com/index.asp?PageAction=VIEWPROD&ProdID=34.)  So if you don't feel like making your own adapter board, you can buy theirs if you want to use a DIP8 in your MT-2.

[the recluse]

I ended up socketing IC3 and trying it with an NE5532.  It sounded fine, but I wasn't able to fit the new chip and adapter in the enclosure and close it so I replaced the in line 4558.  I am using the Cimarron Technology adapters, those are great.

[5thumbs]

I ended up socketing IC3 and trying it with an NE5532.  It sounded fine, but I wasn't able to fit the new chip and adapter in the enclosure and close it so I replaced the in line 4558.  I am using the Cimarron Technology adapters, those are great.

You have to bend the Cimarron adapter over to fit it in.  I put some electrical tape over the non-chip side to keep it shorting against other components, then gently bend them over as far as they'll go.  They will fit inside, but you'll have to be careful about doing it.