Topic: Graham Patten DMIC-20 Question...

[bdasilva]

Bought this old school preamp... It has the Todd Mod to trim between the 5db steps. I replaced the SSM-2017s with THAT 1510 preamp chips and I set about putting a bypass cap across the lesser caps in the unit. (transparent mod) (a "Dorsey" thing).  Sounds great and if you look there has been a shitload of sick pulls made with units like this. My question is... Has anybody just done away those <stupid> dip switches and just put in a pot? All those switches are doing is switching in resistors in parallel. Maybe somebody that been playing with a SSM-2017 or like preamp project could comment? I'm going to do it. Just like some comforting empowerment.

[cmoorevt]

If you successfully replace the dip switches with knobs, please let me know.  I looked into it a while ago, but it was more than I wanted to tackle and don't know anyone else that has done it.  I basically carry around a bunch of golf tees and coffee stirrers to switch those damn things.

Also, what would the transparent mod do to the sound?  Make things less bright?

[bdasilva]

Not sure about the sound...(yet)   Scott Dorsey said (in a post, not to me personally) to put film bypass caps across the taintilum and electrolitic caps to clean up the power supply.  It was discribed as the "transparent sound". The THAT 1510 chips are the latest and greatest generation of the SSM-2017 series.

[cmoorevt]

Interesting.  Where are you finding the 1510 chips?  I've heard of replacing the stock 2017's with Burr Brown INA-217 and those were available thru texas instruments but the 1510 is a new one for me.

[bdasilva]

sampeled them from THAT Semiconductor.  I'm sure I can do away with the dip switches and just use new pots where the todd mod pots were. More to follow.

Interesting.  Where are you finding the 1510 chips?  I've heard of replacing the stock 2017's with Burr Brown INA-217 and those were available thru texas instruments but the 1510 is a new one for me.

[bdasilva]

The gain is set by the resistance between pins one and eight of the ssm2017. (or whatever replaces it) If I lift those two  pins out of the socket and solder my wires on to those, then I can do the mod and never change the stock unit at all. I will remove the todd mod pots and use those front panel locations to to put in my new gain pots. There are the pots.. A series resistor to set the max gain...  and a big womppin cap on each to stop thump or swoosh when the gain is changed. Parts are on order and I'm gonna do this.   Cake.    I'll post the results on this post and help anyone that might want to do "the dasilva mod" on their DMIC. 

sampeled them from THAT Semiconductor.  I'm sure I can do away with the dip switches and just use new pots where the todd mod pots were. More to follow.

Interesting.  Where are you finding the 1510 chips?  I've heard of replacing the stock 2017's with Burr Brown INA-217 and those were available thru texas instruments but the 1510 is a new one for me.

[cmoorevt]

Niiiiiiiiiiiiiiiiiiice.  +T.  Keep us (me?) updated. That would take most of the pain in the ass out of using this unit.  Can I assume that the new pots would maintain the same 5db steps as the dip switches?

The gain is set by the resistance between pins one and eight of the ssm2017. (or whatever replaces it) If I lift those two  pins out of the socket and solder my wires on to those, then I can do the mod and never change the stock unit at all. I will remove the todd mod pots and use those front panel locations to to put in my new gain pots. There are the pots.. A series resistor to set the max gain...  and a big womppin cap on each to stop thump or swoosh when the gain is changed. Parts are on order and I'm gonna do this.   Cake.    I'll post the results on this post and help anyone that might want to do "the dasilva mod" on their DMIC. 

sampeled them from THAT Semiconductor.  I'm sure I can do away with the dip switches and just use new pots where the todd mod pots were. More to follow.

Interesting.  Where are you finding the 1510 chips?  I've heard of replacing the stock 2017's with Burr Brown INA-217 and those were available thru texas instruments but the 1510 is a new one for me.

[halleyscomet8]

off topic, but does this adc hav a usb out? just curious

[Brian Skalinder]

off topic, but does this adc hav a usb out? just curious

Nope.  AES/EBU output only.

[halleyscomet8]

  thanks

[super-phat-al]

i loved this unit before i lost mine.  I made some pretty awesome tapes.  If i still had mine I would do this mod in a second.

[bdasilva]

No... there will  be no 5db steps. Only a smooth  min to max gain.

[eman]

I have installed a two level rotary switch which uses the existing resistor arrays. Problem is that I did the variable gain mod and new amp chips at the same time and I ended up with a non-functioning unit. I think it is from some of the traces I messed up when soldering the gain pot wires. The switch mod seems to be fine. I also had an intermittent power problem before I started and that may have come back (ugh), and the project was depressing so it has been sitting awhile. Right now I would be grateful for a detailed photo of the traces on the back of the circuit board so I can fix that.

I got the rotary switch from Mouser and it works/looks pretty good. It is 100 times easier to use than the DIP switches. You can set the number of positions with itty bitty pins inside the switch. It takes two input signals and routes them to one of up to I think 12 output wires for each. I'll take some pictures.

I realized that the switchable steps are a good idea because you can go in and figure out exactly where you switched and apply a uniform gain to the area in post process, where if you use a pot you can't do this. So you see it going over, turn the knob, and later bump down the wav file up to the point where you switched it.

[bdasilva]

"Right now I would be grateful for a detailed photo of the traces on the back of the circuit board so I can fix that."


I can... send you pictures... tell you that my mod, pots and all... will do away with all that dipswitches/resistors and bad traces...   fix it for you (cuz thats what I do) for the cost af shipping. (karma grabbing) LMK

[china_rider]

Ahh.... Good to see my old EQ going to good use. :-}

I loved the DMIC but hated the dip switches... The thing was solid as a tank.  Would not have sold it if it was not for those damn switches.

BTW Brian... Have not been able to tape with the new silverpath cables you made me yet.  Burned them in in front of the stereo for around 100 hours and am now waiting for a good show.  Wish Victor Wooten allowed stands so I would not have to use the stealth rig on Monday.

Don't kill the DMIC but get rid of those damn switches. ;-}

Stay kind,
Dana