Taking a DI from a Valve Amp that has no DI out

[King Tut]

I've just dug out my old Laney Supergroup 100 which one of my sons resurrected for me with a revalve and overhaul. I've realised how utterly gorgeous this sounds and was thinking about using it for smaller gigs or taking a line out for recording. Trouble is, it doesn't have a DI out.

When we toured with The Groundhogs just prior to lockdown, I remember their Bass Player, Latch, used a DI box from his speaker out to go into the PA.

Ive got an old el cheapo DI box from Thomann (Pictured) - would it be possible to take the speaker out from the amp into this, flick this to the 'speaker' setting, then link this to a cab. I could then go to the desk from the di out on the box.

The amp does have an output that is marked 'Output - connect to power simulator only' - can this be used for recording and does it include the signal coming from the power section or preamp only?

Also has anyone had experience of using power soaks/speaker attenuator's to drop the cab volume to make recording a cranked amp more bearable.

I do understand that ideally I'd mic the cab, but I'd be recording at home with all the associated rattles so not really ideal.

Never stop learning - let me have your thoughts!

Edited October 5, 2020 by King Tut

[BigRedX]

Technically since the DI box has a "speaker" setting it should be possible running it from the speaker output of the amp, with two caveats.

1. You will still need to have the speaker plugged in. The DI goes between the amp and the cab.

2. Check the rating of the DI box in speaker mode. IME most of these devices are designed to be used with small guitar amps rated at under 50W, and transformers aren't suitable to cope with high output bass amps.

You have the same problem using Power Soaks. Most simply aren't designed for the sorts of levels/currents that a valve bass amp in full flight will put out. I used to own a Marshall PowerBreak which technically can go up to 100W, but even with a 50W guitar amp some sounds would cause the cooling fan of the PowerBreak to go into overdrive and often after a gig it would be hotter than the amp!

The other thing you may well find is that it's not the distortion of the power amp valves that is giving you the bass sound you want, but speaker breakup. The only way you get this is by running the amp at full tilt and mic'ing up one of the speakers.

[Beer of the Bass]

I haven't seen the schematic for the Supergroup, but the "Power Simulator" units were simple slave power amps so that's likely to be an output post-preamp.  

Most passive DI boxes with a speaker setting attenuate the signal voltage with a simple resistor divider before the transformer, so whether it's suitable for your output level is more about how much attenuation it's designed for than the transformer spec. I'd say there would be no harm in trying it when playing at a relatively low volume, but if it starts to sound bad or give you too hot a DI signal as you turn it up then you'd want to try a different DI.  Also, when using a speaker level DI, I'd always prefer to run it from the second speaker jack on the amp, provided they're wired in parallel as most are. That way the connection from amp to speaker isn't running through the extra set of jacks and PCB tracks in the DI box.

If you're going for a dirty bass sound, the speaker adds a lot and a mic may be better, but for a little colouration on a mostly clean sound the DI may be quite useful. 

Edited October 6, 2020 by Beer of the Bass

[Bankai]

If you want to spend the money, something like the Radial JDX would be great. It sits between the power amp and the speaker cab, and can take up to 400W, and has both cab simulation for both guitar and bass guitar built in. 
 

That way you capture the full flavour.

 

[King Tut]

32 minutes ago, Bankai said:

If you want to spend the money, something like the Radial JDX would be great. It sits between the power amp and the speaker cab, and can take up to 400W, and has both cab simulation for both guitar and bass guitar built in. 
 

That way you capture the full flavour.

 

Im pretty sure that's what the bass player from the Groundhogs was using!

[SamPlaysBass]

If you’ve got a bit of cash but want the best, this looks like a great solution.

 

[Jack]

I have the same Thomann DI box. Whilst it does have a speaker setting, I'd be a bit scared of something that cheap with such high voltage. Countryman Type 85 is the answer.

[Dan Dare]

If you don't have a speaker connected, you will need to use a dummy load for a valve amp, unless you like paying for new output transformers.

[BigRedX]

Of course it's at this point that you will realise just how much the cab colours your bass sound.

[ezbass]

Just now, BigRedX said:

Of course it's at this point that you will realise just how much the cab colours your bass sound.

^^^^ This