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funkyfarm
Joined: Jan 21, 2007
Posts: 583
Location: France
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 Posted: Fri Mar 23, 2007 5:47 am Post subject:
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| Quote: | | Radio Junk Box design which output signal is out-of-phase ? |
fonik version :
U2A is non inverting (input),
U1 (ad U2B) is an inverting stage (filter),
as the last stage around U3B (summing)
so "+ - -" is "+"
Radio Junk Box schematic :
input stage is non inverting +
filter stage is inverting -
summing stage is inverting -
and the last output stage is inverting too -, so
"+ - - - " is "-", which means out-of-phase for me...
| Quote: | | I just meant that that also uses a dual pot and additional opamp. I didn't claim it was better than the original. |
Hope it sounds better ! If not, that's really a lot of money for peanuts  |
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fonik
Joined: Jun 07, 2006
Posts: 3950
Location: Germany
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| Posted: Fri Mar 23, 2007 6:31 am Post subject:
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| funkyfarm wrote: | Radio Junk Box schematic :
(...)
and the last output stage is inverting too -, (...)or me...
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and that you can easily avoid by using a simple voltage follower as output buffer: signal to OPA +in, OPA out feedback to OPA -in...
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matthias
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fonik
Joined: Jun 07, 2006
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Location: Germany
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| Posted: Fri Mar 23, 2007 6:36 am Post subject:
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the mix/output circuit is really lowtech, i know. at least it works fine for me (i am okay with the result you can listen to in the sample above).
BTW i plan to do a PCB layout for a extension board offering invertible CV in and panning/stereo out ( i really want to do a stomp box with the resonators and these would be great features). this would affect the wet/dry mix, too.
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funkyfarm
Joined: Jan 21, 2007
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Location: France
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Posted: Fri Mar 23, 2007 8:14 am Post subject:
Subject description: inverting mixer + inverting mixer |
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| fonik wrote: | | Quote: | Radio Junk Box schematic :
the last output stage is inverting too |
and that you can easily avoid by using a simple voltage follower as output buffer |
I'm afraid that it is not possible as this final stage isn't a simple inverting buffer but a inverting mixer, blending the cursors of the stereo pot...
So I guess another inverting buffer (ie inverting mixer with only one input) has to be added : one whole TL072 and 5 100K resistors as an output buffer !
(a real load of money ! for sure it has to be better  )
PS : stupid question : can we use TL072/82 all the way, as for input buffer and filters ? or better OP275, OP2277 ?
Some vactrol-based-resonant filter users complain about noise (weak S/N ratio), which I didn't notice through online mp3 samples...
Vactrol design is guilty ?or IC 1458 ? (which is roughly a dual uA741) |
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fonik
Joined: Jun 07, 2006
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Posted: Fri Mar 23, 2007 8:46 am Post subject:
Subject description: inverting mixer + inverting mixer |
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| funkyfarm wrote: | | fonik wrote: | | Quote: | Radio Junk Box schematic :
the last output stage is inverting too |
and that you can easily avoid by using a simple voltage follower as output buffer |
I'm afraid that it is not possible as this final stage isn't a simple inverting buffer but a inverting mixer, blending the cursors of the stereo pot... |
oh, i didn't notice that! 
i didn't try different OPs yet. maybe all the folks currently building this filter could do that?
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matthias
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Scott Stites
Janitor
Joined: Dec 23, 2005
Posts: 4127
Location: Mount Hope, KS USA
Audio files: 96
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| Posted: Fri Mar 23, 2007 9:23 am Post subject:
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A Vactrol, in a suitably designed circuit, should render superior S/N over just about any active electronic device. For example, to process an audio signal through an OTA, the signal must be chopped down to nearly nothing then amplified back up to usable level. The noise picked up in this process is amplified as well. The LDR, on the other hand, is quite tolerant of any signal level.
The MultiPhase at max setting renders the signal through 32 LDRs, and comes out very clean (notwithstanding the fact it also passes through better than 32 op amp stages). I shudder to think of the noise generated by sending it through 32 OTAs, or a 32 stage transistor ladder.
Where an OTA, transistor ladder, or any other active device beats the Vactrol is the speed of response. Each LDR will impart its own signature on actual control of the Vactrol.
Cheers,
Scott |
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funkyfarm
Joined: Jan 21, 2007
Posts: 583
Location: France
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| Posted: Fri Mar 23, 2007 11:06 am Post subject:
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uA741, 1458 really have "poor" sonic specs ? compared to common TL series IC ? (TL071, TL082...)
light-years from an op ? (275, 2277...)
Vactrol-based Mutron BiPhase used 1458 everywhere...I can't hear no extra noise...(or I quite like it ?!) |
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bugbrand
Joined: Nov 27, 2005
Posts: 846
Location: Bristol, UK
Audio files: 1
G2 patch files: 1
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| Posted: Tue Mar 27, 2007 2:37 am Post subject:
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I thought I'd share the view of my module (sorry, still no sounds demoing the feedback)
Still need to do some tweakyness.. but it generally sounds freaking ace!
Quite a squeeze to get everything into 3 fracrak space.!. There's two mixer boards with the 5 pots (3 on top, 2 on bottom pcb) mounted right on the righthand side of the plate and then the main pcb is on brackets right at the bottom (slightly left) of the plate.
Controls are:
CV Section - attenuated CV inputs for each plus master control and LED
(I gotta tweak the LED resistor values maybe - there's still great effects when the LEDs aren't glowing very much... so they're somewhat limited in their display, but good none-the-less)
LFO section - switch for saw / tri / ramp (as suggested in Fonik's PDF) (this is well worth the SPDT c/o switch - the saw and ramp are effectively double the freq of the tri - great!), speed control, positive and inverted outputs, LED speed indicator (driven off positive lfo signal)
Mixer input - two inputs (mixed and kept in-phase) plus feedback channel with +ve or -ve feedback signal
Output mixer - independent levels for dry and wet signals mixed (again, in-phase) to output -- I still don't know whether I prefer this setup to a balance control... a single knob would be good sometimes, but also a little less versatile at others.. swings'n'roundabouts...
One note to Fonik --- I think the resitor R3 is too close to the mounting hole (and there'd be space to move it if a new version board was made) - when I'd got fracrak braket mounted it was touching the signal (ie, not ground) side of R3 = bad! (but I figured I could do away with R3 due to my input mixer, so....)
Will do sounds......!.....
| Description: |
| Fracrak module of PS3100 with additionals..... |
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78.55 KB |
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8947 Time(s) |
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etaoin
Joined: Jun 30, 2005
Posts: 761
Location: Utrecht, NL
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| Posted: Tue Mar 27, 2007 2:45 am Post subject:
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| Quote: |
One note to Fonik --- I think the resitor R3 is too close to the mounting hole (and there'd be space to move it if a new version board was made) - when I'd got fracrak braket mounted it was touching the signal (ie, not ground) side of R3 = bad! (but I figured I could do away with R3 due to my input mixer, so....)
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I have a couple of CGS boards that also have that problem. I usually isolate the board from the screws and bracket with plastic washers. Also reduces the risk of ground loops. |
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bugbrand
Joined: Nov 27, 2005
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Location: Bristol, UK
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fonik
Joined: Jun 07, 2006
Posts: 3950
Location: Germany
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| Posted: Wed Mar 28, 2007 2:22 am Post subject:
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| bugbrand wrote: | | One note to Fonik --- I think the resistor R3 is too close to the mounting hole |
i corrected the layout according to your suggestions.
however i am not sure if there will be a 2nd run. i had only few requests for PCBs lately (which i could fulfill with some spare PCBs i already had) and there are still a couple of PCBs on hold i'm waiting for payment for.
anyway it's great to SEE the offspring of this PCB run, especially a original bugbrand module. can't wait to HEAR your sound samples.
funkyfarm will come up with a very versatile module as well, i bet!
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matthias
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etaoin
Joined: Jun 30, 2005
Posts: 761
Location: Utrecht, NL
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| Posted: Wed Mar 28, 2007 2:39 am Post subject:
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Which silver mica caps did you use and where do you buy them?
I ordered six fom Musikding the other day but those turned out to be far too big. |
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fonik
Joined: Jun 07, 2006
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Location: Germany
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| Posted: Wed Mar 28, 2007 2:54 am Post subject:
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| Etaoin wrote: | Which silver mica caps did you use and where do you buy them?
I ordered six fom Musikding the other day but those turned out to be far too big. |
musikding sells micas rated for 500V. i used them for my prototype. for the PCB i used 100V rated micas (RM 4.5mm) as you can see in the pictures i posted.
i got mine from reichelt, which is unfortunately not very suitable for foreign countries.
micas from reichelt
micas not cheap! so is there any possibility to solder your 500V with enough distance to the PCB so that you can bend them to fit?
EDIT: Glimmer (germ.) = Mica
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matthias
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etaoin
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fonik
Joined: Jun 07, 2006
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| Posted: Thu Mar 29, 2007 12:20 am Post subject:
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matthias
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bambam
Joined: Feb 20, 2007
Posts: 60
Location: australia
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| Posted: Mon Apr 02, 2007 1:00 am Post subject:
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Hi All
My pcbs just arrived today
Any chance someone might have some vactrols spare? im in australia and can paypal etc and am happy to cover postage.
I can order them if need be from the US but figured if one of you has spares it would be cheaper to use the postal service rather than the couriers most suppliers insist on using.
Thanks
Brett |
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krisp14u
Joined: Nov 11, 2006
Posts: 206
Location: uk
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| Posted: Mon Apr 02, 2007 11:09 am Post subject:
vactrols |
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hi brett
pm sent
if anyone else needs any i have afew left up for grabs
2UKP each
cheers
Paul D |
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softfin
Joined: Oct 11, 2006
Posts: 271
Location: Far in the north
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sneakthief
Joined: Jul 24, 2006
Posts: 569
Location: Berlin
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Posted: Tue Apr 03, 2007 9:49 am Post subject:
Subject description: budget parts |
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so you didn't use mica caps then? i've got all the parts and the board sitting here and was just pondering if i should shell out the cash for the mica's.
cheers,
michel
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fonik
Joined: Jun 07, 2006
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Location: Germany
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| Posted: Tue Apr 03, 2007 9:50 am Post subject:
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| softfin wrote: | | I used strictly 'budget'-parts, matched carbon resistors and replaced the tl072 with a cheapish 4558. |
actually the TL072 was what i had on hand. maybe an overkill for a LFO...
| Quote: | | Here's a pic of the module. Could be prettier,... |
don't say that. i like this picture. nice colorbalance and the silky colors correspond with the blob drop soft touch knobs. looks very nice, handcrafted (in a good way) and aesthetical harmonic.
| Quote: | | It's still waiting on my work bench for a couple of adjustments to get the range right with +-12V power. |
let us know your results on this. would be very interesting for some folks.
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matthias
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softfin
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bambam
Joined: Feb 20, 2007
Posts: 60
Location: australia
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| Posted: Tue Apr 03, 2007 4:45 pm Post subject:
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If anyone is trying to find micas cheaper maybe try ebay, i just got 25 x 5% 100v silver micas for $6.99us plus shipping which seems alot better then other options i looked at.
Cant wait to get this pcb done
Brett |
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23isgood
Joined: Nov 18, 2006
Posts: 236
Location: San Francisco, CA bay area
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| Posted: Tue Apr 03, 2007 5:52 pm Post subject:
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Its too bad folks are having such a hard time finding Mica caps. Just 30 mins south from me is Halted. You can just go inside and get parts right off the shelf. They have hundreds of boxes with parts of all kinds. There is a section just for Polystyrene and Mica caps and they are dirt cheap!
www.halted.com/
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funkyfarm
Joined: Jan 21, 2007
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mosc
Site Admin
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| Posted: Thu Apr 05, 2007 10:03 am Post subject:
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| 23isgood wrote: | | Just 30 mins south from me is Halted. |
When I lived in Oakland I used to make regular trips there. Brings back memories... 
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