Does this work in theory? - DBA Robot

[kodiakklub]

Does anyone see any glaring issues with this? I built it into a pcb and its DED. no sound of any kind what so ever. I had to draw this from an unverified drawing i found that was questionable of its correctness. thanks in advance.

HT8950 Datasheet: http://www.sparkfun.com/datasheets/Components/General/8950v110.pdf

[chi_boy]

Looks like the datasheet says to feed it 4.5v, but it looks like it is getting 9.0 from the supply. 

[wavley]

Looks like the datasheet says to feed it 4.5v, but it looks like it is getting 9.0 from the supply. 

Those 1n5227s are 3.6v zeners, they should have used the right symbol on the schematic.

[Scruffie]

Edit: Nvm.

[Govmnt_Lacky]

This might help:

http://www.generalguitargadgets.com/projects/20-modulationecho/124-dh-pitch-shifter

Another project based on the 8950 chip.

P.S. I built this project and... IMHO.... it sounded like complete ARSE!

[kodiakklub]

Looks like the datasheet says to feed it 4.5v, but it looks like it is getting 9.0 from the supply. 

Those 1n5227s are 3.6v zeners, they should have used the right symbol on the schematic.

"they" meaning me
i dont think there is a zener symbol in gm's eagle library but i will double check and correct. or pull it from the stock eagle lib.
i get the proper voltages on both chips = 3.5v and -3.5v at their respective pins. and the way i read the datasheet says anything over 4vdc is a problem for the 8950. i did have 4.1 the first time i wired it, so i may have cooked it. hopefully a tenth of a volt wasnt too much for it.

[kodiakklub]

oh and i did check for solder bridges and grounding issues on the board, checked out fine. ill try taking the FSW out of the path and see if its that. anyone see any other reason why this would not work? why is the 072 being fed -3.5v instead of the usual positive?

[wavley]

Looks like the datasheet says to feed it 4.5v, but it looks like it is getting 9.0 from the supply. 

Those 1n5227s are 3.6v zeners, they should have used the right symbol on the schematic.

"they" meaning me
i dont think there is a zener symbol in gm's eagle library but i will double check and correct. or pull it from the stock eagle lib.
i get the proper voltages on both chips = 3.5v and -3.5v at their respective pins. and the way i read the datasheet says anything over 4vdc is a problem for the 8950. i did have 4.1 the first time i wired it, so i may have cooked it. hopefully a tenth of a volt wasnt too much for it.

Sorry, didn't mean to hate I knew what they were by the way they were being used, shouldn't have gotten nitpicky.

oh and i did check for solder bridges and grounding issues on the board, checked out fine. ill try taking the FSW out of the path and see if its that. anyone see any other reason why this would not work? why is the 072 being fed -3.5v instead of the usual positive?

Looks to me like it's being fed bipolar +/- 3.5

[kodiakklub]

wavely: NO WORRIES HERE  brother!!
everyone: a lack of pulldown resistor shouldnt kill the signal entirely correct? it does pop the first time being engaged after a power up, but i expect that with no pulldown.
BTW, cant say how amazing jack white was last nite at roseland. best encore of anyone ive ever seen. carry on

[Govmnt_Lacky]

When comparing to the project that I linked above ^^^

I noticed that you are tying -VA to pins 4 & 5 of the TL072. The GGG project only has -VA going to pin 4. Pin 5 of the GGG project goes to GND.

Check that out! 

[kodiakklub]

When comparing to the project that I linked above ^^^

I noticed that you are tying -VA to pins 4 & 5 of the TL072. The GGG project only has -VA going to pin 4. Pin 5 of the GGG project goes to GND.

Check that out! 

yes i totally caught that all by myself!! very proud guppy over here  also, on the drawing i copied, the 3 pin of the trimpot went to literally nothing. i guessed and sent it to ground. should it be tied to pin 2 ala vari resistor?
UPDATED!!

[kodiakklub]

Dam: updated again. version 3. corrected pulldown resist value to 1M not 1K
I will etch a new board tmrrw and hopefully have this corrected my the end of the weekend.

[kodiakklub]

anyone have an answer on that trimpot? does lug 3 go to ground or ganged with lug 2? i had to guess and chose ground. i think its purpose is signal attenuation for the entire circuit. but someone please feel free to correct me thanks.......

[sundgist]

anyone have an answer on that trimpot? does lug 3 go to ground or ganged with lug 2? i had to guess and chose ground. i think its purpose is signal attenuation for the entire circuit. but someone please feel free to correct me thanks.......

I would assume the ground on lug 3 should not be there.
Remove the ground connection, linking to pin 2 is optional. That makes the trimmer a gain adjustment in the opamps feedback loop.

[kodiakklub]

thank. you. sir!!

[Seven64]

when i built the layout found on the other site, i wired the v- to both the sleeve of the input jack and the v- on the pcb where it hits the zeners.  it was not working at all until i cut the connection from v- to ground.  a slight trimmer adjustment, and it worked like the youtube clips sound.

[kodiakklub]

what other site? I also made that mistake. it put 4.1v on the 8950 and it was noticeably very warm. glad to hear that didnt cook it for you though.

[Jordan A.]

I don't see a resistor between the input jack and the inverting input of IC2A?  With an inverting opamp the gain is set by the ratio of the input resistor and the feedback resistor, something seems wrong there.  With the trimmer in the middle you have 527k from output to inverting input (with the ground leg unconnected) and 0 ohms from jack to inverting input, if we imagine 1 ohm of resistance from the jack/wires/solder joints (just to make the math easy) we get a gain of -527,000, unless I'm seeing it wrong.

With a 560k resistor from jack to inverting input you would have a gain of about -1 with the trimmer in the middle, and you could go up or down with the trimmer, maybe a place to start?  I have no idea how much gain you will actually want here, but probably less than -527,000.

regards,

jordan

:edit: or is it supposed to clip to the rails?  Maybe it's supposed to be like that?  :edit again: ...but then there would be no reason to have a trimmer there, I think something is weird with the input as drawn.

[sundgist]

what other site?

Take diystompboxes.com, replace "diy" with "free" and "com" with "org".
Search for "Death By Audio Robot"

There is a schem there which is similar to yours and also a few layouts.
Check out how the switching is wired there is a diagram on page 7 of that thread.

I had a play with a slightly different version of that chip. Made some nice noises but never got around to finishing it off. It's still on one of my breadboards.
Good Luck

[kodiakklub]

funny, thats the schem that I copied from but i found it on revolutiondeux.blogspot.com. nice to see the original thread from where it came and a log of all the debugging. i etched the new board yesterday and will hope to have it soldered up by the end of the weekend. stuck inside at work all weekend. blech. at least being at work is where i do 90% of my pedal making