#1
So, you gotta love friends with connections.

I'm doing some wiring work for a good friend who's got a marshall 1990 that he doesn't use anymore. He told me the V30's in it need a re-cone and its missing one speaker.

still, after seeing what some of these will go for....i think I got a pretty good deal


anyway, any good places to get re-cone kits from?

also, say I've got a 15W head, can i run the output of that through an amplifier or run a line out to an amplifier to make the cabinet happy with 50-80 W ? i know the 15W will work, just looking for a little more umph...

one more...anyone around here have a V30 that needs some work they're willing to get rid of?

thanks guys!
#3
So you're saying you want to run your 15 watt head's preamp into the poweramp of a 50-80 watt combo? Totally doable if they both have effects loops.

Also, pics of the cab or its an MG cab
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#4
Quote by LaidBack
So you're saying you want to run your 15 watt head's preamp into the poweramp of a 50-80 watt combo? Totally doable if they both have effects loops.

Also, pics of the cab or its an MG cab


I'm pretty sure it's a cab...

Though I might have been wrong...if I was, disregard my last post!
#5
Quote by jlangholzj
also, say I've got a 15W head, can i run the output of that through an amplifier or run a line out to an amplifier to make the cabinet happy with 50-80 W ? i know the 15W will work, just looking for a little more umph...

As long as it's a line out and not a speaker out, it'll be fine.
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#6
Quote by LaidBack
So you're saying you want to run your 15 watt head's preamp into the poweramp of a 50-80 watt combo? Totally doable if they both have effects loops.

Also, pics of the cab or its an MG cab



HAHAHAHA yeah yeah i know....

It's going to be a treat going from 1x12 to 8x10 !!!!!
#7
Quote by Jhachey22
As long as it's a line out and not a speaker out, it'll be fine.



thats what I was thinking. The head unit i have is from a fender 15W (something like a blues JR tuber) not 100% sure if it is a Jr....anyway....


I figured a line out hooked to a 50W amp would work fine too.


also anyone have a particularly good spot to get reconing kits? He says the V30's have the original paper on em but if i'm going to play this they need to be re-coned.
#8
I'd dump the broken one and pick up 2 Greenbacks and put them in an X config with the remaining V30s.
#9
Quote by jlangholzj
So, you gotta love friends with connections.

I'm doing some wiring work for a good friend who's got a marshall 1990 that he doesn't use anymore. He told me the V30's in it need a re-cone and its missing one speaker.


good deal, reconing is a bit expensive though when you send out (the shipping is killer). many reconers may use a large demagnetizer/magnetizer machine that is hella expensive. you can do alot of a recone without doing that though. the process doesn't look too complicated if you are good with your hands, i bet after you do one or 2 speakers you can be pretty good at it.

Quote by jlangholzj
still, after seeing what some of these will go for....i think I got a pretty good deal


anyway, any good places to get re-cone kits from?


there are lots online, simplyspeakers is one i trip across a bit, seems to be more eminence recone kits out there. have you actually tested the speakers to see if they need a recone though? you may only need 1 or 2 reconed if you are lucky, we find this quite a bit when buying used equipment.

Quote by jlangholzj
also, say I've got a 15W head, can i run the output of that through an amplifier or run a line out to an amplifier to make the cabinet happy with 50-80 W ? i know the 15W will work, just looking for a little more umph...


well, i wouldn't recommend this, this is murder on an amp. won't say it hasn't been done before (i have heard of setups like this before 'distortion' was readily available via boxes and gain knobs).

the amp won't like the impedance issues (it will be far from a nominally rated impedance for it to work at). and the amp you plug into is not designed to take a signal of that magnitude through the preamp. you will most likely blow something.

311 just purposely blew up an amp doing this recently, look in his thread about a 'NAD, ever seen this?'.

edit: thought that was a speaker out, nvm
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Last edited by gumbilicious at Sep 21, 2010,
#10
Quote by gumbilicious


edit: thought that was a speaker out, nvm



so with a line out i should be okay right?
#11
Well which amps are we talking about here? It will help us determine what you're about to do is safe.
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#12
Quote by jlangholzj
so with a line out i should be okay right?


yeah, you should be fine. really the input for a guitar amp is supposed to be passive, but we run stuff all the time with a little hotter signal than is appropriate. it'll drive the first gain stage a bit though. nothing to worry about breaking things though.
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#13
Quote by gumbilicious
yeah, you should be fine. really the input for a guitar amp is supposed to be passive, but we run stuff all the time with a little hotter signal than is appropriate. it'll drive the first gain stage a bit though. nothing to worry about breaking things though.



I was actually thinking about making an amplifier for the cabinet, not actually putting it through a legit guitar amp.

thoughts on this:

1) it is for SURE a blues Jr. head.

2) I could run a 50W amplification circuit from the line out to the cabinet, my only thought is is that this would eliminate the nice creamy tube tones that the head unit makes when directly hooked to a speaker.

2) i could run a x-former type circuit from the speaker connection on the head to the cabinet. This way I wouldn't loose the creamy tone and i should effectively boost the signal output to something that would drive the cabinet with some more authority.

Basically, I want to try and drive the cabinet with some more POW but I'm afraid of loosing tube tone.


other idea....which....i'm thinking is a no-no.....but....the head is rated for a 8ohm speaker, with that many speakers, although they would be in 4 ohms, it shouldn't have enough watts to blow them....bbbuuuuutttt I haven't worked with speakers that much...soo....yeah....lol
#14
What are you using as a power amp?
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#15
Quote by LaidBack
What are you using as a power amp?



could you elaborate on that a bit?

like if i go the route of a 50W amp that gets driven from the line out??? or the amp everything gets plugged into
#17
Wait, so you're going to run the Blues Jr. into the front end of a 50 watt amp? Essentially using the BJr. as an expensive overdrive pedal?
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#18
Why not just run the BJr? 15 tube watts thru a 4x12 is going to pretty loud. Running the 50 will only make it a few decibels louder if I am correct. (Double the wattage = 1 decibal increase or something like that?)
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#19
Quote by LaidBack
Wait, so you're going to run the Blues Jr. into the front end of a 50 watt amp? Essentially using the BJr. as an expensive overdrive pedal?



kinda, my concern was that as the post above asks, why not run it directly into the cab? that it wouldn't quite be loud enough to gig with.

I wasn't going to run it into a full 50W headunit, instead I was just looking to boost the output of the BJ to a higher power to drive the cab a bit more effectively
#20
15 watts is giggable if there is a house PA. As for the 50 watt part, I think you are just a little confused. How would you go about "boosting the output"? I don't want you ruining an amp, care to elaborate?
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#21
if you do that, the 15 watt amp's output transformer will blow up. you can't turn on an amp that doesnt have a load on the speaker out
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#22
Quote by LaidBack
15 watts is giggable if there is a house PA. As for the 50 watt part, I think you are just a little confused. How would you go about "boosting the output"? I don't want you ruining an amp, care to elaborate?



see thats my problem...I'm trying to figure that out

The problem with driving the 8x10 cab with a 15w head is that its not as "efficient". Granted it will still sound decent but you have the tendancy to wear out the cones more by doing this.

baisically a class A amp takes the low gain input from the guitar, puts it on top of a signal given by the OT, and then puts it to a speaker. Based on however that OT is hooked up, you can get different voltage increases, aka 120:120 ; 120:360 ; 120;420 based on how you wire it up.

this was kinda the idea that I had, only instead of needing the full 120:420 it wouldn't need as big of a bump.

I'm just trying to formulate ideas here on how to more effectively drive the cab.

and no, you can turn an amp on without a load, most amps have a circuit to deal with it when your speaker isn't hooked up, its not recomended but it wont blow anything up, cause undo wear possibly on tubes though.
#23
Quote by jlangholzj
see thats my problem...I'm trying to figure that out

The problem with driving the 8x10 cab with a 15w head is that its not as "efficient". Granted it will still sound decent but you have the tendancy to wear out the cones more by doing this.

baisically a class A amp takes the low gain input from the guitar, puts it on top of a signal given by the OT, and then puts it to a speaker. Based on however that OT is hooked up, you can get different voltage increases, aka 120:120 ; 120:360 ; 120;420 based on how you wire it up.

this was kinda the idea that I had, only instead of needing the full 120:420 it wouldn't need as big of a bump.

I'm just trying to formulate ideas here on how to more effectively drive the cab.

and no, you can turn an amp on without a load, most amps have a circuit to deal with it when your speaker isn't hooked up, its not recomended but it wont blow anything up, cause undo wear possibly on tubes though.


Everything you said is wrong. Everything.

Efficiency is to do with matching impedances. If they're matched, you get maximum transfer and minimum loss. If not, you either lose output or blow up the OT depending on what the mismatch is.

An amplifier takes the ~100mV signal from the guitar and ramps it up through several gain stages until it hits the power amp which ramps it up even more. The output impedance is on the order of several thousand Ohms which is then taken by the OT down to a suitable impedance to drive a speaker. This is usually 4, 8 or 16 though there are some odd ball amps with 2, 2.6, 32, etc. Class A is an operating class. It just means that the amplifying devices are conducting throughout the entire input cycle.

And no, you can't turn on an amp without a load without worrying about the OT blowing. It effectively presents an infinite load so the signal has nowhere to go causing arcing and the eventual destruction of the transformer.
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#24
Quote by mmolteratx
Everything you said is wrong. Everything.

Efficiency is to do with matching impedances. If they're matched, you get maximum transfer and minimum loss. If not, you either lose output or blow up the OT depending on what the mismatch is.

An amplifier takes the ~100mV signal from the guitar and ramps it up through several gain stages until it hits the power amp which ramps it up even more. The output impedance is on the order of several thousand Ohms which is then taken by the OT down to a suitable impedance to drive a speaker. This is usually 4, 8 or 16 though there are some odd ball amps with 2, 2.6, 32, etc. Class A is an operating class. It just means that the amplifying devices are conducting throughout the entire input cycle.

And no, you can't turn on an amp without a load without worrying about the OT blowing. It effectively presents an infinite load so the signal has nowhere to go causing arcing and the eventual destruction of the transformer.



ever wonder why you have to match impedences??? its all simple circuits. If the OT is set up to run a 8 ohm, then it doesn't matter what you hook into it as long as its still 8 ohms. but if you've got a crap ton of load on it, you end up either drawing voltage or current depending on how you have the speakers wired. Power is defined as voltage*current. Voltage is a potential difference and current is the ability to do work. Without one or the other, your SOL. The OT might be rated at 8 ohms of resistance but the more you hook up, the less current and voltage you have to drive the speaker coils with. Each 10" speaker takes ~10W of power to drive it well. you under drive it, it will work but rather inefficiently when you try to get volume out of it. There's simply not enough there to drive them without getting warm. The resonse is slower and you don't get a good snappy response as if you were outputing what was recomended.

this is also why an 8 ohm system can drive 16's but not vice versa. The system needs to pump enough power to drive the 8, so extra impedence doesn't matter but it just wont work as well. The other way arround is over powered and you end up going past the rating for the speaker.

also, your wrong in the whole open-circuit thing. Almost all modern amps have built in load resistors to make sure the whole thing doesn't blow up in an event of a speaker failure. again, not recomended for extended periods but its not going to blow up.
#25
The idea that a 16 ohm system cannot power an 8 ohm system is completely wrong. The impedance is merely mismatched; with a 2:1 or 1:2 mismatch you get an 11% reduction in output power from the amp. There's no more or less power produced by an 8 or 16 ohm amp (a lot of amps have impedance switches on the back, and none are louder than the others), it's just a more efficient transfer of power from the power tubes through the OT to the speakers.

Your idea of changing power to compensate for the speaker load is incorrect. What you're really doing is changing the transforming ration of the output transformer, such that the (for instance) 4000 ohm output impedance of the power tubes is matched with the 8 ohm input impedance of the speakers. The optimal situation is matching, but all your doing with different impedances is changing the relationship of the impedances, not the actual power produced.

A good analogy is gear shifting in a car; let's say you are going 45 mph. You're in fourth gear at 3000 RPMs. Shifting down (more cab impedance) puts you at 4500 RPM - that's not twice the power, nor is it going to blow up your engine, but it's not optimal for the power to speed ratio. Shifting up puts you at, say, 1500. Again, the output of the engine does not change, and again it is not the most efficient gearing for going that speed, but it is well within operating parameters, and to say that it is impossible to drive 45 MPH in fourth gear is not correct.

It appears that the reason your explanations are not quite proper is that you are assuming a more simple DC circuit, when what is really happening involves an AC circuit with all sorts of crap flying around that you did not learn about in your high school physics class. I don't mean to be rude, but that seems to be the issue with many, many simplified ideas of how impedance works, yours included.

Speaker efficiency is another thing, but 10 watts is much more power than it takes to properly drive a guitar speaker. 1 watt is sufficient for most speakers unless they have very large voice coils.
#26
Quote by Roc8995
The idea that a 16 ohm system cannot power an 8 ohm system is completely wrong. The impedance is merely mismatched; with a 2:1 or 1:2 mismatch you get an 11% reduction in output power from the amp. There's no more or less power produced by an 8 or 16 ohm amp (a lot of amps have impedance switches on the back, and none are louder than the others), it's just a more efficient transfer of power from the power tubes through the OT to the speakers.

Your idea of changing power to compensate for the speaker load is incorrect. What you're really doing is changing the transforming ration of the output transformer, such that the (for instance) 4000 ohm output impedance of the power tubes is matched with the 8 ohm input impedance of the speakers. The optimal situation is matching, but all your doing with different impedances is changing the relationship of the impedances, not the actual power produced.

A good analogy is gear shifting in a car; let's say you are going 45 mph. You're in fourth gear at 3000 RPMs. Shifting down (more cab impedance) puts you at 4500 RPM - that's not twice the power, nor is it going to blow up your engine, but it's not optimal for the power to speed ratio. Shifting up puts you at, say, 1500. Again, the output of the engine does not change, and again it is not the most efficient gearing for going that speed, but it is well within operating parameters, and to say that it is impossible to drive 45 MPH in fourth gear is not correct.

It appears that the reason your explanations are not quite proper is that you are assuming a more simple DC circuit, when what is really happening involves an AC circuit with all sorts of crap flying around that you did not learn about in your high school physics class. I don't mean to be rude, but that seems to be the issue with many, many simplified ideas of how impedance works, yours included.

Speaker efficiency is another thing, but 10 watts is much more power than it takes to properly drive a guitar speaker. 1 watt is sufficient for most speakers unless they have very large voice coils.



you were doing well until you took a poke at my education.....

I know a good amount about A/c Circuits thank you....but I'm a little weak on the application part. That and speakers are something new to me....I don't really know how they interface with whats few to them completely yet....hence me asking here.

I appreciate finally an educated response. My worry was that I'd wear out the cones faster than normal if i under-drove them.

so, now the question is, If i've got an 8 ohm system can I run 4-5 ohms and have it drive the speakers more efficiently or is that a no-no
#27
Quote by jlangholzj
you were doing well until you took a poke at my education.....

I know a good amount about A/c Circuits thank you....but I'm a little weak on the application part. That and speakers are something new to me....I don't really know how they interface with whats few to them completely yet....hence me asking here.

I appreciate finally an educated response. My worry was that I'd wear out the cones faster than normal if i under-drove them.

so, now the question is, If i've got an 8 ohm system can I run 4-5 ohms and have it drive the speakers more efficiently or is that a no-no


dude, what you're saying pokes fun at your education. your posts are mind numbing. no wonder we have a bunch of confused people running around here.

but alas, there are some really good books on speakers out there, take a look. weber's FAQ on speakers is also very useful.

edit: now that i reread colin's post, i realize he even said 'not to take offense', he was earnestly guessing you had a high school education in electronics and was trying to diagnose the problem. matt's post was also excellent. i am amazed both of them kinda figured out what you were trying to say, i am still confused as to what you wanna do.
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Last edited by gumbilicious at Sep 22, 2010,
#29
I haven't looked at them yet but the guy that has it has had it since the late 70's and used it ALOT....he just figured they would need to be....not gonna re-cone em if they dont need it
#30
Guys, thanks for coming in and helping out. I guess I was taking too much of a round about way. TS, good luck.
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