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Topics - mexicanyella

#1
Hi all, wanted to ask something that's been puzzling me, and which my reviewing of series/parallel wiring info has not answered.

If I were to wire up an array of nine 4-ohm speakers to present a 4-ohm load to an amp, I could

a) wire groups of three each in series, giving me three 12-ohm groups, and then connect those three groups in parallel, bringing me back to 4 ohms...

OR

b) wire groups of three each in parallel, giving me three 1.33-ohm groups, and then connect these three groups together in series, also bringing me back to 4 ohms total.

The first method seems more intuitive to me, but I don't know why. Is there an advantage or disadvantage about either of these two connection schemes? Is there a problem with one or the other I'm unwaware of? Any direction here much appreciated...

Mexicanyellla
#2
Amplifier Discussion / power amp signal meter question
February 01, 2017, 12:20:49 AM
Hi all...

I've been using a Peavey M-3000 power amp as part of a makeshift band-practice bass rig lately, and I have a question about whether I can translate the levels I'm seeing on the LED signal meter into approximate output levels in watts. The meter has 10 LEDs labeled in -dB increments, from -27 dB to -0dB, in 3 dB steps.

Peavey says the amp can deliver 130W into an 8 ohm load, which is what I'm driving. Does a 3 dB drop in output power equate to a halving of the output watts? Like, if I am running settings throughout my signal path that result in all but the last light lighting up on the peaks, does that mean that those peaks are roughly half of 130W, or 65W? Or is that 3 dB thing only applicable to acoustic output, and with electrical signals it's some other relationship?

I'd like to know, roughly, what that meter means in terms of electrical output, in case I ever have to plug into a speaker with a lower power handling capability than what the amp can deliver.

Thanks in advance!

Mexicanyella
#3
I'm refining my long-titled post below into a new thread, after a thrilling and successful experiment.

I removed the tweeter from my Fender Acoustasonic Jr. and tried it as a slave, fed from my Peavey Audition 20's line out, and WOW!!! Exactly what I wanted! Using just the two 8" drivers, it reproduces everything good about the Peavey's gritty almost-clean sound, and it can get much louder.

But I may want to use it for an actual acoustic guitar or full-range portable PA again, so I think I want to install an L-pad in the back so I can adjust the tweeter level down to 0% for slave duty, or varying levels up to 100% for other duties.

Acoustasonic schematic:
http://support.fender.com/schematics/guitar_amplifiers/Acoustasonic_Jr_schematic.pdf

In the lower left of the diagram, more or less, you can see where the "HF horn" taps into the L speaker output with a 22 ohm resistor, a 47 ohm resistor and a .1 mf capacitor. I think I could drill a hole in the back of the chassis and install an L-pad and tap it into this HF horn feed...right?

If so, where in the HF horn's wiring do I insert the L-pad, in relation to the resistors, capacitor and the horn itself?

If the left side speaker is fed by a 40-watt power amp, how much of the wattage am I attenuating to the horn; in other words, what wattage rating of L-pad do I need to buy? Initial searching has shown me 8-ohm L-pads that look like big potentiometers an are rated at 15, 50 and 100 watts.

Thanks in advance.
#4
I would like to send a line-level signal from one amp's 1/4" mono line out jack to another amp's stereo FX return, which is a single 1/4" TRS jack, with the tip being one stereo side and the ring (pretty sure, anyway) being the other. I guess the sleeve is common...anyway, I want to have this mono signal drive both sides of the stereo power section equally, and I'm really shaky on knowledge of line level signal measurements and impedance relationships in that realm.

I have tried plugging a mono 1/4" instrument cord into the TRS FX return partway, until I heard the signal coming out of both speakers. It seemed to work well, but I'm not sure if there's supposed to be some sort of transformer isolation DI signal splitter doodad you're supposed to use for this kind of thing, versus just connecting the two hot terminals of the TRS to the one hot coming from the source amp. Thoughts?

Do I need to post a schematic to get an answer to this question?