I think LooseChange might have better info from experience with loops.
if I can plug it in to a series passive loop should it be before or after my volume control as I have seen schematics with a passive loop either way.
Application determines the best approach.
I personally only have a couple of pedals, and don't use them frequenctly. For me, it's enough just to plug them between the guitar and amp input.
The location of the loop depends on the intended outcome. The guys who use an either a standalone preamp, or an amp with a master volume to generate preamp distortion, generally want their distorted signal to go from the preamp out to effects and back into the amp at the input to the phase inverter. That's because they want the sound that is generated and shaped by the preamp to be altered by the effects, rather than the raw guitar signal.
When you read a lot of bass players like the LA-2A, what you really were seeing (and it might not have been pointed out) is that they were playing through their normal setup (bass, amp, speakers), then having the sound of the speaker picked up by a microphone and sent to a mic preamp and on to tape (or hard disk). If compression is used when tracking, it is purposely light, as it can't be readily undone later. Then during mixing, the bass signal is sent to the LA-2A and squashed down as much as the producer and engineer feel necessary, then sent to the console mixing buss and eventually to 2-track tape (or hard disk).
So the sound altered is the sound of the entire rig, not usually prior to feed into the amp. That's not always true, and some bass amps actually incorporate some kind of compression circuit.
Do I need a buffer circuit? I don't think so as this is part of the LA2A, re gain control, please correct me if I'm wrong. Can I use a simple series passive effects loop and plug in the LA2A?
The current production LA-2A can accept +4dBm or -10dBv inputs. In layman's terms, the +4 input is the old professional recording/broadcasting standard, and the -10 input is the "commercial/consumer" level. -10dBv corresponds to about 0.25v RMS, which is likely more than double what your bass will output on its own. +4dBm is about 4 times bigger than that, almost 1v RMS.
1v RMS is actually bigger than the input signal to most phase inverters, so it looks like we want to at least tap off just prior to the phase inverter. We also have to assume that the original circuit shown in the DIY LA-2A page is copying the original circuit. That means you'll likely need some boosting.
Do I need a buffer circuit? I don't think so as this is part of the LA2A, re gain control...
The LA-2A doesn't work quite like that.
The idea is to keep the signal fed into it from exceeding a level set by the Peak Reduction knob. You might feed a signal into the LA-2A too weak to really cause the limiting circuit from acting on it. To force it to compress and get a resulting sonic change, the Gain control is provided to boost the signal until there's enough to activate the compression circuitry.
But! You really need to make sure you feed the LA-2A a signal of sufficient size. You don't know for certain that there's enough gain available from the Gain control to make up for a very weak signal. Even if it does, you don't want to limit the range of options available.
Active or passive? If you tap off after the preamp, you may have enough signal output from the LA-2A to drive your phase inverter, but maybe you won't. That is possibly the case for severe gain reduction. But stock, the input impedance to the LA-2A is 600 ohms, and is way too low for your preamp (or bass) to drive. You need a buffer of some kind with an output impedance equal to or less than 600 ohms (preferably less). You might need a transformer to reduce the output impedance.
An active loop also gives you the opportunity to boost the signal back up after it returns from the effects. That is probably not necessary with the LA-2A, but if you use any kind of pedal originally designed to go between the instrument and amp input, you will almost certainly need to boost the signal back up to the size needed to drive the phase inverter.
I don't remember if TUT 1 has the effects loop I'm thinking of, but one of the other project books does. It can be series or parallel, has an active and adjustable low-impedance output and a return that reboosts the signal (also adjustable).
We really need some other bass players to chime in, especially those with effects loop experience. For guitar work, I know my choice would be a parallel active loop. But it's not a one-size-fits-all situation.
Topic: LA2A compressor (Read 16773 times)