Using a tube amp w/o a cab... I need a Cab sim/DI

Posted: Wed May 07, 2008 1:49 am

So I'm selling my Ampeg 8x10 because I no longer do gigs at the moment, and I can probably repurchase an Avatar 1x15 or 2x12 if I ever wanted to start up a band again... (plus I need the money!)

But I am never selling my SVT2-Pro. NEVER!

I want to use it to record (well, I have before but if I sell my cab...well, you see the problem).

Long story short, a tube amp with no load = a bad amp.

I hear about all of these active DI, guitar cab simulators and blahblahblah...

But I need a DI for my Ampeg SVT2Pro, preferably one that is passive that does not color the sound that is made purely to give a tube amp a load so that it does not destroy itself and overload it's power section! I'm actually building myself a DI right now but it's more of a standard DI.

Can anyone suggest a studio grade DI that can give a tube amplifier a "fake" load so that it can be used to record straight into an interface at line level? I've heard of the Redbox but I've heard they sound like doodoo for at least guitar amps...

This is 2008, no one actually uses microphones anymore! *wink*

Posted: Mon May 12, 2008 3:28 am

http://spl-usa.com/transducer/2601_kurz_E.html

Alternatively, there are load boxes available in the market, which u can connect the speaker out to from the head. Take a lineout from the head and use an amp sim (with just the speaker emulaion enabled) in your DAW.

Peavey has a nice amp sim 'Revalver', that does impulse speaker responses and is said to be very capable.

Cheers!
Sidhu

Posted: Mon May 12, 2008 5:40 am

You don't need a DI to use the tube head. You need a dummy load to simulate the load of the speakers. Various firms make them, sometimes called a power soak.

Posted: Mon May 12, 2008 5:04 pm

this thing is a bit of a monster and has (6 x 6550) tubes in the output section

it would take one of the largest power soaks / dummy loads to hold this at 50% let alone full grunt
I guess two 150W units in parallel for 300@4 would do the trick
good for warming the room on those cold mornings

find a tube amp tech that has some knowledge and schematics to this amp
and
it might be possible to remove 4 of the bottles and set it up as a low power amp and still retain the sound
it will also be easy to convert back for gigs in the future
or
remove all 6 and keep them aside for the high power gigs
and get 2 just for the recording set-up
your amp tech should advise here

once it is lower power a dummy load with a DI output ... and a low power speaker (on/off) for mic'ed recording if you need
can be found/purchased/ ... DIY
it's do-able and very useful

just at random on google
http://www.terrydownsmusic.com/technotes/dummyload/dummy_load.htm
8 Ohm 100W Non-Inductive Dummy Load Resistor
http://www.partsexpress.com/pe/showdetl.cfm?Partnumber=019-020
lots of info here
http://www.amptone.com/g243.htm

a little research in the DIY stuff will give you knowledge ... even if you choose to buy a commercial one

Posted: Mon May 12, 2008 7:08 pm

While I have to ability to modify and identify components in my amp, I'd rather not do that unless absolutely necessary. I've never heard of the term "power soak" but I've seen what I've been looking for referenced as a dummy load or attenuator. I'm a little confused about what I need. Can I run a dummy load/attenuator on an amp with such power for long periods of time? I'm worried about causing damage to either unit. Like I said I want an uncolored sound, I want to come directly out of the built in DI... So I'm guessing I need something to plug my speaker outs into? The ones I have looked at are usually for guitar and usually have some sort of "speaker emulation" feature which is not what I am looking for... Eep!

Posted: Tue May 13, 2008 11:17 am

hxckid88 wrote:

... I've never heard of the term "power soak" but I've seen what I've been looking for referenced as a dummy load or attenuator.

Like I said I want an uncolored sound, I want to come directly out of the built in DI...

power soak was a product name that just caught on as a generic name
could have been a Sholtz product ... or is it Scholz ?
others are Hot Plate - THD
PowerBrake - Marshall

it's just a dummy load with features
a feature could be the " speaker emulation "
and the " attenuator " is just so you can plug a speaker in and the volume will be reduced while still retaining the the load on the amp so the amp has the LOUD sound
hope that made sense

you want just the DI ?

then a simple small dummy load ... just to keep the output tubes happy BUT remember to keep the MASTER volume down low or you will toast the load

look at those DIY links and you will find an easy way to producea 100W 8ohm or 4 ohm load
double up on the resistors and you can push it out to 400W if you want

the wire wound resistors can be a little reactive but I don't think at bass frequencies it would cause issues
a normal speaker is reactive anyway

non-reactive loads are only an issue if you want to do testing out to max power at the higher frequencies
or if you work with RF amps.
An amp in oscillation can toast a load and itself but your amp is not faulty so no problem.
just keep an eye on the heat of the amp and load until you build some confidence in the dummy load.

Posted: Fri May 16, 2008 2:50 pm

We’re talking about three different pieces here:

-speaker level dummy load (resistors)
-line level output (DI)
-speaker emulation (lowpass)

The boxes available on the market all have different combinations of these. The redbox you mentioned only has speaker simulation, and no dummy load. The THD Hotplate has a load and a line out, but no speaker sim. The Palmer has all three, but is only 100W.

Like Kev said, you need a 300W+ dummy load. But, just use it for the load. Don’t take signal from it. Use the balanced line level out of your SVT-2 into your recorder.

There is a 200W load and some parts to build your own here:

https://amptechtools.powweb.com/truload.htm

That would be cool to wire 4 of those 100w Mass motors in series-parallel like a 4x12 cab. It would be easy and you don’t have to cut any speaker holes for those.

Posted: Fri May 16, 2008 4:07 pm

just remember those Mass motors ...

Quote:

These are speaker motors, they will blow up just like a speaker. So, don't think they are indestructible.

but they do look like fun
not convinced it is worthwhile here for this purpose

the preamp section should not notice if the power section has resistors or mass motors as a load

Posted: Fri May 16, 2008 5:55 pm

You're right Kev, those big 100 watt resistors should work fine.

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