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Can someone please explain?

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I already own one of these amps so I'm not interested in actually buying this:

https://www.ebay.co.uk/itm/Vintage-1970s-WEM-Watkins-Dominator-Bass-MK1-1x15-Valve-Amplifier-Combo/203211789750?hash=item2f505dd5b6:g:nwMAAOSw8Wlfzrar

What caught my eye was

I have wired the speaker/amp with 2 jacks, as I use an inline DI box (much easier and better sounding than a mike).
 
I can wire the speaker straight through to the amp if required.

I genuinely have no clue what this means. I frequently use a DI box, or the DI Out from my amplifier, but clearly he means something else.

 

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I 'think' he has severed the amp output to the cab and put jacks on each end of the cut/split, which he then plugs the amp out into a DI and then a parallel out from the DI to the cab... which is nonsense, so it can't be that!  ...can it?  :/ 

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9 minutes ago, Paul S said:

guitar > amp > DI > cab

Indeed but he's at speaker level rather than line or instrument/mic level and the line out from a DI isn't at a level to drive a speaker.  

 

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8 minutes ago, warwickhunt said:

Indeed but he's at speaker level rather than line or instrument/mic level and the line out from a DI isn't at a level to drive a speaker.  

 

I don't know the technicalities but in a former band both guitarists did this very thing.  Severed the cable twixt amp and cab and placed a DI box of some sort in between.  What sort of DI I don't know.

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51 minutes ago, warwickhunt said:

Oddly you'd normally just put the DI box in front of the amp (if no other output from the amp at instrument/line level), a lot less hassle.  :)    

Yes, but then you wouldn't get the tone of your amp, which is the whole point in doing it the other way.

Some DI boxes are designed to be able to handle a speaker level signal, so you can place them between the speaker out and the speakers of the amp.

Edited by Baloney Balderdash
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Our guitarist does this very thing with a Behringer active DI box that sits between his 100W Marshall head and his cab. I feed it with 48V from the desk and get back the 'tone' of his Marshall.  

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My head still doesn't get that you'd be able to go out of the DI back to a cab and be able to drive it at a volume to be useable (unless the signal is true bypass).  

Also the DI being active/48v driven has to be relevant... yes?  The difference in signal strength between instrument/mic, line and speaker level is huge so does the active actually attenuate the higher level?

 

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9 minutes ago, warwickhunt said:

My head still doesn't get that you'd be able to go out of the DI back to a cab and be able to drive it at a volume to be useable (unless the signal is true bypass).  

Also the DI being active/48v driven has to be relevant... yes?  The difference in signal strength between instrument/mic, line and speaker level is huge so does the active actually attenuate the higher level?

 

Can't see how that would be more difficult to understand than for example a post EQ DI out from the preamp of your amp, or even just a DI box placed between your bass and your amp input, sending the signal of your bass untouched through to the input of your amp and a line output level to a mixer.

Edited by Baloney Balderdash

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1 minute ago, Baloney Balderdash said:

Can't see how that would be more difficult to understand than a DI out from the preamp of your amp.

The actual signal levels are 'approx'.  

.015v - mic/inst

1.0v - line

12v - speaker

So the level out of an amps own DI is line level (about 1 volt) whereas the voltage from the speaker out is 12v (ish).  External DI boxes are generally used to boost from instrument level up to line level.  I've never associated a DI with lowering/attenuating the level from speaker levels; obviously they must but I'd be interested to know if that is true of all DI boxes.    

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Quite a few DI boxes can pad down from a speaker level signal - obviously you still need a speaker connected as the DI box presents very little load to the amp. I've done it with my old BSS, and the results can be quite good. The "thru" socket on a DI is usually just paralleled with the input jack, so the signal to the speaker is not attenuated.

If he really has fitted flying leads ending in a jack plug to both the amp and speaker, that does seem like a daft way to achieve this though...

Edited by Beer of the Bass

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Just read around a bit and every day is a school day.  Most of my encounters with either my own DI box(es) has been inline before the amp or have been in the amp.  I've never personally seen a one post amp/pre speaker and it seems that not all DI boxes can attenuate from speaker level but some can be placed there... with care!  :)  

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The DI box is just a "thing" and it can probably cope fine with the voltage/current of the speaker output - indeed if its wired in parallel with the speaker and high impedence, then those voltages are going to be very much less than 12V or so anyway, so approaching its normal operating range.

Its whether the desk could cope with such a "hot" input which would be the issue.

IMHO I've always preferred the DI box before the amp - this way it guards against some kind of amp fault and acts as a backup in case of amp failure too. Also the tone the amp imparts is really not that big of a deal (IMHO of course...), definitely not worth losing the backup (or taking a 2nd/3rd input etc).

 

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1 minute ago, paul_c2 said:

Its whether the desk could cope with such a "hot" input which would be the issue.

Yes, I think that is the bit I was wary of/unsure of.  I've had basses that have been too hot through the DI (amps own DI and external box) for a desk to handle... I was struggling to see how a speaker level could go to a desk and the level be OK.  

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9 minutes ago, paul_c2 said:

The DI box is just a "thing" and it can probably cope fine with the voltage/current of the speaker output - indeed if its wired in parallel with the speaker and high impedence, then those voltages are going to be very much less than 12V or so anyway, so approaching its normal operating range.

Its whether the desk could cope with such a "hot" input which would be the issue.

IMHO I've always preferred the DI box before the amp - this way it guards against some kind of amp fault and acts as a backup in case of amp failure too. Also the tone the amp imparts is really not that big of a deal (IMHO of course...), definitely not worth losing the backup (or taking a 2nd/3rd input etc).

 

For everyone who doesn't want their amp just to be a glorified stage monitor, and I would think that would at least include those people who still bother dragging a tube amp with them to gigs, getting the actual tone that their amps produce would be by far to prefer.

In fact why bring an amp at all if you are not going to use it anyway, and would be as good off with a regular stage monitor. 

Edited by Baloney Balderdash

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4 minutes ago, warwickhunt said:

Yes, I think that is the bit I was wary of/unsure of.  I've had basses that have been too hot through the DI (amps own DI and external box) for a desk to handle... I was struggling to see how a speaker level could go to a desk and the level be OK.  

I am sure the people who make DI boxes with this purpose in mind have thought of that and taking account for it.

It's not like converting a hot signal to less hot signal is magic or even all that advanced technology.

It's fairly common practice.

Edited by Baloney Balderdash
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2 minutes ago, Baloney Balderdash said:

I am sure the people who made DI boxes with this purpose in mind have thought of that and taking account for it.

It's fairly common practice.

As I say, I've fed desks with DI signals (either my amps DI or their own supplied) where engineers have asked if I can attenuate the signal down as it was too hot.  Personal experience meant my head couldn't get around a signal at speaker level which might be x10 hotter!  LOL

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2 minutes ago, warwickhunt said:

Yes, I think that is the bit I was wary of/unsure of.  I've had basses that have been too hot through the DI (amps own DI and external box) for a desk to handle... I was struggling to see how a speaker level could go to a desk and the level be OK.  

You need a DI with a suitable pad switch. A 40dB pad gives you an output of 1/100 of the input voltage, which gives you a manageable line level from most speaker outputs.

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One of the industry standard DI boxes even obscures the pad behind the labeling of 'pickup' and 'speaker'. Good for over 3000W iirc. 

countryman-type-85-direct-box-24870.jpg

Edited by Jack
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One of my Christmas pressies was a Palmer Junction DI box. When I get back to gigging again I'll be able come from the speaker out of my Peavey VB2 into the Palmer. From there the speaker signal will go into my cab and the DI to FOH. Some of these DI boxes, including the Palmer, include a speaker emulation circuit so FOH gets that too!

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The EMO DI boxes I have, are fitted with 3 sets of inputs, Instrument, Line and Speaker. Both Instrument and Speaker are loop through.

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23 hours ago, warwickhunt said:

My head still doesn't get that you'd be able to go out of the DI back to a cab and be able to drive it at a volume to be useable (unless the signal is true bypass).  

Also the DI being active/48v driven has to be relevant... yes?  The difference in signal strength between instrument/mic, line and speaker level is huge so does the active actually attenuate the higher level?

 

In many cases these days you wouldn't necessarily go back to the cab from the DI. One speaker level output to the DI, one to the cab. Attenuating the signal passively is trivially easy, it just requires two low wattage resistors.

Edited by Passinwind

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