Treble Bleed capacitor values

[Polecat]

Hi all,

I'm having difficulty finding an effective way to stop the perceived loss of brightness when you turn down the volume on my emando (a custom built solidbody 8 string built in the mid 90s by Siegfried Dessl, a luthier in Stuttgart, Germany). I recently installed an Almuse Aggressor humbucker, and changed the value of the tone control capacitor from 47 to 22 mF, the potentiometers are 250k. Wiring in a standard-value 22nF between the sweep and output lugs of the volume pot has no appreciable value, whilst increasing the value by 2 or 3 times merely makes the volume control act as a treble cut (!) for the first part of the sweep, before reducing the volume. I've checked my wiring, everything is correct, and am both puzzled and frustrated. Has anyone got a suggestion as to what I could do differently to get the ***** thing to behave decently?

[Tom Wright]

Here's a page I found that uses the bleed cap (down the page a ways, "treble-saver volume control"), but also a resistor to tailor its response. The poster says he actually uses a trim pot to dial in the effect. Input is outer leg, output is wiper, .001 mfd cap and 150K ohm resistor short from wiper to ground.

http://www.guitartechcraig.com/techwire/tone.htm

[Andy Miller]

A 500k pot might be a better choice for that pickup if it's eating treble super quickly as you turn down. The treble bleed cap should be much lower value than a normal tone cap. .001uf or "102"

[Polecat]

I've thought about increasing the value of the volume pot; the problem is that it has a very small body and I'm having difficulties sourcing a suitable replacement here in Germany. I've realized that my thinking was wrong increasing the value of the capacitor, I need to use a smaller value. Can you tell me what a "102" is?

[Andy Miller]

"102" is the marking you will see on a .001uf capacitor. It denotes the capacitance in picofarads, with the third digit specifying the number of zeros to follow the first two digits. In this case, 1000 picofarads or 1 nanofarad or .001 microfarad.

[pops1]

Most humbucking pickups use a 500k pot, if you can find a small one to fit your cavity I would put it in. If you don't need to turn down to 0 you might try a 250k resistor is series with the pot. You will only be able to turn down half way, kind of, but it might help your high loss.

[thistle3585]

Use a linear taper pot on tone and an audio pot on volume. At 10 both will be 100%, at 0 they will both be 0%. at 5 the linear will be at 50% and the audio will be around 25%. Caps .02 (or .022) and .047 (or .05) change what frequency is rolled off when using the tone control. a higher value cap will give you a darker sound with less treble than a smaller value cap when the tone is at 0. The lower the resistance of the pot then the more treble that will leak through.

[Polecat]

I've now managed to source 500k pots with a sufficiently small body size, and have ordered a selection of capacitors around .001uF, so I can experiment. I'll post the results when the components arrive and I have time to play around.

[pops1]

I would have to look it up for value, but a resistor and cap across the volume input and wiper will retain highs when turned down, some like it some don't. The 500k will help. I also like .02mfd coupling caps in the amp as opposed to .1 and .01.

[thistle3585]

I use Almuse pickups on all of my instruments and always use 500K pots with audio taper on the volume and linear on the tone. I use a .022 capacitor that goes from one leg to the case of the tone pot. I've never had a complaint.

I attached the wiring harness that I use. If you're not using the on/on/on switch then the green wire goes to ground.

[Polecat]

Hi thistle3585,

I think you're confusing the tone control with what I'm talking about here. The tone control cap goes as shown in your attachment, the treble bleed cap goes between the two active legs of the volume pot - its function is to allow high frequencies through uninterrupted by the position of the volume knob, to counteract the apparent loss of brightness when one reduces the volume.

[thistle3585]

I'm with you. I was just wanting to offer up my experience with the Almuse pickup.

[pops1]

Here are a couple of sites I found:

http://www.guitar-mod.com/rg_diag_treble_bleed.html

http://www.ratcliffe.co.za/articles/volumepot2.shtml

[Dave Greenspoon]

I own one of the mandos Andrew made. Works perfectly...trust him.

[Polecat]

Thanks to everyone who has contributed. The parts arrived today and after several hours soldering, unsoldering and soldiering on I came to the following conclusion:
With the high impedance Almuse aggressor, I found to my surprise that a 250k volume pot sounded better to my ears than a 500k one - the higher resistance volume control seemed to reduce the low mid range and make the mandolin sound thinner - wiring a 250k resistor between the end of the pot normally earthed and ground had the same effect. I left the tone control at 250k with a 22mF cap as a high-pass filter to ground. Again, increasing the total resistance of the pot "thinned out" the sound. I have no idea why this should be (electronics is not my strong suit).
A 0.001mF cap as a treble bleed was far too effective - the sound grew brighter and jangly as volume was reduced - I tried playing around with a 250k pot wired as a rheostat both in parallel and series with the cap, but was not happy with the result. Increasing the value of the cap to 0.002mF proved much more satisfactory - the tone still changed with reduction of volume, but in a way I like - there seems to me more definition when strumming hard (and slightly overloading the (valve-) preamp).

[pops1]

Polecat, that's what it's all about, sound, experiment and what YOU like. Glad it worked out. Usually humbucking pickups want the 500k, but the added highs for a mandolin that it gave weren't good for your ear. There have been times I have left the 250k for slide players on guitar as it was not as biting.

[Polecat]

You are so right, pops1 - in spite of the fact that there are a lot more emandos to be had than back in the mid 90s when I commissioned the instrument, and there are now magnetic pickups specifically for mandolin (the original pickup I replaced was designed for electric saz, and was an active single-coil), in comparison with e-guitars and -basses, the equipment available and knowledge base is still pretty meagre. Experimenting is the only way to achieve a good sound.
There are still no amplifiers for mandolins (although I vaguely recall there is a firm in the british midlands who modify early Fender designs) generally available, and plugging into a guitar amp is a sure way to make your emando sound like an e-guitar tuned way too high. As you noted, changing the values of the coupling caps affects the frequency response, as does playing around with the r/c combinations in the tone control. Back in the 90s I built a 15W tube amp because I couldn't afford to get a technician to modify the amp I had (and couldn't tell him what I wanted as I didn't know myself). Right now I have two low-power tube amps (single-end with a 6AR5, about 3W) from the 60s made by the Dutch firm Jennen which I plan to mod., but I don't understand them myself - the preamp uses two EBC 91 tubes, a single-enclosure triode double diode valve, and the diodes are also wired into the circuit (!). I have no idea what they do - the first thing is to draw a schematic; being 60s hand-wired amps, they resemble the birds nest one finds inside old radios, so it will take quite some time. But its fun.

[pops1]

My guess is the diodes are the rectifier for the power supply. It you want, to try use all .02 mfd caps for coupling and in the tone control. It kind of makes the tone control like a second volume, but for harp, slide and mandolin it helps. An 8" speaker works best in my opinion for warmth. I think a tube amp is best for these, but sometimes the small ones can distort too soon. I built one like and old Valco with 6 volt preamp tubes and it was great for mando, my son has it tho in his many amp line up. Sounds very bluesy.

[Polecat]

My guess is the diodes are the rectifier for the power supply...

They're doing nothing! This is what the first tube system looks like:

Attachment 143810

My guess is that Jennen, who also made Radios, had the EBC91 tubes in large numbers (a triode/double diode makes sense in a radio circuit) and chose to put them in these amplifiers for no other reason than that they already had them; the diode plates are connected back to the input to avoid parasitic capacitance (I'm guessing). The 100k voltage-drop resistor on the input is nice - I bridged it, and got a pretty groovy lead sound. As the amp has 2 input jacks, you could switch between rhythm and lead with a foot-switch.

Here's what it looks like:

[pops1]

Attachment didn't work, but that is ok, looks like the perfect rig for a mando or harp. Yea they used up anything back then that was lying around. "A penny saved is a penny earned" was a common saying in that time era over here.

[Polecat]

Here's the attachment again:

[pops1]

Interesting, don't think I have ever seen that configuration in a tube before.