... the only difference between men and boys
is the price of their toys ...
back in the day
Our first piece of test gear was a moving coil VOM acquired about age 12. Next a digital hand held VOM. Sometime in the 70's a Heath 4550 10MHz Dual Channel Oscilloscope was built. Over time, the collection kept growing with meters, signal generators, LCR meters, etc. Techcron IMD Analyzer, Leader portable scope, HP 330x Analog Test Sets, Philips DSO @ ≈$20,000, Audio Precision Portable One...
Upon retirement, we gave away what remainded. We were DONE!
if only Mum had intervened when I rebuilt the telephone... at age 7!
new tinker toys
LOTO Instruments makes a nice range of PC based DSO. The OSC802, complete with probes, is around $100. It includes FFT, Trace Math, Recorder, etc. Software is continually improved with new features, bugs are fixed timely and the company is responsive to suggestions and comments. Well recommended.
Casting about for a distortion set, the LongWei TDM-1911 seemed to have possibilities. It's a Chinese rip of a Leader and under $200. Like a lot of Chinese product, it's sow's ear in a silk purse. As can be seen in the first image, it capable of impressive performance,
accurately measuring the 0.002% distortion of the
superb AkitikA 2PPM Sine Generator.
the Pudding
The Solo, at left, has steadily increasing noise that peaks around 100kHz. Good Enough for the task at hand.
Modified amplifier has slightly lower THD and much less 60Hz in the noise floor. IMD is rather more than expected.
stock 16Ω feedback 1kHz THD
Neither before nor after modification do the amps come anywhere near close to claimed distortion specifications.
AkitikA source THD+N @ 1kHz: 0.002% @ 1V, 0.003% @ 100mV.
modified 8Ω feedback 1kHz THD
the Icing
Schematic, Parts List, CAD chassis layout.
Interior images
PCB available.
Contact for more info.
The design can be modified to use any desired sockets or add a 'patch' bay for almost any tube socket...
...but that's a YoYo: You're on your own