Trem face - unity gain ?

[sfr]

Realized I had the board populated and kicking around for over a year, so I boxed it up the other day.  I love this thing, great sound.  A little clock noise bleeding through at times, still need to see about that.   But all in all, a great pedal.  Only thing that's really getting me is the noticable volume drop when the effect is engaged.  Particularly when a distortion is before it.   Looking over  RGs notes at Geofex, I see he mentions the possibility of this, as the original effect was not true bypass, and always attenuated the signal. 

Anyway - anyone else build this pedal and have the same problem?  It seems weird how the hotter a signal I feed into the front of it, the more noticable the volume drop coming out the back, so I was wondering if perhaps I've got something going wrong.  Or perhaps that's just my natural perception of sound.

I guess I'll look at tweaking the input JFET to get a little gain to overcome the volume drop, did anyone else remedy this, and how much did you tweak it?

[R.G.]

Tremolo can be all attenuation (tremolo down only ) or both gain and attenuation from a middle loudness. I think that the trem face is the down only version.

When the effect is active, even if the full up level is unattenuated, the times when the signal is lowered makes the impression of the overall loudness drop when the tremolo is on. What you really need is no gain when it's bypassed (that's easy!) and just enough gain to make up for the impression of lower overall sound when it's active.

Yeah, put some gain into the input JFET. 'Course, that will invert the signal, which is a problem in some parallel mixed setups.

[sfr]

Thanks, R.G.!

While I understand the concept, I'm not very well versed in the application, so if anyone can help me out with my JFET related followup here:

Looking at the schematic at Geofex, I'm assuming I could get a little gain out the 2N5460 by lowering the resistance at the source (the 6.8K resistor, R3)?  Is this correct?

And is there a particular reason this thing has no resistance at the drain of the 2N5460, as I'm used to seeing in these type of circuit snippets?   Is that part of what makes this portion a buffer and not an amplifier, or is it because this is a p-channel JFET? 

Sorry, I'm not always the brightest.  But any help people would like to offer would be great! 

[R.G.]

Your suspicions are correct - you can't get gain out of a JFET source. You need to add a drain resistor and take the output from the drain terminal. Just at a guess, I'd try about 3.3K to 10K at the new drain resistor, and change R3 down to something like 1K-3.3K. But the exact values will depend on the FET.

[sfr]

Wow, thanks again R.G. 

I'm getting my head wrapped around this stuff slowly, so in the meantime the assistance is greatly appreciated.

[R.G.]

My pleasure. Happy hunting!

[sfr]

Finally got around to tweaking this board today.  Socketed R3.  Cut some traces on the PCB, (inbetween the source and the negative on C2, and inbetween the drain and the trace that runs to the black battery wire.) Jumpered the drain to the negative side of C2 where the source had gone.  Added a resistor on the drain, along that trace that I had cut from drain to the black battery wire. (Actually, used the extra set of pads next to CX [which I still never put anything in there for] after some more trace cutting and jumpering.  The pads allowed me to use sockets for this resistor also.)

Everything worked pretty well.  R3 as a 2k2 and the new resistor as a 6k8 seemed to work well for me, although I'm still playing around.  But there seems to be no noticable volume drop between effected and straight signal now.  Probably a *slight* volume gain, but it helps even things out a bit between straight and effected when using the slower speeds of trem.   

My roomate is sick and still asleep, so I've been testing it with headphones, however, which isn't the best indicator.  If things change dramatically when I get a chance to run things through the amp, I'll post. 

All in all, this is a great sounding trem, and I prefer (at least in principle -  I haven't tried the "vintage" flavour of the schem) having the buffer in front, so this fix makes the thing usable with that added, and I'm pretty sure this thing has a place on my pedal board now.  It's got a surprisingly wide range of trem speeds, from really darn slow to fast enough the guitar sounds almost synthy and bubbly, if that makes sense.  The depth at it's least is pretty much uneffected, and at it's most is pretty choppy, although not totally on/off or anything.  The knobs interact pretty organically, however, so a depth setting that sounds way too choppy at fast rates is apt to sound perfect at a slower one. 

I don't know, it's my favorite trem of the moment, particularly clean.   Looking forward to running it through it's paces on Wednesday at band practice.   I never realized I liked Tremolo so much - I'm going to have to try making a few more.