• chaddavidkelly

Re-Visiting the Re-Amp

Special thanks to Glenn Fricker from SpectreMediaGroup

for sending us this shot. So, it's time to talk about re-amping a little bit...

There's a reason I never really talked about the re-amp box on the Signal Art pages until now, and that's because the box was never really quite right, I guess. I can now say with confidence that I think it is. Although I mainly work on microphones these days, I do have a long history of making little problem solving boxes, from splitters to DI's to saturation boxes, inline pads, bal to unbal interfaces and vice versa, and of course Re-Amps. I also make boutique cables, going back over 20 years.

Back at the beginning of last year, I met up briefly with Glenn Fricker who runs the SpectreSoundStudios media group on Youtube, which covers an incredibly wide array of audio production and gear issues, centered mainly on the challenges of Metal production. It's one of only two channels I subscribe to, the other being the science channel 'Answers With Joe', if that tells you anything. I watch these while I work. I mentioned to Glenn that I'd love to send him my re-amp design, which I've been making for over 15 years in various incarnations (about 5 different versions over the years, including a really budget transformerless one, one with an inductor 'warmth' switch, one with fixed attenuation (no pots), and so on... I finally settled on a good design that used an available Cinemag transformer to unbalance the signal and a pot to provide attenuation, the design became simpler and simpler over the years and eventually removed a resistor network and a loading resistor from the inside because I found it unnecessary. This also opened up a little more gain. I originally made it to track almost identically to the original John Cuniberti Re-Amp(tm), which i used to own and loved, despite a few issues. I had one actually made by the original company, long before the sale to Radial Engineering. While I loved it, I did feel it restricted bandwidth in a slight but audible way. Even though it delivered a really tight focused midrange (guitar-range), I worried it might shave off some bottom if I were to re-amp bass or pinch the sound if I were to re-amp snare or kick drum or voice (yes, those are real techniques). It also had an output out of phase from the input, requiring me to make a special patch cable. I was told they all did that. This may be something Radial fixed, or preserved; I don't know. It always had enough gain for me, but not for others; and I often saw people using it in conjunction with a 10db 'boost' pedal like the Radial HotShot or others. So when Glenn told me mine also did not have sufficient gain; my first instinct (wrongly) was to deny this... but ultimately had to concede he was right. Plus, there's certainly no harm in just making sure the box has plenty enough gain to be robust in any situation.

I initially actually thought about using a discrete op-amp or some other type of buffer circuit in there to make up the difference; and Cinemag even offered to share a circuit they preferred that would work; but I was hesitant to do this. From a technical standpoint, I 'knew' there was sufficient energy in a +4 balanced line level signal coming out of an interface to give someone a high impedance unbalanced instrument level (-30 or so) signal without the need for more electronics and dreaded batteries or wall-warts. And that would do nothing to help THD or noise, for damn sure; at best it would minimally add to those things. So I worked with Cinemag to come up with a 1:2 ratio version of the line isolation transformer I loved, ensuring the box would have nearly 200% potential output from its input in most situations. The attenuation pot gives you a very smooth logarithmic range from unity (200% gain) to essentially off, and everything inbetween. It still has the same good ground isolation as my original design, with the ground being truly isolated with the lift switch engaged. The reason this is important is because in a studio setting, the amp and the source signal may very often be in different rooms and on different circuits!... ground loops can and will happen, and when they do, you flip that switch.

I was pleased this week to have Glenn finally give his thumbs up on the new design, and I thank him for 'kicking my butt' to fix the design. Now, I can finally start making these things as a production model, after 15+ years of my procrastination... lol

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