Passive boost for guitar

[guitarguy]

Hey,
I'm not someone who is technically minded but I would like to build a passive "boost" for my guitar (increase signal with no batteries). I think I can do it with just the signal from the guitar amp. I know that Yamaha has made this work with a transformer. Is there any reason that a transistor circuit wouldn't work?
Thanks!

 

[danadak]

You want to boost just V off a pickup (passive as well ?) or power ?

What is pickup, piezo, magnetic. electro magnetic, accelerometer.?


Regards, Dana.

 

[guitarguy]

Just the voltage. The pickup is electro magnetic. This is normally done by using a small amplifier powered by a 9V battery.

 

[rjenkinsgb]

Transistor circuits are active and need power.

A transformer can change voltage levels, but with a loss of power, and changing impedance.

Also, a guitar pickup needs a very high impedance load or the output is just muffled or killed.
A guitar amp or pedal usually has an input load somewhere between 500K Ohms to 1M Ohms, or more.

An audio transformer with that high impedance is a very special and expensive item, if they even exist??

Can you provide a link to the Yamaha device? I can't find anything about it..

 

[guitarguy]

Heres a link to someone demoing it.

 

[rjenkinsgb]

Have you read the comments? This one covers what I said above, about impedance and loading:

Fender Bass​

3 weeks ago (edited)
With a transformer turns ratio of 1:2, that will indeed double the voltage driving the amp, which is also 6 dB. However, that comes at a price. The load impedance seen by the guitar pickups decreases 4-fold. If the amplifier has a 1 Meg input impedance, that now looks like 250k which will dampen the resonance of the pickups. Further, the cable capacitance will be multiplied by 4. For example, a 10 foot cable with 300 pF of capacitance will look like 1200 pF to the pickups with the boost on. Both of these factors will darken the tone by suppressing high frequencies.
Read more

Another possibility is that they are just using very high output pickups, and the output is halved by the transformer in the non-boost position?? eg. The switch is de-cut, not actual boost.
That would mean the amp load appears even higher in the low output position.

No one seems to have published a schematic for that setup yet, so the actual config is guesswork..

I have a keen interest in guitars as well as electronics, so very interested and curious about this; though most of the time when I do get chance to do anything with them it's renovating or refretting ebay or secondhand shop finds, for friends.. These are some of my "keepers"

Guitars

Some of my guitars & gear

www.flickr.com

 

[Nigel Goodwin]

Hey,
I'm not someone who is technically minded but I would like to build a passive "boost" for my guitar (increase signal with no batteries). I think I can do it with just the signal from the guitar amp. I know that Yamaha has made this work with a transformer. Is there any reason that a transistor circuit wouldn't work?
Thanks!

Yes, because there's no power - but a passive 'boost' is simple - you just have a passive attenuator, and then switch that out when you want boost. Compensate for the original loss by turning your amplifier up - or add a small preamp in the amplifier, as you've got power available there.

 

[danadak]

Given your amp probably has high Z inputs seems a shame to throw away signal.

The transformer idea probably one of the better ideas, as long as its shielded properly.
Keep in mind as you raise Zout of transformer the stray C and cabling C compromise
freq response, but guitars are not exactly a "high" frequency generator -

You can get passive G out of RC networks but very limited both in G and BW.
And Z's messed up.

Lastly a MagAmp, but I think not very practical and its use limited....

Magnetic amplifier - Wikipedia

en.wikipedia.org

Regards, Dana.

 

[rjenkinsgb]

Lastly a MagAmp, but I think not very practical and its use limited....

Magnetic amplifiers still require power!
They were quite common in older machine tools, for both current measurement and power control.

 

[danadak]

He did say with no batteries, but other power sources.....?

Magamps used extensively in Nuc Power Plant instrumentation..


Regards, Dana.

 

[audioguru]

Why can't you simply turn up the volume control on the amplifier? Because the amplifier volume control is already at maximum and it has an input resistance that is too low and it is killing the amount of guitar signal?

Adding a transformer between the guitar pickup and the amplifier to stepup the signal voltage will also kill more high frequencies.

 

[Nigel Goodwin]

Why can't you simply turn up the volume control on the amplifier? Because the amplifier volume control is already at maximum and it has an input resistance that is too low and it is killing the amount of guitar signal?

Adding a transformer between the guitar pickup and the amplifier to stepup the signal voltage will also kill more high frequencies.

Have you never seen a guitar amplifier AG?. They have high impedance inputs specifically designed for a guitar pickup, and have loads more gain than any sensible person is ever likely to need.

 

[AnalogKid]

and have loads more gain than any sensible person is ever likely to need.

HEY - watch your mouth. My brother resembles that remark.

ak

 

[Nigel Goodwin]

HEY - watch your mouth. My brother resembles that remark.

ak

I've done PA for bands over many years, I've a low opinion of male lead guitarists and volume controls

Funnily enough, female lead guitarists aren't a problem - the male ones are probably compensating for something

 

[rjenkinsgb]

and have loads more gain than any sensible person is ever likely to need.

Reminds me of something in a Deep Purple album - "Can we have everything louder than everything else"!

 

[audioguru]

He said he wants to increase the signal voltage. Maybe he should have said to boost the loudness. Then he needs an amplifier with more output power.

I increased the signal voltage from the video he posted by simply turning up my volume control.

He said, "It is normally done by using a small amplifier powered by a 9V battery". That sounds like a preamp designed for a guitar pickup. But he wants a passive circuit that does not need a battery to power it. He asked, "Is there any reason that a transistor circuit wouldn't work?". Of course not.

The video shows a transformer boosting only low frequencies, because its input impedance is too low.

 

[unclejed613]

Reminds me of something in a Deep Purple album - "Can we have everything louder than everything else"!

that was between song chatter on Made In Japan, if i remember correctly.

 

[kubeek]

Hey,
I'm not someone who is technically minded but I would like to build a passive "boost" for my guitar (increase signal with no batteries). I think I can do it with just the signal from the guitar amp. I know that Yamaha has made this work with a transformer. Is there any reason that a transistor circuit wouldn't work?
Thanks!

What leads you to the idea that you need higher output level from your guitar? Only thing I can imagine would be vast amounts of noise being picked up by long guitar lead with poor shielding, and that should be easily remedied by a better cable.
If you need to have higher output level because of the combo or distortion pedal or whatever then the better approach would be to have a pre-amp at the combo end.

Passive guitar pickup has very high impedance already, and combined with the capacitance of the cable creates a filter that kills high frequencies. If you add a transformer to the mix to increase the voltage level, the output impedance will be even higher and the loss of high frequencies even worse.

I would preferably mod the guitar and put a battery powered preamp inside, second choice would be a preamp in the rig (if that is even what you actually need).

 

[unclejed613]

He said he wants to increase the signal voltage. Maybe he should have said to boost the loudness. Then he needs an amplifier with more output power.

sometimes you need more signal voltage for certain effects devices, as well as the unique sounds made by overdriving the preamp on the amplifier (it's different than the sound made by clipping the amp output stage).

 

[kubeek]

Ok having watched that few seconds of the video, I can see the premise is to double the volume on a pull of a button. Transistor circuit or a circuit with an IC will work just fine, you just need to find a place for it and modify the guitar jack so that the amp is allways off when the jack is unplugged so you don´t drain the battery.
But a simple guitar pedal would work just as fine and you don´t need to operate it with the ever busy right hand.