Ohmage Brain Teaser

[Rising Farce]

I recently picked up a 4x12 cabinet that's rather creatively wired with two 8-ohm inputs--one for the left pair of speakers and the other for the right pair.

I want to run my RM100 into both inputs simultaneously, preferably without destroying it, but I'm at a loss as to how to do so.

My options appear to be the following:

1. Run one cable from the main head output and another from the auxiliary output. What would the proper ohm setting be in this configuration?

2. Run one cable from the main head output and split it with a single-female/dual-male 1/4-inch splitter. Is this advisable, and, if so, where should I set the ohm switch?

3. (Your alternate suggestion here.)

Technologically Tormented in Tampa

 

[speed2dirt]

Run it with two cables: one from the primary & one from the extension speaker outs. Ohm setting would be 4 ohm (2 x 8ohms = 4 ohm). You could use a thick Y-cable like the one on the Weber site below, but it'd have to be able to handle the load an amp throws off. Either way whether it's coming out of two outputs or 1 output with a Y-cable, it'd still be a 4ohm load.

https://taweber.powweb.com/weber/acc.htm

 

[Rising Farce]

That's exactly the answer I was hoping for. I'll try the two-cord main/extension setup, since the Y-cable thing sounds a little dodgy.

Thanks much.

 

[Jaded Faith]

The last reply was correct, but the comment "creatively wired" screams red flag to me. I'm not clear if it's factory wired or altered. Please check these two things before you try hooking it up:

1: Verify with an ohm-meter that each side is actually 8 ohms (it should read between 6-8, probably 6.XXX). Measure this both with one one cable plugged in and again on both sides with two cables plugged in.

2: Look at the back of the jack plate and make sure the two sides aren't connected somehow at all.

 

[Rising Farce]

The last reply was correct, but the comment "creatively wired" screams red flag to me. I'm not clear if it's factory wired or altered. Please check these two things before you try hooking it up:

1: Verify with an ohm-meter that each side is actually 8 ohms (it should read between 6-8, probably 6.XXX). Measure this both with one one cable plugged in and again on both sides with two cables plugged in.

2: Look at the back of the jack plate and make sure the two sides aren't connected somehow at all.

It's been modified (by whom, I have no idea), so it probably is a good idea to double-check. Thanks for the recommendation.

 

[eyeball987]

The last reply was correct, but the comment "creatively wired" screams red flag to me. I'm not clear if it's factory wired or altered. Please check these two things before you try hooking it up:

1: Verify with an ohm-meter that each side is actually 8 ohms (it should read between 6-8, probably 6.XXX). Measure this both with one one cable plugged in and again on both sides with two cables plugged in.

How do you check the ohms on a cab with a meter? Yes, noob electronics question.

I can bias the RM100 just fine but am not sure where to put the leads to read the ohm rating of a cab.

 

[MarcoR]

The last reply was correct, but the comment "creatively wired" screams red flag to me. I'm not clear if it's factory wired or altered. Please check these two things before you try hooking it up:

1: Verify with an ohm-meter that each side is actually 8 ohms (it should read between 6-8, probably 6.XXX). Measure this both with one one cable plugged in and again on both sides with two cables plugged in.

2: Look at the back of the jack plate and make sure the two sides aren't connected somehow at all.

It's been modified (by whom, I have no idea), so it probably is a good idea to double-check. Thanks for the recommendation.

Hopefully you?ll find it?s using a normalized jack to connect both sides in parallel for 16 ohms when only one jack is used.

 

[gag halfrunt]

The last reply was correct, but the comment "creatively wired" screams red flag to me. I'm not clear if it's factory wired or altered. Please check these two things before you try hooking it up:

1: Verify with an ohm-meter that each side is actually 8 ohms (it should read between 6-8, probably 6.XXX). Measure this both with one one cable plugged in and again on both sides with two cables plugged in.

How do you check the ohms on a cab with a meter? Yes, noob electronics question.

I can bias the RM100 just fine but am not sure where to put the leads to read the ohm rating of a cab.

Plug in a speaker cable, and on the other end of the cable, put one meter lead on the tip, and the other on the sleeve.

 

[Rising Farce]

It's official: Each side reads around 7 ohms. Looks like the 4-ohm setting is where it needs to be. Thanks, all.

 

[joey_truelove]

I may be a bit over cautious but I would actually open the cab up to check the wiring out for myself, just in case there's something wonky going on. Or at least try and cross measure the inputs. I e.g. know cases where one or more speakers was shared and where feeding both sides could potentially have blown the amp.

Once open you also obviously have an opportunity of wiring it as a 16 ohm cab should you want to should the drivers be so arranged.

 

[gag halfrunt]

I may be a bit over cautious but I would actually open the cab up to check the wiring out for myself, just in case there's something wonky going on. Or at least try and cross measure the inputs. I e.g. know cases where one or more speakers was shared and where feeding both sides could potentially have blown the amp.

Once open you also obviously have an opportunity of wiring it as a 16 ohm cab should you want to should the drivers be so arranged.

This is wise - if the wiring has been modded by someone, there's just no telling what kind of accident could have been made in the connections.

 

[Rising Farce]

I opened up the cab, and everything looks to have been wired correctly. (Since I know vanishingly little about electronics, I referenced it against some schematics I found on the Net.) That being the case--and since the ohm testing checked out OK--do you think it's safe for me to crank this thing up and annoy the homeowners' association (a favorite pastime of mine)?

 

[joey_truelove]

I opened up the cab, and everything looks to have been wired correctly. (Since I know vanishingly little about electronics, I referenced it against some schematics I found on the Net.) That being the case--and since the ohm testing checked out OK--do you think it's safe for me to crank this thing up and annoy the homeowners' association (a favorite pastime of mine)?

Unless of course you feel like wiring it for single cable operation (an easy fix) then the race to scrape by an eviction notice is on!

 

[Rising Farce]

Outstanding.

One final question: If I wanted to run a Hot Plate between the amp and the cabinet, I assume I would need to use the 4-ohm version, while leaving the amp set on 4 ohms as well. Is that correct? If memory serves, those units only have one input (which I would run from the main amp out) but two outputs (one for each jack on the cab).

 

[gag halfrunt]

Outstanding.

One final question: If I wanted to run a Hot Plate between the amp and the cabinet, I assume I would need to use the 4-ohm version, while leaving the amp set on 4 ohms as well. Is that correct? If memory serves, those units only have one input (which I would run from the main amp out) but two outputs (one for each jack on the cab).

My advice is avoid using the Hotplate entirely.

The only reason to justify straining your transformer with an attenuator is if you have a NMV amp (or one with a crappy MV circuit). The RM100 has a great MV, so you'll get better tone using the master instead of an attenuator.

 

[Rising Farce]

OK, I'll keep monkeying with it before going the HP route. I'm just finding that while turning the amp master down, and the module volumes up, works wonders for clarity, it also imparts a brittle thinness that I don't care for. (I've already got the bass and density controls cranked.) I thought that perhaps if I could open up the amp master a bit without blowing my eardrums out, I could find the right balance.

As a side note, my RM50Cs are much easier to dial in.

 

[gag halfrunt]

OK, I'll keep monkeying with it before going the HP route. I'm just finding that while turning the amp master down, and the module volumes up, works wonders for clarity, it also imparts a brittle thinness that I don't care for. (I've already got the bass and density controls cranked.) I thought that perhaps if I could open up the amp master a bit without blowing my eardrums out, I could find the right balance.

As a side note, my RM50Cs are much easier to dial in.

What's your Presence knob set at? I have found on the RM100 that reducing the Presence, as opposed to increasing the Density, can sometimes work better at overcoming any harsh highs.

 

[Rising Farce]

I believe it's set at around noon. Do you run yours lower than that?

 

[gag halfrunt]

I believe it's set at around noon. Do you run yours lower than that?

Yes, if I've got a module that's giving me too much high end. The Camerock did that. It's a great module, but to get the mid and hi-mid cut that I wanted, I had to employ the bright switches. That introduced some high-end sizzle, so I tamed it by lowering the Presence.