Boss DS-1 (MIJ) build - transistor boost config vs selecting transistors?

[Bucksears]

I recently got my prototype DIY build of a MIJ DS-1 going, and noticed two things:

1) It is a LOT thicker than any post-1994 DS-1 I've owned. So much so that I'm looking at reducing one of the coupling caps to make it a bit leaner. I mean, dialed in right, it's competing with a Metal Zone (in a good way) in terms of being a big, tight distortion.

2) Yes, that Q2 transistor boost is SLAMMING the preamp in the classic DS-1 fashion. I've tried selecting transistors with lower HFE (I have all three in the 250-270 range), but I can't keep doing that. After researching the Q2 boost, it seems like the only other option is to change the values of R6/R9 to lower the boosting.

I'm using an ECG1464 (7pin preamp) for the IC, 2SC732TM-GR & 2SC2240-GR transistors and 1S1588 diodes. I removed the JFET switching section and the diode/resistor for the ACA adapter, but left the input/output buffers.

Question: It seems that 'GR-level' transistors (i.e. in the 200-400 hfe range) are standard for this and the SD-1. Is modifying R6/R9 pretty much the best way to adjust the DS-1's Q2 boost? And should I just disregard trying to select lower-hfe transistors if they're already in the 'GR' range?
I've read that Jack Ormans DS-1 'Fat Mod' for R6/R9 reduces the boost level, but is too much of a reduction.

I'll see if I can post pics of my layout tonight.
thx

 

[jesuscrisp]

it's competing with a Metal Zone (in a good way) in terms of being a big, tight distortion.

That sounds like you failed successfully, as tight is not a word that should be associated with the DS-1 at all.

You can reduce the boost level by messing with the 22R resistor off the emitter of Q2. Larger values will give you less gain.

 

[Elijah-Baley]

What's your schematic?

About the thicker sound (A LOT?) and removing the JFET switching, I see some adjustment of the coupling cap, to keep the same low end.
Maybe that's the thing.

 

[Bucksears]

What's your schematic?

About the thicker sound (A LOT?) and removing the JFET switching, I see some adjustment of the coupling cap, to keep the same low end.
Maybe that's the thing.

Here's the schematic:

I basically removed/jumpered Q6 and Q7 in my layout, and omitted the related switching section connected to those in the above schematic. I left the cap values the same, except for C9, which I have plugged in lower values; the DS-1A (post-1994) has .068uF in that location, vs .47uF in the MIJ version.
Last night I bumped up R9 to 47R (leaving R6 at 100K) and was a step in the right direction (for me).

EDIT: The schematic above varies slightly from the DS-1 Service Notes I also have, as the service notes have a C24 150pF cap to ground coming off of pin 1 of the IC, and R21 (on the emitter of Q3) is 10K. In the above schematic, C24 does not exist, and R21 is 100K.

 

[Chuck D. Bones]

2) Yes, that Q2 transistor boost is SLAMMING the preamp in the classic DS-1 fashion. I've tried selecting transistors with lower HFE (I have all three in the 250-270 range), but I can't keep doing that. After researching the Q2 boost, it seems like the only other option is to change the values of R6/R9 to lower the boosting.

HFE does not affect the voltage gain of that stage unless you get a transistor with HFE so low that it's unusable. As @jesuscrisp said, increasing the emitter resistor (R9) will reduce the gain. I've seen mods that bump it up to 470Ω or higher. Here are some mods I did to mine.