Forat's MPC60 Output Boost Mod

Anybody have this official $250 Forat mod? Or did it themselves?

A few old threads discussed it, and there were some schematics floating around at some point, long since gone. Supposedly involved changing some resistors to boost the output of all assignable and main outs from -10dB to +4dB (?).

I don't want to do it, but shed some light on this modification if you can so I can document it. MPC60 outputs are pretty weak compared to the MPC3000 and my other gear, but the headphone output on the MPC60II is nice and hot. Any explanation for this oddity?

I know you can simply use gain or other external gear to boost output, I'm interested in an internal modification, how to do it, and any positive or negative outcomes.

viewtopic.php?f=4&t=68382

Sounds like it has something to do with it being an old 80s machine... I notice some (or most?) old 80s fx racks have input impedances designed for guitar (ie: very hot since guitars are quiet) while at the same time having the outputs designed for guitar amps (ie: very quiet). I've modded one of my old 80s fx racks to lessen the input impedance and raise the output. So maybe when they designed the mpc60, it was a trend/standard to perhaps have similar input impedances and output gains as other gear of its' time? ..then maybe as years progressed, into the late 80s, 90s and beyond, manufacturers/designers started to use line-levels more and more, as more and more people were using electronic keyboards/instruments/gear/fx (and not just guitars anymore) with outboard gear and mixers.

fooddude wrote:Sounds like it has something to do with it being an old 80s machine...
.

This has nothing to do with it.
In the 80's there were plenty of line level fx and now 30 years later you still get plenty of guitar level fx.

fooddude wrote:So maybe when they designed the mpc60, it was a trend/standard to perhaps have similar input impedances and output gains as other gear of its' time? .

That'll be why there's an input impedance switch on the back of the MPC60.

Regarding the output, in some of the threads about the output mod people mention it changes the frequency response of the outputs slightly. Maybe the default setting is the sweet spot between volume and frequency response.

Also, the MPC60 stores it's sounds in a 12 bit format.
The other MPCs are 16 bit giving an extra 24db volume.

Acid Mitch wrote:

fooddude wrote:So maybe when they designed the mpc60, it was a trend/standard to perhaps have similar input impedances and output gains as other gear of its' time? .

That'll be why there's an input impedance switch on the back of the MPC60.

There isn't an input impedance switch on the back of the MPC60, it is a gain switch.

Acid Mitch wrote:Regarding the output, in some of the threads about the output mod people mention it changes the frequency response of the outputs slightly. Maybe the default setting is the sweet spot between volume and frequency response.

Yes, it would change the value of the resistors in the negative feedback loop of the M5220P opamp, thereby changing the gain of the opamp, and moving the signal range within the available response and response curve of the opamp, therefore probably changing the frequency response.

Acid Mitch wrote:Also, the MPC60 stores it's sounds in a 12 bit format.
The other MPCs are 16 bit giving an extra 24db volume.

The difference between 12 bit and 16 bit volume outputs does really not apply to comparing a 12 bit MPC to a 16 bit MPC, differences in volume are due to overall circuit design, not differences in bit depth.

SimonInAustralia wrote:There isn't an input impedance switch on the back of the MPC60, it is a gain switch.

I presumed it was to switch between mic/instrument/line level.
What is the idea behind having the gain switch and adjustable input level on the sampling page if both are doing the same thing ?

Acid Mitch wrote:What is the idea behind having the gain switch and adjustable input level on the sampling page if both are doing the same thing ?

The switch gives you 3 different gain ranges, the sampling page gives you finer gain setting within those 3 main gain ranges.

SimonInAustralia wrote:The switch gives you 3 different gain ranges, the sampling page gives you finer gain setting within those 3 main gain ranges.

What are the gain ranges intended to be used with ?
I thought there only was 2 line levels, -10 and +4 .
Doesn't make much sense me when they could have done it all from the sampling page without the switch.

Acid Mitch wrote:What are the gain ranges intended to be used with ?
I thought there only was 2 line levels, -10 and +4 .
Doesn't make much sense me when they could have done it all from the sampling page without the switch.

I don't think the ranges are specific to -10 or +4 line levels.

More just to give a larger gain range than what the input opamps allow, or to keep the signal within the sweet spot of the opamp response over that larger gain range.


From the manual...

10. Now, let's set the record level.

First, set the GAIN switch on the rear panel. For most applications, use the LO setting.

Move the cursor to the RECORD LEVEL field and set the record level by adjusting the DATA CONTROL and watching the audio levelmeter, displayed to the right of the METER field.

Set the record level so that the meter goes as far to the right as possible when the sound plays, but not into the clipping region (indicated by "!!" to the right of the meter, if full level is exceeded).

If the meter does not go high enough with a record level of 99, move the GAIN switch to MID or HIGH.

LO = 0db
MID = +20 (Line level amp)
HI = +40dB (mostly used for microphone)

Most of the time if LO setting isn't sufficient , the issue comes from the source signal

Acid Mitch wrote:Also, the MPC60 stores it's sounds in a 12 bit format.
The other MPCs are 16 bit giving an extra 24db volume.

As you say the MPC60 stores it's sounds in a 12 bit format, but it's AD converters are 16 bit.

That 12 bit format is non-linear and compressed, so not the same as a linear 12 bit format, therefore not a straight forward comparison to linear 16 bit, and not necessarily a 24dB difference as it might be if comparing linear 12 bit to linear 16 bit.

daddymac wrote:LO = 0db
MID = +20 (Line level amp)
HI = +40dB (mostly used for microphone)

To be exact...

Record input sensitivity:

(HI gain) -65dBm, 45kΩ
(MID gain) -45dBm, 45kΩ
(LO gain) -27dBm, 45kΩ

Acid Mitch wrote:

fooddude wrote:Sounds like it has something to do with it being an old 80s machine...
.

This has nothing to do with it.
In the 80's there were plenty of line level fx and now 30 years later you still get plenty of guitar level fx.

Yes, true, of course there's still plenty of guitar level fx today; but those are pedals. I was referring to a studio-style rack-mount aesthetic.

Today, it is rare to see a guitar-level studio-rack; but in the early 80s and before that, there were plenty of vintage studio-rack fx that were guitar-level similar to pedals (even some synths..ie: the tx81z had notoriously low output gains while its' headphone output was much louder (sounds like low output gain designed for a guitar amp to me)). Most, if not all, fx racks today/currently are line-level (even some guitar pedals have a switch to go either guitar or line level these days). But, a lot of pre-84' fx racks, had guitar-levels (ie: boss, roland, korg too perhaps (never tried the old korgs)), making them difficult to use on an outboard mixer setup with loud synths/drum machines/mixers (resulting in easy to clip/distort fx rack inputs while at the same time had very low outputs - fx loops aux sends sound like cr@p if turned even halfway; but was really needed since the outputs were so low and were hardly audible, etc., etc.)

Resurrecting an old thread, but I'm thinking this mod would successfully allow for CV/Gate/Trigger signals to be recognized by modular gear. I've heard people saying they've gotten this to work but it almost *never* works for me and only semi-reliably works if the sampled signal is clipping, and/or the output is boosted through a preamp. So this might be a great solution if anyone was to do that.

Couldn’t u just take one of the midi’s outputs and stick it in a midi-to-cv/gate converter? Saves a bit of a hassle i guess? Greets

Sure, but being able to modify Gate and CV samples using the sample editor, as well as 16 levels for CV, is much much better and more fun imo.