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#1 2008-12-09 14:22:27

Flemming
The Last Ninja
Registered: 2008-11-27
Posts: 291

The Feedback mod

Been searching the forum for details about the Feedback mod... i'm sure the main part of you have used 500K potmeters?? Those are not available at my local electronics shop sad and my other problem is that i don't get the diagram on Alpha's pages... but here's my guess; I get a 500K pot and solder it between AudioOut and AudioIn while ofcourse keeping a wire to the output connector from AudioOut also... true?? But what about my nice AudioIn-grounding that i've come to love so much?? I know that Alpha has a fix when incorporating Audio Input, but i don't want Audio In (i'm afraid to fry my SIDs)..

Would anyone be so kind to enlighten me in this regard, preferrably in details or at semi-newbie-comprehensable level??

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#2 2008-12-09 15:05:45

InactiveX
The Last Ninja
From: England
Registered: 2008-08-14
Posts: 280

Re: The Feedback mod

What's the closest you can get to 500K? You should be fine as long as it's close.

When using the feedback mod, you do not want Audio In to be grounded directly like you have now. You won't need it.

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#3 2008-12-09 16:20:18

dschohennes
Nebulus
From: Colima, Mex; Karlsruhe, Ger
Registered: 2008-10-24
Posts: 64

Re: The Feedback mod

my experience is that you can use a lower value - i'm using 500k and i only recognize a change in the last third of rotation - i could test that when back home, but i guess 200k-300k might be enough!

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#4 2008-12-09 16:57:36

Flemming
The Last Ninja
Registered: 2008-11-27
Posts: 291

Re: The Feedback mod

Thanks guys.. i'm very insecure towards this mod, so excuse me for asking too much wink also it will be my first mod involving a potmeter

I got a 500k pot from a guitar-store (damn expensive!!) i was thinking if this looks correct???
http://www.audiosonic.dk/private/pot.png

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#5 2008-12-09 17:03:58

dschohennes
Nebulus
From: Colima, Mex; Karlsruhe, Ger
Registered: 2008-10-24
Posts: 64

Re: The Feedback mod

no, don't do any connection to the ground! thats what you dont wanna do. EITHER you ground the input (noise reduction) OR you connect it to the output via pots (feedback).

If you want to do it for both SIDs you could use a stereo potentiometer or 2 mono potentiometers - you would have to connect each SID's ouput to it's input.

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#6 2008-12-09 17:18:05

Flemming
The Last Ninja
Registered: 2008-11-27
Posts: 291

Re: The Feedback mod

dschohennes wrote:

no, don't do any connection to the ground! thats what you dont wanna do. EITHER you ground the input (noise reduction) OR you connect it to the output via pots (feedback).

If you want to do it for both SIDs you could use a stereo potentiometer or 2 mono potentiometers - you would have to connect each SID's ouput to it's input.

So the middle leg on the pot is to be ignored?? and if i swap the in and out on my photo i have the correct solution ??

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#7 2008-12-09 17:19:56

InactiveX
The Last Ninja
From: England
Registered: 2008-08-14
Posts: 280

Re: The Feedback mod

No, he was talking about grounding the audio in, not about legs on the pot!

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#8 2008-12-09 17:23:52

Flemming
The Last Ninja
Registered: 2008-11-27
Posts: 291

Re: The Feedback mod

InactiveX wrote:

No, he was talking about grounding the audio in, not about legs on the pot!

Oh, i see... so i will forget the grounding, but still.. what to do with those 3 legs sad  i tried googling for a pot-related wiki thing, but i only found one in dutch, hehe..

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#9 2008-12-09 17:43:52

InactiveX
The Last Ninja
From: England
Registered: 2008-08-14
Posts: 280

Re: The Feedback mod

Connect the centre and one of the side legs of the pot both to Audio Out.

Connect the other side leg to Audio In.

If the knob is the "wrong way round", as in turning it down causes feedback to increase, swap the connections to the pot's outer lugs around.

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#10 2008-12-09 18:00:38

dschohennes
Nebulus
From: Colima, Mex; Karlsruhe, Ger
Registered: 2008-10-24
Posts: 64

Re: The Feedback mod

i agree smile

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#11 2008-12-09 18:19:23

Flemming
The Last Ninja
Registered: 2008-11-27
Posts: 291

Re: The Feedback mod

InactiveX wrote:

Connect the centre and one of the side legs of the pot both to Audio Out.

Connect the other side leg to Audio In.

If the knob is the "wrong way round", as in turning it down causes feedback to increase, swap the connections to the pot's outer lugs around.

That was just the info i was missing smile Thank you once again InactiveX.

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#12 2008-12-09 19:56:05

Flemming
The Last Ninja
Registered: 2008-11-27
Posts: 291

Re: The Feedback mod

Hmmm, i guess i'll never learn this smile nevertheless the pot works on the TV using the RF-out.. i can hear (primarily the last 1/3) of the pot is adding to the resonance of the sound. but in my audio out jack the sound is the same.. should i connect the output jack to the pot??

What i did..
Pot
- Leg1 connected to Leg2 and Audio out on mainboard
- Leg2 connected to Leg1
- Leg3 connected to Audio in on mainboard

Audio out jack (it's a stereo TRS jack)
- T connected to R
- R connected to T and Audio out on the mainboard
- S connected to ground

Another weird thing; when i plug in headphones in the Audio out jack, the volume of the sound from the TV is decreasing..

While the pot only works 1/3 of the way i suspect it to be logarithmic.. wolud a linear pot stretch the range so finer adjustment is easier?? If not, i'm thinking about just using a switch for feedback instead. In that case, Would a 500K resistor be a substitute for the pot?

Last edited by Flemming (2008-12-10 00:35:05)

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#13 2008-12-09 20:41:20

dschohennes
Nebulus
From: Colima, Mex; Karlsruhe, Ger
Registered: 2008-10-24
Posts: 64

Re: The Feedback mod

as i said, i also have only 1/3 of the way ... and my pot is linear!

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#14 2008-12-10 00:14:51

Flemming
The Last Ninja
Registered: 2008-11-27
Posts: 291

Re: The Feedback mod

dschohennes wrote:

as i said, i also have only 1/3 of the way ... and my pot is linear!

yeah, i see... but do you have an idea how to fix my problem please ??

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#15 2008-12-10 00:28:12

dschohennes
Nebulus
From: Colima, Mex; Karlsruhe, Ger
Registered: 2008-10-24
Posts: 64

Re: The Feedback mod

hm... you GET sound our of your trs jack, but you won't hear a difference concering feedback there? Don't know why this could happen, sorry... but there sure will be people 'round here to help you!

And sorry, i didn't have much time when posting the last entry, so i could not think about your problem smile

Last edited by dschohennes (2008-12-10 00:29:09)

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#16 2008-12-10 01:54:18

InactiveX
The Last Ninja
From: England
Registered: 2008-08-14
Posts: 280

Re: The Feedback mod

Can't see anything wrong with what you've described, but it's late here and I'm tired!

Also I should point out I haven't done the feedback mod myself, so I'm only theorising.

Keep trying.

Last edited by InactiveX (2008-12-10 01:55:26)

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#17 2008-12-10 11:28:31

Flemming
The Last Ninja
Registered: 2008-11-27
Posts: 291

Re: The Feedback mod

InactiveX wrote:

Keep trying.

I am smile it's still only working from the RF-output (feedback or distortion according to the MIX in setting). When i plug some earphones into the output jack the sound on the TV decreases to the extent that the feedback effect dissapears.. and no feedback in the ears either.. i'll investigate further

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#18 2008-12-10 12:03:22

Flemming
The Last Ninja
Registered: 2008-11-27
Posts: 291

Re: The Feedback mod

dschohennes wrote:

hm... you GET sound our of your trs jack, but you won't hear a difference concering feedback there? Don't know why this could happen, sorry... but there sure will be people 'round here to help you!

And sorry, i didn't have much time when posting the last entry, so i could not think about your problem smile

Well, i hope you get some time later smile i saw you did the feedback mod yourself so it must be very easy for you to point out my boo-boo, or just explain to me how you hooked it up yourself and i will find my boo-boo myself according to your explanation wink

Is it normal that the volume of the RF-output decreases if you connect something to the Audio out jack ?? It does here, even when no pot is involved sad

My feedback pot only works with RF-out, but when i connect my earphones to Audio out jack the feedback dissapears - no feedback in either RF-output or audio jack sad like the load is shared between the two outputs.. If i turn down the pot i can hear the ground-noise

Last edited by Flemming (2008-12-10 14:38:25)

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#19 2008-12-10 21:52:24

Flemming
The Last Ninja
Registered: 2008-11-27
Posts: 291

Re: The Feedback mod

Hmm, it seems normal that the audio of the RF-output decreases. at least i did it on another C64 and i got the same result.. Anybody else did the feedback mod with the RF-box still in place.. and did you encounter same behaviour from your C64 that i do??

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#20 2010-03-27 22:00:02

teenager
Gianas Sister
Registered: 2009-01-27
Posts: 26

Re: The Feedback mod

sorry for digging up old topics but I wonder if Flemming found his solution and got his feedback mod to work with his jack outs. it's a pity this topic ended unanswered.

I also did not understand AlphA's feedback schematic and followed the answers here.
I want to try this:

Pot
- Leg1 connected to Leg2 and Audio out on mainboard
- Leg2 connected to Leg1
- Leg3 connected to Audio in on mainboard

but which 'Leg' do I need to connect to my mono jacks (jack for audio OUT and audio IN)?
doesn't Leg 2 have to go to my output jack instead of connecting Leg 1 and Leg 2 together?

hope someone can help me out.

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#21 2010-04-01 20:04:27

teenager
Gianas Sister
Registered: 2009-01-27
Posts: 26

Re: The Feedback mod

anyone?

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#22 2010-04-13 01:35:32

teenager
Gianas Sister
Registered: 2009-01-27
Posts: 26

Re: The Feedback mod

alright, i got the feedback mod working at one of my SID chips.
but when i try to do the same with the other one (SID #2) it decreases the volume instead of distorting it.

what did i do wrong?

please respond. i really want to have this working. thanks!

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#23 2011-04-05 16:14:43

krosov
Bloody beginner
Registered: 2011-04-05
Posts: 1

Re: The Feedback mod

What if you would combine the two needs, being the feedback and grounding?

I will try the following with a 500 log pot:

leg 1: to Ground: The more the knob will be turned counter clockwise, the more the audio input will be grounded.
leg 2: this will go to the audio input.
leg 3: to Audio out, via a 1K resistor The more the the knob will be turned clockwise, the more it will feedback.

I choose a log pot, since audio volume on a logarithmic scale is perceived as linear. This will thus address the issue that dschohennes reported.
The 1K resistor will work as a current limiter, and prevents damaging the SID.

I expect that this setup will enable me to gradually fade from clean tot distorted. I'll keep you guys posted!


@teenager: did you choose the right pin as the audio output of the second SID? I would guess you might have shortened the audio output to another pin.

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#24 2011-04-08 13:07:45

neal beard
Nibbler
From: Portsmouth
Registered: 2010-10-19
Posts: 43
Website

Re: The Feedback mod

hi I'm also working on the feedback mod
I've built mine in a breakout box with audio in/out and video out.

seems to work ok but I can't work out how to activate MIX in in mssiah?

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#25 2011-04-08 13:51:43

DjFluorescent
Space Invader
From: Texas,USA
Registered: 2010-01-16
Posts: 136

Re: The Feedback mod

What do you mean activate? You mean just simply turning it on? or do you just not perceive it doing anything when it on? All the MIX does it sends the audio in thru the filter. If the input is grounded it will do nothing.


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