Search found 7 matches

by el-folie
11 Jul 2011, 21:23
Forum: Pimp-My-Cheap-Pedal
Topic: Behringer VM1 Vintage Time Machine
Replies: 102
Views: 57682

Re: Behringer VM1 Vintage Time Machine

Sorry. R28 can be ommitted. So is C38. In this config the biasing of the 2nd BBD is done by the DC offset of the opamp. This will change a little by altering the gain of that opamp. This configuration is theerfore the most "correct" from an original DMM design perspective. The C38 cap should have a...
by el-folie
11 Jul 2011, 18:49
Forum: Pimp-My-Cheap-Pedal
Topic: Behringer VM1 Vintage Time Machine
Replies: 102
Views: 57682

Re: Behringer VM1 Vintage Time Machine

late response. Sorry. Hi and thanks for your input! Are R28 (connected somewhere?) and C38 still necessary or can they be omitted? As an experienced electronics engineer do you think it´s worth the hassle of converting the VM1 to DMM specs? There are so many differences in filtering, gain staging a...
by el-folie
11 Jul 2011, 14:18
Forum: Pimp-My-Cheap-Pedal
Topic: Behringer VM1 Vintage Time Machine
Replies: 102
Views: 57682

Re: Behringer VM1 Vintage Time Machine

I just made a simulation of the pre bbd1 filter stages. As it seems the main filter capacitor is C8 (10n) which forms a first order lowpass filter with R19. For AC sine output (1.5V) the result of the complete circuit is a curve with -3dB loss at about 800Hz and an eq cutoff freq at 1592Hz for R19,C...
by el-folie
10 Jul 2011, 15:53
Forum: Pimp-My-Cheap-Pedal
Topic: Behringer VM1 Vintage Time Machine
Replies: 102
Views: 57682

Re: Behringer VM1 Vintage Time Machine

A few observations so far about VM1: - 50:50 mix level seems to be at 7.3 mix pot position due to log pot. What I don´t like is that the pure delay has very very low output on my unit. The pure pre amp level can be much louder depending on input level. Is my unit faulty or is that normal for the VM1...
by el-folie
09 Jul 2011, 22:10
Forum: Pimp-My-Cheap-Pedal
Topic: Behringer VM1 Vintage Time Machine
Replies: 102
Views: 57682

Re: Behringer VM1 Vintage Time Machine

Ok, I thought I could do a quick and dirty 2nd draft, so here it is. Please let me know what you think - I´m really curious... On one hand it seems to be right now due to the insight on the non inverting op info from wikipedia (thanks for the link!), on the other hand the DMM gain circuit seems to b...
by el-folie
09 Jul 2011, 20:15
Forum: Pimp-My-Cheap-Pedal
Topic: Behringer VM1 Vintage Time Machine
Replies: 102
Views: 57682

Re: Behringer VM1 Vintage Time Machine

First of all, welcome on board ! And thanks for trying to design things yourself, instead of asking for a "solder-by-numbers" layout. That's the way to go if you wanna learn ! As you said, there is a problem with your schematic : the opamp has no negative feedback, and an adjustable positive feedba...
by el-folie
08 Jul 2011, 17:38
Forum: Pimp-My-Cheap-Pedal
Topic: Behringer VM1 Vintage Time Machine
Replies: 102
Views: 57682

Re: Behringer VM1 Vintage Time Machine

@Jim and Dirk Hendrik: Hi, it´s my first post here and my head is spinning. I spent the whole night above Jim´s VM-1 schematic and the MN3005 DMM schematic. I´m waiting for my own VM-1 right now - just ordered it. I´d like to contribute an idea about the gain trim stage that´s preventing the origina...