Al Heeley Posted February 17, 2009 Share Posted February 17, 2009 (edited) Having fitted some new pots to my P-bass I find there is a huge amount of treble loss when I turn down the volume. Keeping tone full up anything under 2/3 vol goes muddy as a very muddy place. I know the treble bleed cap in parallel to resistor thing across the vol pot's in and out terminals for guitars (stay with me if I get too technical guys, heh) but never heard of it being fitted or [i]needed[/i] for a bass. The common values I have for a guitar treble bleed are 100k resistor in parallel with a 1 or 2nF cap (0.001 - 0.002uF) Am I likely to need different values for it to be effective for a bass? Anyone ever had to put this mod in a bass to keep some bright edge when playing at low volume? Edited February 17, 2009 by Al Heeley Quote Link to comment Share on other sites More sharing options...
Guest MoJo Posted February 17, 2009 Share Posted February 17, 2009 I'd be interested to know too Quote Link to comment Share on other sites More sharing options...
BOD2 Posted February 17, 2009 Share Posted February 17, 2009 I've never seen any specific info on this mod for a bass. However, given that it's TREBLE bleed I'd be inclined just to try the standard guitar values and see what happens. The values I've used on guitar were 0.001uF and 150 ohms. I get the impression that varying the values (e.g 0.002uF and 100 ohms) will not make a huge amount of difference. Quote Link to comment Share on other sites More sharing options...
Al Heeley Posted February 17, 2009 Author Share Posted February 17, 2009 I found a technical post (as they all are on Guitar Nutz) from my old pal, Cynical, but it's a bit above me. [url="http://guitarnuts2.proboards45.com/index.cgi?board=coffee&action=display&thread=3797&page=3#34252"]http://guitarnuts2.proboards45.com/index.c...mp;page=3#34252[/url] If anyone can shed light on his virtual java oscilloscope traces it may be of interest for a bass treble bleed mod. failing that I'm just going to solder in my 100K/0.001uF cap and see what it sounds like. Quote Link to comment Share on other sites More sharing options...
Al Heeley Posted February 18, 2009 Author Share Posted February 18, 2009 Oh boy, have a look at this: [url="http://people.smartchat.net.au/~l_jhewitt/circuits/GuitarFreak_2_0.xls"]http://people.smartchat.net.au/~l_jhewitt/...arFreak_2_0.xls[/url] Electronics heaven! Fiddle with the resistors, pots and caps and pickups and watch how the frequency responses change. Quote Link to comment Share on other sites More sharing options...
Al Heeley Posted February 18, 2009 Author Share Posted February 18, 2009 Heres some graphs I snapped and photoshopped together, this shows a virtual parallel treble bleed in action, helping to preserve the high frequencies as the volume is rolled off. To be really accurate you have the ability to input your pickups individual resistance, capacitance and inductance, as well as choose a 10 foot, 20 foot cable or buffer. What an amazing spreadsheet model! Quote Link to comment Share on other sites More sharing options...
Al Heeley Posted February 18, 2009 Author Share Posted February 18, 2009 (edited) These graphs show the change in treble response as vol is rolled off, for a 100k and a 220k resistor in parallel with the 1nF cap: You can see that with a larger resistor, the treble enhancement is increased as the volume is rolled off. For this circuit a 56k resistor gives a more natural flatter profile over the volume range. And here, if you whack the cap up to 47nF (0.047uf = sort of cap value you would have on a tone pot) you get a mid-boost response when you turn the vol down: Edited February 18, 2009 by Al Heeley Quote Link to comment Share on other sites More sharing options...
Al Heeley Posted February 20, 2009 Author Share Posted February 20, 2009 OK I've wired this into my P-bass. I fitted a mini DPDT switch [on-on-on] and 2 caps to the end pair of lugs. It sounds good - the trebles are preserved down to low volumes but to be honest the shift in tonal response with the different value bleed caps is quite subtle - maybe a little redistribution of the mid frequencies is heard, if anything. Here's the spec: 250k vol + tone pots with a 0.047uF cap on the tone pot. treble bleed: 220k resistor in parallel with choice of 560pF cap, 2.2nF cap or both together. What is really different is the tone shaping of the tone pot. Not the normal drop off of tone but again a shifting of the mids, quite noticable and pleasing. The top end sparkle drops off a bit, but it seems to reshape the mid range more. I've not tried it thru the main gig amp at proper volume yet, but will give it a test run tomorrow at the band practice. Here's the circuit: Here's the bass with the toggle switch: Quote Link to comment Share on other sites More sharing options...
BOD2 Posted February 20, 2009 Share Posted February 20, 2009 Thanks for that. Some useful information there and you seem to have answered the question on what value of capacitor and resistor to use for treble bleed on a bass. Quote Link to comment Share on other sites More sharing options...
Protium Posted February 21, 2009 Share Posted February 21, 2009 Typical the only cap value I don't have is 1nF Quote Link to comment Share on other sites More sharing options...
Protium Posted February 21, 2009 Share Posted February 21, 2009 Question What's the difference in sound between the components in series vs parallel? Quote Link to comment Share on other sites More sharing options...
Al Heeley Posted February 21, 2009 Author Share Posted February 21, 2009 Got a 2nF or a 1.6? That will do fine Series is interesting, it has more of an influence on the tone pot taper. With a series treble bleed, with vol and tone half way, there is a broader hump in the mid to treble end (this is all on the graphs made by the modelling spreadsheet I linked to further up) With a prallel treble bleed, at half tone and half vol, there is a flatter overall response with a narrower peak in the treble. Does that make sense? Download the spreadsheet, tinker with the values and see the response curves, its a lot easier to visualise on a graph than it is to talk about! Quote Link to comment Share on other sites More sharing options...
Protium Posted February 21, 2009 Share Posted February 21, 2009 I'm trying to find my copy of excel Quote Link to comment Share on other sites More sharing options...
Al Heeley Posted February 21, 2009 Author Share Posted February 21, 2009 [quote name='Protium' post='416260' date='Feb 21 2009, 05:50 PM']I'm trying to find my copy of excel [/quote]Heh Quote Link to comment Share on other sites More sharing options...
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