Jazzmaster OBEL

Jazzmaster OBEL

Postby dark_star » Tue Nov 21, 2017 6:04 am

Hello all- longtime lurker here, first time poster. Guitarist since I was 11 and a Dead since I was 13- so most of my life!

First, thanks to all for providing so much OBEL information, it's really a great resource.

I am thinking of modifying my '65 Jazzmaster reissue to add an OBEL- the idea is not to clone the Jerry sound, but rather to get the benefit of an OBEL as I am a) a tinkerer, and b) I've always struggled to get the sound I'm looking for while using a volume knob and effects (or effects in general). After having a pedalboard that surrounded me years ago, about a decade ago I started plugging straight in as much as possible and have played this way for a while, which really is a great way to improve your relationship with the guitar. But an OBEL seems like a great idea and I'd love to build one.

If I do it I'm planning on doing it myself, but have one or two questions that I'm wondering if anyone here has experience with. I am hesitant to mod my jazzmaster because I LOVE the bright sound right now when the instrument goes straight in (to say nothing of drilling a hole in the pickguard...). Looking at the circuit, I think a lot of this has to do with the impedance of the volume/tone pots in the guitar, both of which are 1MOhm for the "lead" circuit. Most of the OBEL circuits I've seen discussed used lower impedance volume/tone (e.g., 25k). Assuming the guitar's passive pickups are sitting around 7k output impedance (a guess, haven't measured), the pickups are seeing a ~140x increase in load hitting the volume pot at full volume/wide open. So- for a buffered circuit with ultra low output impedance (50 Ohm?), hitting the volume pot at 1M is a big difference and I imagine it will be too noisy. But- I'd love to find that "sweet spot" that recapitulates my sound as it is now. Is 25kOhm for the volume pot the place to start?

Hopefully this makes sense and my logic is sound. Has anyone done this mod to a Jazzmaster? If I want to keep the sound as-is, any suggestions for the tone/volume pots?

EDIT: Should mention that at least one effect in the loop will be buffered, and probably the last one as well (which is boss digital delay), so output impedance back to the guitar will be low.
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Re: Jazzmaster OBEL

Postby MattMan » Tue Nov 21, 2017 10:01 am

Quick answer is that you do not need to add a buffer to use an OBEL, but you will need a 25K pot if you do use a buffer. You can experiment. I noticed a fairly significant difference in the tone with the buffer and the 25k pot, especially with regards to clarity, brightness, and lack of tonal degradation when adding multiple effects. You can also do this by adding just the jack by getting yourself a 25k push/pull pot https://www.allparts.com/EP-0225-000-25K-PushPull-Pot_p_1292.html

You will need room for the two jacks (both will need to be stereo because the guitar output is actually stereo to engage the buffer battery), and room in the cavity for the buffer and the battery. Use an OBEL breakout box for convenience https://www.iocustomguitars.com/shop?olsFocus=false&olsPage=products/deluxe-io-breakout-box

Contact Mike Wald directly via email to order the buffer, and you can use the Tiger wiring layout for wiring the buffer, pups, and push/pull: http://www.wald-electronics.com/tiger.html

Good luck!

Send pics!
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