Voice of Music 102, the rest of the story.

Discussions about Voice Of Music (VM) consoles, tube and solid state, stereo and mono.
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William
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Voice of Music 102, the rest of the story.

Post: # 19484Post William »

As Paul Harvey would say, "And now the rest of the story".

While experimenting trying to figure out where the hum came from, I discovered something that I would never have thought could/would be the problem.

To recap, from the get-go both the main unit and the speaker/amp motorboated and sounded bad when hooked together. I triple checked everything I did and really could not find a problem, yet there was a problem. With the speaker/amp disconnected from the main unit, the motorboating stopped, in the main unit, but it still sounded bad and had a slight hum. Playing just the speaker/amp unit by itself, with my RCA 45 player as the input source, I still had the motorboating and sounding bad. I tried switching the 45 player with my KLH FM tuner but still the same problems so I went back to the 45 player. Since the motorboating was gone with the main unit I decided to tackle that unit first as it just had a slight hum and sounded bad. I plugged it in, put on a record, hit reject, and much to my surprise the hum was gone, but it still sounded bad. I'm kind of scratching my head as to why the hum was gone, but I was not complaining. After listening, I decided the 12" woofer was the reason it sounded bad and I just happen to have an exact replacement, so I switched them out and everything was great. No hum, great sound.

Now, the speaker/amp was another story. It still motorboated, hummed, and sounded bad. If you remember, when I touched the amp or the controls with my finger it would change the motorboating. As I experimented, I noticed by wiggling the power wires that went to the on/off switch I could get the motorboating to stop. And if you remember there is a protective cover that goes over the end of the switch that covers the terminals so one would not get a shock. After I removed that cover, the motorboating stopped completely. I still cannot figure out the "WHY" for that either, but I still have the hum and bad sound. My next round of experimenting was to unsolder all the wires that came from amp and inputs, clean all the terminals on the bass, treble, and volume controls, cut the wires back to reveal fresh copper, and then reattach the wires. I also replaced two resistor that were right on the boarder, and I tested the disk capacitors that were there and found one to be weak, so I replaced that too. At the same time, I rechecked all my work in the amp and found everything was still good except one of the 6BQ5 tubes, that originally tested good, was now totally DEAD. No shorts, just DEAD. I replaced that tube and fired it back up again. This time things sounded better, but I still had the hum. Still wanting to figure out the poor sound I went into my overflow room and pulled my Bell mono receiver. It has PP 6BQ5's and a 6CA4 rectifier so kind of equal to the speaker/amp. Still using my 45 player and the same record, I fired everything up and took a listen. Still got the hum, and it still sounds bad. With that experiment done I'm now thinking the amp is not the problem, because it still sounds bad, it's probably the speaker. I'm guessing the previous owner liked things loud and killed both the main unit woofer and the speaker/amp woofer. With this experiment, Bell replacing the VM amp, I'm wondering why I have the same hum in both units. Just so you know, the Bell is all original so I could have a problem with it too. But is that really the case? Is there a common denominator that is the cause. My next experiment answers that question, and there are actually two reasons.

I will cover the bad sound first, and it is the RCA 45 player. As part of my rebuilding of the 45 player I installed a new cartridge that I got from Gary. I have used this player lots of times, but never with a higher end amp like the one in the VM speaker/amp. Up to that point, the 45 player was used with a radio with a phono input or as an input device for another amp I was working on. Once hooked to a good amp, with some frequency range and woofers and tweeters, you could hear all the noise the 45 player makes being pickup in the cartridge and transferred to the speakers. All of this was confirmed once everything was all hooked back up to the main unit.

Now for the hum, and it turns out to be something I would never have guessed. With the Bell receiver and the VM amp and the main unit all having what I figured was the same hum, what's the common denominator. I will give you a hit, what caused the main unit to lose its hum once I took the speaker/amp away. Here's another hint, when I was starting this project, I had the main unit and the speaker/amp in the family room for its initial fire up. After deciding the speaker/amp had lots of issues I separated them and moved the speaker/amp to the shop. Once it was gone, the motorboating and hum in the main unit was gone. Again, there is a common denominator. Something followed the speaker/amp to the shop. Any thoughts??? WAIT FOR IT! It was my Variac contraption causing the hum. Variac out of the picture, no hum. I never in a million years would have ever thought it could be the problem. I have used that Variac lots of times and never noticed it produced a hum, and maybe it did not, this could be something new.

Anyway, now you know the rest of the story and I now have a beautiful sounding VM 570 main unit and a beautiful sounding VM102 speaker amp. Lots of lessons learned with this project, ones that I hope I do not forget.

Bill
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electra225
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Re: Voice of Music 102, the rest of the story.

Post: # 19486Post electra225 »

I know how much trouble you have been having with this record player and how hard you have worked to get it sorted. All the fits and starts and the weird problems you encountered. It feels good to finally get it working right, particularly with how much effort you have put into it. Thanks for sharing your story. You never know who is reading this that your experience might help. ;) :D
A good leader is someone who can tell you where to go, and make you look forward to the trip.

Never allow someone who has done nothing to advise you on anything.
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Re: Voice of Music 102, the rest of the story.

Post: # 19489Post Hi-Fi-Mogul »

Congrats Bill, good detection work.

I had a weird, unknowable problem with a 1950's
RCA consolette with the standard RP-205 changer.

The amp was perfect, speakers were good, but there was
a low hum that I determined only occurred when the platter
was turning.

When the speed selector was in "N" neutral position,
and motor turning, no hum.

So, I looked at the spindle mech, platter bearings,
et cetera, and nothing was amiss.

I had a spare platter that I thought I'd put on the changer,
in case the other platter had a micro-burr or whatever on
the platter drive spindle.

Wow ! No hum with the substitute platter.

I looked at both platters side by side, placed on their
mat sides.

The difference was the original platter's painted inside rim
was devoid of paint, exposing the steel of the platter.

I was skeptical, so I tried that platter in another RCA
RP-205, and yup, there was the hum again.

Some kind of elelctro-mysterio coupling of sumpin'
apparently was going on.

You never know WHAT'S gonna try to stump you.
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William
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Re: Voice of Music 102, the rest of the story.

Post: # 19492Post William »

Thanks for sharing, Mr. Mogul, that was a stumper too but with perseverance you figured it out. This was my second, lets scratch the head trying to figure it out unit. The first was my Magnavox Imperial. :roll: :)

Bill
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Re: Voice of Music 102, the rest of the story.

Post: # 19496Post hermitcrab »

Nice looking set... Troubleshooting a hum can make you pull your hair out....The maggie imperial I have has a background hum that drove me nuts , until I found out it was the step Bass control...one of the couplets has a bad component causing the hum ... if you turn the bass all the way up it disappears :roll: Never heard of a variac causing a hum before... Good catch Bill!
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