Phase 45 / Univibe volume drop

[hilbi]

I Just build the phase 45 /univibe from torchy's layout. It is phasing fine. BUt there is quite a volume drop when it is turned on and mixed to full effect. I did not match met 2n5458's yet, but the phasing is sounding fine.

I found this thread from the past, any one and idea?

http://www.diystompboxes.com/smfforum/index.php?topic=36798.msg260976#msg260976

[hilbi]

I matched the fet's now, by the procedure of jc maillet, this helped a bit, but it is still not unity gain.

Especially the bass side has been cut off.

http://www.lynx.bc.ca/~jc/pedalsPhase45.html

[mdc]

I can't help (yet) I'm afraid but I plan on building this same layout. Keep us posted on your progress. The orig phase 45 changes tone quite a bit when engaged but definately no volume drop. If anything a slight boost. Any chance of a few pics and/or soundclips when you get this baby going?

[smank]

It's simple: you must decrease the 20k/22K resistor around the op-amp input stage (connected betweem pin - and the reference zener voltage point). I've used a 12K resistor: with clean sounds the gain seems more than unity, but with overdrive and distortion, this value work perfectly.
Because the effect affects the overall tone, the change in output volume is apparent. Neverthless, changing this resistor you can obtain a good compromise.

[hilbi]

It's simple: you must decrease the 20k/22K resistor around the op-amp input stage (connected betweem pin - and the reference zener voltage point). I've used a 12K resistor: with clean sounds the gain seems more than unity, but with overdrive and distortion, this value work perfectly.
Because the effect affects the overall tone, the change in output volume is apparent. Neverthless, changing this resistor you can obtain a good compromise.

Ok thanks, I will that a try.

[hilbi]

MOdding the R2 (22k) to 12 k worked for some degree, but still it is thin sounding because the bass has been cut off, so the highs are at the same level now, but the bass isn't.

I double checked the fet mating again, I got two 2n5457 who match both at 03:00.

Maybe get more fets?

Also i hear not much difference between phase or univibe setting, alltthough the switch is correctly working.

I got a 5.1V zener, if this value is to high can this also be the cause? Original phase 45 had 4,7V zener if I'm correct.

[oldrocker]

I just matched my fets today and I'm not sure if I like it with the Univib mods.  It phases ok but I hardly hear much difference with the switch except the phase sound is more choppy in one position.  Which is another thing.  Before I did the Univibe mods the phase was smooth from when the phase reaches it's peak before coming back down.  With the mods I hear a huge clarity of the peak when the LED turns on so it's not a smooth phase anymore.  And since I don't hear much difference in the Univibe mode I'm now thinking of removing it.
There's not much drop in volume although I don't have a bypass in mine so I can't tell as much.

[smank]

If the Phase45 sounds thin and the FETs has been correctly selected, you must try to set the trimmer in a sligth different position. Be careful, because very small variations have great impact on the effect and its width.

[hilbi]

I use the modded schematic of the phase 45



I has no trimmer on the system board like the original 45 but 3 controls on outside, maybe the internal trimmer is now moved outside in the bias or mix control?

Anyway if I said the bias control to the matched location of the fets, the mix control should be in the middle it is sounding ok. If I turn the mix control left the phasing is gione and the volume turns up a bit. I f I turn the mix control righ, then there is still some phasing/vibrato and the volume is also coming up a bit. But the deep phasing is gone. If I understood correctly this is also how it should work.

[smank]

You're right: the bias control has the same function of the internal trimmer.

In my version I've used just the UniVibe cap mod. But I've used the internal trimmer and I haven't the mix control.
I've used a 500k linear pot in series with a 680k resistor instead of the 1M resistor starting from the trimmer/bias control: this new pot works like DEPT control.
Once you've found the optimal setting of the internal trimmer (from tone / dept point of view), this dept pot affect the tone just a bit, but it controls really the dept.
To set the trimmer, you must set the dept control to the max and you need to check it's working correctly in both stock and univibe (cap mod) position.

[MartyMart]

Answer is simple, reduce R4 - the 150k to ground just before output jack
Or perhaps just use a pot, 47k to ground and 100k log should give you enough
to play with.
I think I remember trying a few to get "unity" against bypass and 120k worked for me.

MM.

[hilbi]

Thanks Marty, will give that one also a try.

[hilbi]

http://members.chello.nl/~h.nauta7/mp3/phase45uni.mp3

Can someone confirm if my sound sample is sounding like a phase 45?

First part is phase 45, from 0,38 sec it is univibe setting.

It's recorded with telecaster, both pickups, fender amp setting on pod.

Marty, you suggestion fixed my volume drop issue. I used a 200k trimpot and 10 k resistor. I turned the trimpot almost completely down and now i have a slight boost.

[smank]

In my version, the UniVibe cap position seems to have sligth more mid scoop, but I'm speaking about a small difference from your P45.

For Marty: I don't understand why reducing R4 (150k out resistor) increases the output level... One can thinks the exact opposite...

[MartyMart]

MY BAD  - of course i meant "Increase" not "decrease" !! 

I was just thinking about the "decrease" of signal bleeding off to ground ....

so I must have used a 220k and not a 120k

"We all make mistakes" - said the hedgehog getting off the yard brush !!

MM.

[hilbi]

Luckily I used a 200K pot  , so it rotated it probably to its max resistance setting. so i'm at 210K then.

Thanks guys,

So the sound sample is sounding like a phase 45 then?

I used ceramics caps all the way, i will replace the caps in signal path with film caps.

[MartyMart]

That sounds absolutely great to me , I wouldn't mess with it, unless you have any "hiss" ?
Mine is all poly/mica caps and is very quiet

MM

[hilbi]

There is no hiss. The highs are a bit sharp, i expect the ceramic caps to cause that, so that's why I would like to replace some ceramics by film caps in signal path to soften it a bit.

[smank]

Try to substitute the ceramic caps, probably you can remove a bit of harsh.
Obviously, we are speaking about sligth diferences... just to reach the perfection!

Marty, the only problem I can see increasing R4 is the input impedance of following effects or preamp. If this impedance is enough small, it can change the effect of this set of resistors. But normally, it will be enough higher than 220K to produce a small effect.
Just to reduce this effect, in my version I've used small values for the 10K/10K/150K resistors: 2,2K/2,2K/33K. In this case to compensate the difference in output level we can increase the 33K resistor to 47K.

[hilbi]

Try to substitute the ceramic caps, probably you can remove a bit of harsh.
Obviously, we are speaking about sligth diferences... just to reach the perfection!

I agree, it is just a small difference.