LM13600 vs LM13700 Revisited

ExpAnonColin · April 29, 2005, 03:04:34 AM

What do you mean, the lower frequency? You mean the lower side of the peak?

-Colin

gez · April 29, 2005, 03:31:08 AM

Quote from: Paul Perry (Frostwave)Gez, you can make that triangle as flat as you want by overdriving half of a ... 13700!

Paul, it was Colin who had this problem!

gez · April 29, 2005, 03:38:51 AM

There's a schematic on the net (DOD?) which is worth playing around with. It's wrong, but if you know your stuff you can figure out the mistakes. There's also the Penfold wah, plus the SVF in the LM13700 data sheet.

Breadboard them, tweak them, learn and you'll get a stupendously good filter (my favourite type is a SVF constructed from the LM13700 - try the lowpass output)!

Brian Marshall · April 29, 2005, 03:52:56 AM

Quote from: ExpAnonColinWhat do you mean, the lower frequency? You mean the lower side of the peak?

-Colin

yes... its not a true bandpass... its a hi pass and a low pass in one... the more i play wiht it the more useless it sounds... i know the HPF frequency in theory should be moving very little...

So far im just playing arround with it. seems to me the tremelo would be pretty easy... but its late... gotta get up early tomorrow... this weekend should be fun...

Truth is that an hour of experimentation was worth 20 hours of reading for sure.

Im off to bed... my head hurts. Learning is hard... but worth it.

puretube · April 29, 2005, 04:25:40 AM

http://cache.national.com/ds/LM/LM13700.pdf
fig.11+12, or 14...

Brian Marshall · April 29, 2005, 08:32:54 PM

Quote from: puretubehttp://cache.national.com/ds/LM/LM13700.pdf
fig.11+12, or 14...

yes, ive looked that over quite a bit... I'm more or less trying to simplify it. I dont care if its a true perfect bandpass filter, just trying to make something interesting. Basically the filter is a very minor part of something else im trying to make... so using 20 parts for a band pass isn't really what im looking for.

A good nights sleep has really refreshed me though.. Im going to get back to work soon.

Anyways, I feel like i have my head wrapped arround these things a little better now. wish me luck.

puretube · April 30, 2005, 02:23:55 AM

err, actually I wanted to point brother Colin`s attn. to those 3 figs...

ExpAnonColin · April 30, 2005, 02:37:09 AM

I haven't tried the app note filters I'm afraid. Mine is based off of Tim's 9v MS-20 clone as well as the version for synth by the french guy. But like I say the LFO sweep is just not big enough, and before Ic ould get it figured out I was in England, now I'm back with other things on my hands... Someday soon

-Colin

Brian Marshall · April 30, 2005, 02:57:33 AM

Well im reporting back with my findings. I found that the 13700 ota's were just not what i was looking for in a filter circuit. I was able to get some interesting results, but with a lot more parts than i really wanted to use.

My original (meaning first attempt... im sure someones done it before) fake bandpass filter probably sounded the best. it used only one side of the 13700. It still lacked resonance, but the sweep was actually pretty good.

Then i tried using one side as a variable low pass filter (see datasheet for approximation of what i was doing), and sending the trasistor output from the first low pass filter through a cap to the output of the other OTA. I was hoping that i could create a band pass filter (or a fake one anyways) by using the variable output impedance of the 2nd ota. I biased the 2nd ota to 4.5 volts so that i could use the darlington output. I was hoping that the cap from the first and the output impedance of the 2nd stage would form a strong filter resonance. In short it did something, but i coldnt really tell if there was true resonace, or what... It didnt sound even, and the sweep seemed limited. I may go back and try again, but I think an opamp based filter i made last year, with a lot less parts sounded better.

I am feeling discouraged.

Sorry i didnt draw any of it up... I still remember the jist of them, so maybe tomorrow.

ExpAnonColin · April 30, 2005, 03:18:06 AM

What are you using to control resonance? Just listening? I would try some sort of all-encompassing feedback loop as I am not currently picturing what you're doing

Sorry you're feeling discouraged. Go to bed man! It must be at least midnight where you are.

-Colin

Brian Marshall · April 30, 2005, 03:58:22 AM

yeah, im sort of working backwards here... i started breadboarding to gain some insight... i need to sit down and draw up what i want instad of just throwing more parts at it.

anyways... I will try and try again... this wasnt acutally the purpose i originally had in mind for the ota's anyways, so it's not that big of a deal...

BTW yours will ship tomorrow.... 5 duals right?

gez · April 30, 2005, 04:52:26 AM

QuoteMy original (meaning first attempt... im sure someones done it before) fake bandpass filter probably sounded the best. it used only one side of the 13700. It still lacked resonance, but the sweep was actually pretty good.

Try both halves in a SVF configuration, if you take the time to set it up right you can get a superb sounding filter which uses less parts than its op-amp counterpart. Resonance galore if you want it!

ExpAnonColin · April 30, 2005, 12:41:07 PM

Righto, Brian. And if you want you can let me know what's going on in your filter and we can sort of work on it together.

-Colin

Brian Marshall · April 30, 2005, 03:25:45 PM

I think ive found what i was looking for with an opamp design.

I think i will revisit the 13700's later. For now, i think ive learned what i wanted to learn. I dont feel like want to reinvent the wheel on this one, as I already have this project drawn up with opamps. I just wanted to see if i could get away from using opto's if i could. As it stands right now, the opamp filter only has 7 or 8 parts to it, and uses a single opamp. For me, this is a lot less holes to drill on circuit boards.

I think ill sit down with the OTA's in a couple weeks, and find some other uses for them

troubledtom · April 30, 2005, 05:53:19 PM

i can't get the data sheet to open :evil: :evil: :evil: :evil:
help,
- tom

puretube · May 01, 2005, 02:23:48 AM

you need "Acrobate Reader" (Adobe) installed on your PC (a .pdf viewer)

(sometimes a bit slowish loading...)

Paul Perry (Frostwave) · May 01, 2005, 07:27:59 AM

I have no idea why, but it is always MUCH faster to download the .pdf as a file, then open it from there (that is, not via the browser). This is a reasonably big file from memory, so it might just be taking a while or clogging the browser. Maybe try downloading from another site, also.

troubledtom · May 01, 2005, 11:41:25 AM

i had too many windozzzzzzzzzzzzzzzzzzzze open, thanx gents.
peace,
- tom

News:

LM13600 vs LM13700 Revisited