Sekova - Fuzz ( FA-II , Apollo , Crestwood )  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
RnFR
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Post by RnFR »

I just made a vero layout for this pedal. of course it is not yet verified, but it looks good to me. i haven't put the values of the parts up yet, but the part numbers match AG'S schemo. if anyone builds it, make sure to let me know so we can get it up in the ready to build pages.

oh yeah, i added a power filtering cap- C11.

Image
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Post by analogguru »

Funny, on my HD I found guts where the diodes are silicon, the 27k resistors are 33k and the 5k6 resistors are 4k7. The pcb has also minor differences.
On these guts the capacitor which was in doubt is a 100n as I expected. The tantalum is a film cap.

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Post by royaltoots »

analogguru wrote:Funny, on my HD I found guts where the diodes are silicon, the 27k resistors are 33k and the 5k6 resistors are 4k7. The pcb has also minor differences.
On these guts the capacitor which was in doubt is a 100n as I expected. The tantalum is a film cap.

analogguru
On the old DAM forum Andy/MoreCowbell posted this pic of a 9V Sekova, is it this one?

Image

more - http://dam.10.forumer.com/viewtopic.php ... ght=sekova

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Post by analogguru »

Yes, that´s the one.

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Post by gigelmargel »

Hello,

I've just finished one of this using some SFT242 with gain between 70 and 90 and it sounds pretty OK, but I am not sure if it's as the original or not.

My voltages, using a 8.70 battery, are:

Q1: C = -5.75 B = -3.08 E = -2.95
Q2: C = -5.70 B = -3.03 E = -2.93

R4/R5 node: -0.06

Anyone can tell me if these voltages are OK or not?

Thx a lot !

RnFR
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Post by RnFR »

i've got a silicon version of this on the breadboard now. i made some mods including an extra booster stage for more volume, diode switch, and i adjusted the bias a bit. later today i'll try to make it stock, pop in some Ge's, and test the voltages for you.
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Post by gigelmargel »

RnFR wrote:i've got a silicon version of this on the breadboard now. i made some mods including an extra booster stage for more volume, diode switch, and i adjusted the bias a bit. later today i'll try to make it stock, pop in some Ge's, and test the voltages for you.
Thx a lot RnFR!
What silicon transistors did you use?

RnFR
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Post by RnFR »

i used a 2n5087 into a 2n2907, but that's pretty much because i was set up for PNP because i tried it first with Ge transistors. i personally like this circuit better with silicon. you could try an NPN version with an 2n5088 into a 2n222 and it would probably be close. i messed with R6 a bit, too. i think i changed it to 3K9 or 4K7. that took care of any gating that was happening. i added a simple Ge booster after the tone section, and pregain control at the front of the circuit as well. now it's plenty loud, there is a tone control, and a gain control as well as an on/off/on diode switch. much more versatile and usable in my opinion. i heard this pedal at midwest buy and sell here in chicago years ago and always kicked myself for not buying it. it does a great swarm of bees kind of tone. :mrgreen:

i'll try to get those voltages measured tonight, but i think the difference in our Ge transistors used will affect the readings. do you have some silicons like i mentioned above? that would probably solidify it a bit.

i'll try and get a schematic of what i did drawn up one of these days, too.
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Post by gigelmargel »

RnFR wrote:i used a 2n5087 into a 2n2907, but that's pretty much because i was set up for PNP because i tried it first with Ge transistors. i personally like this circuit better with silicon. you could try an NPN version with an 2n5088 into a 2n222 and it would probably be close. i messed with R6 a bit, too. i think i changed it to 3K9 or 4K7. that took care of any gating that was happening. i added a simple Ge booster after the tone section, and pregain control at the front of the circuit as well. now it's plenty loud, there is a tone control, and a gain control as well as an on/off/on diode switch. much more versatile and usable in my opinion. i heard this pedal at midwest buy and sell here in chicago years ago and always kicked myself for not buying it. it does a great swarm of bees kind of tone. :mrgreen:

i'll try to get those voltages measured tonight, but i think the difference in our Ge transistors used will affect the readings. do you have some silicons like i mentioned above? that would probably solidify it a bit.

i'll try and get a schematic of what i did drawn up one of these days, too.
Thx a lot RnFR!

2N5087 it's impossible to find here, but I have some BC560 (or something like that)...booster I will not add because I used booster almost all the time, so that's not a big problem.

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Post by gigelmargel »

I replaced Q1 with a BC560, Q2 with a 2N2905 and the germanium diodes with silicon ones and it sounds better.
I will try in the next days to tweak it a little.

Thx a lot RnFR again for your advices!

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Post by RnFR »

gigelmargel wrote:I replaced Q1 with a BC560, Q2 with a 2N2905 and the germanium diodes with silicon ones and it sounds better.
I will try in the next days to tweak it a little.

Thx a lot RnFR again for your advices!

you are very welcome! sorry i didn't get around to posting those voltages. try lowering the 5K6 collector resistors a bit. this helped get rid of some gating that i was hearing at the very final end of the decay. you might not be able to hear it with the diodes clipping, but without them it is very noticable.

also, i put a schematic up in the Ready To Build section with all of the mods i've done.

https://www.freestompboxes.org/viewtopic.php?f=13&t=6885
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Post by gigelmargel »

RnFR wrote:
gigelmargel wrote:I replaced Q1 with a BC560, Q2 with a 2N2905 and the germanium diodes with silicon ones and it sounds better.
I will try in the next days to tweak it a little.

Thx a lot RnFR again for your advices!

you are very welcome! sorry i didn't get around to posting those voltages. try lowering the 5K6 collector resistors a bit. this helped get rid of some gating that i was hearing at the very final end of the decay. you might not be able to hear it with the diodes clipping, but without them it is very noticable.

also, i put a schematic up in the Ready To Build section with all of the mods i've done.

https://www.freestompboxes.org/viewtopic.php?f=13&t=6885
Thx a lot again! You're great man !

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Post by LucifersTrip »

sorry to dig up an old thread, but there was a question about whether it gates (yes)...the answer to the the low output volume was obvious (yes).

there's one on eBay now with a sound file:

http://thenoir.net/pedal-samples/sekova-faII-01.mp3

...of course, the gating could also simply be from degenerated / misbiased transistors...

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Post by edkoppel »

I would say that is a pretty accurate audio clip.

not sure if it's anything you guys don't already have, but I did a blog post on a Sekova a few months back:
http://tonemachines.blogspot.com/2011/1 ... -1969.html

the strange thing is that is sounds extremely similar to the fuzz-side of the 6-tranny Shin Ei Fuzz Wahs, but doesn't seem to be related circuit-wise at all?
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Post by GodSaveMetal »

analogguru wrote:Ok, then here is the final
Sekova Fuzz (FA-II) schematic

Circuit and frequency-plot discussion follows later when I find some time.

analogguru
Please man can you repsot the circuit of the versions of SEKOVA FUZZ? great man!!!

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Post by d312a »

I found this schematic
Image

Some values in the tone section is incorrect:
1nF shold be 2,2nF
1uF should be 100nF
1,2 should be 220nF

I have built several variants of this circuit and IMHO it sounds better without the diodes.
I also increased the volume pot 500kB to increase the output level.

Cheers

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Post by d312a »

Ooops, don't know how to ad images or edit post to the forum so here is the link to the schematic

https://78462f86-a-87c6d4c2-s-sites.goo ... edirects=0
Sevoka FAII.png

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Post by GodSaveMetal »

d312a wrote:Ooops, don't know how to ad images or edit post to the forum so here is the link to the schematic

https://78462f86-a-87c6d4c2-s-sites.goo ... edirects=0
Please man you would post the lay+PCB you have build?? thanks a lot, it´s awersome you post!!!

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Post by dukeofearl »

Sorry to reactivate this very old thread! I've been searching for info on this Sekova FA-II pedal and haven't had any luck.

I'm not sure but there appear to be 3 film caps on mine. Maybe some are tantalums? One of these capacitor leads is broken. The other two look fuzzy. I was hoping to replace these but can't find values. Any suggestions?! Thanks!
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IMG_6790.JPG

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Post by dukeofearl »

one more pic...
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IMG_6788.JPG

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