adamg67 Posted July 16, 2015 Share Posted July 16, 2015 (edited) I've got some odd behaviour with an Ibanez BTB 456 that I bought second hand. It's in really good nick and everything works perfectly apart from the pickup blend knob. I get good volume with the blend all the way to the neck or all the way to the bridge, but a noticeable volume drop when I'm halfway between the two. It's not like it's half volume or anything, but it's enough that I couldn't use it like that live. My first thought is phase - if the pickups are out of phase, could that cause an issue like this? Or would it be much worse? Anything else obvious it might be? Edited July 16, 2015 by adamg67 Quote Link to comment Share on other sites More sharing options...
Marc S Posted July 16, 2015 Share Posted July 16, 2015 Is the pickup blend pot original? If not, it may be incorrect value? Just a thought... Hope you get it sorted mate Let us know when you find out Quote Link to comment Share on other sites More sharing options...
KiOgon Posted July 16, 2015 Share Posted July 16, 2015 Not all blend pots give you 100% from both at the centre position, this could be your problem. Quote Link to comment Share on other sites More sharing options...
iiipopes Posted July 16, 2015 Share Posted July 16, 2015 Is it a Jazz bass style instrument? The impedance drop from both pickups on may cause a little bit of volume drop off. Quote Link to comment Share on other sites More sharing options...
adamg67 Posted July 16, 2015 Author Share Posted July 16, 2015 It's a few years old, so checking the wiring and the pot is a good idea anyway, I'll have the back off and see what's what. They're Ibanez soap bar pickups. Quote Link to comment Share on other sites More sharing options...
adamg67 Posted July 17, 2015 Author Share Posted July 17, 2015 (edited) I found the wiring diagram for my bass, and looking at that (and having a bit of a think about how this has to work), it looks like a blend pot is basically just two stacked volume pots? So as you turn one pickup down you turn the other up? If that's the case, I can imagine they're not always perfectly balanced. I don't know if they're tweakable though, it might need replacing but that doesn't look like a very hard job. Edited July 17, 2015 by adamg67 Quote Link to comment Share on other sites More sharing options...
brensabre79 Posted July 17, 2015 Share Posted July 17, 2015 (edited) Yes a blend pot is just two stacked volume pots, one working in reverse. The problem may be that the taper on the pots isn't right for a blend control. You can get pots that don't start to resist until past the centre position specifically for this job. But if it's not one of those, chances are you're getting about 50 - 60% volume from each pickup. Combined with the comb filtering effect you get from blending pickups this would give a significant drop in volume. One thing you can try is not shunting the pot to earth, just leave the third lug of the pot unconnected (but shield the casing still) - this can help, but I'd recommend getting a suitable pot. e.g. [url="http://www.cdguitars.co.uk/bourns-dual-500k-mn-blend--balance-pot--ep-5386-000-1027-p.asp"]this one (assuming you're running passive humbuckers)[/url] If the pickups were out of phase you would lose all of the bottom frequencies too, so that can be ruled out pretty quickly if it just goes quieter. Edited July 17, 2015 by brensabre79 Quote Link to comment Share on other sites More sharing options...
adamg67 Posted July 17, 2015 Author Share Posted July 17, 2015 Yeah, just been playing with it again and I don't think it's out of phase, I think the pots just aren't quite right. Quote Link to comment Share on other sites More sharing options...
HowieBass Posted July 17, 2015 Share Posted July 17, 2015 This isn't just the typical mid-scoop you get with a jazz type bass is it? Try dialling in some boost on the mids to see how this affects the volume. Quote Link to comment Share on other sites More sharing options...
pfretrock Posted July 17, 2015 Share Posted July 17, 2015 (edited) [quote name='KiOgon' timestamp='1437068948' post='2823371'] Not all blend pots give you 100% from both at the centre position, this could be your problem. [/quote] 50% of each at centre position? Is it Log or linear? Edited July 17, 2015 by pfretrock Quote Link to comment Share on other sites More sharing options...
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