Does a DI box affect vintage fuzz/wah pedals?

[DaxLiniere]

Hey gang,
We all know that using a buffered pedal before certain vintage fuzz and wah pedals can (usually) negatively affect the sound of the fuzz or wah, but is that also true when an active DI box with a passive thru is being used?

In other words, if a guitar is connected to a vintage fuzz/wah pedal which is in parallel* with an active DI box, will the signal be affected? (impedance match, etc.)
*the 'link out' socket of most DI boxes is literally a parallel connect to the 'guitar input' socket.
If so, is there any particular DI topology which could avoid or minimise this?

I'm building a switcher device which is intended to not affect the signal in any meaningful way. The idea being that the output of the device (1 in, 5 out (but only one at a time)) is essentially identical to the input (from the guitar), to enable it to be able to be used with abovementioned vintage fuzz and wah pedals.

(Same goes for a buffered tuner output which I'd also like to include.)


Thanks for reading this far, I look forward to reading the forum's sage advice.

All the best!
Dax.

 

[DFischer]

The higher the input impedance of the DI, the less it will effect the interaction with the guitar and fuzz pedal. But note that even quality DI's have a great range of input Z. The Countryman 85 has an input Z of 10Meg, while Radial's J48 has an input Z of 220K. Is 220K enough? That's probably a function of your ears and the fuzz/wah that you are using. 10Meg probably won't have any effect under any normal circumstances.

Also be sure that the guitar output is truly parallel to the input. The Bo Hansen DI is an awesome DI, but the guitar out is buffered and probably wouldn't play nice with a fuzz.

 

[totoxraymond]

The Bo Hansen DI is an awesome DI, but the guitar out is buffered and probably wouldn't play nice with a fuzz.

That's why i disregarded the amp output from my own Bo Hansen DIs but instead added a linked jack.

 

[DaxLiniere]

Thanks for the responses.

I've done some research into those devices you mentioned and see that both Countryman and Hansen are transformer-coupled at the output.
For the switcher unit, I'd like to find a transformerless design, if possible. I guess this can be done with TL072. I can't find the exact input impedance of a TL072, but I did find this useful information, including a comparison table which says JRC4558 is "around 5M ohm" and that TL072 is higher, so I guess that IC would be a great start.
https://www.avaq.com/technology/jrc...ferences-and-how-to-choose#simple-list-item-2

The other restriction I have is that only single-rail (+12v DC) is available, but I suppose there are ways around that, too.

 

[NOON]

Yes, any FET based opamp used as a buffer will have a very high input impedance and be unlikely to affect your effect. Make sure you include ground lift switching, as ground loops can be an issue.

 

[JohnRoberts]

"DI boxes" cover a pretty diverse spectrum of SKUs.

These range from relatively low impedance passive transformer DI boxes that step up the input impedance by the transformer turns ratio squared, all the way up to several megOhm high input impedance active DIs that present very light loads.

JR

 

[DaxLiniere]

Thanks, guys.

I found this post from Jakob (Gyraf) which has me enthusiastic about using the TL07x variant:

https://groupdiy.com/threads/very-high-impedance-direct-box.30607/

 

[Newmarket]

Thanks, guys.

I found this post from Jakob (Gyraf) which has me enthusiastic about using the TL07x variant:

https://groupdiy.com/threads/very-high-impedance-direct-box.30607/

No need to make this opamp specific tbh - any opamp based DI/buffer will have a high input Z - set by the impedance to 0V typically set by a resistor/ resistors to 0V rather than the opamp itself. But, of course, the TL07x is a "GoTo" device. But if interested in lower noise and distortion then there are better alternatives now.

 

[DaxLiniere]

But if interested in lower noise and distortion then there are better alternatives now.

Thanks Newmarket. Yes, DEFINITELY interested. OPA2134?? OPA1642??

The bonus would be that there are 2 outputs in one chip, that way I could do both DI and buffered output for tuner in one package. Everything will be SMD, so no limits on my end.

 

[Newmarket]

Thanks Newmarket. Yes, DEFINITELY interested. OPA2134?? OPA1642??

The bonus would be that there are 2 outputs in one chip, that way I could do both DI and buffered output for tuner in one package. Everything will be SMD, so no limits on my end.

OPAx134 definitely. Lots of others - look through the TI website. But in context of electric guitar TL07x would be fine if you have them to hand or they are more convenient to obtain. The main point is that you can realise any required input impedance with any opamp buffer circuit. The input impedance is not the datasheet input impedance of the opamp itself.

 

[DaxLiniere]

Thanks Newmarket.

 

[JohnRoberts]

FWIW Last century I designed an active direct box for Peavey (EDB-1). I used a TL072 bifet op amp and the input impedance was defined by a 3M resistor termination across that input.

JR

 

[micolas]

I am very curious how this interesting project will evolve. I have always felt (and used as creatively as possible), directly, the interaction between the guitar (selection/combination of pickups, volume/tone potentiometers, interpretation technique) and fuzz.

 

[cliffsp8]

Hi folks. First post here, but this subject is close to my guitar's heart

To me, there is nothing quite like playing a strat neck PU into a Fuzz Face type fuzz with fuzz knob dimed, turning down the guitar volume to about 3 and getting the sweetest clean tone. Then gradually turning up the volume control and having the tone warm up and thicken with very little increase in volume until about 7 it start to break into warm fuzz and at 10 it is so thick you can paint the walls with it.

Using the link out of the DIs that I have does not affect fuzz effect, but the Fuzz Face DOES affect the signal that the DI gets.

This is because the input impedance of the Fuzz Face is about 20K - which when it is connected directly to the poor strat PU (i.e. when the gtr vol knob is at 10) it causes the signal voltage to drop and the high frequency response to plummet. This also the signal the DI will get - if this what you want, then great!

When the gtr vol is turned down the series resistance of the volume pot adds to the 20k of the FF and reduces the load on the PU - hence sweet tone, and the gradual warming as the series resistance reduces as the gtr vol knob advances to 10.

So in this instance the input Z of the DI is certainly not critical and any decent op amp with 1M bias/pull down resistor will do.

Fuzz rules!

Cliff

 

[JohnRoberts]

When I designed my Active DI (long ago) I included a TS unity gain buffered through output, as well as the low Z differential output for feeding a mixer mic input.

JR

 

[DFischer]

Cliff makes an excellent point. I forgot about the low Z input of the fuzz affecting the guitar's dry tone, and hence the DI tone. So if the guitar output is buffered, the fuzz doesn't sound right, and if it's not buffered, the DI signal doesn't sound right. Is there any way to get both to be right?

 

[cliffsp8]

I guess it depends on what the DI signal is to be used for. If it is to go to a DAW for recording, it will be just right for post-processing with a Fuzz Face plug in, but not much use for anything else.

Unfortunately the it's the lowest Z load of two parallel feeds that effectively loads the source down, and a zillion ohms input Z of a second feed will just get a highly accurate version of that loaded source.

Maybe stereo pickups are the way to go?

BTW, the trick of using a transformer to mimic the magnetics of a pickup (so you can run a Fuzz Face after a buffer, or a wireless connection) doesn't really work!