Quick question on opinions re: the "effects loop"

[aprilia1k]

Hi -

Built my first (and only thus far, unless you count my DumWreck that I've been twiddling the last couple weeks - started as an express and ended up wiring up that unused triode and adding trimmers, etc.. until it's rather ODS-like (relatively anyway))... But, to the "loop" question:

This little unbuffered hook between the MV and PI, of course not much use without a D'lator or somesuch buffering box - yet, I have plugged in my little Line6 reverb stombox, the Verbzilla - and somehow the levels seem quite close. I have not bothered to see what this pedal wants (guitar/instrument level signal I would safely guess) at it's input, or what it puts out - BUT, without extreme settings, the thing just works- and when I unplug it my volume doesn't change much at all. I don't understand this, as I thought that the levels would be HORRIBLY MISMATCHED and that it would be either noisy/too quiet-or-loud/etc.. but it sounds fine, doesn't really add appreciable noise or (to my ears anyway) alter the tone very much. I would appreciate a couple of the masters' thoughts on this. It isn't supposed to work very well, and again, it's just this one pedal, no rack-gear or other stompers, just the 'verb - but it just confuses me that it seems to work as well as it does. I'm not planning on plugging a pedalboard or rack in to it now, the verb is plenty - just very curious on the technical reason(s) why this at least _seems_ to be working fine when the loop is just an insert point with no buffer(s).

THANKS,

Stephen

[Structo]

Well I'm not a master or an expert but I think the pedals you have tried were buffered.
So it keeps the signal (10db?) at a level that the PI can live with.

When I built my D'Lite I was told the passive effects loop would take a reverb pedal well.

And since most guys only run time based effects in the loop it works out pretty good most of the time.

I would also hazard a guess that impedance matching there is fairly important.

I was told if I wanted to use this passive loop that I should keep the cables very short to and from the pedal.

In the end, you risk nothing trying the passive loop to see if a given pedal will work well there.
The Dumbleator FX loop is supposedly almost required equipment for the ODS amps, in that it is more of the complete package when connected to the amp and many feel an ODS just doesn't have the tone they want without the Dumbleator.

I ended up installing the Ironsounds active FX loop that has an opamp buffer.
It works pretty slick.

There is also a loop available at Metro Amps that uses high voltage FET's that guys are liking a lot on their Marshall clones.
But it is $90 vs $50 for the Ironsound.

[butwhatif]

Installing a tube, and making it run an efx loop isn't that tough, and it's the best solution. Any of the other stuff is a 1/2 measure, and isn't true to these amps. Also depends on the efx involved, as u might not need add'l loop architecture if you have an item last in the chain that can deliver a big signal output, that is, if you need efx in the loop at all. Years ago I used several top of the line rack efx in my loop, and actually built a balanced tube/transformer send and return. That was the best sounding, totally noise free efx loop I ever had, the xformers made the lines balanced mic level- which could run the 50' of cable w/o any change or losing anything. But these days I haven't used the loop much at all, preferring the ease of everything front end. If it works, so be it.

[aprilia1k]

OK - So, yeah, for me, the reverb works fine in the unbuffered loop and to my ears there's very little if any change in tone. I put the pedal right on the amp and run 8" patch cords to the loop. Of course a buffer would be cool, but not at this time - and there's hardly room in an ODS (mine anyway - Ceriatone chassis, pretty full in there). The problem with running reverb or delay in front of the amp, of course, is switching from clean to gain tones (especially if the gain is on the front end)... a perfect reverb level on a low-gain input is totally over-the-top when switching to hi-gain. Not to mention, while a matter of preference, I prefer to reverb a distorted signal rather than distort a reverb'd signal ;)

I bought two of those IronSounds loops last year some time, never installed them (yet). Seems like a good idea, just rough to put SS in the path ;)

Thanks,

Stephen

[Structo]

Well you should try the Ironsounds loop.

They do work and if you can hear any degradation then you have better ears than I.

You can also use pots for the send and return if you wish.

One change I did make was to the opamp I used in the loop.
It comes with a TL072.
I can't remember if the kit comes with a socket for the opamp but I have one on my board, makes swapping out opamps a breeze.

I used a Brown Burr 2134P which is supposedly much lower distortion and has a faster slew rate.

I'd like to think it sounds better anyway.

If you are totally opposed to using a SS loop then you should build a Dumbleator.
Plans and parts numbers are on this site somewhere.

[aprilia1k]

Thanks Tom - nah, I doubt that I'd hear the difference - well, I suppose if doing an A/B, you might sense a little more warmth from an amp with a tube buffered loop, but - as I will not be doing an A/B, and the amp has a whole lot o' warmth already ;), I will go ahead and install the IronSounds. I assembled one of 'em right when they arrived last year iirc, so should be able to just pop it in there pretty quickly.

I thought the instructions were a little odd in one or two places. They say hook up power on the 2nd filter cap (Screen supply then...) and they mention hooking up to the PI "input filter cap"... what the hell is an "input filter cap"? It's either the coupling cap or the PS filter (thinking not the PS)... I have never heard of an input filter cap... FILTER is universally afaik used for Power Supply, as in DC (ripple) filter, whereas for coupling they're sometimes called DC Blocking capacitors. imho it's misleading to call it a filter capacitor if they refer to the DC blocking cap.. oh well... I don't have any diagrams that show a complete install, just little snippets. I know how it _should_ install, just want mainly to make sure I don't put HT where it doesn't belong on that little pcb :)

THANKS

SNIPPET FROM FX LOOP INSTRUCTIONS:
"5. Connect the Vin terminal on the power PCB to the second power filter in your amplifier (after the
first filtering RC network).
6. Connect the GND terminal on the power PCB to a ground nearest the power filter section (for Iron
Sound JA-TMB model refer to the JA-TMB Installation Diagram).
Note: A bad ground spot will make the loop noisy!
Effects Loop Installation Guide
v.1.0 Page 3
7. Using the supplied diagram, connect the signal PCB to the power PCB.
8. Locate the filter input capacitor to the phase splitter in your amplifier.
9. Using the supplied diagram, connect the IN and OUT terminals on the signal PCB to your
amplifier.
Note: You MUST use shielded wire, or you will get noise.
..."

[butwhatif]

The biggest problem with using 'chips' for the loop, is they can't handle a lot
of peak voltage. If you're talking about installing one in a modern ss or chip based preamp, fine, the voltages never go higher than the supply voltage. But a tube amp loop location just before the PI can have large voltage swings on peaks that are beyond what a dual linear ic can handle gracefully, both in and out.

[aprilia1k]

Hmmm... I wonder how they deal with these peaks then... Tom - any added ugly clipping going on or ?

Thanks