Question about the Dr. Boogey schematic.

[Hupla]

Im just having a look at the Dr. Boogey schematic on Guassmarkov's site http://gaussmarkov.net/layouts/drboo/drboo-schem.png And I'm a tiny bit confused by it.

See the potential divider at the top to the left? It gives off Va and Vb. And from what I can see Va will be 0v and Vb will be 4.5v DC.

I cant see how this schematic will work with Va (being 0v) going to the first 2 FETs and Vb goin to the rest?

Am I missing something here?

[DUY1337GUITAR]

100 ohms is not going to drop the 9V by 4.5V each.  What the gaussmarkov version special for is it's extra filtering to reduce noise.  You may see many pedals which has a 100 ohm resistor following right after the 9V input with electrolytic caps connecting that to ground.  This is just filtering.  All the Va connects together and all the Vb connects together.  What makes the 4.5V is the adjustment of the 100k trimpot. 

I think Va is at the end with TWO 100 ohm resistors because the first two gain stages need extra filtering (which are vulnerable to noise I believe). 

this is the first time I closely looked at this schem
I think I'm gonna make a perfboard layout for the gaussmarkov layout to share sometime...

[shadowmaster]

Va can't be 0V because for DC signals ,caps will be open circuit.

[Hupla]

I wrote out a huge reply there and then was thiniking about it and I just copped on that the dc was blocked to ground by the caps.
Thank god my reply was stopped by Shadowmaster replying. Ha thanks alot guys. I know feel like more of a tool.

[DUY1337GUITAR]

cmon, learning is fun 

EXCEPT SCHOOL!
I got a 2-3 on my last AP English essay and now I'm pissed.

[Hupla]

cmon, learning is fun 

EXCEPT SCHOOL!
I got a 2-3 on my last AP English essay and now I'm pissed.

Well i wouldnt call it learning I'd call it missing the blatently obvious haha

I dunno what that means haha. Im irish and weve got different marking systems.

[DUY1337GUITAR]

Advanced placement (AP) classes are high school courses which have college level courses.  Essays are graded on a scale of 1-9.  9's are super rare, and each grade has a specific definition (which are critical).  In AP classes, our goal is to get a 6 which is really hard to get and considered passing in college.  My last essay was placed between 2 and 3 and I got mad at that.  Even though it would be an A+ for a regular high school English class, it's considered a failing paper in AP.

I wish I waited before I took this class, because I've become more into stompboxes and it's making me procrastinate.

I just finished taking pics of my finished homemade guitar and going to make a video of photos, my subscribers and friends have been bugging me about it.
After that, I'm going to try to make a perfboard layout for the gaussmarkov layout if I have time, just for fun because I think I'll use it too in the future.

I wish you luck when you start building   

[PRR]

I know you figured this out but...

> See the potential divider at the top to the left? It gives off Va and Vb. And from what I can see Va will be 0v

Why zero? There's no ground. Ignoring Vb, Va is two FETs each with 1.8K under them. The worst possible case is with Trim1 Trim2 set to zero, the FETs somehow biased dead-short. Then Va is two 1.8K resistors parallel, 900 ohms. The "potential divider" is 100+100+900. And (still ignoring Vb) this puts Va at 900/1100 of 9V, or 7V. That's not unreasonable.

However this "dead short" DC assumption also implies a dead-short on the signal. Four places. We don't need that many parts to short a signal. Surely the FETs are acting like bigger resistors, and the trims are not zero. Knowing a little about typical FET bias, the 1.8K resistors will show 1V-4V, current will be 0.5mA-2mA each, 1-4mA for both. This flowing in the 100+100 resistors gives 0.2V-0.8V drop. Good 8V, bit over.

Now Vb also powers two FETs, similar except one has 3.9K under it. Be lazy, pencil another 1-4mA. Then R16 has 2mA-8mA (both Va and Vb) and drops 0.2V-0.8V. Vb is over 8V. R17 flows 1mA-4mA, drops 0.1V-0.4V, sits near 8.7V-7.8V.

Since the Trims go up to 100K, and since the drain often sits near halfway up the supply, we might assume there is a case (some FETs) where each FET stage acts more like a 200K resistor. Against the 100+100 ohms in the supply filter, this is roughly 200,00/200,200 or 0.999 of 9V, 8.99V. I happen to think this extreme is unlikely. However it does not matter. The one ridiculous extreme says 7V, the other unlikely extreme says 8.9V, either way will work fine.


> it would be an A+ for a regular high school English class, it's considered a failing paper in AP.

I dunno your side of the pond, but in the US there is a BIG shock from high school to college. You think you are smart in high school, but half your class will become car salesmen, carpenters, shopping-trolley cowboys. Some of the semi-academic students go to trade schools or community colleges, get a good mid-level education. When you get into a real College, you are with the top 10% (whatever) of all high school students. Now you don't look so smart.

I slacked-off and got-by through high school, but when I got to college I was unprepared to do the hard work. I got a few B and A grades and a lot of Fs. After a few years they threw me out, with nothing to show but heavy bills and loan payments. Along the way I lucked into a once-a-lifetime Ideal Job, but do NOT bet on that.

Decide if you want to get a degree or be a fishmonger. A guy with a degree has more spare cash for playthings.

Even if you are thinking a technical degree, study English. My father was a brilliant computer engineer, but he wished he had more teaching and learning in communications. A good idea is no good if you can't propose it clearly to the dweebs who decide which project goes ahead and which project gets axed. Part of keeping my job 29 years was learning (took a while) to explain things clearly to bosses and underlings, nothing to do with the technology.

[Hupla]

Advanced placement (AP) classes are high school courses which have college level courses.  Essays are graded on a scale of 1-9.  9's are super rare, and each grade has a specific definition (which are critical).  In AP classes, our goal is to get a 6 which is really hard to get and considered passing in college.  My last essay was placed between 2 and 3 and I got mad at that.  Even though it would be an A+ for a regular high school English class, it's considered a failing paper in AP.

I wish I waited before I took this class, because I've become more into stompboxes and it's making me procrastinate.

I just finished taking pics of my finished homemade guitar and going to make a video of photos, my subscribers and friends have been bugging me about it.
After that, I'm going to try to make a perfboard layout for the gaussmarkov layout if I have time, just for fun because I think I'll use it too in the future.

I wish you luck when you start building   

Ah right. Sure I still dont understand my college's overall gradings

But yeah best of look with that. And link me to the video when your done and good look with the layout.

Thanks

[DUY1337GUITAR]

http://www.youtube.com/watch?v=hCVpBTJ9gLQ
Be warned about the music, there's some explicit language in there.  I let people contact me about letting me use their music on my videos.  Benefits me for being in terms with YouTube and benefits them by promoting their music

I think I'll try to attempt the layout in the weekend