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Ernie Ball VP Jr and Tone Suck, what ideas do you have?
Ernie Ball VP Jr and Tone Suck, what ideas do you have?
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Old 24th October 2019, 08:21 PM   #11
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Adam Reed View Post
...Newman Mints tin...
The one with the ram on it? That almost looks like an ElectroHarmonix product.


-Gnobuddy
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Old 24th October 2019, 09:03 PM   #12
IceFyre13th is offline IceFyre13th  United States
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I like what I see above, all great suggestions.

Yes the tube idea was a little hair brained, its a "What If " idea.

I did a little de-construction last night on the EB VP Jr, the original designer must not of been thinking. I am surprised it even works for some as it really loads down the pickups (that little resistor that can be added via switch to change the swell, oh god what were they thinking).

So I actually ordered that little buffer board I linked to earlier to play with, because from what I can see so far the pot needs to be isolated from the pickups being loaded as well.

Passive circuits have their time and place, used like this....not so good.

Tubes in the circuit, could be done, practical nope (maybe with a JFET follower)....I'm not really tied to them, like I said....What if

What I think we need is a buffer on the front end with an Input Impedance of 500KΩ - 1MΩ

This will keep the pot from being a variable load on the pickups, it will be real easy to change the pot in the pedal to anything usable for a volume cut (unity gain wanted,,,,,maybe a little boost.

Then to an output stage with an Output Impedance of 1KΩ - 10KΩ....

What really would be nice is a input circuit that has impedance matching (adjustable input impedance to match the pickups of the guitar). Bootstrap circuit???

Then cram all that on a PCB that can replace the original one....now I have my work cut out for me....and try to stay away from surface mount stuff so anyone can build it themselves.......and runs on 9 volts (standard pedal power).
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Old 25th October 2019, 06:34 PM   #13
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by IceFyre13th View Post
...What really would be nice is a input circuit that has impedance matching (adjustable input impedance to match the pickups of the guitar). Bootstrap circuit???...
For a guitar pickup, we don't actually want impedance matching. Instead, what we want is an extremely mis-matched load, a load so high that it's virtually infinite.

In Merlin Blencowe's tube preamp book, he has a section on electric guitar pickups. In a nutshell, the inductance of the guitar pickup interacts with the capacitance of the guitar cable, and any parallel resistance (volume pot, input impedance of amplifier, etc.)

What happens is that the inductance and capacitance together create a peak in the (treble) frequency response, which we hear as a nice attractive treble sound. However, the parallel resistance - the load on the pickup - reduces this treble peak, and makes the pickup sound duller.

If the pickup is unloaded (or loaded by a very high resistance, 1 meg or higher), not much damage is done to the treble peak. But as that resistance drops, the treble peak is suppressed more and more. If you lower that resistance all the way to around 100k, even single-coil pickups become dull-sounding, as the treble peak is almost completely lost. Humbuckers suffer the same fate at even higher input resistance.

All of which means, the ideal load impedance for your guitar is, basically, no load at all, infinite input resistance from the amp! But "infinite" is silly for many reasons, not least because there's already a 250k or 500k pot inside the guitar, and we can't reduce the load below that no matter we do outside the guitar.

So a more practical way to look at it, is that our guitar amp input (or buffer) should have an input impedance that's much greater than 500k.

1 M really isn't "much greater than 500k", so there's maybe a little room for improvement. I think 1 meg was about the practical limit with valve amps, because there is a little bit of grid current flow through that input grid bias resistor. So that value (1 M) is where the industry settled, back in the 1950s or 1960s.

Today we can do better, if we use a JFET as the input stage. There is no harm (and may be a slight benefit) in going up to, say, 2 or 3 M input resistance. I often use 2.2M.

All this time, we've talked about the load resistance. But, let's not forget, the load capacitance plays a huge part in the pickup sound as well!

And that, I think, is where there is room for experimentation. Switching different small-value caps in parallel with the pickup can be an effective treble control, and it doesn't take away the resonant treble peak that makes pickups shimmer and sound good. There was a small company that sold a 12-way rotary switch with a bunch of small SMD caps on it, designed to replace the stock guitar tone control.

I've also seen a clever circuit using a bootstrapped capacitor tied to the input. By varying the amount of bootstrapping, you vary the input capacitance. The idea was this would interact with the guitar pickup in the same way as the rotary switch with caps.

There is a catch, though: the rotary switch thing works because it's inside the guitar, wired straight to the pickups. But there's a volume control between the pickup(s) and the bootstrapped-input-cap circuit - and if that volume control is turned down from max, everything goes bad; the clever bootstrapped input capacitance just rolls off all the guitar treble, causing major "tone sucking".

In short, I don't think there really is a clever way to load a guitar pickup using an external buffer or preamp! We don't want an optimum load, and we can't add an optimum capacitance. All we can do is follow the doctor's Hippocratic oath: "First do no harm." All we need is just a buffer with at least 1 M input impedance, maybe a bit more if possible.


-Gnobuddy
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Old 25th October 2019, 07:22 PM   #14
IceFyre13th is offline IceFyre13th  United States
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I always like reading your responses, between me over thinking and you being a voice of reason.....we could be a good engineering team...
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Old 25th October 2019, 09:00 PM   #15
JMFahey is offline JMFahey  Argentina
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Short answer: forget tube buffers.
Lots of disadvantages and ZERO advantages.
WTF you want a tube for?
You won´t even HEAR the d*mn thing because it feeds a Tuner!!!

Not that a tube buffer adds anything useful to low level sound anyway.

Not sure about your tuner either , IF designed for guitar use it should have 1M input.
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Last edited by JMFahey; 25th October 2019 at 09:02 PM.
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Old 25th October 2019, 09:08 PM   #16
Gnobuddy is offline Gnobuddy  Canada
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Thanks for the kind words!

I over-think the heck out of things, too. Sometimes so much that it completely stops me from even getting started, because why even start if it's not going to be the bestest possible?

"Paralysis through analysis", as a ballroom dance teacher I knew once called it. In his line of work, if you stop to think, it's all over!


-Gnobuddy
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Old 25th October 2019, 09:55 PM   #17
IceFyre13th is offline IceFyre13th  United States
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I will leave this here as I don't want to be evil.


YouTube


Someone didn't see where I said, just for fun....or get that it might be a fun exercise.


But back to the fun,


The pre-built board will be here tomorrow, I will see what they did and report back. Maybe it will be fine, maybe be something that needs a few better parts to "clean up".


This is it, VPJR Volume Buffer Retrofit Kit - Griffin Effects
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Old 26th October 2019, 12:06 AM   #18
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by IceFyre13th View Post
I will leave this here...
It's been a long time since I saw the movie. But I remember being quite impressed by Madonna's work, both as an actress, and most especially as a singer.

The thin, whiny, nasal voice I remember from her 1980s hits was gone, and in its place was the beautiful vocal tone colour of a singer who has been taking singing lessons, learning classical singing technique, and working hard at becoming a better singer.

I have no respect at all for Madonna's public persona or the road she took to fame. But I do respect an artist who continues to work to improve her craft.
Quote:
Originally Posted by IceFyre13th View Post
That looks nicely engineered. I would never have imagined such a niche product existed! It's a bit like finding that somebody makes an upgraded rear window for 1982 Fiat Spider 2000s, to replace the factory one that always turned into an opaque yellow mess within a few years...


-Gnobuddy
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Old 26th October 2019, 05:08 AM   #19
PRR is online now PRR  United States
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Fender liked 1Meg, but when humbuckers overloaded early input he compromised on a 136k divider.

A range of Ampegs used 2.7Meg even 3.9Meg. Different? Probably not a lot, but perhaps audible in the factory break-room.

You adjust guitar load capacitance with cable. A 3-foot cable is bright but limiting. A 30 foot cable dulls the sound. If you only play cowboy rhythm you could make a 100 foot lead, but many amps have a way to dial the treble right out without having to pack a reel of wire.
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Old 26th October 2019, 06:46 PM   #20
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by PRR View Post
Fender liked 1Meg, but when humbuckers overloaded early input he compromised on a 136k divider.
I've always wondered about the choice of such a low input impedance, in an era when all pickups were passive. All the humbuckers that have crossed my path become noticeably duller-sounding with a 150k load, compared with 1000k.

I've read that Gibson (the only humbucker-equipped guitars at first) initially aimed their electric guitar offerings at jazz, with its typically duller and more muted sound compared to later genres of popular music.

This applies even to Gibson's first solid-body, the Les Paul; not only did the carved top and traditional body shape mimic their hollow-body archtop jazz guitars, they even signed up a fellow who was primarily a jazz guitarist, albeit one who dabbled very successfully in pop in his later years, to endorse it and put his name on it. The Les Paul is still used for electric jazz: The Les Paul Guitar Can Play Jazz (Here’s Why!) - Tone Topics

So I wonder, did Leonidas or his electronics tech go with that very low input impedance for humbuckers because, at the time, guitars with humbuckers were supposed to sound like jazz guitars?
Quote:
Originally Posted by PRR View Post
You adjust guitar load capacitance with cable.
Most of my guitars use humbuckers. I used 10-foot (3 m) cables for a while, but they are so short that they almost mandate sitting down next to your amp while you play. Eventually I compromised on 15-foot (5 m) cables.

At least one of my guitars (a 335-style semi-hollow) gets very dull-sounding as soon as the volume knobs are turned down from "10". The stock pickups are over-wound and too muted on their own, and the lack of treble bleed caps on the internal volume pots makes that worse.

A pickup change and the addition of treble bleed caps are in the works. But this is the hardest type of guitar to do that sort of work on, as you have to install and remove the harness through the narrow f-holes.
Quote:
Originally Posted by PRR View Post
If you only play cowboy rhythm you could make a 100 foot lead
I remember reading about some rock guitarist who liked to use a long, coily guitar cable. The cable surely rolled off lots of treble, but the heavily overdriven fuzz-box / distortion pedal / guitar amp put it back.


-Gnobuddy
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