parislyons Posted February 20, 2022 Share Posted February 20, 2022 I've very recently come into a problem I didn't know existed when I got hold of a used bass in a trade. The blend pot doesn't blend, it functions more like an on/off switch where the extra pickup will only be added in when getting very close to the centre notch, and for 90% of the travel, you just hear one pickup. I looked up the issue and I've seen a couple of similar problems but they reference specific things that don't apply to my case so I'm wondering how the differences affect me. I have an OBP-2 loaded bass (the bass was originally shipped with a different preamp that was swapped out) with dual EMG 35DC active pickups and the pot in question is a MN500K, I tried ungrounding the blend as I've seen a few forum users suggest, but it made no difference. Is my next step to just try a lower pot value and seeing what difference that makes? From what I understand the default configuration of the OBP-2 is to use Vol Vol rather than Vol Blend so I'm wondering if something may have been overlooked in the initial install also. Any thoughts or perspective are appreciated! Quote Link to comment Share on other sites More sharing options...
Delberthot Posted February 20, 2022 Share Posted February 20, 2022 (edited) For the preamp and pickup you should be using 25k pots. 500k pots are more normally used for passive humbuckers. I actually have no idea what effect 500k pots would have but I'm sure that someone will be along to explain. the Aguilar and EMG websites both specify 25k pots Edited February 20, 2022 by Delberthot Quote Link to comment Share on other sites More sharing options...
gjones Posted February 20, 2022 Share Posted February 20, 2022 They're all the same really. The blend controls,that I've had experience of, just act as an on/off switch. There may be a smidgeon of a blend, a mm either side of the centre but in my experience they give you bridge pickup on full, neck pickup on full, or both on full together. Quote Link to comment Share on other sites More sharing options...
parislyons Posted February 20, 2022 Author Share Posted February 20, 2022 (edited) 22 minutes ago, Delberthot said: For the preamp and pickup you should be using 25k pots. 500k pots are more normally used for passive humbuckers. I actually have no idea what effect 500k pots would have but I'm sure that someone will be along to explain. the Aguilar and EMG websites both specify 25k pots My understanding was that 25k was for Volume and Tone, and that blend didn't matter as much? If I did need 25k that would explain the issue though. 6 minutes ago, gjones said: They're all the same really. The blend controls,that I've had experience of, just act as an on/off switch. There may be a smidgeon of a blend, a mm either side of the centre but in my experience they give you bridge pickup on full, neck pickup on full, or both on full together. That's the thing, the blends I've had up until this point are nothing like this. The blend I have in my Warwick works perfectly and the blend I have in my Ibanez SR isn't perfect but it's a lot better than this one, so that's why I'm confused. Granted, they both have passive pickups on an active circuit rather than both active Edited February 20, 2022 by parislyons 1 Quote Link to comment Share on other sites More sharing options...
ikay Posted February 21, 2022 Share Posted February 21, 2022 The 500k pot value is the problem. The EMG specs recommend 25k vol and tone pots for this pickup so I'd try a dual MN25K pot for the blend. Quote Link to comment Share on other sites More sharing options...
itu Posted February 21, 2022 Share Posted February 21, 2022 What is slightly different with your pickups is that they are lo-Z, compared to most others (which are high impedance, "passive"). The blend pot is the first in signal path after the pickups. You can use a hi-Z pot (250k MN or 500k MN), but the feasible area of the pot tracks will be short. From this point of view two volumes would work. You can also opt for the "active" mixing via the battery operated Noll Mixpot. Quote Link to comment Share on other sites More sharing options...
parislyons Posted February 21, 2022 Author Share Posted February 21, 2022 8 hours ago, ikay said: The 500k pot value is the problem. The EMG specs recommend 25k vol and tone pots for this pickup so I'd try a dual MN25K pot for the blend. I guess that's a good place to start, just need to get hold of one of those pots then, thanks! 5 hours ago, itu said: What is slightly different with your pickups is that they are lo-Z, compared to most others (which are high impedance, "passive"). The blend pot is the first in signal path after the pickups. You can use a hi-Z pot (250k MN or 500k MN), but the feasible area of the pot tracks will be short. From this point of view two volumes would work. You can also opt for the "active" mixing via the battery operated Noll Mixpot. Vol/Vol would be easier but Ideally I want the blend for quicker dialing, I guess that would be what I'd go for if I can't get the blend to work. What makes you recommend active mixing? I saw the EMG active pot but it seems excessive and it claimed to solve a problem I don't have. Quote Link to comment Share on other sites More sharing options...
itu Posted February 21, 2022 Share Posted February 21, 2022 Loading affects the pickup response. Active mixing does not load pickups. This is especially feasible with hi-Z pickups. Buffered output is very stiff, therefore the blend can be a simple pot. If the 250k is too big, you can solder metal film resistors in parallel with the individual tracks. Then the pot tracks look smaller in resistance. Few alternatives: 100k resistors in parallel - 71k tracks 68k - 53k 56k - 45k7 47k - 39k5 33k - 29k 27k - 24k And so on. EMG has 10k output impedance, 27k resistors would be a nice match. Quote Link to comment Share on other sites More sharing options...
parislyons Posted March 3, 2022 Author Share Posted March 3, 2022 On 20/02/2022 at 21:22, Delberthot said: For the preamp and pickup you should be using 25k pots. 500k pots are more normally used for passive humbuckers. I actually have no idea what effect 500k pots would have but I'm sure that someone will be along to explain. the Aguilar and EMG websites both specify 25k pots On 21/02/2022 at 09:35, ikay said: The 500k pot value is the problem. The EMG specs recommend 25k vol and tone pots for this pickup so I'd try a dual MN25K pot for the blend. Just an update to this, I got a 25k MN pot and it works perfectly now. Thanks to Delberthot and ikay for steering me in the in the right direction! On 21/02/2022 at 20:57, itu said: Loading affects the pickup response. Active mixing does not load pickups. This is especially feasible with hi-Z pickups. Buffered output is very stiff, therefore the blend can be a simple pot. If the 250k is too big, you can solder metal film resistors in parallel with the individual tracks. Then the pot tracks look smaller in resistance. Few alternatives: 100k resistors in parallel - 71k tracks 68k - 53k 56k - 45k7 47k - 39k5 33k - 29k 27k - 24k And so on. EMG has 10k output impedance, 27k resistors would be a nice match. Thank you for the alternate suggestions itu, I ended up getting a lower resistance pot since it seemed less fiddly than wiring up resistors and I definitely didn't want to dip in for the active blend due to the price. £4 for 3 pots off ebay was a lot more enticing than $80 + shipping from EMG or the Noll. 1 Quote Link to comment Share on other sites More sharing options...
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