kb

I've VTP1 sit in my rack for a long time but still like the look of this unit. I'd like to turn this mic pre to be a usable mic pre with more open high frequency than the original one. I like the way they handle the noise floor. Any idea to modify the part in side this unit? Thanks in advance.


okgb

Re: Any Idea to Mod junk Digitech VTP1 mic pre to be an usable mic pre?
« Reply #1 on: August 31, 2009, 08:17:30 AM »
Allot more work without a schematic for sure
that would be the first step

you could try tracing the circuit and replacing caps
with better quality, but that may not make a noticable difference
[ on some things in past i've noticed less mud not so much more air
from replacing caps ] more to do with the actuall design of circuit .

curious , they've been popping up on ebay lately and i wondered if
they were usable without the convertor [ usually about 200.00 ]

good luck
GKB Audio / Greg Boboski

kb

Re: Any Idea to Mod junk Digitech VTP1 mic pre to be an usable mic pre?
« Reply #2 on: September 01, 2009, 12:06:49 AM »
Hi okgb
Actually I think what I have to do is "mod the output circuit" inorder to get a better signal...  but not sure about the result I understand that we cannot improve much performance if the original circuit design spec. is not allow. I use to saw some discussion talk about swap the chip.... Anybody use to play with this unit before?

Adky

Re: Any Idea to Mod junk Digitech VTP1 mic pre to be an usable mic pre?
« Reply #3 on: January 08, 2010, 11:50:32 AM »
As of now, I am Modding the super troublesome VTP-1 , I have good result from the things, what I did is I bypassed the Phase inverter IC and jump a short wire from the middle of Mic / Line switch to Phase Switch middle point and that will by pass the useless phase inverter switch which costing all the trouble and then I added a oil cap and 5k/600 output transformer from the tube pin 1/6 directly I am still testing it , by doing this you will lost the Trim and the pre gain control and EQ, but that Trim and Gain things are what really making the sounds really bad, which I think they are on the wrong path also the phase inverter IC, I will futher investigate the possibility on this VTP becasue I spened good money years ago buying it brand new !!!!!! >:( I dont want it to be a BIG DOOR STOP ........... , FYI, I also swaped all chips to AD827 and OPA 2604 also the TUBE to GE6207( AT7) , next I will swap out the SSM2017 to THAT 1510 I will add a direct gain control to the 1510 which that were missing int he first place , and ofcoz I swaped all the audio caps to wima and Slimox II and then  bypass all the Audio Electrolytic with ERO 0.1 uf Poly.  be aware this thing do pump out 235VDC avoid of getting zap! Next step is I will add a UTC transformer in the Mic input so I can loose the DC Blocking CAP so this will become a really nice Preamp. Hope this help, I will keep posting my result.
« Last Edit: January 08, 2010, 11:54:22 AM by Adky »

Adky

Re: Any Idea to Mod junk Digitech VTP1 mic pre to be an usable mic pre?
« Reply #4 on: January 09, 2010, 01:47:55 AM »
Finally, this is how the mod are done, Reroute the singal path , from Mic/Line selector to EQ board, then from EQ board route to TUBE gain stage, then Tube gain stage to Balance stage, but added Transformer output option direct from tube to output, so then you got 2 different output options Added Mic gain control to the SSM2017 , losse the phase invertion chips, upgrade from +/- 15VDC to +/- 18VDC and replace with fast recovery diode rectifier bypass with 0.1 uf , replace all electic to audio grade and added 0.1 uf bypass , added 150:600 ohm input transformer swap the tube to 12AT7 , this is it, hope this help. this way you can still have the Gain control and EQ to use, infact the EQ is pretty nice and by doing this you can use the EQ to drive the TUBE to work harder.


 

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