Build Your Own Clone Message Board

Hi,

Can anyone tell me how I can do the Keeley mod on the OD1? I never bought the kit for the TS-808 so I don't know what component's need to be changed. Thank's

As I understand it the Keeley generic mods are -

C4 = 0.1UF more bass, less mid-range hump
R7 = 2.4K more max gain
R6 = 20K cleans up more
C5 & 6 = 0.18uF more tone range
1uF electrolytics replaced with 1uF film caps
Gold contact IC socket fitted

Keeley replaces the op-amp with TI RC4558P
Part IDs reference the BYOC schematic in the download instructions.

Some of this is already taken care of in the BYOC kit. I believe also there is some nonsense with two output resistor values on some of the original pedal issues that cannot possibly make any difference to the sound. As far as I can recall this is all described on the Keeley web site.

Thank's, I'll try it out... If I change the input impedence to 1M ohm, will that change the tone in any way? Would it make it better?

Also, in order to change the input impedence, that would mean changing all three 511K resistor's to 1M, correct?

Increasing the input impedance of an effects pedal will generally mean that it places less load on a guitar so you get more output and an increase in treble. However some distortion pedals rely on guitar loading as part of the effect. The classic Fuzzface for example places quite a heavy load on the guitar and the design is such that the guitar controls affect the feedback circuit.

In the case of the OD1 it is likely to do more good than harm. There are two 511K resistors in the input circuit R1 and R3 (there are three 511K resistors in the entire pedal, but only these 2 affect the input impedance). These are effectively in parallel, resulting in an input impedance of 250K odd. To arrive at an input impedance of around 1M you would have to increase these to 2M or 2.2M for a standard value. However there may be a problem with the input transistor bias if you raise the base bias feed resistor to 2.2M. The transistors supplied may be any of four different types. The MPSA18 often have very high gains so will likely bias OK with a 2.2M. A very low gain 2N3904 might not.

One of the 511K - R1 is fitted as a switch click stopper so I suppose you could alternatively change R3 to a 1M and R1 could be much bigger - say a 4.7M.

If the bias is OK the top of R4 (10K) should sit at around 4 volts. If the base is starved of bias current this voltage will be noticeably lower.

Is this for the current Overdrive kit?

http://www.buildyourownclone.com/overdrive.html

If it is, this is exactly the information I've been looking for. Just want to be sure before I start soldering.

Thanks all

-ImpossiblyFunky

Yes it is for the current version of the OD1.

While I'm here - the Tube Screamer is often regarded as being at its best with a single coil Strat style guitar. Presumably because the TS 'mid-boost' suites the single coils for lead tones and over cooks the mid range a bit for 'buckers. The single coil Fender guitars commonly use 250K controls and lower impedance single coil pickups so they are less likely to be loaded down by the 500K input impedance of a genuine TS. The BYOC clone input impedance as noted is lower at 250K because of the 511K pop stopper.

On a humbucker equipped guitar the pickups are generally higher impedance and 500K control are used.