electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Articles  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links  |  Store
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
Live streaming at radio.electro-music.com

  host / artist show at your time
  Faux Pas Quartet and friends Music From Last Thursday
Please visit the chat
 Forum index » DIY Hardware and Software
filter
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 2 [26 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Goto page: 1, 2 Next
Author Message
blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sat Feb 16, 2013 2:38 am    Post subject: filter Reply with quote  Mark this post and the followings unread

fiilter
Last edited by blackyellow on Sun Mar 03, 2013 8:46 pm; edited 2 times in total
Back to top
View user's profile Send private message
blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sat Feb 16, 2013 2:55 am    Post subject: Reply with quote  Mark this post and the followings unread

filter
Last edited by blackyellow on Sun Mar 03, 2013 8:49 pm; edited 1 time in total
Back to top
View user's profile Send private message
blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sat Feb 16, 2013 4:25 am    Post subject: Reply with quote  Mark this post and the followings unread

filter
Last edited by blackyellow on Sun Mar 03, 2013 8:49 pm; edited 1 time in total
Back to top
View user's profile Send private message
wmonk



Joined: Sep 15, 2008
Posts: 485
Location: Enschede, the Netherlands
Audio files: 13

PostPosted: Sat Feb 16, 2013 6:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Did you use a virtual ground for the ground on the positive input of the opamp?
_________________
Weblog!
Kits for synthesiser modules in Europe
Back to top
View user's profile Send private message Visit poster's website
JovianPyx



Joined: Nov 20, 2007
Posts: 1214
Location: West Red Spot, Jupiter
Audio files: 157

PostPosted: Sat Feb 16, 2013 8:25 am    Post subject: Reply with quote  Mark this post and the followings unread

R2 looks suspicious.

Even when at full resistance for 5K you will get only 1/3 of your signal as input voltage.

If the chosen pot is 1K, your input sees only 1/15 of the input voltage at best.

_________________
FPGA Synth Stuff
FatMan Mods
dsPIC Synth Stuff
I am formerly known as ScottG here

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
Back to top
View user's profile Send private message Visit poster's website
blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sat Feb 16, 2013 10:53 am    Post subject: Reply with quote  Mark this post and the followings unread

filter
Last edited by blackyellow on Sun Mar 03, 2013 8:46 pm; edited 1 time in total
Back to top
View user's profile Send private message
wmonk



Joined: Sep 15, 2008
Posts: 485
Location: Enschede, the Netherlands
Audio files: 13

PostPosted: Sat Feb 16, 2013 11:12 am    Post subject: Reply with quote  Mark this post and the followings unread

blackyellow wrote:
wmonk: I connected positive input to ground exactly as shown in the diagram.

my supply is +V= +5 volts and -V= 0 volts.

For this filter to work correctly, the 'gnd' should be connected to 2.5V (that is, virtual ground between V+ and V-).

_________________
Weblog!
Kits for synthesiser modules in Europe
Back to top
View user's profile Send private message Visit poster's website
blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sat Feb 16, 2013 11:19 am    Post subject: Reply with quote  Mark this post and the followings unread

filter
Last edited by blackyellow on Sun Mar 03, 2013 8:50 pm; edited 1 time in total
Back to top
View user's profile Send private message
blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sat Feb 16, 2013 1:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

what about a simple transistor amplifier with an 2n3904 or something of the such?
Back to top
View user's profile Send private message
JovianPyx



Joined: Nov 20, 2007
Posts: 1214
Location: West Red Spot, Jupiter
Audio files: 157

PostPosted: Sat Feb 16, 2013 2:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

REMOVED
_________________
FPGA Synth Stuff
FatMan Mods
dsPIC Synth Stuff
I am formerly known as ScottG here

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?

Last edited by JovianPyx on Sat Feb 16, 2013 6:08 pm; edited 1 time in total
Back to top
View user's profile Send private message Visit poster's website
blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sat Feb 16, 2013 2:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

filter
Last edited by blackyellow on Sun Mar 03, 2013 8:47 pm; edited 1 time in total
Back to top
View user's profile Send private message
JovianPyx



Joined: Nov 20, 2007
Posts: 1214
Location: West Red Spot, Jupiter
Audio files: 157

PostPosted: Sat Feb 16, 2013 2:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

you can increase the output one of 2 ways:

1) add an opamp as a DC amplifier stage

2) modify the right side LM324 to have gain more than 1 (which is what is shown in the drawing)

DC amplifiers are very common in synthesizer circuits. I would suggest reading about "Op Amp DC Amplifier", there are many sites which will explain the theory and give example schematics. This information will come in handy very often for you.

_________________
FPGA Synth Stuff
FatMan Mods
dsPIC Synth Stuff
I am formerly known as ScottG here

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
Back to top
View user's profile Send private message Visit poster's website
blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sat Feb 16, 2013 3:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

filter
Last edited by blackyellow on Sun Mar 03, 2013 8:48 pm; edited 1 time in total
Back to top
View user's profile Send private message
blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sat Feb 16, 2013 3:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

filter
Last edited by blackyellow on Sun Mar 03, 2013 8:48 pm; edited 1 time in total
Back to top
View user's profile Send private message
JovianPyx



Joined: Nov 20, 2007
Posts: 1214
Location: West Red Spot, Jupiter
Audio files: 157

PostPosted: Sat Feb 16, 2013 3:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

The reason I show 0V and a ground symbol is that they are different. 0v is the "minus" side of the 5 volt supply. It should NOT be the circuit's ground. If it is the circuit's ground, all AC signals will have their negative part clipped.

The virtual ground is created because you don't have a dual voltage or bipolar supply. It is a reference point halfway between 5v and 0v. This creates a situation similar to having a +2.5v and -2.5 supply. This allows you to pass a real AC signal into the opamp without distortion. Wmonk made this point as well, so I drew it into the schematic. The signal ground from the input and output circuits should connect to the virtual ground. Take the ground symbol for "system ground", that is, all grounds outside of this filter circuit go to the ground symbol point.

The ONLY place to connect 0v is the op-amp power terminal and the bottom resistor of the virtual ground circuit.

Note that the original schematic uses a 741 and a dual supply, that is +v went to some positive supply while -v went to a negative supply and where ground is not the negative supply, but rather a point of connection between the positive and negative supplies.

_________________
FPGA Synth Stuff
FatMan Mods
dsPIC Synth Stuff
I am formerly known as ScottG here

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
Back to top
View user's profile Send private message Visit poster's website
richardc64



Joined: Jun 01, 2006
Posts: 609
Location: NYC
Audio files: 25

PostPosted: Sat Feb 16, 2013 5:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

There should be a resistor in series with the pot so the resistance can never be zero. The pot could be as much as 20k allowing the filter to be tuned lower. The gain can be boosted by increasing R3. (not greater than 680k.) This will give the filter some resonance.

To operate from a single supply, Ground pin 4 (-v) and connect pin3 to a voltage divider as shown, creating a false ground for the (+) input.


igmf_bpf.gif
 Description:
 Filesize:  8.8 KB
 Viewed:  2647 Time(s)

igmf_bpf.gif



_________________
"I am endeavoring, ma'am, to create a mnemonic memory circuit... using stone
knives and bearskins." -- Spock to Edith Keeler
Back to top
View user's profile Send private message Visit poster's website
analog_backlash



Joined: Sep 04, 2012
Posts: 371
Location: Aldershot, UK
Audio files: 21

PostPosted: Sat Feb 16, 2013 5:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't want to complicate the situation further, but when I was asking about lunetta mixing:

http://electro-music.com/forum/topic-55327.html

I was persuaded that the two resistors producing Vcc/2 should have a value of at least 100K as confirmed by this document:

http://www.eng.yale.edu/ee-labs/morse/compo/sloa058.pdf

That's what it says in section 1.2 (although it shows 100kW by a mis-conversion of the ohms symbol!). I had been using lower values (e.g. 10K or so), but ever since I've been using higher value resistors. I don't know how much difference it makes in the filter circuit above, but I've been using it as a rule of thumb ever since.

Any thoughts?

Gary
Back to top
View user's profile Send private message
JovianPyx



Joined: Nov 20, 2007
Posts: 1214
Location: West Red Spot, Jupiter
Audio files: 157

PostPosted: Sat Feb 16, 2013 6:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah, I see, yes DO NOT USE MY SCHEMATIC ABOVE

One thing I see in the IGMF filter is that both cutoff and Q are affected by BOTH resistors. So the idea that the 330 K affects ONLY Q is not correct.

This is a simple, but non-ideal filter if you want to control ONLY Q or ONLY cutoff using a pot.

The pot as shown in the original schematic will affect both Q and cutoff. But it also affects overall gain.

Also, the IGMF filter does not include the pot (as shown above) for frequency control. This is a rather cheesey way to accomplish tuning IMO. As such, this filter deviates from the pure IGMF theory. When the pot wiper is at the top, there is no input signal at all... In fact, I'm not even sure it controls frequency. My first thought when I saw it was that it was a shunting mechanism to control input amplitude.

Also, the grounding looks wrong. You should not be connecting the input signal's ground to the zero volt side of the 5 volt supply.

blackyellow - did you put that pot in there as a modification or did you find the schematic drawn like that?

_________________
FPGA Synth Stuff
FatMan Mods
dsPIC Synth Stuff
I am formerly known as ScottG here

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
Back to top
View user's profile Send private message Visit poster's website
JovianPyx



Joined: Nov 20, 2007
Posts: 1214
Location: West Red Spot, Jupiter
Audio files: 157

PostPosted: Sat Feb 16, 2013 6:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

as for the resistors in the virtual ground - The size of the resistors will determine how "stiff" the ground is. Larger resistors are less "stiff". It may well be that 100K will work in this circuit. Higher resistors will draw less current which is probably the point of what you read. With a regulated 5 volt and only this circuit - I think the difference is pretty minimal. 200K at 5 volts is 0.025 mA, 20 K is 0.25 mA.... really depends on the supply as to how far you push it.
_________________
FPGA Synth Stuff
FatMan Mods
dsPIC Synth Stuff
I am formerly known as ScottG here

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
Back to top
View user's profile Send private message Visit poster's website
blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sat Feb 16, 2013 7:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

filter
==============

Last edited by blackyellow on Sun Mar 03, 2013 8:49 pm; edited 1 time in total
Back to top
View user's profile Send private message
JovianPyx



Joined: Nov 20, 2007
Posts: 1214
Location: West Red Spot, Jupiter
Audio files: 157

PostPosted: Sat Feb 16, 2013 7:21 pm    Post subject: Reply with quote  Mark this post and the followings unread


Last edited by JovianPyx on Sat Feb 16, 2013 11:33 pm; edited 3 times in total
Back to top
View user's profile Send private message Visit poster's website
blackyellow



Joined: Feb 12, 2013
Posts: 19
Location: Los Angeles

PostPosted: Sat Feb 16, 2013 8:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

filter
Last edited by blackyellow on Sun Mar 03, 2013 8:51 pm; edited 1 time in total
Back to top
View user's profile Send private message
elmegil



Joined: Mar 20, 2012
Posts: 1341
Location: Chicago
Audio files: 14

PostPosted: Sat Feb 16, 2013 8:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Self Oscillation, aka "screaming like a bitch" is sometimes desirable Smile
Back to top
View user's profile Send private message
richardc64



Joined: Jun 01, 2006
Posts: 609
Location: NYC
Audio files: 25

PostPosted: Sun Feb 17, 2013 2:13 am    Post subject: Reply with quote  Mark this post and the followings unread

blackyellow wrote:
SO I SHOULD KEEP THE POT GOING TO THE Virtual ground created for the positive input and ignore the red X he placed on the igmf bpfilter image? AND ignore the ground symbol under the pot?

The circuit works fine if the pot is at ground.

analog_backlash wrote:
I was persuaded that the two resistors producing Vcc/2 should have a value of at least 100K as confirmed by this document:

Hmmm. I had been using 100k until I read that the Vcc/2 source should be a low impedance. I've seen 10k used, which seems low enough, but as a compromise I've been using 47k, mainly because I have hundreds in that value.

JovianPyx wrote:
One thing I see in the IGMF filter is that both cutoff and Q are affected by BOTH resistors. So the idea that the 330 K affects ONLY Q is not correct.

This is a simple, but non-ideal filter if you want to control ONLY Q or ONLY cutoff using a pot.

The pot as shown in the original schematic will affect both Q and cutoff. But it also affects overall gain.


Yes, I found there was interaction. When I've built this with variable Q, to limit the range I've used 220k in series with a 500k pot as Resonance.

Quote:
Also, the IGMF filter does not include the pot (as shown above) for frequency control. This is a rather cheesey way to accomplish tuning IMO.

Yeah, but it works!

_________________
"I am endeavoring, ma'am, to create a mnemonic memory circuit... using stone
knives and bearskins." -- Spock to Edith Keeler
Back to top
View user's profile Send private message Visit poster's website
analog_backlash



Joined: Sep 04, 2012
Posts: 371
Location: Aldershot, UK
Audio files: 21

PostPosted: Sun Feb 17, 2013 2:57 am    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
as for the resistors in the virtual ground - The size of the resistors will determine how "stiff" the ground is. Larger resistors are less "stiff". It may well be that 100K will work in this circuit. Higher resistors will draw less current which is probably the point of what you read. With a regulated 5 volt and only this circuit - I think the difference is pretty minimal. 200K at 5 volts is 0.025 mA, 20 K is 0.25 mA.... really depends on the supply as to how far you push it.


richardc64 wrote:
Hmmm. I had been using 100k until I read that the Vcc/2 source should be a low impedance. I've seen 10k used, which seems low enough, but as a compromise I've been using 47k, mainly because I have hundreds in that value.


Thanks for those points of clarification. I also noticed that the TI document wrongly describes Vcc/2 as a virtual ground, which I now know should apply to (e.g.) a shared op-amp inverting input in a mixer circuit.

Gary
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 2 [26 Posts]
View unread posts
View new posts in the last week
Goto page: 1, 2 Next
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
emSynth

Please support our site. If you click through and buy from
our affiliate partners, we earn a small commission.


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use