Filtrex works in series but not on mixer insert (solved)

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Paradigm X
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Filtrex works in series but not on mixer insert (solved)

Post by Paradigm X » Mon Jan 06, 2020 7:04 am

Hi TOny hope you are well.

I have an odd problem with my filtrex II. it works fine if you plug something into the input, then a lead to the mixer, but if i use an insert jack on the mixer, it doesnt work (silence). Ive tried numerous cables (including brand new ones) and the insert jack of my (brand new) mixer work as expected with other gear, but not the filtrex

Very odd.

Any ideas at all?

Also, i threw my second one together with bits and peices I had lying around, and it doesnt sound as nice as the first one i built. WHich components have a (big) effect on the sound and are worth replacing for decent parts? I am thinking of going the opposite route and putting in really nice film/whatever capacitors etc where it would make a difference.

many thanks, all the best, Ben
Last edited by Paradigm X on Mon Feb 17, 2020 7:34 am, edited 1 time in total.

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Re: Filtrex works in series but not on mixer insert

Post by Synthbuilder » Tue Jan 07, 2020 7:18 am

Hi Ben,
Paradigm X wrote:
Mon Jan 06, 2020 7:04 am
if i use an insert jack on the mixer, it doesnt work (silence).
Do you know if the signal is getting to the Filtrex? That is, does the peak LED light up when you send it a signal and turn up the gain? If so the problem is probably your wiring from the Filtrex circuit board to the output socket. I think perhaps you have the tip (T) and sleeve (S) connections reversed inside the Filtrex.

You'd still get audio if you used a TRS (balanced) cable from the output of the Filtrex to a balanced input on your mixer. However, most insert Y cables use a TRS plug to go into the back of the mixer and two unbalanced TS plugs for the send and receive. Since the Filtrex has a balanced output, it'll work just fine with T and S swapped if you are using balanced TRS cable into a balanced input. But using a TS plug/cable will produce no output if T and S have been swapped when you wired the output socket to the PCB.
Which components have a (big) effect on the sound and are worth replacing for decent parts?
I'm not sure any of the components will make a big difference unless they are the wrong components. I know it's difficult to describe a sound but in what way is the second one worse than the other. For example, is it bass light, overly distorted, too bright?

Tony

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Re: Filtrex works in series but not on mixer insert

Post by Paradigm X » Wed Jan 08, 2020 7:33 am

Hi Tony, thanks for the swift reply!

I will test it tonight, i dont honestly remember whether the lights come on.

But it might be worth mentioning ive never used a balanced cable with it, only mono cables in either configuration (insert or series). I had guessed it was something to do with TRS wiring, ill open it up and have a look.

In terms of the difference between the two, well, im going to have to use a load of useless hifi like terminology im afraid.

They both basically sound the same, but the old one just sounds more 'expensive' (sorry). Like the difference between a badly made x0xb0x and a good one. Basically the same, but one is obviously better. It just sounds 'classier', the sweeps from the lfo seem more defined, the resonance seems harsher when up high, or less defined when lower, it sounds 'warmer' i know, all of these words are literally meaningless. Sorry. Well i hope this gave you a little chuckle if nothing else.

I know i put in a load of mega cheap chinese green mylar (?) caps i had lying around which made me think it might be them. The only other difference i know is you changed the 'posh' opamp at some point, and the old one used the earlier version.

I suppose the obvious solution is to replace everything with your recommended caps. But i was wondering if any could benefit from nice WIMA type boxes or polystyrene or anything like that, in a no expense spared kind of way, while i am taking it apart? But i think you've mentioned previously that you dont believe too much in magic voodoo capacitors and the like.

Sorry if this is all a waste of your time. Many thanks as always.

Cheers, Ben

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Re: Filtrex works in series but not on mixer insert

Post by Synthbuilder » Wed Jan 08, 2020 10:33 am

As far as capacitor replacements, I would look to the four ladder capacitors first. These are C12 through C15. Don't bother with polystyrene since they'll be massive and cause more problems than they will fix. Use a good 5% polyester or even polypropylene film. C16 through C19 should also be of good quality. 10% or 5% WIMA or Kemet polyester film should be fine.

Setting the balance trimmer correctly can also have an effect on the sound of the ladder.

Tony

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Re: Filtrex works in series but not on mixer insert

Post by Paradigm X » Wed Jan 08, 2020 2:53 pm

OK, well I opened it up and it seems like pin 1 and 3 of the output were the wrong way round. but on top of that the ground was hanging by a thread and broke completely when i moved it. so i have to rewire that pronto.

My brain still cant figure out why mono in mono out works, but a ycable, which is two mono cables, didnt. But never mind.

Also the four main filter caps are the cheap mylars. the other ones you mentioned are your recommended parts.

I will order some more filter caps and rewire the socket and retrim the balance trimmer and retry.

Many thanks for the help, much appreciated.

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Re: Filtrex works in series but not on mixer insert

Post by Paradigm X » Mon Feb 17, 2020 6:16 am

all fixed, thank you. i had pin 3 and 1 mixed up on the output. it now works fine on an insert.

i changed the 4 filter caps to 5% poly, measured the 10 i got and install the 4 closest. no idea if it helped but i had a component tester so thought i may as well. sounds excellent now. really really good. I recalibrated it and reduced the resonance a bit, also halved the lfo rate and now it sounds better than ever ! thanks again

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Re: Filtrex works in series but not on mixer insert

Post by Synthbuilder » Mon Feb 17, 2020 12:32 pm

Paradigm X wrote:
Mon Feb 17, 2020 6:16 am
all fixed, thank you. i had pin 3 and 1 mixed up on the output. it now works fine on an insert.
Excellent news.

I like story with a happy ending. :tu:

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Re: Filtrex works in series but not on mixer insert (solved)

Post by Paradigm X » Tue Feb 18, 2020 8:45 am

thanks tony. you should do a roland filtrex! cheers

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Re: Filtrex works in series but not on mixer insert (solved)

Post by Synthbuilder » Tue Feb 18, 2020 9:29 am

Paradigm X wrote:
Tue Feb 18, 2020 8:45 am
you should do a roland filtrex!
I think the time for any such thing has passed now. The Oakley Sound Filtrex in its various guises has been around for over twenty years now. Sales were pretty slow in the later part of the production run. I don't think even an exciting new variant of the same thing would sell well enough to make it worth the effort on my part.

That said, maybe a stereo table top thing might do well. And it would be a lot easier and cheaper to send through the post than those long thin boards.

Tony

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Re: Filtrex works in series but not on mixer insert (solved)

Post by Paradigm X » Tue Feb 18, 2020 9:43 am

TBPH personally i feel the moog thing has been done to death. to the older ravers the roland filter(s) is the one. so many old records with 09, 02, 101, 106 etc. the cota just reeks of it and its fantastic. for me rack stuff is great as its out of the way, i have too many little boxes with wall warts cluttering up the place.

that said i fully understand your point re sales and shipping etc. but if im dreaming, the cota in a box with a couple of the electric druid chips doing cool midi synced LFO sweeps would be awesome... maybe even add in a cut down SRE chorus, a sorta-106 in a box (minus vco etc).... theres a good chance others might too.

two smaller pcbs could always fit in a 19" rack, the pcb itself doesnt necessarily need to be the full width.

sorry, dont mind me just thinking out loud. i know nothing about the realities of these thing.

Thanks for all your help and great designs tho. Ive got my scope back now and watched some videos on how to use it so going to have a look at the svco.

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Re: Filtrex works in series but not on mixer insert (solved)

Post by Paradigm X » Wed Feb 26, 2020 6:15 am

Had a really good play with this again last night. Its really sounding superb! I think ive finally got it to how you intended it to sound! 909 hats into a swept bandpass filter sounds both lush and cutting at the same time. either the dodgy wiring, or the cheap nasty caps meant it didnt sound to its full potential. loving the slower LFO as well.

Thanks again. So glad i got these.

As a curiosity, everything is working fine, but i took the motm power output you made for the second filtrex to 3 banana plugs in the back in case i ever needed them. is there any benefit in connecting the ground to the grounds added to the PSUs for connecting the modular cases ?

thanks again, Ben

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Re: Filtrex works in series but not on mixer insert (solved)

Post by Synthbuilder » Wed Feb 26, 2020 7:10 am

Hi Ben,

Glad to hear you like the Filtrex and you're getting good use out of them.
Paradigm X wrote:
Wed Feb 26, 2020 6:15 am
is there any benefit in connecting the ground to the grounds added to the PSUs for connecting the modular cases ?
There is a benefit but whether it is audible is another thing. Ideally, all 0V points should be connected together with a solid low resistance connection. This prevents signals, including power supply noises, from contaminating each other. The idea being that return currents that normally travel down the screens of connecting cables develop unwanted voltage drops between units. Usually, the return currents are very small and the resistance, even of a screened cable, is quite low, so these unwanted voltages are very low. They are always there though, and the more return currents and the higher the cable resistance, the more likely you are of hearing them.

So if you do start noticing hums and buzzes, VCOs being modulated by unpatched LFOs and so on, think about reinforcing those 0V (ground) connections.

Tony

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Re: Filtrex works in series but not on mixer insert (solved)

Post by Paradigm X » Thu Feb 27, 2020 5:21 am

OK, thanks. Ill build up a cable when i get a chance (having too much fun playing at the moment!). Im amazed at how quiet my entire studio is tbh, theres a load of cables and old hardware. everything is remarkably clean.

cheers

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