Schematic for Ibanez Soundtank CR-5?

[Chill]

A friend wants mods to his Ibanez Soundtank CR-5 Crunchy Rhythm.  A quick google search did not turn the schematic up.  A quick forum search turned up some posts which suggested it's similar to the DS-10 Distortion Charger but it was not entirely clear to me what the differences are.

Do you have the schematic, or do you know where it is posted online?  Thanks.

[JHS]

http://www.8bitsindgenug.net/mn0bit.htm

JHS

[Dirk_Hendrik]

it's similar to the DS-10 Distortion Charger but it was not entirely clear to me what the differences are.

Indeed it seems to be for the input stage (pre-clipping diodes)  Fun since it seems to be the first time (other than a TS) that I see a Maxon design leverage into a soundtank (non-maxon).
And again, as is the case for a DS10 it seems they've made some kind of discrete opamp design driving the clipping diodes.

Plenty of moddabilities in there. Succes

[Chill]

Thanks for the link.

I think I get most of the schematic, but I have a few questions:

TR3, 4, 5 look like they have some kind of negative feedback thing going on.  TR3 and 4 are PNP with TR3 set up as a gain block, TR4 acting as a buffer for the injection of the NFB from NPN TR5's collector.  As the distortion pot wiper nears TR5's collector, more signal is fed back, and the whole unit has a lower gain; as the distortion pot wiper nears R17-C8, less signal is fed back and the unit has a higher gain.  Correct?  Do R15-R18-C8 set an RC knee as in the TS9?

IC1B is set for low gain and recovers some volume after the diode clippers and also provides a low impedance input to the tone control.  TR6 looks like some kind of voltage or current source to keep IC1B under control.  True?  Does TR6 also alter the frequency response of IC1B?

And the tone control is a simple RC filter with VR2, R25, and C15

[Chill]

b-dum *BUMP*   

[Rob Strand]

TR3, 4, 5 basically form an opamp, made of discrete transistors,  where:  the output is at TR5's collector, the - input is TR4's base and the + input is TR3's base.  If you imagine plugging an opamp into the circuit you should see how the feedback arrangement isn't much different to other distortion units using opamps.   The feedback arrangement isn't quite the same as the MXR Distortion plus or the Tube screamer but functionally it's more like the MXR.  The 1-2 terminals of the pot form the feedback resistor and the 2-3 terminals form the other feedback resistor "to ground", R17 is in series with that resistor.  The circuit does have an RC roll-off, but the roll-off is variable like the MXR due to Pot 2-3 + R17.  The cap is large so the cut-off is quite low, almost achieving nothing.

The second opamp is for EQ.  It boosts the bass using a gyrator circuit formed by TR6.