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  #1  
Old 02-12-2014, 10:08 AM
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Tube amp Isolation for recording, safe?

I'm about to start working on a new DIY band demo... Since this is a home grown production, we're going to record the basic rhythm tracks and overdub the rest as needed. In an attempt to isolate sounds, I'm running the bass DI (Monique), keys DI, and I'm going to run the guitar amp (my Fender Twin) as isolated as possible. The drums should be the only 'live' sound in the room.

Luckily we have a 2 room practice space, and I'll put the guitar in the OTHER room (no door, though). My plan is to build an impromptu isolation box for the amp (which we won't be cranking anyway).

My question with my Twin, do I risk overheating with this?

The box is going to be double-thick corrugated cardboard, and it will be a couple inches taller than the twin, it will extend about 2 feet out front of the twin, and with a couple inches on each side. The inside of the 'box' will be completely lined in mattress topper foam. Most of the space in the front of the box (in front of the speakers with a bit of 'breathing room')will be stuffed with other 'fluffy' items (pillows or blankets). The top will be removable for access. There will probably also be additional 'damping placed OVER the whole box.

Now the amp stuff:

-Fender 135w Silverfaced Twin Reverb
-4x 6L6 tubes plus 12AX7/12AU7's
-We won't be running it cranked. It probably will actually be closer to idling, given we use it for clean tone and don't want extra volume in the room.

We'll be running an afternoon of pre-recording rehearsals to get our 'sounds' and get everyone used to headphones and tweak the HP mix. The following day we'll be tracking 5 to 6 songs, and I can certainly 'open' the box during breaks or even every few takes.

What's the tube amp consensus with this?
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Last edited by BurningSkies : 02-12-2014 at 10:14 AM.
  #2  
Old 02-12-2014, 10:24 AM
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Keep a close eye on the temperature of the amp. You could easily overheat it if you left it running in there all day. Should be fine if you open it up to let it cool off every once in a while. Definitely on breaks, more often if it seems to be getting too hot.
  #3  
Old 02-12-2014, 10:26 AM
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sounds good

I don't think you'll have an overheating problem,

but I think a 3 sided baffle about 1 ft in front on the amp would do the trick too.

Plexiglass if the budget allows
  #4  
Old 02-12-2014, 10:30 AM
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rather than leaving 2 feet in front of the amp (stuffed with pillows), I would put the speakers right up against the box,, or a couple inches from the box to allow for the mic, and then leave the room int he back of the amp. That amp essentially cools itself by circulating air in the back - so leave room in the back.

Once the amp is in the box, you could further isolate by covering the box with blankets, hanging a curtain (or something like a down comforter) where the door should go, etc...

you could put a computer fan in the box pretty easily to vent it, and turn the fan off when you are tracking. Might not be enough.

I would for sure remove the box when not tracking. The amp needs to breathe. Just keep a close eye on it!
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  #5  
Old 02-12-2014, 10:30 AM
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The problem is that it has an open back too, and as we know, speakers work in both directions. I'm really aiming at keeping the exterior volume down to a whisper, or as close as I can given the materials, funds (zero) and abilities I have available.

I have a wireless thermometer, maybe I'll bring it and set it up in the box too.
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  #6  
Old 02-12-2014, 10:32 AM
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Why not reamp?
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  #7  
Old 02-12-2014, 10:32 AM
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Quote:
Originally Posted by hennessybass View Post
rather than leaving 2 feet in front of the amp (stuffed with pillows), I would put the speakers right up against the box,, or a couple inches from the box to allow for the mic, and then leave the room int he back of the amp. That amp essentially cools itself by circulating air in the back - so leave room in the back.

Once the amp is in the box, you could further isolate by covering the box with blankets, hanging a curtain (or something like a down comforter) where the door should go, etc...

you could put a computer fan in the box pretty easily to vent it, and turn the fan off when you are tracking. Might not be enough.

I would for sure remove the box when not tracking. The amp needs to breathe. Just keep a close eye on it!
That's sort of what I'm thinking. I'll pull the top off the box when not in use. Good point about the air at the back. I'll work with it and try to find a compromise between damping the front output and the rear while giving it enough space.

Luckily, the guitar tone is not bass heavy, clean and crisp up top and not extending very low.
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  #8  
Old 02-12-2014, 10:34 AM
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can you use a wall? Set the amp facing and right up against the wall (leaving room for the mic), and then put the box around that.
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  #9  
Old 02-12-2014, 10:35 AM
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Originally Posted by M0ses View Post
Why not reamp?
I've never re-amped before, and I'm concerned about my comfort level in doing it correctly and/or successfully for something that we're investing a fair amount of time in. As with any techniques there's a learning curve, at least for me. Maybe I'm a bit slow.
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  #10  
Old 02-12-2014, 10:35 AM
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might even be able to stuff pillows in between the wall and the face of the amp once your mic is in place. This way you won't mess up your set up, mic placement, etc when moving the box.
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  #11  
Old 02-12-2014, 10:36 AM
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I'd start without the box and see how bad the bleed is in the drum overheads. You may well have plenty of isolation.

The other thought would be to run a power soak to pad down the guitar amp's output level.

Yet another thought is to DI the guitar.

Yet another another thought - do you have access to someone with experience as a studio engineer? That's a pretty aggressive schedule, and one of the things an experienced engineer brings to the party is the ability to work fast.
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  #12  
Old 02-12-2014, 10:42 AM
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Quote:
Originally Posted by hennessybass View Post
can you use a wall? Set the amp facing and right up against the wall (leaving room for the mic), and then put the box around that.
I can use a wall...and that was another 'layer' of isolation I was planning on. So basically the amp would face the wall a foot or two out, the box over/around the amp. Our practice/recording room setup is 2 rooms, One being about 15x15 (amp room) and the other being about 15x20. Both carpeted. I also have a stack of drop-ceiling acoustic tiles I plan on layering around the 'box' (they conveniently came with the room).

For reference, here's what sticks to tape (hard drive) when we just multitrack a practice.
https://soundcloud.com/burning-skies/babylontree1
https://soundcloud.com/burning-skies/sorry1
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  #13  
Old 02-12-2014, 10:42 AM
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Ideally, you would like to put only a speaker cab in the chamber with the amp outside. An amp outside of its case MAY pick up noise, the top of the amp case often has aluminum tape or screen on it to shield the inside of the chassis. Much like an instrument cavity is shielded. If you remove the amp from the box, laying it on a thin aluminum sheet (hardware store) will help.

With the amp in the chamber, heat will be an issue that you will need to monitor. Four 6L6GC tubes in a box is going to throw off some heat. If it gets too hot, you can open the chamber when not playing and blow a small desk fan into it to cool things down. I know, a bit of a pain.
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  #14  
Old 02-12-2014, 10:48 AM
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Borrow an extension speaker cab and put that in the isolation box, just use the combo amp as a head. Make sure you use a proper speaker cable to connect the extension cab to the amplifier. Obviously you'll want to disconnect the combo speakers, and make sure the amp and speaker impedance (ohms) are matched.

Tube amps consume about 4 times as much electricity as their output power, and most of that energy is converted to heat. So a 135-watt Twin is like putting a 500-watt space heater in an insulated box.
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  #15  
Old 02-12-2014, 10:49 AM
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Quote:
Originally Posted by BurningSkies View Post
So basically the amp would face the wall a foot or two out, the box over/around the amp.
Since you are essentially close miking the amp and not trying to get a room sound in the guitar, I would stick that sucker right up on the wall.

I think you will be fine as long as you remove the box now and again to let some fresh air in.

I dig your band.
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  #16  
Old 02-12-2014, 10:53 AM
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Originally Posted by Interceptor View Post
I'd start without the box and see how bad the bleed is in the drum overheads. You may well have plenty of isolation.

The other thought would be to run a power soak to pad down the guitar amp's output level.

Yet another thought is to DI the guitar.

Yet another another thought - do you have access to someone with experience as a studio engineer? That's a pretty aggressive schedule, and one of the things an experienced engineer brings to the party is the ability to work fast.
I don't have the funds for a soak right now, and I did consider it. I also wish I had a smaller amp to work with (like a single 12" setup) but the Twin actually sounds great and doesn't need to be cranked since it is used for clean tone.

I do have a friend who is/was trained as a recording engineer. And can lend a hand. The only problem is that he tends to be a fan of 'garage' style tactics and prefers a rough and ready punk vibe, which isn't what I'm really looking for. Our time-frame of two days is literally just for the basic rhythm tracks. Its probably all we would be able to afford in a studio anyway, although before we spend the money (which the band fund doesn't have and I don't promote anyone putting in their own cash), I think this will be a good experience to show everyone a situation that is CLOSE to a studio situation to maybe rattle them a bit.



The good news is that the songs are already well rehearsed, with the 6th one being an 'optional' or stretch. Most of the material we've been playing out for a year or two.

The kit mic'ing is the hardest part, and I'm not going to try anything too esoteric. Close mic on snare, hat, kick and single rack tom. Two compressors for overhead to give some air and a bit of spread. I'll compress some of those to tape to even things out a bit (snare, kick).
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  #17  
Old 02-12-2014, 10:56 AM
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Sounds like you have a plan... Get good drum sounds, and focus on creating a good vibe and having a good performance!
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  #18  
Old 02-12-2014, 11:01 AM
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Quote:
Originally Posted by beans-on-toast View Post
Ideally, you would like to put only a speaker cab in the chamber with the amp outside. An amp outside of its case MAY pick up noise, the top of the amp case often has aluminum tape or screen on it to shield the inside of the chassis. Much like an instrument cavity is shielded. If you remove the amp from the box, laying it on a thin aluminum sheet (hardware store) will help.

With the amp in the chamber, heat will be an issue that you will need to monitor. Four 6L6GC tubes in a box is going to throw off some heat. If it gets too hot, you can open the chamber when not playing and blow a small desk fan into it to cool things down. I know, a bit of a pain.
Tough times call for drastic measures. Actually, I have a clip fan I used to use on the back of my 400+ that I can use when we pull the top off the box. And yeah, I know the amp itself may make some noise, but I think I can work with that, assuming I'm not getting more guitar/drum crossbleed. One of the hidden agendas here is that I want clean isolation so I can do some dub mixes out of these tracks too. I appreciate your input since I know your tube amp knowledge is vast.

Quote:
Originally Posted by Crater View Post
Borrow an extension speaker cab and put that in the isolation box, just use the combo amp as a head. Make sure you use a proper speaker cable to connect the extension cab to the amplifier. Obviously you'll want to disconnect the combo speakers, and make sure the amp and speaker impedance (ohms) are matched.

Tube amps consume about 4 times as much electricity as their output power, and most of that energy is converted to heat. So a 135-watt Twin is like putting a 500-watt space heater in an insulated box.
Unfortunately, I don't know any other players with borrowable extensions. The only guy I know who has one, it's a matching 2x12 for a Twin!

I won't mention the space heater thing to our singer...she'll have her feet in the isolation box in no time.

Quote:
Originally Posted by hennessybass View Post
Since you are essentially close miking the amp and not trying to get a room sound in the guitar, I would stick that sucker right up on the wall.

I think you will be fine as long as you remove the box now and again to let some fresh air in.

I dig your band.
Thanks! I appreciate the compliment. Those practice recordings have done us well and been used widely. Time for something better, hopefully.

I'll one up the 'stick it against a wall...Its going to be in a corner, so up against TWO walls. I have an empty room to work with.
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  #19  
Old 02-12-2014, 11:44 AM
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Originally Posted by BurningSkies View Post
I know the amp itself may make some noise, but I think I can work with that, assuming I'm not getting more guitar/drum crossbleed. One of the hidden agendas here is that I want clean isolation so I can do some dub mixes out of these tracks too.
I wasn't referring to typical amp noise. What I was saying is that if heat is an issue, remove the Twin Reverb amp from the Fender cabinet that it comes with. Isolate just the cab. Run a speaker cable from the amp chassis to the cab. The noise I was referring to is the hum that the amp could pick up because the chassis, removed from the cabinet, wouldn't shielded from interference. Placing the open face of the chassis on an aluminum sheet would help reduce noise.
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Last edited by beans-on-toast : 02-12-2014 at 11:46 AM.
  #20  
Old 02-12-2014, 11:48 AM
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Quote:
Originally Posted by beans-on-toast View Post
I wasn't referring to typical amp noise. What I was saying is that if heat is an issue, remove the Twin Reverb amp from the Fender cabinet that it comes with. Isolate just the cab. Run a speaker cable from the amp chassis to the cab. The noise I was referring to is the hum that the amp could pick up because the chassis, removed from the cabinet, wouldn't shielded from interference. Placing the open face of the chassis on an aluminum sheet would help reduce noise.
Thanks for the clarification. I will take this into consideration, should it prove that the heat is too much. Tonight I'm going to build this and test run it alone in the room to see how it functions. and how hot it gets (assuming my cardboard, spray glue and gaffer's tape skills are up to par).
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