Treble Boost

[borge]

Sorry, missed this.

decrease the emitter resistor (R6).

Whats the voltage at the collector? probably easiest to test at lug 3 of the pot.

just over 4V


need to do some more audio messing (r6 etc) on the one here, but mrs rocky is watching tv..

now I'm confused.. I was measuring the voltage at the emitter, not collector, cos the emitter is directly connected to pin 3 of the pot, not the colllector.. the collector (pin 1 of the xistor) has 9V...
there some confusion here? what have I messed up?

I'm confused too Yes, I mixed E & C up, but to me, that doesn't explain 9v at C, there should be some voltage drop across R6, maybe there is but the power supply is above 9V? either way It's at the limit of my limited knowledge did you have an audio input or short the input while testing? May be a job for FSB?

[rocklander]

noper.. no audio.. just powered it up and banged the DMM across it...

I did start an FSB thread.. mictester (seems pretty on to it) suggested the 20K pot instead of 10K, which I did (well, since PB wanted this thing to always be full on, I just threw a 20KR in there) and when I tested it on the jansen there was a boost, but because it's treble filtering and dropping the mids + bass the total vol was pretty close, sliiightly more - thought that was the desired effect, but without the original here to compare, an assumption was (and had to be) made.

[handlefras]

Hey rocky, PB, borge et al. I just breadboarded my rangemaster up today following the tonepad schematic here:
http://www.tonepad.com/getFile.asp?id=83

Concerning the pinout, I'm 90% sure I'm correct in saying the collector is connected directly to lug 3 of the pot. From what I've read it appears the emitter is denoted by an arrow on the schematic (the direction of the arrow changes depending whether its NPN or PNP).

PNP transistor symbol

Transistor_PNP_symbol.png (5.48 KiB) Viewed 21 times

now to my other findings:
I used a Germanium CV7003 (OC44) transistor measured at 129hFE. According to R.G Keen the optimal hFE is between 75-100 so its a little off. I found it really difficult to bias this up correctly to get around 7V on the collector. I ended up making Rb = 100k and Re = 2k4 to get the 7V bias. Using the specced values (admittedly for the rangemaster not T-boost) I only had 2V at the collector. The change to 7V added a bit more gain but not a lot. I was surprised as I expected more gain/distortion. In the end it seems to be just a boost which emphasises the treble frequencies, good for pushing an already gritty amp but not as a standalone distortion on a clean amp. YMMV etc..

It would be worth dialing in the transistor to around 6-7V as Borge said but I don't think that will give you a high gain tone. The 20K pot seems like it might be on the right track but other than that and a change of transistor, nothing else can make a difference (I swapped just about every other component and couldn't get more gain).

Note: changing of the input cap (C2) did allow nice tonal adjustments. E.g: a larger value added mids and bass, a smaller value adds more treble if that is possible!