BBD probe

[Dirk_Hendrik]

OK, something different but handy as hell!

If there's something I really can's stand it's the adjusting the bias of BBD based circuits in order to tune the distortion to minimal while coping on the BBD's output. The signal is sampled and when scoping the output of a BBD one has to "see" the correct signal (from a sinewave generrator) "through" the samples. pretty tough to determine hom much distorting there's left. The rough tuning is easy but the details are not.

So, I took the output filtering of an Ibanez AD-9 delay and made a small probe containing this circuit:


and the bottom where the electronic parts live:


When hooking this up to your scope and probing on the BBD's output pins one will get a perfect, filtered signal to see which is really easy to adjust.

And.... it's a giveaway:
http://www.dirk-hendrik.com/temp/bbd_probe.pdf

(5 pages long including board layout and silkscreen)
the transistors are emitterfollowers so, in this case, the type barely matters.

[gtrwrks]

Very cool.

[bajaman]

thanks for sharing Dirk - very nice easy solution
cheers
bajaman

[noelgrassy]

Big ups Dirk! That's a brilliant test implement. That's so cool of you to share.

[lolbou]

Dirk,

I looked at the reticon specs and tried to understand the purpose of filtering the output signal. I just can not...

May I ask here for a tiny explanation? I think I'll try to make a through hole version of your probe to check my SADs, but don't really know what could be needed...

[IggY]

Dirk,

I looked at the reticon specs and tried to understand the purpose of filtering the output signal. I just can not...

May I ask here for a tiny explanation? I think I'll try to make a through hole version of your probe to check my SADs, but don't really know what could be needed...

ever been to DIYstompboxesforum and did a search for anti aliasing?

[bajaman]

ever been to DIYstompboxesforum and did a search for anti aliasing?

ever posted anything other than a reference to another forum which continues to deny this forum's existence
bajaman

[lolbou]

ever been to DIYstompboxesforum and did a search for anti aliasing?

Wow. Friendly man... You help a lot, and anybody seeking info here will bow in front of you...

I tried twice to log on this so-called forum. It failed twice and never got an account created. Don't you worry, I know what anti-aliasing is since I'm a graduated man, and was able some years ago to put it in beautiful equations, which is quite useless to me now...

I come here for help and instruction and have been through the max things I've found. Still I have problems in understanding. I'll look on your topic, which looks interesting, but send me to other BBD datasheets, which I hope will be clearer about filtering than the SAD1024A one...

The thing I don't get is what do you (or could you) observe on a scope with a fully working SAD+clock fed with an audio signal. What if the filtering is out?

[IggY]

something similar to this:
http://en.wikipedia.org/wiki/Discrete-time

[IggY]

ever been to DIYstompboxesforum and did a search for anti aliasing?

ever posted anything other than a reference to another forum which continues to deny this forum's existence
bajaman

yes:
https://www.freestompboxes.org/viewtopic ... a&start=20

Whatever happened to the RECENT thread/ post regarding my advice to change all the electrolytics!!!!
bajaman

just click your "profile" box, from there in the User statistics "search user`s posts"
you`ll get a list of your last posts sorted chronologically,
with indication of the forum and the topic

and don`t forget:
https://www.freestompboxes.org/viewtopic ... a&start=40

Further learning here:
http://www.opamp-electronics.com/tutori ... _03_01.htm

OH dear
The band is the cathode - what a terrible faux pas.
Thanks IggY for bringing this error to my attention.
My convention has always been to draw the end with the band as the + end.
This signifies the direction and flow of positive current in the circuit.
On the diode symbol the + end is the end that the stylised arrow symbol points to - this is rightly termed the cathode not anode as I earlier infered.
To make matters more complicated, the current flow referred to actually flows in the oposite direction, as an electron is a positively charged particle
In the diode symbol we have a stylised arrow pointing to a straight line (the end with the band on the physical diode).
It denotes the DIRECTION of positive flow from the anode to the cathode - the anode is connected to the POSITIVE terminal and in this case the diode is said to be forward biased and consequently passes the positive current through the cathode to the rest of the following circuit (although for silicon 0.65v is dropped through the internal action of the diode conducting - 9 volts on the anode becomes 8.35 volts at the cathode).
I do hope this explains things correctly.
Once again thanks to IggY for the learning link - I suggest you visit it if still confused with bands, anodes, cathodes, + signs, and current flows.
Cheers
bajaman

[lolbou]

Wow again. This makes the thread even more informative and clear...

Keep poping Iggy...

[IggY]

o.k. last try: http://acapella.harmony-central.com/sho ... ?t=1867732 click to start the first appearing youtubeclip
and watch and listen only for the first 35 seconds:
imagine the triangle wave to be the clean audio which is getting to be truncated by reducing the rate of sampling
which again is similar to reducing the clockrate of a BBD.
The stairsteps that appear is what is being filtered by the outputfilter to smear the stairs to a smooth slope like at the start of the clip.

[mastercaster]

This is cool indeed.
I never worked with a scope before, so i have some stupid questions:
I connect the BNC out from the scope to the input jack of the probe ?
Does this probe need 9 volt power ?
Do i need an additional grounding clip on the probe ?

kind regards