Firestorm wrote:I'm fascinated by this from jjman:
"I verified that the 3rd stage’s clipping causes reverb/delay to not sound right if located before the input."
I'm too old-school to use a scope (yet), but I always suspected the third stage clipped a bit. jjman, have you got data, traces, anything to look at?................
I've used my scope to verify that my 3rd stage clips last on the volume dial. (top trace in pic.) And it's clipping is asymmetric and from being driven into cutoff (not saturation.) The output clips 1st and the PI second, both on the top and bottom.(not shown)
The 2nd stage does not reach clipping when I scope mine. (See bottom trace in pic.) Mine is not a clone so other's could behave differently. However many here have said that this is the "order" in which an Express should clip.
Using my reverb or delay unit in front "works" somewhat into the distortion zone on the volume, but stops working properly as I turn up more than 60% or so. The problem also behaves the same if I use a reduced setting on my PPIMV. All of this leads me to believe that the clipping in the 3rd stage is the culprit. Basically I think it's compressing, thus making the reverb "rush out" after stopping a note. So I want to place the reverb (or delay) after this apparent compressor. I won't know for sure until I can get it put together.
I think IF one plans to crank an Express or Liverpool into fairly high distortion (just about anything passed about 1/3 on the volume dial with most pots) an effects loops is a total waste of time. There is just too much going on in the power stage to retain any fidelity of such things as delay and reverb if you really plan to crank the amp. Doing it totally post amplifier with a wet/dry setup, or simply from the soundboard in a PA situation is the way to go.
Back in '89 when I first got my Express I came up with a wetdry setup that used a simple 2 resistor pad off the 2nd speaker jack to bring the signal down to line level. That in turn drove a Yamaha SPX900 effects processor and then a 1 space power amp. By running that to a 2nd guitar cab the effects tone was studio quality, and then the dry cab was connected to the 1st speaker jack for a 100% unmolested dry sound. Folks also do this by miking the amp and then reamping the effects into full range cabs. I think by simply using a guitar speaker for the effects and a direct tap for the line signal you can simplify the rig and get just about the same quality with less gear. Either way I think the key to a wet/dry rig is to not reamp the dry signal if you can help it, and keep that straight to the cab.
A 56k resistor in series with the speaker signal, terminated to a 1k resistor tied to ground. Take the signal output at the top of the 1k and the grounds of the circuit at the bottom of the 1k. You can tweak the 56k up or down a bit to trim the line level output.
I'll pass along one of my all time favorite gems from days gone by. In those days Guitar Player Magazine had a lot of cool tech tips and I always thought this was a great item.
I don't know how close it is to Glen's idea, but I suspect they are similar. It has a variable output and a couple more components, but seems like the same general idea.
Gerald Weber also has a similar line-out detailed in his original book.
I've used this on a lot of different builds and have never noticed it as a problem. I have recorded direct from it on a few occasions and the sound is good, albeit a bit different than what was coming out of the speaker.
The only time I've found it gets to be a problem is trying to explain to the sound man that I still need to have my amp go to a speaker and yes it has to be that loud... so I tend not to mention it and use it for my own purposes and ask for a mike on my amp.
rj
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