Amp Tech Thread / Ask a tech Q

[moose23]

Could one of you guys recommend a transformer for matching mic level to line level like this:



http://www.colomar.com/Shavano/cable_xlr_to_phone.html

[VOLVO)))]

Mort,  Depends on your competence. It could be simple, it could be a labyrinth of fuckfuckfuck.

[The Shocker]

New old amp day.
Montgomery Ward GIM-9011A








Came with about 10 of these:


And the reason I posted here as opposed to new acquisitions:


Any idea where it goes?

[Mr. Foxen]

Gonna be a hunt the legs mission.

[The Shocker]

Been looking.  Going to send it to a buddy that doesn't need bi-focals.

[bass sic]

I have a toob question. On my Egnater Tweaker 15wt I swapped out all the tubes experimenting. I put a matched set of Tung Sol 6v6gt's in and the tone improvement was very noticeable. But after about 15/20 minutes of lower volume playing the volume dropped almost all the way off. And I notice one of the tubes is glowing hot. I turn it off for a few seconds and it comes back on normal, then craps out again later. It didnt do it before the tube swap, could it be the new tube? Or fucked up amp? Ill swap tubes back later.

So here's a little update, I put the stock tunes back in and had no problems since. Then last week they sent me the replacement Tung Sol tunes and they've been working fine for a week now. It had to be bad tubes from stock.

[liquidsmoke]

When a solid state amp is cranked way up and clips somewhat is it hard/damaging on certain components of the amp? You'd think 380 watts would be enough for all the volume one would ever need for guitar with 2 cabs but it clips pretty easily. I don't have 2 grand for EVM12L's and a 1,000 watt amp so this will have to do.

edit: Mosvalve 500. I think it's loud enough without clipping, just barely. Better than the SS150 by itself which gets nasty and too sludgy too quick.

[Mr. Foxen]

Generally they aren't designed to be run in clipping for long, but doesn't necessarily mean it will break. Rigging a high pass filter is your best bet for making it run cleaner much louder

[liquidsmoke]

Generally they aren't designed to be run in clipping for long, but doesn't necessarily mean it will break.

Ah. I was running the SS clipping for 90+ minutes at practice.

Rigging a high pass filter is your best bet for making it run cleaner much louder

Doesn't this effect tone? I do use an eq pedal to take out some of the lows.

[liquidsmoke]

380 watts and the thing is clipping and smelling weird. It's older but still.. WTF? Guess I need 600 watts? My cabs can each handle 300.

I have no idea how people manage with those 120/150 watt SS heads.

[liquidsmoke]

Looking like it's either upgrade my cabs/speakers for higher wattage handling(which will cost a shit ton) so I can maybe go up to a 600-800 watt SS power amp or look into a '70s SVT head(also pricey I bet) assuming it wouldn't blow two 300 watt cabs which would also be expensive. This shit never ends with this band. Cabs are either shutting down, clipping, or melting. Perhaps we should do acoustic. I have no idea how much vintage SVTs go for but I understand that they sound pretty good for guitar unlike the newer ones with preamps designed specifically for bass.

[Mr. Foxen]

Rigging a high pass filter is your best bet for making it run cleaner much louder

Doesn't this effect tone? I do use an eq pedal to take out some of the lows.

It will take out clipping and speaker fart, depends if those are part of your tone. You pretty much set the filter to below what your cab is capable of outputting, with a sealed SVT type probably 50-60hz, 40hz for a reasonable ported cab, awesome ported cab 30hz. If its guitar and you have a bassist, can set it higher still, give bassist some room. Wattage handling in cabs is pretty much irrelevant to clipping, you want more sensitivity if you want to be louder without clipping, since you need less power to get there, plus if its the speakers farting, the watt rating is irrelevant to that, since its excursion limit that determines when they fart.

[liquidsmoke]

Rigging a high pass filter is your best bet for making it run cleaner much louder

Doesn't this effect tone? I do use an eq pedal to take out some of the lows.

It will take out clipping and speaker fart, depends if those are part of your tone. You pretty much set the filter to below what your cab is capable of outputting, with a sealed SVT type probably 50-60hz, 40hz for a reasonable ported cab, awesome ported cab 30hz. If its guitar and you have a bassist, can set it higher still, give bassist some room. Wattage handling in cabs is pretty much irrelevant to clipping, you want more sensitivity if you want to be louder without clipping, since you need less power to get there, plus if its the speakers farting, the watt rating is irrelevant to that, since its excursion limit that determines when they fart.

Interesting.

"Wattage handling in cabs is pretty much irrelevant to clipping"

Now I'm really confused. I would expect clipping at even moderate volume levels if I ran a 400 watt amp into a 100 watt cab. No?

[beerrhino]

I have a sound city that suddenly started a loud buzzing and popping while it is being played.  If I just plug the guitar in there is no noise, the moment I hit the strings the noise starts--loud enough to be heard over anything being played.  At the same time the noise problem started the amp experienced a severe volume drop.  Before it would peel the paint off the walls on 7, now the drums drown it out fully cranked.  I've tried different guitars, cabinets and cables all with the same results. 
I realize I'll need to take it in to a tech but they're closed for the week for the holiday and I'm trying to get a general idea of what I'm looking at.
Any thoughts?

[Mr. Foxen]

Interesting.

"Wattage handling in cabs is pretty much irrelevant to clipping"

Now I'm really confused. I would expect clipping at even moderate volume levels if I ran a 400 watt amp into a 100 watt cab. No?

Factors other than watts determine how loud and when it clips. If the cab is 125db when fed 10w, its going to be loud without clipping, and you just don't need to push the amp so hard. Also, you could clip a 500w rated cab with a 400w amp if the cabs excursion limit is 100w (which is often the case with 4x10s). It is the xmax of a speaker that determines when it will clip, which is unrelated to the thermal power handling. Thermal handling ratings on speaker are almost totally irrelevant but its the biggest number so it gets shouted about most.

I have a sound city that suddenly started a loud buzzing and popping while it is being played.  If I just plug the guitar in there is no noise, the moment I hit the strings the noise starts--loud enough to be heard over anything being played.  At the same time the noise problem started the amp experienced a severe volume drop.  Before it would peel the paint off the walls on 7, now the drums drown it out fully cranked.  I've tried different guitars, cabinets and cables all with the same results. 
I realize I'll need to take it in to a tech but they're closed for the week for the holiday and I'm trying to get a general idea of what I'm looking at.
Any thoughts?

I've had some do this, turned out to be bad solder joint/resistor, I just brute force replaced resistors in the pre until it worked right, the carbon comp resistors in there are a bit shit anyway, so better with new ones.

[The Gentlemen Bastards]

I have an old Marshall cab that I run a Sovtek Mig-100 head into. Lately, certain notes will cause the entire cabinet to emit this overwhelming buzz. It's not feedback, more like a massive vibration. Thinking a speaker was loose, I tightened all of them. But, it didn't help. Any ideas? I'm hoping it's not some kind of a crack in the frame itself.

[Mr. Foxen]

Anything else being loose. Wood inside, a wire touching a cone sometimes, a crack in the case, dust cap on a speaker separating.

[The Gentlemen Bastards]

Okay, I'll investigate all of those possibilities. Thanks!

[VOLVO)))]

Fender Bandmaster, Vibrato knob turns volume down, what the hot fuck?

[justinhedrick]

Fender Bandmaster, Vibrato knob turns volume down, what the hot fuck?

hmm. something in the vibrato circuit is allowing the uneffected signal to pass through . . . what kind of circuit is it? tube? photo cell?

[VOLVO)))]

Fender Bandmaster, Vibrato knob turns volume down, what the hot fuck?

hmm. something in the vibrato circuit is allowing the uneffected signal to pass through . . . what kind of circuit is it? tube? photo cell?

Tube!

[The Bandit]

Did you figure it out Jake?

[VOLVO)))]

Haven't cracked it, been working on his yamaha sy-2

[liquidsmoke]

From the Rocktron Velocity 300 manual-

"unbridged"
"150 watts per channel @ 4 ohms
75 watts per channel @ 8 ohms
37.5 watts per channel"

"bridged"
"300 watts @ 8 ohms
170 watts @ 16 ohms"

"These standard ¼" jacks provide outputs for Channel 1 to speaker cabinets. Do not connect these outputs
to a load of less than 4 ohms (or less than 8 ohms in mono-bridged mode). These jacks are used when
using the Velocity 300 in "BRIDGED" mode."



This makes no sense to me at all. If the amp puts out 300 watts total stereo(both channels total) at 4 ohms how can it put out 300 watts bridged at 8? The math seems wrong. Bridged is both channels combined together, no?

So if you have two 8 ohm cabs, one getting the signal from channel A and one getting the signal from channel B they are each only getting 75 watts BUT if you have them both hooked up to channel A bridged then the amp somehow tries to put out more than 300 watts and overheats because the load is 4 ohms? Where does this mysterious extra power come from for bridged mode? If I am understanding this correctly it seems like a very strange design. Why not allow the amp to put out 300 watts bridged at 4 ohms and 150 watts bridged at 8?

[moose23]

From the Rocktron Velocity 300 manual-

"unbridged"
"150 watts per channel @ 4 ohms
75 watts per channel @ 8 ohms
37.5 watts per channel"

"bridged"
"300 watts @ 8 ohms
170 watts @ 16 ohms"

"These standard ¼" jacks provide outputs for Channel 1 to speaker cabinets. Do not connect these outputs
to a load of less than 4 ohms (or less than 8 ohms in mono-bridged mode). These jacks are used when
using the Velocity 300 in "BRIDGED" mode."



This makes no sense to me at all. If the amp puts out 300 watts total stereo(both channels total) at 4 ohms how can it put out 300 watts bridged at 8? The math seems wrong. Bridged is both channels combined together, no?

Bridged will be the two amps in series. In unbridged mode each output is 4 Ohm with 150 watts of power so you can connect a cab of 4 Ohm to each output and get 150 Watts to each, substitute these for 8 Ohm cabs and the power available halves (according to them, more likely it'd be around 2/3s).

So if you have two 8 ohm cabs, one getting the signal from channel A and one getting the signal from channel B they are each only getting 75 watts BUT if you have them both hooked up to channel A bridged then the amp somehow tries to put out more than 300 watts and overheats because the load is 4 ohms? Where does this mysterious extra power come from for bridged mode? If I am understanding this correctly it seems like a very strange design. Why not allow the amp to put out 300 watts bridged at 4 ohms and 150 watts bridged at 8?

It explicitly says do not hook up less than 8 Ohms to in mono bridged mode so you would not hook up two 8 Ohm cabs in parallel i.e. 4 Ohms. If you hooked them up in series you'd have 16 Ohm so you would get 170 watts between the two cabs. There is no mysterious extra power it can only ever put out 300 watts be that in mono or stereo so you've just fucked up the OT by hooking up two low of a load.

There's no way of allowing the amp to put out 300 watts bridged at 4 ohms as it is still two 150 watt 4 Ohm amps in series which will give you an 8 Ohm minimum load.