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DIY Stompboxes => Building your own stompbox => Topic started by: Bunkey on December 10, 2019, 08:36:14 PM

Title: Hollis Flatline capacitor selection
Post by: Bunkey on December 10, 2019, 08:36:14 PM
Hi there,

I'm putting together a parts list to build a flatline compressor.

I built a pretty successful Bazz Fuss before this with some invaluable help from members on this forum but my knowledge of circuit design is entirely limited to that pedal..

I'm wondering why the output cap (C2) on the flatline is spec'd as a polar electrolytic type instead of film like the input? Is this something specific to FETs? Is it possible to use a film cap here instead?

Thank you
Title: Re: Hollis Flatline capacitor selection
Post by: vigilante397 on December 10, 2019, 08:54:03 PM
From what I'm seeing it's a 1uF capacitor. You can absolutely use film if you want, but I'd imagine some people would choose electrolytic over film because 1uF is the range in which caps tend to be cheaper and smaller if you get them as electrolytics.
Title: Re: Hollis Flatline capacitor selection
Post by: Bunkey on December 10, 2019, 09:17:19 PM
Nice one thanks. I like the look of the fat yellow axials so I try to use them where I can  :icon_lol:

What about the 100n bypass cap on the LED - does this have to be polarised to discharge correctly across the LED or can I use film here too?
I'm guessing there's no audible benefit to be had from using a film here over an electrolytic in either case?
Title: Re: Hollis Flatline capacitor selection
Post by: vigilante397 on December 10, 2019, 09:41:45 PM
I'm not sure what schematic you're looking at that has a cap on the LED, but there is no reason for a 100n to need to be polarized. Polarization of caps is only done to allow them to be made smaller. I use mostly SMD components and I have non-polarized caps as high as 22uF. There is no difference in operation as long as current only needs to flow one way.
Title: Re: Hollis Flatline capacitor selection
Post by: Bunkey on December 10, 2019, 10:46:58 PM
Sorry, here you go.

It's just tripping me up as it's part of the rectifier section and has the (+) stated.


(http://stompville.co.uk/wp-content/uploads/2012/02/104SV2.png)

Title: Re: Hollis Flatline capacitor selection
Post by: Bunkey on December 10, 2019, 10:54:10 PM
Just noticed that schematic doesn't actually have C2 marked as an electrolytic. Not sure where the first version I saw came from  :icon_confused:
Title: Re: Hollis Flatline capacitor selection
Post by: sharp01 on December 21, 2019, 05:30:11 AM
http://www.hollis.co.uk/john/flatline.jpg

Looks like 100 uF to me. Not 100 nF
Title: Re: Hollis Flatline capacitor selection
Post by: rankot on December 21, 2019, 09:48:05 AM
C2 can be non polar (MKP, for example) as well, and even better than electrolytic. C3 should be 100u if you're using home made LDR (with fast decay photoresistor), or 100n if you're using NSL32 or VTL5C2 (decay time 500ms). But you shall definitely try few caps and see which one works best for you.

See this for more explanation: http://stompville.co.uk/?p=50 (http://stompville.co.uk/?p=50)
Title: Re: Hollis Flatline capacitor selection
Post by: deadastronaut on December 22, 2019, 09:25:07 AM
ive been playing with this on breadboard a bit lately.

i found c3 as a 470uf was better.....nice smooth fade off rather than a rippling decay.

i also put an identical led in parallel with the ldr led too.
Title: Re: Hollis Flatline capacitor selection
Post by: rankot on December 12, 2020, 03:00:45 PM
ive been playing with this on breadboard a bit lately.

i found c3 as a 470uf was better.....nice smooth fade off rather than a rippling decay.

i also put an identical led in parallel with the ldr led too.

Did you just put another diode, or made some kind of resistor divider for them?
Title: Re: Hollis Flatline capacitor selection
Post by: lapsteelman on December 12, 2020, 09:15:37 PM
I recently breadboarded and built the Flatline... I rolled my own vactrol and went with 100uf. definitely auditon a few photoresistors if you have a few varieties. I have a pretty large stash and the difference between them could be quite dramatic. With the right photoresitor it's really an amazing compressor.
Title: Re: Hollis Flatline capacitor selection
Post by: rankot on December 13, 2020, 04:13:21 AM
Which photoresistor did you settle on? I've built this few years ago, and used an original VTL5C2. Worked really nice!
Title: Re: Hollis Flatline capacitor selection
Post by: lapsteelman on December 13, 2020, 05:38:36 PM
Which photoresistor did you settle on? I've built this few years ago, and used an original VTL5C2. Worked really nice!

Not sure what it's specs are... many years ago Jameco used to have a grab bag of photoresistors and it was crazy cheap so I picked up a few... Electronic Goldmine used to do this as well.... so now I have a big ziplock bag with several hundred... This particular one was a bit larger than the ones you usually see but it really worked well..   The ones from Tayda actually didn't work too bad.