Anyone have 'stereo blend' control experience?

My long gone Dynaco PAT4 preamp had stereo blend but I can't remember exactly what it was for. Maybe for their three speaker with center channel application that was supposedly specially suited to the Dynaco A-25 speakers. Whenever I used it in two channel I had the eerie feeling it was neither stereo nor mono and that made it seem strange. It wasn't progressive, just on or off. I'll betcha somebody has the circuit diagram for a PAT4 and the directions for building one underneath a pile of old stereo reviews. Good luck in your search.

The PAS 3x blend control was especially handy when listening over headphones.

Bob P.

Hi Zaik
Stereo blend is commonplace in radio reception even today; basically the high frequencies are progressively blended as signal to noise ratio deteriorates. This is easily accomplished via the switching of progressively larger sizes of audio blending capacitance across left + right channels. The larger the cap, the lower the audio frequencies that are blended.
You can probably fabricate an add-on switchbox connected via a tape loop to accomplish this. Use decent quality cabling, capacitors, & hardware of course. If you want to actively buffer the signals for isolation & a better impedance match, vs. taking a minimalist passive approach, then use at least high quality low noise j-fet op-amps if not good discrete circuitry. A sophisticated power supply is also recommended if going active. I'd suggest trying the passive approach initially just to see/hear how it works out.

Thanks for the tips so far. This request is for playback of material such as Viridian mentions - early stereo recordings which suffer from hard left/right panning techniques. Although mono-ing the signal can work, it often results in some frequency cancellation, and preserving a part of the stereo effect would be nice to achieve. Bob P. is correct about the severity of the situation when using headphones especially. It's interesting the Dyna stuff seems to have featured fixed postition switching instead of continuous variability. The tuner version of this idea that Bob B. mentions is supposed to not change the stereo soundstage, and so wouldn't be what I am after here, but it might have something to do with the impetus for the Dyna control, if it dates from the era of the advent of FM stereo.

Don't know much about the older equipment, but stereo width controls are common in modern digital processors. Take a look at t.c. electronic Finalizer or the Drawmer 2496. Hi-end digital reverbs (Lexicon & t.c. electronics) also have this feature. A frequent use is to fatten up mono synthesizer patches.