Active splitter in bass guitar

Thread Starter

Amalgam

Joined Sep 4, 2019
27
Could this splitter be used to split a bass pickup's output? I'm trying to fit two EQ's in a three pickup bass which would have six volumes, or a volume per pickup per EQ. Kind of crazy, but this is the one component I know the least about, and the one that could possibly make it happen. I know pickups use very little energy so that's got me wondering. Also, since this would be inside the bass, the smaller the battery usage, and size the better.

I believe the pickups would produce less than 500mV.

This would be my first electronics project. Any feedback is appreciated.


http://www.muzique.com/lab/splitter.htm
 

MrChips

Joined Oct 2, 2009
22,067
I am not sure why you have the FETs configured as common drain as opposed to common source.

You don't need R1.

R2 and R3 bias resistors don't look right to me.
 

Alec_t

Joined Sep 17, 2013
11,735
Welcome to AAC!
I don't see why each output needs its own buffer JFET. You could derive two (or more) outputs from one buffer JFET like this :-
BassGuitarSplitter.png

Edit: This circuit draws about 300uA.
 
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DickCappels

Joined Aug 21, 2008
6,640
In spite of the critiques above, your circuit should be just fine. Alec_T's comments in post #3 would allow significant parts count and cost reduction.
 

Thread Starter

Amalgam

Joined Sep 4, 2019
27
I am not sure why you have the FETs configured as common drain as opposed to common source.

You don't need R1.

R2 and R3 bias resistors don't look right to me.
Yeah, not sure why R1 is there. It's taken from a website so I'm not sure of their reasoning for R2 and R3's values, but it makes sense to use common drain for this purpose. In guitar electronics it's important to keep pickups in phase and have high input impedance, and low output impedance. Also, changing phases is often looked down upon unless it's necessary.

Welcome to AAC!
I don't see why each output needs its own buffer JFET. You could derive two (or more) outputs from one buffer JFET like this :-
View attachment 187340

Edit: This circuit draws about 300uA.
The goal is to have two exact copies of the pickup output sent to two volumes, then each of those go to EQ's with their own characteristics.

If only one JFET is needed to split the pickups that's great, but I wonder if there are two buffers so the signal stays clean, and can't travel backwards or interfere with each out (1 and 2)?
In spite of the critiques above, your circuit should be just fine. Alec_T's comments in post #3 would allow significant parts count and cost reduction.
That does look nice, and small too.
 

DickCappels

Joined Aug 21, 2008
6,640
The buffer would present a fairly low impedance to each following channel. Because of this they would not see the effects of each other because (supposedly) the output impedance of the source follower will be much lower than the impedance of the inputs.
 

Thread Starter

Amalgam

Joined Sep 4, 2019
27
The buffer would present a fairly low impedance to each following channel. Because of this they would not see the effects of each other because (supposedly) the output impedance of the source follower will be much lower than the impedance of the inputs.
So in Alec_t's schematic, the JFET offers low impedance to each channel, which isolates them. Then the individual channels will have lower impedance than the volume controls which feed the EQ's.
 

Thread Starter

Amalgam

Joined Sep 4, 2019
27
With the components shown, the buffer output impedance is about 150 Ohms.
That sounds like a lot more resistance than I'd need. Are there other JFETS that wouldn't use as much power that would work better for this use than the J304? The original schematic was for pedalboards I believe.
 

Alec_t

Joined Sep 17, 2013
11,735
That sounds like a lot more resistance than I'd need. Are there other JFETS that wouldn't use as much power that would work better for this use than the J304?
That 150 Ohms is a dynamic impedance. Power consumption of the buffer is determined by the 10k source resistor and is only ~2.6mW. Current draw is ~ 300uA. Substituting other JFETs makes no significant difference to the output impedance in the simulation, although power consumption does vary depending on the cut-off voltage of the particular JFET.
 
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Thread Starter

Amalgam

Joined Sep 4, 2019
27
That 150 Ohms is a dynamic impedance. Power consumption of the buffer is determined by the 10k source resistor and is only ~2.6mW. Current draw is ~ 300uA. Substituting other JFETs makes no significant difference to the output impedance in the simulation, although power consumption does vary depending on the cut-off voltage of the particular JFET.
Okay, thank you. I'm going to try to make a few of these. I should get my soldering iron in the mail soon. Next, ordering components.
 

Alec_t

Joined Sep 17, 2013
11,735
Oops. I was determining the output impedance incorrectly. It's ~1k5.
Edit: The J304 was an arbitrary choice for the simulation. Other n-JFETs should be suitable for this project. R1 could be 2.2 meg if that's easier to obtain than 2 meg.
 
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Thread Starter

Amalgam

Joined Sep 4, 2019
27
How would the OPA1641 compare to the J304? How would I determine the difference in power consumption?

I'm looking at power dissipation as well. Will three of these create much heat? They seem like really small components.
 

Thread Starter

Amalgam

Joined Sep 4, 2019
27
I don't have a Spice model to test that, but from its datasheet it looks ok.
The OPA1641 would be more of a current hog (1.58 mA per channel).
Okay, thanks. I ordered some J201's, LSK189's, OPA1641's, and all the resistors and capacitors. Next are breadboards, and breadboard components + 18v battery source. Went with Ansar capacitors and Vishay resistors. I was surprised at how much talk there is about which is best, and how much people are willing to spend (up to $50ish) for a single capacitor, but mine were about $4 each, I think, and the resistors were $.50 each or less depending. Everything should be here by Thursday, except for the bass pickups which will arrive probably around two weeks from now. It'll give me time to do everything else though.
 

Alec_t

Joined Sep 17, 2013
11,735
mine were about $4 each
Even that seems very expensive :eek:.

Edit:
You may find you need to alter the jfet gate bias or attenuate the pickup signal, to avoid distortion if you use the J201, since its cut-off voltage is low (in the -0.3V-1.5V range).
If you breadboard the circuit keep all connecting wires to the minimum length needed. With the high impedances involved at the fet gate, the circuit will be prone to pick up interference. You will need screened wire for the pickup wiring.
 
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Thread Starter

Amalgam

Joined Sep 4, 2019
27
Look in my example at the distortions. The scheme of #3 will give even more distortions. I think the author of the scheme can count them himself.View attachment 187474
Can you see how much the different JFETs, say the CPH3910, would affect the distortion for the schematic in post #3? I doubt it'll make up the difference, but it'd still be interesting to see. I know the J304 isn't meant for use in audio applications.
 

Thread Starter

Amalgam

Joined Sep 4, 2019
27
Even that seems very expensive :eek:.

Edit:
You may find you need to alter the jfet gate bias or attenuate the pickup signal, to avoid distortion if you use the J201, since its cut-off voltage is low (in the -0.3V-1.5V range).
If you breadboard the circuit keep all connecting wires to the minimum length needed. With the high impedances involved at the fet gate, the circuit will be prone to pick up interference. You will need screened wire for the pickup wiring.
I'll keep that in mind. What do you think of Bordodynov's post? It looks like a 20 times difference in distortion when the components are the same as the ones he used.
 
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