okabass

Optimal Jazz Bass summing resistor values
« on: March 02, 2021, 10:53:00 AM »
Hi
Like to find *best summing resistor values* for connecting two passive Jazz Bass bass pickups (DCR 8 kΩ each).
The original has 220 kΩ resistors which are, as I understand, unnecessary big.
https://www.talkbass.com/attachments/1960-vtvt-jpg.765431/
This is said to be better wiring. And it is ok.
https://www.talkbass.com/attachments/robbiek-vtvt-jpg.765433/
But like to count the optimal resistor values.
« Last Edit: March 02, 2021, 04:50:24 PM by okabass »


ruffrecords

Re: Optimal Jazz Bass summing resistor values
« Reply #1 on: March 02, 2021, 11:28:36 AM »
I don't know who is telling you this but I see no reason the alternative scheme would be any better. In fact I can easily see reasons why it would be worse.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

okabass

Re: Optimal Jazz Bass summing resistor values
« Reply #2 on: March 02, 2021, 12:07:35 PM »
I don't know who is telling you this but I see no reason the alternative scheme would be any better. In fact I can easily see reasons why it would be worse.

Cheers

Ian

HI
Ok. Tell me more, why it would be worse. Can you then suggest better wiring and better resistor values? I like keep the wiring passive.

ruffrecords

Re: Optimal Jazz Bass summing resistor values
« Reply #3 on: March 02, 2021, 12:51:04 PM »
HI
Ok. Tell me more, why it would be worse. Can you then suggest better wiring and better resistor values? I like keep the wiring passive.

The second is worse because at full volume the pickup is loaded with 15K which is perhaps 10 times lower than it should be. In the original, the worst case loading is the 250K pot in parallel with the 200K mixing resistor which is over 100K.

You mention the dcr of the pickups is 8K but that is only half the story. The other half is the pickup inductance.  A p90 pickup for example has a typical DCR of 8K and an inductance of around 7 Henries. This inductance is effectively in series with the coil dcr so the output impedance is the sum of these. A bass guitar's fundamental frequency ranges from about 40Hz to 1KHz. This means the output impedance of the coil varies from about 10K to 52K. If you load that with 15K ohms you will loss all the all the harmonics and many of the higher notes.

Bottom line is there is little wrong with the original circuit.

Cheers

Ian
« Last Edit: March 02, 2021, 03:40:34 PM by ruffrecords »
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Matador

Re: Optimal Jazz Bass summing resistor values
« Reply #4 on: March 02, 2021, 01:42:21 PM »
Everything Ian says is spot on:  even at 100K loading, the loss of highs can be significant (some manufacturers exploit this, for example, http://www.audereengineering.com/LowZ.htm, which if memory serves was between 50K and 100K).

If you want to lower the mix resistors, you'll need to buffer the output of the pickups with something like a JFET follower to get the impedances down below a few hundred ohms.  Then you can use smaller mix resistors and not clobber the output voltage of the pickups (or severely low-pass filter the system).

okabass

Re: Optimal Jazz Bass summing resistor values
« Reply #5 on: March 02, 2021, 01:44:39 PM »
The second is worse because at full volume the pickup is loaded with 15K which is perhaps 10 times lower than it should be. In the original, the worst case loading is the 250K pot in parallel with the 200K mixing resistor which is over 100K.

You mention the dcr of the pickups is 8K but that is only half the story. The other half is the pickup inductance.  A p90 pickup for example has a typical DCR of 8K and an inductance of around 7 Henries. This inductance is effectively in series with the coil dcr so the output impedance is the sum of these. A bass guitar's fundamental frequency ranges from about 40Hz to 1KHz. This means the output impedance of the coil varies from about 10K to 52K. If you load that with 15K ohms you will loss all the all the harminis and many of the higher notes.

Bottom line is there is little wrong with the original circuit.

Cheers

Ian

HI
Thank you about the analysis.
The inductances of the PUs are 3,7 H (DCR 8,9 kΩ) and 3,2 H (DCR 8,7 kΩ).

The loading is only half of the story. The both PUs, their vol and tone pots should work as independent as possible. Like if you turn tonepot 1 down it shouldn't take highs away on pickup 2.  *And* the volume drop compared to "standard" wiring should be as lo as possible.
"Standard", later wiring.
https://www.talkbass.com/attachments/standard-vvt-jpg.765432/
I know using active electronics solves the problem, but just like to use passive wiring/mixer.
Like to find ideal resistor values for lowest volume drop and best separation of the PUs and pots.
Any formulas to find the best resistor values?
« Last Edit: March 02, 2021, 01:55:21 PM by okabass »

ruffrecords

Re: Optimal Jazz Bass summing resistor values
« Reply #6 on: March 02, 2021, 03:52:01 PM »
HI
Thank you about the analysis.
The inductances of the PUs are 3,7 H (DCR 8,9 kΩ) and 3,2 H (DCR 8,7 kΩ).

The loading is only half of the story. The both PUs, their vol and tone pots should work as independent as possible. Like if you turn tonepot 1 down it shouldn't take highs away on pickup 2.  *And* the volume drop compared to "standard" wiring should be as lo as possible.
"Standard", later wiring.
https://www.talkbass.com/attachments/standard-vvt-jpg.765432/
I know using active electronics solves the problem, but just like to use passive wiring/mixer.
Like to find ideal resistor values for lowest volume drop and best separation of the PUs and pots.
Any formulas to find the best resistor values?

Unfortunately the interactions of passive mixing tend to work in the opposite direction to what you want. Any reduction in interaction tends to result in an increased volume drop. It's basic physics. To reduce interaction increase the 220K resistors. The volume drop depends on the value of these resistors and the input impedance of what you plug it into but basically less interaction will cost you more volume loss.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

john12ax7

Re: Optimal Jazz Bass summing resistor values
« Reply #7 on: March 02, 2021, 04:33:00 PM »
This is a case where you just need to try a few different values and see what you prefer.  You can clip them in temporarily before soldering. There is no "correct" answer,  it's what works best for you,  could be 220k, 100k, 15k, 0, something else,  etc.

That's what I did to pick tone control capacitors, more useful than trying to calculate things. I also realized my personal preference was vastly different from what was the more standard recommended choice.

okabass

Re: Optimal Jazz Bass summing resistor values
« Reply #8 on: March 02, 2021, 04:39:13 PM »
Unfortunately the interactions of passive mixing tend to work in the opposite direction to what you want. Any reduction in interaction tends to result in an increased volume drop. It's basic physics. To reduce interaction increase the 220K resistors. The volume drop depends on the value of these resistors and the input impedance of what you plug it into but basically less interaction will cost you more volume loss.

Cheers

Ian

Hi
Thank you.
That's what I presumed.
So if I play the bass to tube amp with 1 MΩ input, those 220 kΩ resistors are quite ideal?

okabass

Re: Optimal Jazz Bass summing resistor values
« Reply #9 on: March 02, 2021, 04:47:33 PM »
This is a case where you just need to try a few different values and see what you prefer.  You can clip them in temporarily before soldering. There is no "correct" answer,  it's what works best for you,  could be 220k, 100k, 15k, 0, something else,  etc.

That's what I did to pick tone control capacitors, more useful than trying to calculate things. I also realized my personal preference was vastly different from what was the more standard recommended choice.

HI
Yes. That's what I have made. But like to know the "mathematical correct" resistor values. If that over all is possible.
One clever alternative is to use the stack pots for looks, but only use the vol pots and one tone pot in normal JB wiring. I.e. leave one tone pot out of the wiring. So called Vol,Vol,Tone instead of VolTone, VolTone.


ruffrecords

Re: Optimal Jazz Bass summing resistor values
« Reply #10 on: March 02, 2021, 06:05:17 PM »
Hi
Thank you.
That's what I presumed.
So if I play the bass to tube amp with 1 MΩ input, those 220 kΩ resistors are quite ideal?

Probably not. With 220K resistors the loss with be close to 6dB. You could increase them to 470K with little change in the loss and a noticeable reduction in interaction. You could increase them to 1Meg but then you get increased loss and possibly loss of top end due to cable capacitance (but this may not matter for bass). I would suggest trying 470K.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

okabass

Re: Optimal Jazz Bass summing resistor values
« Reply #11 on: March 02, 2021, 06:36:25 PM »
Probably not. With 220K resistors the loss with be close to 6dB. You could increase them to 470K with little change in the loss and a noticeable reduction in interaction. You could increase them to 1Meg but then you get increased loss and possibly loss of top end due to cable capacitance (but this may not matter for bass). I would suggest trying 470K.

Cheers

Ian

Hi
Ok, I'll try those.
Thank you very much for your analyse and advise.

PS Looked your site. Very interesting. I'm also interested in tube gear. I've for example built an SVT-type 300 W bass amp.  Some Pultec type eq , some guitar amps etc.
« Last Edit: March 02, 2021, 07:06:29 PM by okabass »

john12ax7

Re: Optimal Jazz Bass summing resistor values
« Reply #12 on: March 02, 2021, 08:23:38 PM »
I would imagine you already have significant high end loss with 220k. In a guitar with a 6k pickup,  and no series resistor, it's very easy to hear the difference between regular cable and low capacitance cable.  Bass is lower,  but only an octave, while you are increasing the series driving resistance by way way more than 2x by going to 470k or 1M.  Imo you should be lowering the series resistor,  if anything,
to regain some high end clarity. Then again there is no right way to make a tone and you might like the effect.
« Last Edit: March 02, 2021, 08:39:00 PM by john12ax7 »

Gus

Re: Optimal Jazz Bass summing resistor values
« Reply #13 on: March 02, 2021, 08:47:51 PM »
You could LT spice
Sim the pickups, volumes, tones, caps, resistors cable and amp input

john12ax7

Re: Optimal Jazz Bass summing resistor values
« Reply #14 on: March 02, 2021, 09:05:24 PM »
You could LT spice
Sim the pickups, volumes, tones, caps, resistors cable and amp input

I was curious and just did that.  220k is actually rather well optimized,  in the sense that it is the smallest resistor that minimizes the interactions.  Going higher doesn't gain much,  just more loss and high end rolloff.

Going lower increases interaction,  lowers loss,  and extends high end.

You actually get some interesting responses with increased interaction. Might be some cool tones in there to experiment with.

CJ

Re: Optimal Jazz Bass summing resistor values
« Reply #15 on: March 02, 2021, 10:11:19 PM »
what kind of tone are you after?

Jamerson?  Jaco? Geddy?

that jazz bass was made to give you tonal variation by adjusting the two pickups, thus making it more versatile than the P bass.

i find that i can get a killer Jamerson tone by adjusting both pickup volume controls down about 20 percent each, with the tone all the ay up.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
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okabass

Re: Optimal Jazz Bass summing resistor values
« Reply #16 on: March 03, 2021, 02:14:59 AM »
I would imagine you already have significant high end loss with 220k. In a guitar with a 6k pickup,  and no series resistor, it's very easy to hear the difference between regular cable and low capacitance cable.  Bass is lower,  but only an octave, while you are increasing the series driving resistance by way way more than 2x by going to 470k or 1M.  Imo you should be lowering the series resistor,  if anything,
to regain some high end clarity. Then again there is no right way to make a tone and you might like the effect.

Yes. I have tried several resistor values between 4k7-220k. And nothing sounds bad in my opinion. Only different compared to nowadays standard Jazz Bass VVT wiring.
Just tried to get the most "mathematical correct" values. And the original 220 kΩ seems to be quite correct.

okabass

Re: Optimal Jazz Bass summing resistor values
« Reply #17 on: March 03, 2021, 02:18:31 AM »
what kind of tone are you after?

Jamerson?  Jaco? Geddy?

that jazz bass was made to give you tonal variation by adjusting the two pickups, thus making it more versatile than the P bass.

i find that i can get a killer Jamerson tone by adjusting both pickup volume controls down about 20 percent each, with the tone all the ay up.

HI
No persons sound I'm after. Trying to optimize the stack JB wiring. Seems that Leo Fender found quite right resistor values.
I'll try that P sound setting.   
« Last Edit: March 03, 2021, 02:33:40 AM by okabass »

okabass

Re: Optimal Jazz Bass summing resistor values
« Reply #18 on: March 03, 2021, 02:28:42 AM »
I was curious and just did that.  220k is actually rather well optimized,  in the sense that it is the smallest resistor that minimizes the interactions.  Going higher doesn't gain much,  just more loss and high end rolloff.

Going lower increases interaction,  lowers loss,  and extends high end.

You actually get some interesting responses with increased interaction. Might be some cool tones in there to experiment with.
HI
Thank you "to spice" the circuit. I think too that VTVT gives more interesting sounds than standard wiring.
I have tried some half dozen different resistors and wiring, and needed some advice or point which direction to continue. Or what is not sensible to try.

clintrubber

Re: Optimal Jazz Bass summing resistor values
« Reply #19 on: March 17, 2021, 08:17:37 PM »
Just tried to get the most "mathematical correct" values.

If any, it might still depend on where your preferred mix-setting of the two pickups is.

If you tend to (say) have the bridge-PU full on most of the time and just want to blend in some more body from the neck-PU, "mathematically correct" values will differ from situations where you go for vastly different blends.

Generally speaking, the 'obligation' to use the volume-pots in signals-go-into-wipers fashion is a fact of life with such fully passive circuits, but will be a moot point (drawback vanishes) in case you use both PU's at or near full-on. Using those added mixing-resistors, obviously they'll always be there, with adverse effect.

Long story short: depending on your blending-taste you could optimize the topology & values.
If your blending-needs are all over the place then perhaps make some configurations, switchable.


 

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