#1
Hey guys,

I've ran into a small issue with my Kustom amp's preamp. Instead of fixing it right now, I had another hope of a solution. I need your thoughts!

I have a Marshall MG100DFX combo amp I want to use as a head. It has an external speaker output jack on the back. I have a Kustom WAV 212 130watt combo that has left and right power amp inputs. I was curious, using a splitter, could I split the external speaker output and run it into the power amp inputs of the Kustom, pending the ohms match up? Would it damage either amp?

Thanks for reading and helping out!
#3
Well, because the Kustom wAv is a great sounding amp. The Marshall's preamp is actually very solid-sounding when pushing quality speakers. I don't see why people always go to the excuse "Oh, just buy something more expensive". Price means nothing in today's age.
#4
That scenario will damage both amps.
Speaker outputs only go to speakers, attenuators, or load boxes.
The power amp input is for a guitar/line level signal only.
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#5
So I need to find a way to wire the two speakers from the Kustom so it's just going straight to the speakers and not even hitting the power amps.
#6
Quote by cjc1990
So I need to find a way to wire the two speakers from the Kustom so it's just going straight to the speakers and not even hitting the power amps.

The only way to use the Marshall pre-amp into your Kustom is if the Marshall has a line-out jack, a pre-amp out jack, or an effects send jack. If it does not have any of those, then you're out of luck unless you mod it, but why bother?
If you want to use the Marshall to run the Kustom's speakers (& not even turn the Kustom on), then you can just unplug the Kustom's speakers from the amp & use a double sided female cable adapter (about $5.00) & another speaker cable to connect the MG to the Kustom's speakers. Be sure to unplug the Kustom, because you don't want to turn it on with no speakers connected. That will almost ceratinly damage the Kustom.

Edit: ALSO, YOU MUST MAKE SURE YOU MATCH THE MG IMPEDANCE WITH THE SPEAKER LOAD!! If the MG says 8 ohm ext speaker, be sure your Kustom's speaker load is 8 ohms also!!
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Last edited by riffhog at Oct 17, 2011,
#8
Yes, the Marshall does have a line out jack on it. I'll give it a try and see how it sounds. I'm going to stop by GC and grab me a female 1/4" adapter just in case, and wire the speakers to that. Both amps are 8ohms as that was one of the first things I checked. I just wasn't really familiar with the use of the power amp inputs, so I wanted to find somebody with more knowledge. I appreciate the courtesy, bro. Some posters here are a-holes through and through.

Quote by riffhog
The only way to use the Marshall pre-amp into your Kustom is if the Marshall has a line-out jack, a pre-amp out jack, or an effects send jack. If it does not have any of those, then you're out of luck unless you mod it, but why bother?
If you want to use the Marshall to run the Kustom's speakers (& not even turn the Kustom on), then you can just unplug the Kustom's speakers from the amp & use a double sided female cable adapter (about $5.00) & another speaker cable to connect the MG to the Kustom's speakers. Be sure to unplug the Kustom, because you don't want to turn it on with no speakers connected. That will almost ceratinly damage the Kustom.

Edit: ALSO, YOU MUST MAKE SURE YOU MATCH THE MG IMPEDANCE WITH THE SPEAKER LOAD!! If the MG says 8 ohm ext speaker, be sure your Kustom's speaker load is 8 ohms also!!
#9
Quote by cjc1990
Yes, the Marshall does have a line out jack on it. I'll give it a try and see how it sounds. I'm going to stop by GC and grab me a female 1/4" adapter just in case, and wire the speakers to that. Both amps are 8ohms as that was one of the first things I checked. I just wasn't really familiar with the use of the power amp inputs, so I wanted to find somebody with more knowledge. I appreciate the courtesy, bro. Some posters here are a-holes through and through.


No problem, man. That's why this forum has the "Who to Listen to List" sticky as the first thread. Those guys & gals know their stuff, & won't give you bad advice. There's a lot of very knowledgeable people here that aren't on the list, but there's always a few smartasses that will mess with anyone just for fun. Good luck with the line out. It should work fine. By using the line out, I don't know if it automatically shuts down the MG's power amp stage. I'd leave the MG speaker connected when you try it. Run a guitar cable (not speaker cable) from the line out into the front of the Kustom where you'd plug in the guitar, or into the FX loop return if the Kustom has an FX loop. Then just play with the volumes on both amps to get the tone you want. You may have to play around with your settings for a while to dial it in, but you should get a decent tone that's adjustable to almost any volume.
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#10
The line out might have speaker emulation that could hurt the tone. You could get a pot and wire it to the speaker out and attenuate the output so you can run into the amp. Any value from 10 to 100K will work.
#11
Quote by fly135
The line out might have speaker emulation that could hurt the tone. You could get a pot and wire it to the speaker out and attenuate the output so you can run into the amp. Any value from 10 to 100K will work.


I don't think it's that simple, otherwise, we wouldn't have attenuators.
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#12
sell everything and buy a decent combo??
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#13
It is that simple. Attenuators do something else. Technically speaking a pot is an attenuator. But power attenuators are for attenuating power and maintaining a rated load on the amp. His amp is I believe SS so it doesn't need a load. A pot like I suggested is basically a line level attenuator.
#14
Hey guys, I just went and took another look at the two amps. I tried the line out (which does have speaker emulation). Honestly it sounded like balls.

Here's the reason I'm trying to do this:

my Kustom wAv 212 combo is an amazing sounding combo amp. But as of last week, during playing it'll drop volume quite a bit by itself and then kick back up and so forth. If I can fix THAT, the rest of this whole discussion won't matter. If anyone has an idea as to why it'd be doing this, I'm all ears. I just replaced the preamp tube last week around the time it started doing this. I don't know how it'd be the culprit. I guess, if anyone has any ideas I'm all ears.
#15
I think it's doing it because of cracked solder joints on some of the control pots or the input jack. I would get access to the bottom of the circuit board and reflow all the solder pads on those things I mentioned. You can't always see the cracks. I've fixed 4 amps so far like that.
#16
Hrmm, we're going to pull the board out in a few and take a look at everything. Hopefully we can figure it out. The week I've had...... Originally, it seemed like it was my guitar cutting in and out, like bad soldering with the pickups because it was such a sudden drop out and what not. My guitar was in a box getting ready to head back to MF, when I tried the amp again with a different guitar, and 25-30 minutes into playing it did the same action. So it's been hectic! I'll let you know what comes of us pulling the board out and what we find! Thanks.
#17
Well we pulled the board out and looked at every visible connection. Aside from it being a bit dirty, we didn't find anything that would cause this. We tightened up some nuts that connect to the gain knob for both channels. I tried the amp and it took awhile but it definitely did it again. I'm at a loss at this point. I'm thinking maybe taking the whole board out and turning the box into a cab with those speakers and getting a nice head.. Those Super 65s sound nice.
#18
Quote by fly135
It is that simple. Attenuators do something else. Technically speaking a pot is an attenuator. But power attenuators are for attenuating power and maintaining a rated load on the amp. His amp is I believe SS so it doesn't need a load. A pot like I suggested is basically a line level attenuator.


So why not just use the effects loop send instead of the speaker out? I'm sure the MG has one.

If anything, I would put a high wattage resistor the same resistance as the current speaker, and then put the pot after. This will ensure that the resistor takes the heat put out, instead of the potentiometer, which OP will be touching.
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#19
Quote by cjc1990
Well we pulled the board out and looked at every visible connection. Aside from it being a bit dirty, we didn't find anything that would cause this. We tightened up some nuts that connect to the gain knob for both channels. I tried the amp and it took awhile but it definitely did it again. I'm at a loss at this point.
Did you not read my post? There is a very good chance that you cannot see the cracks in the solder joint. You need to get a soldering iron and reflow all of the pots and jacks on the control panel.

And yeah if the Marshall has an FX loop the FX send is the way to go. But just fix the amp is a better idea.
#20
Quote by Reincaster
So why not just use the effects loop send instead of the speaker out? I'm sure the MG has one.

If anything, I would put a high wattage resistor the same resistance as the current speaker, and then put the pot after. This will ensure that the resistor takes the heat put out, instead of the potentiometer, which OP will be touching.
Reincaster, you don't need to get any heat when tapping from the speaker output. There are a couple formulas that everyone interested in speaking authoritative about this should know. The first is Ohm's Law (I = V/R or V = IR). The other is power (P = IV = V(sq)/R = I(sq)R).

Let's take a 100 watt amp cranked to 100 watts into 8 ohm speaker. power = 100 = V(sq) /8 where V(sq) = 800 or V= about 27V.

Since you are feeding a hi impedance input (500K - 1M) a source impedance of around 10K - 100K is good. So lets put the resister before the pot at a 10:1 ratio to step down the voltage to 1/10 with the pot at max. I'd go with a minimum of 10K/1K for resistor/pot all the way up to 100K/10K.

The max power using a 10K resistor will be V(sq)/R = 800/(10K + 1K) = 0.8/11 = 0.07 watts. See no heat and no power.
#21
My peavey XXX did this for some time when i had it. It turned out to be radio signals from my TV / microwave in my house that was messing with the amp hah.
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#22
Anyone have 311's video of this handy?

Hint: It ended with fire.
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#23
Quote by fly135
Reincaster, you don't need to get any heat when tapping from the speaker output. There are a couple formulas that everyone interested in speaking authoritative about this should know. The first is Ohm's Law (I = V/R or V = IR). The other is power (P = IV = V(sq)/R = I(sq)R).

Let's take a 100 watt amp cranked to 100 watts into 8 ohm speaker. power = 100 = V(sq) /8 where V(sq) = 800 or V= about 27V.

Since you are feeding a hi impedance input (500K - 1M) a source impedance of around 10K - 100K is good. So lets put the resister before the pot at a 10:1 ratio to step down the voltage to 1/10 with the pot at max. I'd go with a minimum of 10K/1K for resistor/pot all the way up to 100K/10K.

The max power using a 10K resistor will be V(sq)/R = 800/(10K + 1K) = 0.8/11 = 0.07 watts. See no heat and no power.


I am aware of these formulas, however, things like these tend to change in perception when in a different context. I always assumed that the wattage would be discharged as heat, which is the purpose of a resistor. However, I think I just overestimated the amount of heat of 100 watts. did some light googling and found the following: http://www.rru.com/~meo/Guitar/Amps/Kalamazoo/Mods/ezlo.html

Again, I'm clarifying that this is theory, having never tried this myself, that's just how it would seem to me at first thought.
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#24
The wattage is discharged as heat. But if the load resistance is 11K the heat is only 0.07 watts, when running the amp at an output level that would produce 100Watts into an 8 ohm load. You may be aware of the formula, but you don't understand how to use it. I just showed you how to use the formulas.

That link is saying pretty much the same. They are using 100:1 ratio resistor to pot instead of my 10:1. No biggie. Also there is no need for 1/2Watt resistors at 47K. But since they are so common there is no reason not to use them.
#26
Quote by fly135
The wattage is discharged as heat. But if the load resistance is 11K the heat is only 0.07 watts, when running the amp at an output level that would produce 100Watts into an 8 ohm load. You may be aware of the formula, but you don't understand how to use it. I just showed you how to use the formulas.

That link is saying pretty much the same. They are using 100:1 ratio resistor to pot instead of my 10:1. No biggie. Also there is no need for 1/2Watt resistors at 47K. But since they are so common there is no reason not to use them.


OMG, my last post meant I AGREE WITH YOU. I posted the link because that's what made it click in my head. I mistakenly had a thought in my head that the amp was putting out 100 watts (which would then be stepped down to 0.7W, when the resistance in the circuit determines the actual amount of watts put out.

I understand how to use the formulas, I made a small misunderstanding. I haven't done any physics theory in the last 7 years, so forgive me if a few grenades and a 7.62 round to the back of my head have jarred me a bit

You win, you are on the ball when it comes to physics. Let's not continue this.
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Last edited by Reincaster at Oct 18, 2011,
#28
Quote by Reincaster
OMG, my last post meant I AGREE WITH YOU. I posted the link because that's what made it click in my head. I mistakenly had a thought in my head that the amp was putting out 100 watts (which would then be stepped down to 0.7W, when the resistance in the circuit determines the actual amount of watts put out.

I understand how to use the formulas, I made a small misunderstanding. I haven't done any physics theory in the last 7 years, so forgive me if a few grenades and a 7.62 round to the back of my head have jarred me a bit

You win, you are on the ball when it comes to physics. Let's not continue this.

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#29
Okay so quick question, the two speakers in the Kustom are 65 watts each. The Marshall is 100 watts and 4 ohms into 1 channel. Wiring the Kustom's speakers so I don't blow anything, do I need to wire them in series or parallel? I've been reading up on the differences but it's just a tad confusing.
#30
Quote by cjc1990
Okay so quick question, the two speakers in the Kustom are 65 watts each. The Marshall is 100 watts and 4 ohms into 1 channel. Wiring the Kustom's speakers so I don't blow anything, do I need to wire them in series or parallel? I've been reading up on the differences but it's just a tad confusing.


How many ohms are the speakers in the Kustom?

-If they're both 8 ohm, wire them in parallel, be careful of the phase.
-If they're both 16 ohm, the amp can deal with a mismatch that's greater, so also wire it in parallel.
-In they're both 4 ohm speakers (unlikely), then wire them in series.

Rein-Haven't seen you in a while. I didn't realize you were military. Thanks for serving, man. You guys never will know how much your service is appreciated. Are you back in Guam? I thought that's where you were for a while. Anyway, good to see you back!


You don't have to thank me for serving, it's an honor to put on the uniform. I'm NG, as I'm a local here. I've been back for a few months here actually.
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#32
When you connect them in parallel, make sure the positive of one speaker are connected to the the positive of the other, and same with the negative.

When in series, connect the negative of the first speaker to the positive of the second, and the negative of the second speaker back to the amp head.

Speakers put out AC current. If the phase was reversed from one speaker, you would get a thin sounding amp, because the speakers would move in opposite directions and cancel each other out.
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#33
So by phase, you mean just make sure I do it right. lol Got it. Yeah I have instructions for both I can use, and there will be someone else working on it with me tomorrow. I'm knowledgeable with plenty of stuff with guitars, effect pedals, etc. But getting into wiring I'm out of my area. Thanks for the advice!
#34
Just to give everybody an update, I removed the electronics of the Kustom, and we re-wired the speakers in parallel. The set up sounds pretty dang sweet. I appreciate the help from all of you guys!