Feedback "ringing"

Hardware questions and issues with the FV-1

Moderator: frank

Post Reply
iampoor
Posts: 27
Joined: Sat Nov 15, 2014 4:44 pm

Feedback "ringing"

Post by iampoor »

Im trying to build a hardware based feedback loop. Im taking an output after the 3.3uf cap and feeding it back in through the 1k resistor on the input. Nothing else is on the circuit. I do not have he 2.2nf or 10k resistors to ground.

The circuit certainly works, but even a moderate feedback levels, I get a sor of "ringing". It sounds like a filter with a high Q.

Any ideas where I should start? No compensation cap in the feedback loop, typical invtering stage with a gain of 2 (tl074).
frank
Posts: 1244
Joined: Wed Oct 19, 2005 12:26 pm
Contact:

Post by frank »

Need to see code and schematic to really help. How long a delay are you doing in the FV-1?
Frank Thomson
Experimental Noize
iampoor
Posts: 27
Joined: Sat Nov 15, 2014 4:44 pm

Post by iampoor »

frank wrote:Need to see code and schematic to really help. How long a delay are you doing in the FV-1?
Cool, Ill post it up. Im not currently doing any filtering on the feedback in he code, probably need to.

Here is the code, built in SpinCAD Designer. I using 200ms of predelay in he delay block, and the reverb utilizes the rest of the delay memory, so all of it. :lol:

Ive tried it with both of these programs and have had similar results, leads me to believe its a hardware filtering issue.

Reverb
; Program: Render Block exported from SpinCAD Designer
;------ Input
;------ Pot 2
;------ Mixer 2-1
RDAX ADCL,1.0000000000
WRAX REG0,0.0000000000
RDAX ADCR,1.0000000000
RDAX REG0,1.0000000000
WRAX REG0,0.0000000000
;------ Pot 1
;------ Single Delay
WRAX REG2,0.0000000000
SOF 0.0000000000,0.4500000000
WRAX REG2,0.0000000000
RDAX POT1,0.9990000000
SOF 0.2030000000,0.0000305176
WRAX ADDR_PTR,0.0000000000
RMPA 1.0
WRAX REG1,1.0000000000
MULX REG2
RDAX REG0,0.5000000000
WRA 0,0.0
RDAX REG1,1.0000000000
WRAX REG1,0.0000000000
;------ Pot 0
;------ Constant
SOF 0.0000000000,0.0000000000
WRAX REG3,0.0000000000
;------ Constant
SOF 0.0000000000,0.0000000000
WRAX REG4,0.0000000000
;------ Reverb
RDAX POT0,1.0000000000
SOF 0.5500000000,0.3000000000
WRAX REG6,0.0000000000
SKP RUN ,1
WLDR 0, 0, 4096
RDAX REG1,1.0000000000
WRA 6652,0.0
CHO RDA,2,REG | COMPC,6652
CHO RDA,2,0,6653
WRAX REG8,0.0000000000
CHO RDAL,2
RDAX REG3,-0.5000000000
WRAX RMP0_RATE,0.0000000000
RDAX REG8,0.2500000000
RDA 11585,0.25
WRAP 11253,-0.25
RDA 12034,0.25
WRAP 11586,-0.25
WRAX REG7,0.0000000000
RDA 32414,1.0
MULX REG6
RDAX REG7,1.0000000000
RDA 13478,0.6
WRAP 12035,-0.6
RDA 14822,0.6
WRAP 13479,-0.6
WRAX REG5,1.0000000000
RDFX REG11,0.7297498315
WRLX REG11,-1.0000000000
RDFX REG10,0.3128781375
WRHX REG10,-1.0000000000
RDAX REG5,-1.0000000000
MULX REG4
RDAX REG5,1.0000000000
WRA 14823,0.0
RDA 17768,1.0
MULX REG6
RDAX REG7,1.0000000000
RDA 19351,0.6
WRAP 17769,-0.6
RDA 21333,0.6
WRAP 19352,-0.6
WRAX REG5,1.0000000000
RDFX REG13,0.7297498315
WRLX REG13,-1.0000000000
RDFX REG12,0.3128781375
WRHX REG12,-1.0000000000
RDAX REG5,-1.0000000000
MULX REG4
RDAX REG5,1.0000000000
WRA 21334,0.0
RDA 25310,1.0
MULX REG6
RDAX REG7,1.0000000000
RDA 26585,0.6
WRAP 25311,-0.6
RDA 27968,0.6
WRAP 26586,-0.6
WRAX REG5,1.0000000000
RDFX REG15,0.7297498315
WRLX REG15,-1.0000000000
RDFX REG14,0.3128781375
WRHX REG14,-1.0000000000
RDAX REG5,-1.0000000000
MULX REG4
RDAX REG5,1.0000000000
WRA 27969,0.0
RDA 16699,1.5
RDA 23427,1.1
RDA 30762,1.0
WRAX REG9,0.0000000000
RDA 15746,1.5
RDA 22568,1.1
RDA 30236,1.0
WRAX REG9,0.0000000000
SKP RUN ,2
WLDS 0,45,50
WLDS 1,53,50
CHO RDA,0,COS | COMPC,12085
CHO RDA,0,COS ,12086
WRA 12135,0.0
CHO RDA,1,REG | COMPC,17819
CHO RDA,1,0,17820
WRA 17869,0.0
CHO RDA,1,COS | COMPC,25361
CHO RDA,1,COS ,25362
WRA 25411,0.0
;------ SVF 2P
SOF 0.0000000000,0.0000000000
RDAX REG9,1.0000000000
RDAX REG18,-1.0000000000
RDAX REG17,-1.0000000000
WRAX REG16,0.2622747070
RDAX REG17,1.0000000000
WRAX REG17,0.2622747070
RDAX REG18,1.0000000000
WRAX REG18,0.0000000000
;------ Crossfade
RDAX REG18,1.0000000000
RDAX REG9,-1.0000000000
MULX POT2
RDAX REG9,1.0000000000
WRAX REG19,0.0000000000
;------ Output
RDAX REG19,1.0000000000
WRAX DACL,0.0000000000
RDAX REG19,1.0000000000
WRAX DACR,0.0000000000
delay
;------ Input
;------ Mixer 2-1
RDAX ADCL,0.5000000000
WRAX REG0,0.0000000000
RDAX ADCR,0.5000000000
RDAX REG0,1.0000000000
WRAX REG0,0.0000000000
;------ Pot 0
;------ Pot 1
;------ Volume
RDAX POT0,1.0000000000
MULX POT1
WRAX REG1,0.0000000000
;------ Pot 2
;------ Volume
RDAX POT1,1.0000000000
MULX POT2
WRAX REG2,0.0000000000
;------ ThreeTap
;------ Mixer 3-1
RDAX REG3,0.3333333333
WRAX REG3,0.0000000000
RDAX REG4,0.3333333333
RDAX REG3,1.0000000000
WRAX REG3,0.0000000000
RDAX REG5,0.3333333333
RDAX REG3,1.0000000000
WRAX REG3,0.0000000000
;------ Gain Boost
RDAX REG3,1.0000000000
SOF -2.0000000000,0.0000000000
SOF -2.0000000000,0.0000000000
WRAX REG4,0.0000000000
;------ Output
RDAX REG4,1.0000000000
WRAX DACL,0.0000000000
RDAX REG4,1.0000000000
WRAX DACR,0.0000000000
As far as the schematic goes, is basically just a buffer right now. Ill check and enter it properly tomorrow, MS Paint isnt cutting it :lol: :mrgreen: :roll:

Image

:lol:
frank
Posts: 1244
Joined: Wed Oct 19, 2005 12:26 pm
Contact:

Post by frank »

You're feeding back a reverb, it's going to ring. Why are you feeding back a reverb?
Frank Thomson
Experimental Noize
iampoor
Posts: 27
Joined: Sat Nov 15, 2014 4:44 pm

Post by iampoor »

frank wrote:You're feeding back a reverb, it's going to ring. Why are you feeding back a reverb?
Quite a few reverbs have a feedback control now. So I wanted to try it. Im well aware that its going to ring at a point, but i is ringing very quickly. Same with the delay. If I do a single quarter note delay, I can hear it starting o "ring" without really hearing any feedback.

So it appears that I doing something wrong. :lol:

I might make a video. Much easier to hear it! :D
Digital Larry
Posts: 338
Joined: Mon Nov 12, 2012 1:12 pm
Contact:

Post by Digital Larry »

Looks like your delay patch doesn't really have any delay in it.
iampoor
Posts: 27
Joined: Sat Nov 15, 2014 4:44 pm

Post by iampoor »

Digital Larry wrote:Looks like your delay patch doesn't really have any delay in it.
I must have exported the wrong patch, or a previous revision, because I know the delay works, the hardware feedback is just strange!
Digital Larry
Posts: 338
Joined: Mon Nov 12, 2012 1:12 pm
Contact:

Post by Digital Larry »

It's hard to tell based on your delay patch, which as presented would not make any sound at all.

However, if your delay patch has "dry" signal in the output, and you feed this back, you may well get some oscillation.
iampoor
Posts: 27
Joined: Sat Nov 15, 2014 4:44 pm

Post by iampoor »

Digital Larry wrote:It's hard to tell based on your delay patch, which as presented would not make any sound at all.

However, if your delay patch has "dry" signal in the output, and you feed this back, you may well get some oscillation.
Yeah, I must have copied it wrong because the delay patch works fine, thats what I get for posting at 4am :twisted:

Well I fixed it! Apparently using an inverting buffer for the feedback is a bad idea. Another 4am mistake......lol
Post Reply