The Synchro-Bleed Circuit

Discussion in 'Technical Side of Things' started by Synchro, Feb 17, 2020.

  1. Synchro

    Synchro The artist formerly known as: Synchro Staff Member

    Jun 2, 2008
    Tucson
    Admin Post
    For some time, I have had some problems with the sound of my G6122-1959 when the volume was rolled back 90 degrees. Cranked all the way it sounded fine to me, but my stage strategy is to roll the master volume back 90 degrees as my default setting, so I have some room to increase volume on the fly.

    A couple of months ago, I visited Lavonnes in Savage, MN and Pancho gave it a listen, coming up with the perfect explanation; when the volume was rolled back, it lost all presence. He suggested a treble bleed and when the word “presence” was used it all made sense.

    The basic idea of a treble bleed is to use a small value capacitor to allow highs to bypass the volume control, which means that the highs will remain strong, even when the volume control is rolled back. For the non technical people reading this, simply think of a treble bleed circuit as a shortcut that allows the higher frequencies (especially overtones) to get out to the amp without going through the volume control. In theory, if the volume is turned all the way up, the treble bleed has little, if any, effect. As the volume is turned down, the volume of treble frequencies does not drop,as quickly. If you have a Fender amp with a bright switch, this is a treble bleed at the amplifier.

    Treble bleed circuits come in a variety of designs and, like everything in our modern world, there are all sorts of approaches. My challenge was to find one that worked for my needs. I did some research and found a virtual smorgasbord of information here: https://drkevguitar.com/2016/11/24/treble-bleed-mod-roundup/

    After reading that, I came up with my own idea. Keep in mind that our perception of sound is not analog, it is logarithmic. Specifically, a doubling or halving of a value is a relatively minor change. So if you put a resistor in parallel with the capacitor in a bleed circuit it would require a doubling of halving of the value of that resistor in order to produce a perceptible change.

    When a resistor is placed in a treble blade circuit, the taper of the pot will be affected. Is this problematic? Faced with that dilemma I decided to try something a bit different. As I understand it, a .001 uf cap’ with a 150 k-ohm resistor in parallel will make the pot taper more gradually. So, being an obstinate old cuss, I decided on a .001 uf cap’ with a 75k-ohm resistor in parallel and a 75 k-ohm resistor in series with the cap/pot in parallel. My theory was that the taper of the pot would be somewhat less affected. So, how did it do?

    My G6122-1959 is somewhat unique, in that I have Supertrons in both the neck and bridge positions. This gives it a bit stronger highs on the bridge pickup than the Classic + and suits my tastes quite well. I like some degree of brilliance in my playing, even when I’m playing Jazz and I like to use my various Gretsch for straight ahead Country (think Telecaster) sounds.

    Once I soldered then treble bleed in place, I did a quick setup to balance the pickup volume between pickups and to balance the low strings with the higher strings. Then I rolled back the master volume by 90 degrees and gave it a listen. The results were pleasing.

    First off, the taper of the master volume was quite well preserved. I got a decent volume cut at -90 degrees from full-up and a nice smooth taper up to full volume on the master volume control. I had wanted to avoid creating an unusable taper, but this was not the case. I can live with this taper and do so happily.

    The timbre remains bright and brilliant as the volume is rolled down. The sound on the neck pickup is somewhat reminiscent of a Gibson Johnny Smith model. The Smith is designed for stronger highs than the typical archtop, while maintaining a strong bottom end the effect is a mix of typical Jazz guitar warmth with great strength in the upper register.

    Switching between pickups, I found that the highs were strong without being overwhelming. On the bridge pickup, I got as close to a Telecaster as any archtop could get. In fact, the overall effect is somewhat reminiscent of a solid body, with regard to the strength and focus of the higher frequencies, while preserving the warmth and sonic girth of an archtop.

    Is it perfect? Good question. I will opine that it could be improved upon, but considering the ordeal of performing surgery on an archtop without F holes, I doubt that I’ll be tinkering with the success I’ve achieved so far.

    I plan to add this same treble bleed to my G6120-DC, which is somewhat challenged when it comes to highs, by virtue of the fact that the mute moves the bridge pickup about an inch further away from the bridge itself. It’s a guitar with powerful mids and quite useful for filling a lot of sonic space, but it’s somewhat lacking in the upper frequencies sparkle that I desire. Strangely, my two G6119s don’t seem to need a treble bleed, so I’ll reserve judgement on the matter until I’ve had some time to compare them back to back. It’s interesting that my G6119-1962 and my G6120-1962 (the DC) have the same basic wiring harness, but sound quite different from one another.

    Overall, I’d say that I’m definitely in favor of treble bleed circuits and can say for a certainty that my G6122-1959 is a much more versatile instrument for having performed the mod. Every modification, especially electrical mods, nvolces a degree of trade off, but I see this treble bleed as being an excellent compromise. You could tweak the cap values, cutting the cap value in half would make the highs that pass through a bit higher and result in a bit less “in your face” effect. I feel that the compromise of using two 75 k-ohm resistors in series with the cap in parallel with only one of the resistors is a good one. The taper is quite nice and the bleed circuit does not have quite as much authority as it would with a more conventional design. Overall, I would say that the circuit is exceeding my expectations.
     
  2. new6659

    new6659 Country Gent

    Could you please show that treble bleed wiring arrangement in a diagram?
     
  3. Ricochet

    Ricochet I Bleed Orange

    Nov 13, 2009
    Monkey Island
    So in a nutshell, you cleverly combined the Seymour Duncan and the Kinman treble bleed?
    Ok since you’re in the pioneering spirit, how about making them adjustable resistors and see which one affects the circuit most?:)
    I always felt results were affected by pickup impedance mostly and then the total load of the circuit. Then I realised I’m not an engineer.
     
    pmac11 likes this.
  4. thunder58

    thunder58 Super Moderator Staff Member

    Age:
    61
    Dec 23, 2010
    tappan ny
    Admin Post
    .......I'll second that
     
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  5. DennisC

    DennisC Synchromatic

    Age:
    37
    862
    May 11, 2017
    Germany
    That could be really interesting - and I am an engineer.

    ... But not one in the field of electronics and stuff...
     
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  6. Synchro

    Synchro The artist formerly known as: Synchro Staff Member

    Jun 2, 2008
    Tucson
    Admin Post
    I'll third that. :) See attachment.


    It would be dependent upon the values of the rest of the circuit. As clearly as I can think before having my morning caffeine, if you used these resistor values on a Tele (with 250 k-ohm pots) it would make the taper of the volume pot much more gradual. If you used it on a Jaguar, (with 1 meg-ohm pots) the effect on the taper would be significantly less noticeable than the effect on the Tele, and somewhat less noticeable than the effect on a guitar with 500 k-ohm pots. The impedance of the pickups would come into play, to some degree, but it would require a doubling or halving of pickup impedance before it became noticeable.
     

    Attached Files:

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  7. Synchro

    Synchro The artist formerly known as: Synchro Staff Member

    Jun 2, 2008
    Tucson
    cowmoo likes this.
  8. Synchro

    Synchro The artist formerly known as: Synchro Staff Member

    Jun 2, 2008
    Tucson
    Admin Post
    I did breadboard some ideas, but it’s hard to shield breadboards, so the tests were a bit noisy and of little value. I’m sure it could be done, but not with items I have around the house.
     
    Ricochet likes this.
  9. capnhiho

    capnhiho Gretschie

    476
    Feb 16, 2013
    California
    Thanks for your R&D work on this project, Synchro. I think I’ll try it on my modded 5420. I have a Supertron neck pup, Classic+ bridge pup as a TVJ non-treble bleed wiring harness. I installed a treble bleed from some parts I had on hand (don’t remember the component values) which improved tone somewhat, although not dramatically. Your description sounds like what I need (the tone in my head).
     
  10. Synchro

    Synchro The artist formerly known as: Synchro Staff Member

    Jun 2, 2008
    Tucson
    Admin Post
    I think it will work very well with that pickup combo. The Classic + is not quite as bright as a bridge Supertron, but it’s still fairly bright. A treble bleed with these values should compliment the Classic + quite well.

    The Classic + hits a sweet spot, for many purposes. It’s powerful enough to have some body, but not so powerful that it is hard to keep clean. It’s a Filtertron with just a little bit extra and that pushes it into an entirely different realm.

    Tonight I started preparations to put the same treble bleed into my 6120-1962, aka 6120-DC. It has Duo-Trons and the guitar has a naturally strong midrange both acoustically, and also because the bridge pickup is set about an inch from the bridge in order to leave room for the mute. I’m hoping that the bleed will strengthen the highs a bit and bring it more closely in line with the rest of the Gretsch family.

    The DCs are a great instrument, having been used on the Let It Be album and was also an instrument Chet respected. He kept one in his office, for a time in the ‘60s. It probably feels as nice to play as any instrument I’ve ever had in my hands. Allowing a few more highs to make their way out the output-jack should only make things better.
     
  11. Synchro

    Synchro The artist formerly known as: Synchro Staff Member

    Jun 2, 2008
    Tucson
    Admin Post
    Tonight I installed the Synchro Bleed (TM) on another guitar, my trusty G6120-1962 A.K.A. a 6120 DC. This guitar has somewhat different pickup placement which gives it a stronger midrange. While I’ve loved the feel and playability of the instrument, the output to the amp has always been a bit of a quandary, because it had such strong mids.

    After installing the bleed, as detailed above, I gave it a test play. It maintained its brilliance, even with the master volume at roughly 50% rolled back. The sound is different from the typical 6120, but doesn’t stray too far from the classic single cut sound.

    I had been concerned that it might be too shrill, but the effect was more one of strength and solidity in the upper range, but no harshness. Overall, it’s pleasing and makes the instrument more usable than ever. It still sounds great for Jazz.for something that costs, roughly nothing, you can get some great sounds,
     
  12. EarleG

    EarleG Electromatic

    20
    Dec 19, 2013
    Hendersonville TN
    I installed just the .001 uf capacitor on my master volume and it works perfect. Some
    other wirings like Telecaster with the cap only usually overcompensate and thin the sound
    more as volume is decreased rather than keeping it the same. I guess it must be the Gretsch
    overall wiring and how the master volume fits in that makes it work as intended.
     
  13. Synchro

    Synchro The artist formerly known as: Synchro Staff Member

    Jun 2, 2008
    Tucson
    Admin Post
    There are several approaches to treble bleeds and each of them has their own charms. For me, it came down to volume taper. I looked at all sorts of approaches and came up with this as the best compromise.
     
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