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stg post-lawsuit filter resonance
MUFF WIGGLER Forum Index -> STG Soundlabs  
Author stg post-lawsuit filter resonance
wutierson
Hi all,

Every time using a slow and deep filter sweep with resonance with this nice filter I can hear a kind of crosstalk or part of the incoming signal like "scape" from the cutoff. It's more noticeable when cutoff point is very low and resonance is more than a 25%.

I ask to arp 7012 and 7015 user and ask if this occurs, and say no.

I'm thinking that the resonance compensation of the Post-lawsuit that makes the bass don't fall when the resonance is going up will make this "secondary effect".

Any user from this forum can make some light at this incidence?

Thanks.
Madrayken
Interesting...

On mine, you can hear bleed-through of the original signal when resonance is between 1 and 9, regardless of frequency cutoff.

Is this a batch issue? Does the Sea Devils do this too?
suitandtieguy
it's only the P-L/LPF and no we have no idea why it does this.

fortunately since it's not called "direct clone of the ARP 4072 filter" then any differences aren't criminal.
Madrayken
I was less concerned with the 'perfect cloneyness' than I was the 'potentially broken/damaged in transit-ness'. It's just come a long way from the US. Thanks for clarifying so sweetly.
suitandtieguy
i'm sorry if that reply seemed curt. i typed it quickly and without thought.

i just got an ARP Pro/DGX which is being worked on right now and when it's finished i'll be able to perform a direct comparison. it will be interesting to see the result.
wutierson
Hi Eric,

I'm not technician but reading the yusynth page about the 7012 filter I'm thinking to remove the inverter buffer stage resistor, but I will not do anything until you say that doing this it will not damage the filter.
The theory is delete the buffer stage to avoid the resonance compensation and make the filter to work like the original arp's with the bass drop.

What do you think about?

Thanks.
suitandtieguy
hey so i've spent some time with this now, since you asked again and i actually have one in my system to play with (i was out of boards for a few months due to a revision.)

i had already revised one component on the last batch to get rid of the DC offset which the circuit generated, so i figured i'd dive in again about this issue. my gut reaction was "well it wouldn't hurt anything to cut it out" and then i thought i'd look a bit more at it. (if you're curious the change was C10 ... i changed it from a 22uf polarised electrolytic to a 2.2uf ceramic. all of the 7 P-L/LPFs i shipped to AH today have this.)

the answer to your immediate question is yes you absolutely can just cut R43 out. this will not violate your warranty. but everything else i'm going to discuss will.

the next thing i tried was changing the value of R43 from 10K to 27K. this will cut down the crosstalk significantly, though you may still hear it.

the next thing that irritated me about the filter was the phase reversal that the additional buffer added. i just cut it out completely.

it wound up looking like this:



the chip did not get hot or any warmer to the touch but an unterminated opamp cell will consume more current. i have an enormous power supply so i'm not too concerned about it. i made the change because i wanted to experiment with feeding multiple filters and mixing them.

i may change it back.

soundwise what do i think? well it does sound a bit different in response to regeneration, but not that much. the crosstalk was definitely coming from that second buffer stage. thanks for drilling me about it.

what am i going to do in the future with this? i don't know. i'm going to do some A/B comparisons between different solutions and think about it.

i have been told (by more people who have questioned the crosstalk issue) that this module sounds better than the Bananalogue LPFA. this output buffer stage is one of the electrical differences. i don't want to make the module sound worse in an attempt to make it sound better. i'm going to have to spend some more analysis time on the issue before i make any change in what's shipping.
Madrayken
I recently talked to Yves about his original design and this issue in particular, and he had this to say:

Quote:
Hello

It is stupid of not having thought of this very obvious and simple solution to the bleeding thru problem.
The cure is to replace the resonance potentiometer by a dual gang model. Connecting the CW lugs in parallel, the CCW lugs in parallel, and one wiper lug connected to the normal resonance circuit while the other wiper lug
connected to the R43 resistor.


I am going to test that and eventually publish it on my site !

Cheers


Hope this is of some use.
Bryan B
I would be curious to hear if that dual gang pot suggestion worked.
negativspace
I've got one of Yves' 4072 PCBs en route and I'm going to do it with the ganged-pot. I'll share my results. thumbs up
dr. jacoby
i'm quite curious as well.
nightowl
Howdy, folks.

Just resurrecting this thread, wondering how those tests went, and if any conclusions were come to.

It's a beauty of a filter, but that particular quirk jumped out at me almost straight away.
EMwhite
I justly picked up a kit from Bridechamber (aka it's been sitting in a bag for a year and I'm just now getting to it!). I have a number of dual pots that I bought for JH triple res so I'll see about wiring this up this way during the week and report back unless somebody beats me to it.
Madrayken
I got someone else to make one for me. It works beautifully.
tonepanic
I just got one of these and couldn't handle the bleed so I went the route of removing R43 (mainly because it was easy to do, and easy to reverse if I didn't like it). It completely eliminated the bleed, and the volume drop when you crank the resonance really isn't that bad in my opinion.

With the mod, this filter is quickly becoming one of my favorites.
anderson303
Not sure how to make this mod? Any advice from 2 years ago?
hza
Any idea what pot one will use in this modification ???
50k? How should it be configured mountable wise?

Best regards
/H

Madrayken wrote:
I recently talked to Yves about his original design and this issue in particular, and he had this to say:

Quote:
Hello

It is stupid of not having thought of this very obvious and simple solution to the bleeding thru problem.
The cure is to replace the resonance potentiometer by a dual gang model. Connecting the CW lugs in parallel, the CCW lugs in parallel, and one wiper lug connected to the normal resonance circuit while the other wiper lug
connected to the R43 resistor.


I am going to test that and eventually publish it on my site !

Cheers


Hope this is of some use.
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