> the input jacks on the PCB are stereo types
They are physically the same as stereo headphone jacks, but they are used (mis-used?) here as "Balanced". This is a "professional" amplifier, the amp-rack might be hundreds of feet from the mixer, so balanced interconnects are favored. Whether the Koss-type "stereo jack" should be used as mono-balanced is debatable. The 3-contact jack actually originates in telephone switchboards, where it was mono-balanced; though no telephone company used this exact jack-plug but an expensive form of similar dimensions.
Yes, the "U" switch position is clearly intended to take two unbalanced 1/4" plugs as a 2-channel amplifier (which can be a stereo application).
They are physically the same as stereo headphone jacks, but they are used (mis-used?) here as "Balanced". This is a "professional" amplifier, the amp-rack might be hundreds of feet from the mixer, so balanced interconnects are favored. Whether the Koss-type "stereo jack" should be used as mono-balanced is debatable. The 3-contact jack actually originates in telephone switchboards, where it was mono-balanced; though no telephone company used this exact jack-plug but an expensive form of similar dimensions.
Yes, the "U" switch position is clearly intended to take two unbalanced 1/4" plugs as a 2-channel amplifier (which can be a stereo application).
In the 70´s and early 80´s it was popular to use stereo jacks as balanced microphone inputs.
From my point of view, it should have stayed that way: cheap universally available connector, works well with unbalanced inputs without need of switching or anything (the mono plug body automatically grounds the "-" input), inexpensive, takes little front panel space ... what´s not to like?
But the general public thought "XLR is Pro, 1/4" plug is Amateur" and everybody and his brother started using XLR needlessly.
Because when in a Club situation microphone is 10/12 meters away from the box mixer, you don´t *really* need full balanced signal, being low impedance is good enough.
But much worse, XLR input was often FAKE (happens even today), simply grounding pin 3 and using pin 2 as Hot ... with a few such as Yamaha doing the opposite .
Either one "works" if fed from a true balanced system or a Fake one which is wired the same way.
So that 80's HH Electronics amplifier, a high quality Pro amplifier, used the then common "Stereo Jack Balanced input", no big deal.
They even added a selector switch to optimize it, instead of relying on the use of Mono or Stereo plugs to "switch mode".
But now even small Acoustic Guitar or Keyboard combos, meant to be used 2 meters away from performer, are forcd to include XLR inputs ... the "new normal" even if unneeded.
From my point of view, it should have stayed that way: cheap universally available connector, works well with unbalanced inputs without need of switching or anything (the mono plug body automatically grounds the "-" input), inexpensive, takes little front panel space ... what´s not to like?
But the general public thought "XLR is Pro, 1/4" plug is Amateur" and everybody and his brother started using XLR needlessly.
Because when in a Club situation microphone is 10/12 meters away from the box mixer, you don´t *really* need full balanced signal, being low impedance is good enough.
But much worse, XLR input was often FAKE (happens even today), simply grounding pin 3 and using pin 2 as Hot ... with a few such as Yamaha doing the opposite .
Either one "works" if fed from a true balanced system or a Fake one which is wired the same way.
So that 80's HH Electronics amplifier, a high quality Pro amplifier, used the then common "Stereo Jack Balanced input", no big deal.
They even added a selector switch to optimize it, instead of relying on the use of Mono or Stereo plugs to "switch mode".
But now even small Acoustic Guitar or Keyboard combos, meant to be used 2 meters away from performer, are forcd to include XLR inputs ... the "new normal" even if unneeded.
I have an HH IC100S on the bench, it's been got at with wires cut . I looked at the mains switch which is just a a SP/ST SW with a neon inside, the SW has three tags, mains in/out and a nuetral for the neon. The SW is a very cheap and nasty job and the neon had blown, if yours is the same or similar could it be the cause of the BR shorting?
Andy.
Andy.
Thanks for all the replies, Andy (didn't know you were a member of diyaudio.com), Fahey and PRR. I was broadly aware of the way the circuits work, and how the jacks in the 150 are wired. Since my post I've set the amp up with two mono Jack plug to RCA Leads, and get very good results from CD's played on a rather old Bush DVD/CD Player, and, though I haven't as yet performed sensitivity and Frequency response tests, my ears tell me that the HH Amp. is working very well. As to the on/off switch, it is indeed one of those rocker types with a red plastic lens and built in neon. What had happened in this case was that one pole of the D.P. switch had failed O/C, which may have been what caused the demise of the rectifier, thus blowing the secondary fuses. So far, the amp. has been playing, albeit mostly at normal listening levels (I'd get complaints from the people in the shop above my w/s if I played it at high volume for any length of time!) for 2 or 3 hours continuously with no sign of repeated problems, so I consider it a 'job done' The owners-a local studio-tell me they have another VX-150 with a failed switch, so it may also have a dud rectifier and blown fuses. IMHO a weak point in these otherwise good amplifiers is the small slide switches used on the i/p PCB, which can suffer from the usual intermittent problems, but I guess after maybe 25 years use that's only to be expected.
I have HH electronics 150W performer from March 1981 and not working.
Need schematic for this guitar amp.
Need schematic for this guitar amp.
They DO offer one, but you have to register to download:
https://www.hifiengine.com/hfe_downloads/index.php?hh_electronic/hh_electronic_vx150_schematic.pdf
https://www.hifiengine.com/hfe_downloads/index.php?hh_electronic/hh_electronic_vx150_schematic.pdf
