Hello everyone,
I have a Crate GFX-212T (120W) combo amplifier that I would like to run into headphones to practice with.
The Crate combo amp is spec'd to drive a 4Ω load and does in fact drive two 8Ω speakers in parallel. There is an external speaker output per the attached manual and schematic that is wired in series. Essentially, I would like to disconnect the speakers and use the external speaker output signal through a cabinet simulator circuit with a headphone output. The headphones I have are 47Ω.
The cabinet simulator circuit I was looking at building is the "With headphone output" version located at the following address:
Speaker simulator based on Marshall JMP1
If I want to use the external speaker jack on the Crate amp while also bypassing/disconnecting the internal speakers, I would have potentially 120W at 4Ω at the external speaker output. To what level and how can I knock the power level down so it could safely feed into the cabinet simulator circuit at the link above, with also not damaging the amplifier (if it even would damage it)? Would it be wiser to put a resistive load in place of the internal speakers and something else to decrease the signal before heading into a cabinet simulator circuit?
I will probably have follow-up questions as I'm new to DIYaudio, and also thank you in advance for the advice. It is much appreciated.
I have a Crate GFX-212T (120W) combo amplifier that I would like to run into headphones to practice with.
The Crate combo amp is spec'd to drive a 4Ω load and does in fact drive two 8Ω speakers in parallel. There is an external speaker output per the attached manual and schematic that is wired in series. Essentially, I would like to disconnect the speakers and use the external speaker output signal through a cabinet simulator circuit with a headphone output. The headphones I have are 47Ω.
The cabinet simulator circuit I was looking at building is the "With headphone output" version located at the following address:
Speaker simulator based on Marshall JMP1
If I want to use the external speaker jack on the Crate amp while also bypassing/disconnecting the internal speakers, I would have potentially 120W at 4Ω at the external speaker output. To what level and how can I knock the power level down so it could safely feed into the cabinet simulator circuit at the link above, with also not damaging the amplifier (if it even would damage it)? Would it be wiser to put a resistive load in place of the internal speakers and something else to decrease the signal before heading into a cabinet simulator circuit?
I will probably have follow-up questions as I'm new to DIYaudio, and also thank you in advance for the advice. It is much appreciated.
The power amp will be quite happy without a load.
Can you conveniently disconnect the speaker so it won't speak?
The ~~28V coming out of the amp can be conveniently cut-down with a 2.2k 1/2W resistor feeding about 100 ohms to ground. Output across the small resistor. Vary this from 220 to 22r to get a good signal level.
Can you conveniently disconnect the speaker so it won't speak?
The ~~28V coming out of the amp can be conveniently cut-down with a 2.2k 1/2W resistor feeding about 100 ohms to ground. Output across the small resistor. Vary this from 220 to 22r to get a good signal level.
An amplifier doesn't put out watts by itself. Your 120 watt amp won't put 120 watts into a1k resistor for example. The power is drawn by a load. That is why your amp puts out 120 watts into 4 ohms and only 60 watts into 8 ohms, and 30 watts into 16 ohms. (cloze enough) The amp puts out a voltage and the load impedance determines the current, and thus the watts.
Just an opinion, but if it were mine, I would plug into the INSERT jack and use that signal to feed my simulator. That is a TRS jack, and the RING contact is the preamp out. SO I'd wire up a TRS plug with the hot to RING, and the TIP left unconnected. Or maybe ground the tip. The other end of this special cable would be wired to suit your simulator, whatever kind of jack it will have.
Plug into the INSERT and it disconnects the power amp input. And that silences the speakers. The power amp is not adding much to the tone.
Just an opinion, but if it were mine, I would plug into the INSERT jack and use that signal to feed my simulator. That is a TRS jack, and the RING contact is the preamp out. SO I'd wire up a TRS plug with the hot to RING, and the TIP left unconnected. Or maybe ground the tip. The other end of this special cable would be wired to suit your simulator, whatever kind of jack it will have.
Plug into the INSERT and it disconnects the power amp input. And that silences the speakers. The power amp is not adding much to the tone.