Making a line out box to use on a valve amp

[umph]

[quote name='Christophano' post='1072756' date='Dec 30 2010, 02:29 PM']Interesting stuff bheys.

After considering the comments, I have started ordering bits to make a Firezog Line out box. It will incorporate a switch to shut the speaker off and a 100w 8ohm dummy load so I don't fry the thing!

I'm not in to spending loads of money of stuff if I could actually make cheaper while learning about it.

Will post up if/when I get it working![/quote]

make sure you had an adaquet heat sink for the dummy load a 100W resistor is only rated at about 25watts without a heatsink and fan

[Christophano]

In the pictures, they look like they have big heatsinks.... I will of course make sure they are decent enough... I don't want things cooking!

[Bill Fitzmaurice]

[quote name='Christophano' post='1073036' date='Dec 30 2010, 02:26 PM']In the pictures, they look like they have big heatsinks.... I will of course make sure they are decent enough... I don't want things cooking![/quote]
Dummy loads don't give the same result as speakers, because speakers are complex reactive loads, not resistive.

[Christophano]

But the dummy load should manage to stop my amp from being damaged surely? Unless the internet has fooled me....

[Bill Fitzmaurice]

[quote name='Christophano' post='1073206' date='Dec 30 2010, 05:03 PM']But the dummy load should manage to stop my amp from being damaged surely? Unless the internet has fooled me....[/quote]
Tube amp? They don't like higher impedance loads than the tap is rated for, and aren't bothered by lower impedance loads. Most come with output jacks that short the transformer with no load. But I thought this was a direct out? Why run with the speakers disconnected? For silent recording run your bass into the board.

[Phil Starr]

Your amp should be safe enough but I too don't really understand the thinking behind running silently. On-stage you need to hear yourself and when recording you need a good clean feed which you can more easily shape after you've recorded, unless you want the sound coming from the amp, in which case you need to mic' up the speakers.

One problem with dummy loads is you can't hear if anything goes wrong, normally if you get any strange noises or high levels of overload distortion from an amp you turn it off/down pronto to save damage. you won't be able to do this if you can't hear.

[Christophano]

Sounds like I haven't explained what I actually want to use it for.

I want to be able to run an AB type set up with my current head and cabs. The switch was so that I could silence the speaker, in order for me to run the amp fairly hot in to the effects loop in on the head. I would run an AB pedal in order to utilize the sound like I would with a normal pedal. It wasn't really for recording, just to have some variation with the sound I can chuck out.

In essence, I would be treating the amp like a pedal.

Shoot me down if this is a stupid idea.

[Bill Fitzmaurice]

[quote name='Christophano' post='1073629' date='Dec 31 2010, 07:34 AM']In essence, I would be treating the amp like a pedal.

Shoot me down if this is a stupid idea.[/quote]
A forty pound pedal does seem over the top.

[Christophano]

Well, it will be sitting next to my big rig at our studio, like it always does. I just thought I would try and incorporate it in to my rig and sound and it sounds sweet cranked up, just not loud enough. Not saying I will be trucking it to gigs or anything. If it works, it works, if it doesn't I will take it home and use it as a practice amp.

Just looked you up, Bill. You make some very sweet looking stuff!

[Beer of the Bass]

On the subject of post power amp DIs, does anyone feel there's much benefit of this approach over taking a line out after the preamp if the amp is being played pretty much clean? I'm considering building a box using this schematic to use in between my head (a 100 watt Carlsbro) and speaker. This would be used when PA reinforcement is required, or possibly for recording if I like the sound.
Though I could also use a standard DI box from the echo send (preamp out) of my amp.

[umph]

[quote name='Beer of the Bass' post='1075750' date='Jan 2 2011, 09:22 PM']On the subject of post power amp DIs, does anyone feel there's much benefit of this approach over taking a line out after the preamp if the amp is being played pretty much clean? I'm considering building a box using this schematic to use in between my head (a 100 watt Carlsbro) and speaker. This would be used when PA reinforcement is required, or possibly for recording if I like the sound.
Though I could also use a standard DI box from the echo send (preamp out) of my amp.[/quote]

the big power amp valves add nice harmonics and distortion and i like the way pentodes compress things to, also have to take distortion added by the transformer and frequency limiting into account to. Whether you'll be able to hear much difference though is anyones guess since they're all very minimal

[AlX]

I guess you are looking for one of these.
[url="http://www.suhrguitars.com/tonetools.aspx#lineOut"]http://www.suhrguitars.com/tonetools.aspx#lineOut[/url]



What it is:

The ISO Line Out box is used to provide a transformer-isolated signal from any guitar amplifier speaker ouput jack. One common purpose is to provide a line level signal that feeds an effect processor. The wet only output of the effect can feed another amps effect loop return or power amp with speakers to have a Dry/Wet setup or even Wet/Dry/Wet.

What it is NOT:

The ISO Line Out box is NOT a load box. In other words, the amplifier MUST have a speaker connected at all times. The ISO Line Out box is not a speaker cabinet emulator.

Operation:

Connect any available speaker output jack to one of the Speaker Thru jacks on the ISO Line Out box. If the amp has only one speaker output jack, connect this to one of the Speaker Thru jacks on the ISO Line Out box and plug the speaker into the other Speaker Thru jack. Connect the Line Out jack to a balanced or unbalanced jack of your mixer, effect or recording device. Set the appropriate level.

Line Out:

The Line Out jack is wired for balanced or unbalanced connections. The transformer is wired to the tip and ring connections of the jack. The cable shield is floated and can be referenced to the box ground ONLY when a balanced cable is used.

Phase Switch:

The phase switch is used to invert the phase of the signal. Set the switch in the up position to invert the phase, down for normal phase.

GND Ref Switch:

The ground reference switch can be used to reference the box ground to the Line Out cable ground. This should ONLY be used with the use of a balanced cable. For mono cables, leave this switch in the down position.