Speaker or cab sim?

[bancika]

Hi,
I'm not sure what I need speaker or cab sim, but I need something for recording on PC directly into soundcard from tube amp
What DIY project would you recommend?
Thanks

[d95err]

What kind of recording software are you using? If you're using a VST-compatible host, check out the free plugin MDA-Combo (www.mda-vst.com  download the free plugin pack).

For hardware solutions, the ROG Condor is supposed to be very good. (haven't built it yet but I've got an etched card ready to solder...). It's designed for guitar level signals thogh, so I don't know if it can handle the line level signal from the amp.

[bancika]

I know about condor, that's my I asked. Not sure how will it work with amp speaker-out levels.
What about adding resistor on it's input that will lower input level?
Any projects intended for amp->sound card use?

[d95err]

You could simply build the Condor and see if it works with the amp line out. If it distorts too much, increasing the voltage should give more headroom.
Looking at the schematic, it looks like you could increase the voltage without having to change anything in the circuit (exept for re-adjusting the trimpot for the transistor bias). You could try 12V, 15V or even higher...

(I'm sure you already know this, but just in case... The speaker signal cannot be used for direct recording (it could destroy the Condor, amp AND PC); you must have a line out jack. If you use a line out from a tube amp, you also need to have a speaker or dummy load connected, or you will blow the output transformer)

[bancika]

The thing is, I don't have line out on my Firefly amp, and there's no space on back (or front panel) for it. I looked at firezog schematics (Doug H line-out mod for firefly) and Lineout is basically 1M level pot with 150K resistor in series, wouldn't it be the same to add pot and resistor to Condor in front of original circuit?
Thanks!

[d95err]

The thing is, I don't have line out on my Firefly amp, and there's no space on back (or front panel) for it. I looked at firezog schematics (Doug H line-out mod for firefly) and Lineout is basically 1M level pot with 150K resistor in series, wouldn't it be the same to add pot and resistor to Condor in front of original circuit?
Thanks!

I wold keep the line-out part in a separate box. I wouldn't feel safe pluggin a speaker signal into a small signal device.

Build a simple box with speaker in, speaker out, line out and a line out volume pot. You could even add a dummy load (e.g. an 8 ohm 5W resistor) with a switching speaker out jack, so the dummy load is automatically connected when you unplug the speaker.

The advantage of doing this is that there would be plenty of room to improve and experiment on the line out. I've found that using an amp line out into a soundcard often results in a lot of ground loop hum. For best results, you should have a transformer isolated line out.

I'm building a 15W tube amp and I will experiment with various line out solutions. Right now I'm looking at building something like the opamp splitter at geofex, using only the isolated output. I'll use a fixed line out (i.e. two fixed resistors instead of a pot) followed by the opamp circuit.
http://www.geofex.com/FX_images/oaspltr.gif

If that doesn't work, I'll get an audio transformer to isolate the line out.

[ildar]

I've got a Weber Headphone Tap, a combination 50w dummy load/headphone out/line out. I use the line out for recording.
My concern about the last post by d95err is that if you build a dummy load/line out box, the wattage rating on the 8ohm resistor should be equal to or exceed the power rating of the amp, especially if you plan on diming the amp.
A hundred watt signal into a 5 watt load? Do the math.

[Eb7+9]

Any projects intended for amp->sound card use?

here's a circuit I've used going straight into a ADC (Zin ~10k typ) feeding off the speaker ... you can use it on delay pedals and also with small SE amps going into bigger slaves with awesome results ...

http://www.lynx.net/~jc/pedalsAmpLineOut.html

it's a good idea to keep the pot resistance low - this helps keep noise down on the line between the pedal and your card ... other advantage to using low pot resistance is you can stick an isolation transformer at the output (to elliminate a ground loop problem) and keep the circuit variable ... you can also stick a scaled down RCA shunting  tone stack where the mute switch lies ...

[bancika]

Well, my Firefly is just about 1.5W so 5W resistor works just fine I installed one on switching speaker jack, just in case.
About other thing, I'll read it, thanks!

[d95err]

My concern about the last post by d95err is that if you build a dummy load/line out box, the wattage rating on the 8ohm resistor should be equal to or exceed the power rating of the amp, especially if you plan on diming the amp.
A hundred watt signal into a 5 watt load? Do the math.

As bancika pointed out, I was referring to the Firefly which puts out 1-1.5W. So what I really meant to say is that a dummy load should preferably be several times the rated power of the amp. Tube amp power is rated at the point where it starts clipping. Since that's usually where the fun begins, you want to push them a lot more. In fact, that's the main reason to use an attenuator or dummy load. This will produce more power than the rated value (AFAIK).

[Doug_H]

Actually, the Firefly puts out about 1/2 W clean. Someone over at the ax84 forum is building a line-out in a separate box right now. You might check around over there for ideas on how to do it.

Doug