Stereo Amps and Isolation Transformers

I have an old amp I bought back in the day, a Crate TD50-C I was thinking of donating because it is not worth more than $50 to $100. It has a great clean channel as a Google search will attest to. It occurred to me that I could use it as a stereo amp in my studio. It is solid state so it would be complementary to my little tube amp and provide some interesting stereo effects. I love the tightness of solid state amps as well as the saturation of tube amps. So I connected the right channel of my Rocktron Chameleon to my Blackheart Little Giant and the left channel to my Crate TD50-C and immediately got a nice 60 cycle buzz. Hmm, time for an isolation transformer. When two amps are connected together with a common ground it is very common that one or both of them will start buzzing because of ground loop currents. Being the tight wad that I am and a design engineer at heart, I wanted a way to fix the problem without resorting to buying a “Guitar” box to fix it. Alas the lowly car stereo noise suppressor. These devices are really nothing more than two transformers used to isolate a stereo preamp output and a stereo power amp input in your car. Their bandwidth is more than enough to support guitar frequencies as they are designed for 20hz to 20khz response. I’m sure they get more like 40hz to 15khz or so but this is well over spec for guitar. I knew this would work well with my amps. Off to Ebay, where I purchased a Camis GL-200 stereo auto noise suppressor for $7 including shipping! I cut the circuit board in half on my band saw, soldered two 1/4″ phone jacks to one of the transformers, jammed it all back in the box it came in and voila! A ground isolator was born. I connected it, NO BUZZ, there was a slight expected signal loss due to transformer losses but that was made up by volume and tone adjustments on the Crate. And it sounds great! So for $7 I isolated my two amps. The nearest thing I found on the market is the Radial ToneBone which is a nice box with some features that I did not need in my studio, so I saved about $60. And it works the same way my $7 isolator does. Life is good! I’ll get some pics up soon!

2015-09-20T15:57:11+00:00