In yesterday's post we had finally discovered a magical transistor family that would soon become the standard devices in all our products. The Motorola MPS 8099/8599. This low cost transistor was designed primarily as a lamp driver—turning brighter and dimmer lamps of equipment.
We weren't making lamps. We were designing state of the art preamps and phono stages and this device was not recommended for such designs.
At the time, this was the only device made that fulfilled all our requirements for building low noise, low distortion, high-slew rate preamplifiers and phono preamplifiers. Turns out the major drawback to the device (and why it was not recommended) was its occasional tendency to exhibit what we call 1/f noise (an unacceptable, bumpy low frequency sputtering noise). This required us to hand select these devices, rejecting perhaps 20% of any batch.
Small penalty to pay for such a glorious device.
Products like the venerable PS IV, PS IVH, and PS V preamplifiers were all built using dozens upon dozens of these little gems. Low noise, high voltage, high speed, low distortion products were not that hard to design with this terrific little transistor.
So, when it came time for me to design our new Moving Coil Amplifier, I figured it'd be a snap. Using a pretty cool circuit I dreamed up based upon these Motorola transistors, I had a good deal of confidence I'd have a design knocked out in a few weeks—which I did. Gain->perfect. Distortion->a challenge for my HP analyzer. Speed->50kHz. Noise->ugh.
Uh, oh. Remember that 30 times gain we were striving for? Gain we needed to bring the low output of a MC cartridge to that of an MM cartridge? That was easy and it sounded great. Only, that sound had to struggle through the 30 times greater hiss from the amplifier.
*spoiler alert. It would take me another year of research and education to figure out how to eliminate that noise.
We continue tomorrow.
