Yamaha RBX375 pickup/electronics question

subdude67 · #1 11-03-2012, 02:14 AM

i bought this bass very cheap a few years back as my first and only 5 string bass and i am happy with it.

now, one tone control pot and the blend pot are worn out and need replacement.

i found some quality replacement pots but now i am wondering, would it be possible to run the stock pickups without an active circuit? leave the pickups and remove the rest replacing it with 2 volume and 2 tone pots instead?

i have the wiring diagram if needed but i am unable to post it, sorry.

thaks for any help

Stealth · #2 11-03-2012, 04:52 AM

Yes, it would. The RBX375 has passive pickups, and I've heard they're fairly good on their own and that the preamp is actually the weakest link. So, yes, you can simply run them into a V/T/V/T or similar control layout.

Take note that because it'll be a strictly passive circuit, having two tones in a circuit means each tone will affect both pickups. There's a way to isolate the two using resistors, but that usually means you'll lose a bit of volume and will have to turn your amplifier's input gain up a bit.

I'll draw you the schematic with the resistors as soon as I find the time today.. Which pot values and tapers did you get? 250k-s, 500k-s? Are they audio (logarithmic), linear or are some one way and some the other? Usually with a V/T/V/T the pots should be the same value, the volumes should be linear and the tones logarithmic.

subdude67 · #3 11-03-2012, 09:58 AM

hey stealth,

many thanks for your quick and informed reply!

Quote:

Originally Posted by Stealth

...... Which pot values and tapers did you get? 250k-s, 500k-s? Are they audio (logarithmic), linear or are some one way and some the other? Usually with a V/T/V/T the pots should be the same value, the volumes should be linear and the tones logarithmic.

i have got the same pot values as the stock ones have, bass and treble are B50K center dent, volume is B20K and the blend is an A+C500K center dent.
if you think i need anything else i can order it and have it brought.

thenks again for your help, i really appreciate it!

Stealth · #4 11-03-2012, 01:44 PM

Here's the thing, the B50K-s, B20K and A+C500K work fine for an active circuit because it only needs 50K resistances to sweep the bass and treble and only 20K to sweep the volume after the preamp. But low resistances like those would make the bass sound dull and lifeless without any treble whatsoever even if you wired it properly.

Here's an earlier wiring I made for someone who wanted a V/B/T/T setup. Of the components you have, only the blend could stay, the rest have to be higher values (B250K for volume, A250K-s for tone). The 220k resistors are what keeps the tone controls from interacting, though I've heard 47k ones also work.

V/T/V/T still to follow, haven't got around to drawing it yet..

subdude67 · #5 11-04-2012, 01:51 AM

stealth, you rock!

this is fantastic, many thanks for the diagram!

since i want a V/T - V/T configuration, i don't mind buying the correct pots and do it properly.

thanks again!

Stealth · #6 11-04-2012, 08:24 AM

Here's the finalized version.

Remember to solder all the grounds together.
The simplest way is to solder one pickup's ground to its tone pot's casing, then that tone pot's casing to its volume pot's casing, and then from that volume pot's casing to the output jack's ground.
Finally, repeat for the other pickup and its tone and volume.

Also, since you'll have a total of four controls in the bass, I highly recommend using 500K-s (two linears, two logarithmics). This'll keep the sound mud-free.

subdude67 · #7 11-04-2012, 11:24 PM

stealth,

i have no way to thank you enough for what you did here!
so all i say is thank you so much for taking the interest and time to help me with this, you are a very kind indeed!

i let you know how things are once i have changed over to passive, i am really excited to hear the sound.

thanks again

Hawkbone · #8 11-05-2012, 12:36 AM

I'm curious how this will turn out, subdude. I have a RBX-375 that I've been meaning to mod in some way. Look forward to hearing your opinions on a passive mod.

subdude67 · #9 11-05-2012, 03:31 AM

i am ordering the new pots and the rest as i write, all going well i get the parts next week thursday so i will do the changes over the weekend. i will let you know how it went, i am curoius too!

Stealth · #10 11-05-2012, 03:37 AM

I'm planning to mod my RBX-375 with a repro MusicMan preamp. It'll retain the Vol/Blend/Bass/Treble layout.

subdude67 · #11 11-05-2012, 04:31 AM

since i have already the replacement parts for the stock layout, i'll keep the original preamp and fix it, one day i migt swap back to active.

however, for now i am just interested how the bass sounds passive.

Hawkbone · #12 11-14-2012, 02:58 PM

hey, any progress?

subdude67 · #13 11-14-2012, 11:22 PM

Quote:

Originally Posted by Hawkbone

hey, any progress?

not yet, very sorry!

i could not find the parts locally so i had to order them from germany, a mate of mine is arriving from frankfurt today bringing them along.

i should be soldering on saturday and i will let you all know as soon as the swap is complete.

Stealth · #14 11-15-2012, 02:28 AM

Do you have any way of recording the result? I'd be interested in hearing how it sounds passive. I'm still waiting on my own parts for the replacement preamp in my own.

subdude67 · #15 11-15-2012, 02:54 AM

Quote:

Originally Posted by Stealth

Do you have any way of recording the result? I'd be interested in hearing how it sounds passive. I'm still waiting on my own parts for the replacement preamp in my own.

i will try once i have done the conversion.

i'll have to send you the clip as an MP3 via email because i am unable to post it here

i let you know here once it is done, thanks again for your help stealth, you rock!

subdude67 · #16 11-15-2012, 11:34 AM

stealth, a quick question.

would you use rather use 250k or 500k pots for the tone control? i have both available.

would it make sense to use a 500k on the neck PU and a 250k on the bridge or vice versa?

thanks!

subdude67 · #17 11-18-2012, 07:41 AM

i have rewired the pickups and i am very happy with the results! to me it sounds much better passive than active.

allthough the sound is less variable than with the active setup, i really love the pure sound of the soapbars. i used 500k pots for the tone control.

stealth, again many thanks for your help and for taking the time to make me the tailor made schematics of the wiring.

i will send you some sound clips when i have the opportunity.

subdude67 · #18 11-27-2012, 02:16 AM

Quote:

Originally Posted by Stealth

Do you have any way of recording the result? I'd be interested in hearing how it sounds passive. I'm still waiting on my own parts for the replacement preamp in my own.

hi stealth,

i have the sound clips ready, i sent you a PM.

and if anybody else wants to hear how the bass sounds just let me know.

Stealth · #19 11-27-2012, 07:36 AM

I got your PM and replied to it, so it's odd that you haven't received it.

Anyhow, I'm sure others are as interested - can you make a Box, Minus or SoundCloud account and upload there? All three websites are simple to use.

subdude67 · #20 11-28-2012, 07:02 AM

Quote:

Originally Posted by Stealth

I got your PM and replied to it, so it's odd that you haven't received it.

Anyhow, I'm sure others are as interested - can you make a Box, Minus or SoundCloud account and upload there? All three websites are simple to use.

ok, thanks for the links, i try to get it going!