Here is a little project of mine to build a "last piece of the puzzle" piece of rack gear that I badly needed.
It went very well.
It went very well.
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Topics - Kaz Kylheku
To fill in the vacuum left by the defunct ADA Depot website, I've decided
to start my own mailing list. (Today!)
No BBS crap with animated smileys, no bullshit. Not even a subscription needed
to start a topic. Just send an e-mail to <firstname.lastname@example.org> with your ADA related ideas or questions.
If you want to subscribe, go to the GNU Mailman interface at
http://www.kylheku.com/mp1. Archives will be accessible through that page also.
If interest builds, I will add a file download area (for which no registration will be required).
This is completely non-commercial. You will not see any ad in any web page or
list message footer, unless some third-party spam sneaks through.
Recently I became curious about what exactly the "reactance" control of a Rocktron Velocity 300 does. (I don't have one of these units, thank goodness). According to the marketing spin, it has something to do with speaker interaction. Quote from website:
The Velocity 300 has a unique “Reactance” circuit that actually replicates the output impedance of tube amplifiers—so you can get the same great sound that a tube amplifier delivers in a reliable solid state design. And, because it is a variable control, you can customize your Velocity 300 to sound like any of your favorite tube amps. Best of all, this feature is available in the mono bridged mode too!
If you Google for what users say about the amp, you can see that people are falling for this bullshit.
The old 1990's schematic shows this to be purely a tone control which mixes between two paths through different op-amp filters. There is no possible way it has any effect on output impedance. I'm guessing that it produces various amounts of a "frown curve" EQ.
In the newer amp, there are two tone controls. The schematic reveals these to be an obvious variation on the Baxandall tone control topology, again, purely in the preamp. Bass must be the reactance, and treble is called this:
In addition, the Velocity 300 has “Definition” controls to give you that little bit of edge you need to bring your playing out in the mix.
I suppose that if you hear tube sound when you tweak a pre-amp Baxandall bass knob, you deserve Rocktron equipment and the lies that sell it.
« on: July 19, 2011, 02:26:45 AM »
In the schematic of this amp (easily Google-able), at the very end of the output chain, the output is shunted to ground through a 0.33 ohm resistor R59 in series with a 0.22 uF capacitor.
Is this really just a low pass filter or is something else going on? That cap value seems quite aggressive. Wouldn't this kill the sparkle from the cleans?
« on: July 15, 2011, 02:53:00 PM »
I'm trying to add a damping control pot to my Alesis 100 amp (one channel for now; if it works, then the other channel too).
I have reverse engineered enough of the amp to find the feedback path. The feedback goes through a 39K:1K voltage divider to feed 1/40th of the output stage voltage.
I'm going to rip out the 39K resistor and patch into there. The 39K resistance will be replaced with 100K to reduce the voltage feedback a little bit, so the current feedback is more significant (without having to use a larger current sense resistor that makes more heat!)
I plan to use a 0.22 ohm, 5W current sense resistor, and use a 50K pot.
The schematic is attached. The terminals on the left are where we patch in place of the 39K resistor. The terminals on the right represent where we patch into the speaker return circuit and obtain ground.
Any advice is kindly appreciated.
« on: July 15, 2011, 01:39:50 PM »
can anyone rationalize why in the Alesis RA-100, two parallel 18 gauge hookup wires go from each power amp board to the speaker out terminal, but from the return terminal to ground, there is just one 18 gauge wire (per channel?)