Anyone have 'stereo blend' control experience?

I'm interested in any details anyone may be able to provide concerning 'stereo blend' controls, for progressivly reducing a 2-channel signal down from full separation towards a mono blend, presumably through cross-mixing.

What older equipment might you be familiar with that featured such a contol? Did any incorporate a 'defeat' provision, or was the control always in the circuit? If you ever used one, how well do you remember it working?

Do you have any electrical design knowledge of previous implementations of this idea, or suggestions on how to make one? What kinds of parts were used in any older designs you may have seen? Do you know of any schematics?

I realize this probably was a pretty obscure feature even in its day, but maybe some of you more, ahem, experienced hands out there know what it is I'm talking about. TIA for any info!
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.
Not obscure at all Z man. The Dyna Pas features a four position stereo blend control. I found it useful on older jazz recordings that were mixed with instruments hard left and hard right with a hole in the middle. I better shuttup before mentioning the great Rudy Van Gelder as being guilty of this sin. A lot of early stereo recordings wanted to show off the characteristics of the medum and so there were a lot of weird mixes (as if there aren't today). In the end though I just reach for the mono button; mono listening avoids all of these distractions. Good luck.
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.
I have a Dyna PAT4 as well as an old AR tuner, both of which feature Stereo-Blend swithcable (not variable) controls. This switch on my tuner (which still works perfectly) blends the high frequency signals to mono operation, which can reduce noise on FM fringe reception broadcasting and it does work. On the PAT 4, either the left, right, or both channels may be switched to mono operation. I rarely used these switches except to experiment. There is also a high frequency filter, that variable switches a frequency "roll-off" @ 15 khz, 10 khz, or 7.5 khz. This switch is useful in getting rid of "tape-hiss", noisy records, or any high frequency unwanted noise. I have frequently used the 15 khz roll-off with good results. Hope the helps you. Good Listening.
I guess that Zaik wants to blend the entire freq. spectrum at variable ratio's, not just hi-blend & not pure mono, but somewhere in-between & adjustable. A L/R analog mixer would be needed with control of the amount of L signal emerging from R (R + some left) channel and conversely, control of the amount of R signal emerging from L (L + some right) channel. Anyone aware of a design like that? Perhaps a custom designer such as Andy Bartha could fabricate such a device?
Correct, Bob B., and I'm pretty sure some older preamps or receivers featured such a control, like the Dyna's and AR mentioned. Onhwy61, I'm not looking to digitize anything for this, just to get somewhere in between full stereo and full mono when listening to 60's recordings with unatural panning extremes. Any more citings of gear that had this feature would be great.
The Apt Holman preamp (great 70s gear available on Ebay)has the best stereo blend control I have seen. Complete infinity variable blend/separation of channels. A real eye opener.
Adding to the above.The HK Citation I and IV.Both have a varible blend control.It also controls a center channel speaker if you want.Out of the circuit when not in use.I would also reccomend the IV over the I for a very open smooth sound.The I sounds a bit restricted/compressed.IV has much simpler circuit.They also have a switch to take tone controls out of the circuit.Mono,Chan A and B.Reverse switch also.The IV is a very cool Preamp and has a classic look.Uses 6 12AX7's.
The Crown IC-150 was a top rated pre-amp back in the early 70s. It has a stereo blend control. I had one back then and found the blend control very useful--more blend for small groups or solo performers, less for big orchestras.
I wonder why this feature has disappeared today?
Craig Zastera
CraigZ I completely forgot about the Crown IC150 & yes that was a real nice preamp back in the day. I've even seen one up for sale here not very long ago. Zaik I think you'd like that one.