Vibra-tone cap question

[snoof]

All my 1uf caps are electrolytic polarized,  how should these be oriented??



...and C16 as well.

[markm]

Hi there Scott!
I don't know how well this will work with Electros but, now that I say that I think ulysses built his with tants so, I may be wrong.
The LFO section of this circuit is the EA Trem for the most part.
Therefore, in looking at the layout here's my take on the polarity;

C10 = + toward the Source of Q4.
C17 = + toward the Base of Q7.
C19 = + toward C18.
C18 = + toward the Emitter of Q8.
C16 = + toward the Base of Q9.

That should do it however, R.G. does reccommend in the schem the use of Film caps in the LFO section which is
how my build is so, I cannot comment on whether this will effect performance of the circuit or not.
Probably won't but, don't hold me to that!
I did all of this by using ROG's perf build and schems from ROG and GEO as a guide. I am not even close to mine right now!!
Good luck!   

[snoof]

thanks for the reply mark.  on your recomdendation, I found some NP caps at my local place, spendy!  anyway It's all built, but there's a vol drop when engaged.  that said, i have not matched the 2 sets of trannys yet.  i hope that'll make the vol drop go away cause it sounds great, execpt for the vol drop.  good job on that layout by the way!

[markm]

Just out of curiousity, what transistors did you end up using?

[snoof]

i used all the correct parts as called for in the schem...  man, it does sound good, i just need to fix the vol drop.

[markm]

i used all the correct parts as called for in the schem...  man, it does sound good, i just need to fix the vol drop.

Okay.
R.G. had mentioned some potenial gain issues with different transistors.
And Yes, I completely agree, the sound is like nothing else but a Brownface Fender.
Very sweet! 

[ulysses]

you will need to do the mods RG suggested to get the gain right. either that or keep trying matched sets of transistors until you dont get a drop in volume.

cheers
ulysses

[ulysses]

you should also try my "brown swing" mod, which is available in the layouts gallery. it sounds really nice

cheers
ulysses

[snoof]

i'll have a look at that mod, thanks.  i tested and matched all my 5952's, still a gain loss .  i guess i'll have to tack a perf board gain stage on the end, i don't wanna mangle my board with modding the follower on the end.  maybe that last stage should be redesigned into a gain stage w/ a vol pot in this crkt permanently and included in the layout(s)??  the two of us have had the same issue w/ the vol drop.  Mark's multiple builds have apparently turned out well w/ no vol drop, hmmm.

[markm]

i'll have a look at that mod, thanks.  i tested and matched all my 5952's, still a gain loss .  i guess i'll have to tack a perf board gain stage on the end, i don't wanna mangle my board with modding the follower on the end.  maybe that last stage should be redesigned into a gain stage w/ a vol pot in this crkt permanently and included in the layout(s)??  the two of us have had the same issue w/ the vol drop.  Mark's multiple builds have apparently turned out well w/ no vol drop, hmmm.

No issues on my side with the volume drop. Could be the variables of JFETs?
I will let you know that my plan is to alter Q4 into a "mild" gain stage and add a trimpot to the output allowing the user to adjust the output to personal "taste".
I am awaiting R.G.'s advice about this as I really don't want to upset the overall tone and performance of this circuit because the sound is
fantastic!
Seems we are begining to see more reports of volume issues so, my thoughts are that this should remedy the problem.

[snoof]

I agree about the trimpot/gain stage addition,(or reg pot to be brought out to the case, user preference) as long as the tone/performance remains unchanged as you point out.  Again, great job on the layout by the way!  It takes me FOREVER just to do a layout for a simple crkt, you da MAN .  And thanks to R.G. for the schem.

[R.G.]

Guys, I think the right thing to do is to just put an opamp gain stage after Q4. I messed with the thing a bit in the simulator and it takes a lot of junk to make it get reliable and stable gain. If I were reworking the schemo, I'd probably use a dual and use one section instead of Q1, the second instead of Q4. If you have a board built, just add some gain after it.

[GREEN FUZ]

Any soundclips available yet?

[markm]

Any soundclips available yet?

Ulysses has some in his gallery! 

[reb]

What doess the brown swing mod do / sound like?

[R.G.]

After my first thoughts I was struck by the possibility of adapting the output stage to a "JFET Darlington" so I went back and tried it. That seems to work.

Check the new entry on "New at GEO" for the update. It adds Q10, an NPN, converts Q4 to self biased (kind of) and gives a trimmer with a 1 -10x gain. The problem I had with this one was that it provided too much gain and I had to spend some time taming it.

I think it can be hacked onto the same PCB, the only problem being where to put the trimmer.

[markm]

Looks like that may be the solution R.G.!
One thing I did in between communications with you was to implement the mods you wrote about in another thread
to try and up the output.
R.G. had explained to me that uping the gain on Q4 could upset the bias hence, effecting the whole circuit.
As far as the trimmer is concerned, This here is how I added the trimmer for the previous mod;



Looks to me as though there is room for the additional transistor, some re-arranging would be in order though.

[markm]

After looking at the new schem.....yeah that trimmer could be a challenge huh? 

[snoof]

just FYI...  R.G., it seems that there are 2 "Q10's" on the version 2 schematic on your site.  can I assume that the NPN tranny in the darlington pair is a 5088, and that the FET is 5952??

[markm]

just FYI...  R.G., it seems that there are 2 "Q10's" on the version 2 schematic on your site.  can I assume that the NPN tranny in the darlington pair is a 5088??

In my humble opinion I'd say it could be any of the basics like 5088, 3904, 4401 etc.