Amplifiers: Tubes vs Transistors

By: Dirk Schubert

Ever wonder what your system would sound like running on tube amps, but don’t want to buy them and go through ‘all that? Here’s an easy way to get 90+% of the sound of a tube amp from a transistor amp.

A little background- beyond the differences in topology and feedback the biggest difference is the output impedance. A (good) tube amp is 1 to 2ohms output impedance. A transistor amp strives to be zero ohms output impedance and gets pretty close. So add a 2ohm high power resistor in series with your speakers and take a listen. The least expensive way to do this is to get 4- 8ohm 10watt resistors and put them in parallel, creating a 2ohm 40watt resistor. The whole concept viewed with a longer lens reveals that transistor amps will double their output when the load is reduced from 8ohms to 4ohms. A tube amp that’s rated for 100watts (for example) will put out the same hundred watts at 4,8 or often 16 ohms.

A real-world example from the past -

In the ’80s and ’90s when we ran proprietary systems, we added a DC blocking capacitor AND a 2ohm resistor in series with our JBL drivers, and I was often told that our JBL drivers sounded a lot like TAD drivers. TAD drivers had beryllium diaphragms. Beryllium has a much higher modulus (stiffness) than aluminum or titanium, so the resonances and rising impedance were more constant than other brands.