Replies to This Discussion

Permalink Reply by Tom Lauten on December 19, 2014 at 12:37am

Thanks.

My only reservation about putting the preamp ...

(The Tillman one here without gain or volume pots...http://tagboardeffects.blogspot.co.uk/2014/05/a-pair-o-preamps-echo...)

After the pots is not having decent tone control as it is a passive system at that point coming off a piezo, I have heard the tone influence is minimal that way.

• ▶ Reply

Permalink Reply by Tom Lauten on December 19, 2014 at 12:39am

Actually, it looks like the preamp in that photo is between the pickup and the pots.

• ▶ Reply

Permalink Reply by Scott aka Farmer Ted on December 19, 2014 at 2:05am

Hi Tom,

Saw this discussion and did some research. First, it seems that with this circuit, as with many alternate versions of FET based bass pre-amps, the potentiometer is 50K. It should be of the linear-taper kind. Second, the alternate versions indicate that the pre-amp should be in the signal path AFTER any pickup selector switches, and volume/tone pots.

I have attached on link to a schematic & description that gives some useful help:

http://www.till.com/articles/GuitarPreamp/index.html

On a side note, I am currently working on a series of overdrive pedal circuits...as well as continuing with my 1/2 watt amplifier circuits. These are lots of fun, and bridge the time-gap when waiting for glue to dry.

• ▶ Reply

Permalink Reply by Scott aka Farmer Ted on December 19, 2014 at 2:07am

I should add that there are likely, other applications of the circuit in question, where the pre-amp receives the piezo signal, and then sends that through the vol/tone pots, and then out to the output jack. Experimentation is always a good idea to see what results suit your ear best.

• ▶ Reply

Permalink Reply by Scott aka Farmer Ted on December 19, 2014 at 8:43am

While logarithmic pots are used for the volume controls of a guitar (reason is that humans perceive audio volume in logarithmic form), using a linear taper pot for the pre-amp control allows for a more precise and proportional variable resistance of the pre-amp signal. The more precise, the more easily one can fine-tune the response in the preamp.

• ▶ Reply

Permalink Reply by Tom Lauten on December 20, 2014 at 1:14am

Thanks everyone. Really interesting info.

I'm not arguing but I really find the idea of tone (especially) being before the preamp very odd as most posts about tone control of piezo output say that it doesn't work very well at all. Apparently it acts more as a secondary volume.

What you guys suggest is seemingly diametrically opposed to this. Surely boosting the raw signal to a impedance/level more inline with a magnetic pickup BEFORE the tone and volume makes sense or is there something else at play here that I'm not seeing?

• ▶ Reply

Permalink Reply by Scott aka Farmer Ted on December 20, 2014 at 1:48am

The link I had mentioned earlier had a lengthy discussion thread about the Tillman circuit, and its variations. But at no time did any of the participants mention if they were using a rod piezo or a disk (but I believe it was the former). I imagine each of those piezos has a different influence on how the Tillman reacts and operates.

But in the bigger picture, it really comes down to what works/sounds best to you. Why not test each theory in your specific application to see?

• ▶ Reply

Permalink Reply by Tom Lauten on December 20, 2014 at 2:41am

Yeah, I think the "suck it and see" approach is the only way through this. I'll make up a preamp with some screw terminals so I can reconfigure the set up till I find what I'm happy with. Nice thing is that a DIY Tillman or op amp preamp costs pennies to do.

I will keep this thread going as I get results.