tri-vibe on ROG

floris · Post by **floris** » 26 Feb 2012, 12:11

rocklander wrote:I'm wondering if its possible to raise the output vol.

In the schematic of ROG, you can increase the 47k feedback resistor of the output opamp U1b (between pin 6 and 7) to increase the output volume.
Try something between 47k and 100k for a few extra dB.
http://runoffgroove.com/tri-vibe.html

B Tremblay · Post by **B Tremblay** » 26 Feb 2012, 15:44

rocklander wrote:so my 1590a build out on its own (into a ruby ss amp) is not bad, but output vol is slightly low (not much)... into my valve amp it's more noticeable.. I'm wondering if its possible to raise the output vol.. would increasing the 100K at the output do that? if not.. what could I do? any suggestions? thanks in advance

My first thought is that your amp has a lower input impedance than Ruby. That's likely since the Ruby's buffer provides a high impedance. What sort of amp is it? Is there a higher gain input and if so, is there a difference in the perceived volume?

Is the volume drop consistent across the three modes?

I haven't noticed any volume drop with my build, but I'll try it with each of my different amps and note any differences in performance.

rocklander · Post by **rocklander** » 26 Feb 2012, 19:23

thanks to you both...
floris.. will look at that fb resistor thank you.

Brian... yes.. that's exactly what I did.. I put it in the lower impedance input cos we were having a practice at home rather than the actual gig (where I'd normally use the high impedance input, to get it louder).. or the other way round (I don't get which is which

).
the vol drop was consistent.. and baffling since I'd tested it a week or so ago at practice (in a practice room so I used normal gig volume.. nobody else had arrived as yet) and it was sweet as then... hmm.
I'm wondering if it's worthwhile (for me) adding a 50K pot after the 47K floris has suggested?

B Tremblay · Post by **B Tremblay** » 26 Feb 2012, 20:08

I just checked my Tri-Vibe with three different valve amps and found no volume drop.

Will you please check for a difference in output level between bypassed and the Tri-Vibe engaged with Depth at minimum in Vibe mode?

rocklander · Post by **rocklander** » 26 Feb 2012, 20:19

okay.. will do.. not able to right now, but will get onto it today

rocklander · Post by **rocklander** » 28 Feb 2012, 23:52

righto.. have been crook with a cold, but finally tested this.. issue still appears on both low and high impedance.. it's not insanely quieter, but notably... also quieter when depth is on zero.. possibly a bad build? possibly my layout is bad? regardless, would a volume pot (in the spot suggested by floris) be a bad call/good call? I would have thought a volume pot could be a nice addition..?

B Tremblay · Post by **B Tremblay** » 29 Feb 2012, 01:27

rocklander wrote:righto.. have been crook with a cold, but finally tested this.. issue still appears on both low and high impedance.. it's not insanely quieter, but notably... also quieter when depth is on zero.. possibly a bad build? possibly my layout is bad? regardless, would a volume pot (in the spot suggested by floris) be a bad call/good call? I would have thought a volume pot could be a nice addition..?

I'm not sure what could be the cause of the drop in volume. I haven't heard of this particular issue before, so I would recommend first verifying that no errors are present before making a modification.

floris · Post by **floris** » 29 Feb 2012, 08:10

rocklander wrote:... would a volume pot (in the spot suggested by floris) be a bad call/good call?

It would actually be a Gain pot instead of a volume pot. IMO it is overkill.
But perhaps check the build first like B Tremblay suggests.
I hear no volume drop with my Tri Vibe. It does have a slightly "sharper" sound than in bypass due to a bit more high frequency content.

rocklander · Post by **rocklander** » 29 Feb 2012, 09:09

yeah, I'd say it's my build (or possibly the layout) cos the other ones I've made (in 1590B rather than 1590a) have been fine.

phatt · Post by **phatt** » 01 Mar 2012, 12:56

Hi Rocklander,
First I must commend you on getting it all in the box

Re the output level issue;
Any time you have an Inverting last stage there is always the potential for transfer loss as you are then depending on the next stage Z to be high for max transfer. (not a comforting thought)
Please don't ask me to explain the in depth details as I'm not that clever at the deeper hidden meanings of electronics

But I've worn out 3 tu 4 breadboards in 30 odd years of messing with circuits and you get know what circuit ideas are full of holes.

Notice how Member *Mictester* is always banging the door down about *Buffer stages* ?? Well now you know Why. Winky.
If you want trouble free pedals it becomes obvious (even without a full understanding) that one needs to use buffers.

IME, use a non inverting stage as output will help but even then I've noticed there can still some transfer loss.
Even by adding a simple BJT follower would likely improve the situation.

Where you have Inter-stage coupling *inside a circuit* the issue would never arise as any loss is never going to be noticed BUT with pedals the In/Out/bypass difference can become problematic.

It may work on your setup but the moment you change the setup things can go belly up real quick.
As a working muso this is something you hardly need to have happen on stage.

The amount of dirt box schematics that hang a tone stage off the end with no buffer stage is just asking for signal loss issues to arise somewhere.
Sure they work but such ideas can be greatly improved.
----
I've been messing with a trem/vibe circuit myself and with luck it should end up on this site one day but I'd like to worm out the bugs. My view is if you want it to work you have to spend a lot of time finding all the bugs.

I did have a listen to your sound clip and it certainly has the makings of something good though the tremolo was still very freq modulated. It seemed to have trouble getting that real volume up/down happening,, but hey still a useable effect.

I have no doubt that better qualified folk may well be able to give you a more definitive answer about the loss.
Phil.

rocklander · Post by **rocklander** » 01 Mar 2012, 18:46

thanks phatt.. it's my layout but not my design.. all that stuff you said is well and truly over my head sorry but hopefully B tremblay (and/or others) will be able to make sense/use of it...

interesting to note however, that the cct is fine in other builds I've made (via the ROG layout rather than mine), it's this particular build in my layout that I'm struggling with.. I'm yet to go over it and ensure I didn't goof somewhere.. been laid up with man flu this week

and have been working on my ross phaser in a 1590a ... it's nearly done (pics to come).

floris · Post by **floris** » 01 Mar 2012, 20:23

phatt wrote:... Any time you have an Inverting last stage there is always the potential for transfer loss as you are then depending on the next stage Z to be high for max transfer. (not a comforting thought)
... IME, use a non inverting stage as output will help but even then I've noticed there can still some transfer loss.
Even by adding a simple BJT follower would likely improve the situation.

The opamp output U1b of the Tri Vibe is a very low impedance output, which can source and sink more than enough current to "drive" any following cable and circuit.
Because opamp outputs are low impedance outputs, it does not matter if its used as an inverting or as non-inverting amplifier stage.
It does not need a BJT follower.

phatt · Post by **phatt** » 02 Mar 2012, 14:49

@ floris,

Yes I do know that is what the text books say about ideal circuitry But I've built enough stuff to realize there are other very complex things happening but sadly it's beyond my capacity to fully understand let alone explain in detail.
Some of this is mentioned in books like *Art of Electronics* but a bit deep for Me.

Heck my mental abbacus only has one row of beads. LOL.
But I got enough info from reading such books to grasp that there are a whole pile of pitfalls just waiting to trip you up.
I have tried a few times to raise some quirky points but It tends to descend into text book debates. I have far more important things to do,, like build circuits.

If someone raises a detail that questions what I have learnt so far I WILL go and breadboard test it as I'm open to any help I can get.
(if it does not require purchase of exotic components)

Please understand I'm not stating that MY Way is Right,,, No I'm simply waving a flag and saying hey there maybe something else going on as Electronics is a very complicated thing.

@ Rocklander,
Hey man don't sweat it as I'm not much further ahead and that's due to the fact that I've likely blown up more transistors than You. LOL.
I've found that my mistakes have been the best learning tool as it forces you to dig harder for the answers.

Cheers, Phil.

rocklander · Post by **rocklander** » 03 Mar 2012, 12:50

well, I ripped it open to check it out and now I can't fault it :facepalm:

one of those lovely intermittent faults.. awesome

oh well, it's been bumped off the 1590a board for the ross cos as much as I like the tri-vibe, I just love the ross so much... did I mention I love it?

marshmellow · Post by **marshmellow** » 04 Apr 2012, 17:17

Inspired by rocklander's build, mine is also meant to go into an A-enclosure. Not boxed up yet,
since I forgot to get one on my recent order of course.

Wonderful sounding circuit, thank you very much Brian!

mictester · Post by **mictester** » 04 Apr 2012, 17:41

That's tiny! Really neat build (especially since you've soldered SM components by hand!)

rocklander · Post by **rocklander** » 04 Apr 2012, 19:00

marshmellow wrote:

Inspired by rocklander's build, mine is also meant to go into an A-enclosure. Not boxed up yet,
since I forgot to get one on my recent order of course.

Wonderful sounding circuit, thank you very much Brian!

great stuff! sharing the layout/pcb?

marshmellow · Post by **marshmellow** » 04 Apr 2012, 19:58

mictester wrote:That's tiny! Really neat build (especially since you've soldered SM components by hand!)

Thanks! Passives are all (but one) 0805, that's pretty comfortable to solder. The SOICs are 1,27mm pitch, which is easy to do as well. I would actually prefer a bit smaller pitch, that's better to drag-solder instead of soldering every single pin. The pcb measures 34mm x 38mm, so should fit the intended enclosure without problems. The pots are pcb-mounted from the back side.

rocklander wrote:great stuff! sharing the layout/pcb?

Sure, no problem, I'll give it a quick overhaul and post it then. But it's two-sided of course, there are a bunch of components on the bottom side, too. And there are several vias, so not really diy-able. I also have some pcbs left which I was gonna post in the sales section soon.

rocklander · Post by **rocklander** » 04 Apr 2012, 20:36

marshmellow wrote: But it's two-sided of course, there are a bunch of components on the bottom side, too. And there are several vias, so not really diy-able. I also have some pcbs left which I was gonna post in the sales section soon.

boo to double sided, but yay to selling some boards!!

mictester · Post by **mictester** » 06 Apr 2012, 10:57

It might not be as small as an SM version, but this is a fairly small Vero layout. Lots of links, and loads of track cuts, but it works very well, there's no oscillator ticking, and the sounds from it are excellent! It's a cheap and simple build, and a very clever oscillator circuit. The peculiar waveshape works very well for both vibrato and phasing effects. If you look at the Ross phaser, there's a different circuit that achieves a similar waveshape using OTAs, but draws more current and costs more to make.

Further experimentation shows that it is worth adding another two phase stages (switchable) and using capacitors of 15n and 5n6 in them. You get inherently deeper phasing sounds, and the pseudo-leslie effect available is really quite convincing! It's also worth experimenting with stereo output - you get really fabulous leslie sounds from a pair of amplifiers! I've also used the oscillator to drive OTA voltage-controlled amplifiers for stereo panning effects!

Here's the Vero:

: Runoffgroove's best design!

I used the other side of the DPDT to switch a bi-colour LED for "mode" indication, and the "Rate" LED is switched on and off by the bypass footswitch - another bi-colour LED with green for the Rate and red for "on" - you get an LED that varies in colour over the oscillator cycle!