Do-it-yourself pedal building
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Tue Jan 30, 2018 8:22 am
Last night I built a simple 2 transformer, 4 diode ring mod into a snazzy VHS box.
I used BAT85 diodes and they all had a forward voltage of 0.27 and those cheap little LT44 transformers.....
The primary side has a nominal impedance of 20K Ohms. The secondary side is nominally 2k Ohms and has a centre tap. The D.C. resistance of the primary is approximately 480 Ohms, and that of the secondary is 107 Ohms. The theoretical voltage and turns ratio is 3.2 and something close to this is seen when testing at 1kHz with the appropriate input and output impedances connected. These have input and output impedances that are more useful for making ring modulators than the LT700s.
It works pretty well using a little Chinese sine wave generator I got off ebay. There's some bleed through and the sound is a little harsh and lacking in bass.
I'm wondering now if the sound can be 'improved' in another build by using a pair of larger, high quality 1200ohm 1:1 transformers and trying some different diodes. And something less shit than a VHS box to house it in.
Tue Jan 30, 2018 11:09 am
If your source signals are free of DC offset you can do away with the coupling caps.
All three lines are interchangeable as in/out/carrier (this may or may not make much of a difference).
Decent transformers are nice, but it's the modulators job to throw away your original signal, so any bass frequencies coming out are chopped and screwed (so to speak). I feel the easiest solution is actively recovering gain from the diode ring and employing a clean blend for bass retention.
I doubt your VHS enclosure impacts anything beyond "player feel".
Tue Jan 30, 2018 1:45 pm
Are you sure? It's an old Steve Coogan live box from the late 90s.....I might try it with my spare Buffalo 66 box just to test.
OK, so posh transformers that would look impressive would make as much difference as a photo of Vincent Gallo and Christina Ricci on the enclosure? The Xfrmrs already handle the bandwidth?
Tue Jan 30, 2018 2:48 pm
crochambeau wrote:I doubt your VHS enclosure impacts anything beyond "player feel".
Tue Jan 30, 2018 4:12 pm
Dude Buffalo 66 makes everything sound better. It's just a fact.
Tue Jan 30, 2018 6:06 pm
Ben79 wrote:OK, so posh transformers that would look impressive would make as much difference as a photo of Vincent Gallo and Christina Ricci on the enclosure? The Xfrmrs already handle the bandwidth?
Not knowing how shitty your current transformer bandwidth is I cannot say... better transformers will result in improvements, in some way, shape, or form...
Wed Jan 31, 2018 12:24 am
I've had this document for a while and I don't remember where I got it, but old boy makes some great points. It's super cool if you ask me and looking at his schematic you're after the same thing it looks like
sorry if this wasn't helpful.
Edit: I hope this is ok to post.
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