9V vs. 8v in Boss pedals

[Kent S.]

Hey all,
Interesting thing, I wanted to know if anyone had an explanation as to the following. In a lot of the newer BOSS pedals I've noticed that instead of running them on the filtered 9V and then selecting  4.5V as a bias, some of the newer pedals take the filtered 9V to a Jfet (wired as some type of preset resistor apparently) which knocks the voltage down to 8V, they take that and then make a bias of 4 volts ... the switching and led system uses 9Vs, but the audio portion uses 8vs. Any idea as to why they do this on some pedals? Thanks.

[Elektrojänis]

Are you sure it is a jfet and not a small 3 leg regulator like 78L08?

Or maybe the jfet is somehow wired as a regulator? Maybe they wanted make sure that the power suply to the audio circuit is smooth and quiet.

[cd]

It's probably for polarity protection (how's that for alliteration?)

[jplaudio]

[Kent S.]

Are you sure it is a jfet and not a small 3 leg regulator like 78L08?

Or maybe the jfet is somehow wired as a regulator? Maybe they wanted make sure that the power suply to the audio circuit is smooth and quiet.

Well on my FW-3 Foot wah it say SK118 (being discussed in another thread BTW) ... to my knowledge that's a jfet ... the did this in the DS-2 turbo distortion (I hate that pedal ... sorry), but I don't think the did it the same way or using the same components. It definitely is 8V with a 4V bias, and the Led and switching uses the full 9V ..? Odd, I'd love to know the reason.

[Kent S.]

It's probably for polarity protection (how's that for alliteration?)

? What the heck would that have to do with polarity issues, I mean it's the audio portion of the circuit ... the only difference other than normal is that it has 8V with 4V bias as opposed to 9V with 4.5V bias ... I don't get it? :?

[Kent S.]

Hey all,
Interesting thing, I wanted to know if anyone had an explanation as to the following. In a lot of the newer BOSS pedals I've noticed that instead of running them on the filtered 9V and then selecting  4.5V as a bias, some of the newer pedals take the filtered 9V to a Jfet (wired as some type of preset resistor apparently) which knocks the voltage down to 8V, they take that and then make a bias of 4 volts ... the switching and led system uses 9Vs, but the audio portion uses 8vs. Any idea as to why they do this on some pedals? Thanks.

The circuit Boss(like in the BD-2) uses is a series regulator in its simplest form.  Unlike a 3 terminal regulator or a zener type regulator there is no "drop out" voltage so the regulation is constant even at voltages below 9v.  It is effective in reducing ripple in the DC supply.

Yeah but why did they drop it down to 8V is still my question, or are you saying that that's just a byproduct of the regulation process used?

[jrc4558]

Lover headroom for certain purposes? I would see it as a positive in a distortion cirquit...

[Kent S.]

Lover headroom for certain purposes? I would see it as a positive in a distortion cirquit...

Hhmm, I didn't think of that;hwever I still wonder why they did it in a wah, and other pedals as well. Gives me something to think about though,thanks.

[jimbob]

the did this in the DS-2 turbo distortion (I hate that pedal ... sorry)

i hate that pedal too--mines in pieces :twisted:

[strungout]

Hmm as I've heard and experienced, high gain distortions sound better with a lower voltage (I'm currently using 7V on the last pedal I build)...

[jplaudio]

[Kent S.]

I should correct my previous post...the circuit is not a regulator but a capacitance multiplier similar to a gyrator.. the capacitor in the base circuit is multiplied by the current gain of the transistor. If a zener diode is used in the base circuit it becomes a regulator. The voltage drop is function of the transistor junction. The voltage drop is about 0.7 volts. with a 9.6 vdc input the out put  is 8.89 VDC.

So basically they used a preset miller capacitor to increase the filtering of the power supply to the actual audio portion of the circuit? And the voltage drop was merely a byproduct ...correct? That would explain it, I was looking at it from the perspective of the voltage drop alone, the circuit is marked 8V then as a reference (visually). I didn't notice a cap in that part of the circuit though, I'll have to go back and check that. This is interesting and makes good sense ... especially when used in a gain based circuit. Thanks.