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800C Volume Pot problem.

It's not butchering, but a slight mod that when the proper part is found in great
condition everything can be put back the way it was before, but right now I'm
enjoying the great channel balance and separation that comes with the Alps Blue
Velvet pot brings.

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for those of you who installed the alps pot, are there pictures of that somewhere? and what did you for a power switch? I know one person put a power switch where the headphone jack was. but what other options are there? an external one maybe?
 
keithpgdrb said:
for those of you who installed the alps pot, are there pictures of that somewhere? and what did you for a power switch? I know one person put a power switch where the headphone jack was. but what other options are there? an external one maybe?
Click to expand...

I guess you could put a switch directly on the electrical cord (lamp style) or wire the amp always on and power it via a powerbar.
 
I took out one of the plugs on the back of the amp and left the original wiring in,
that goes from the rear to the front, it work out very well. I also left in the loudness
circuit as well, but the switch is dead, does nothing just for cosmetic reasons.

Tube
 
If you are disabling the loudness switch anyway (I wanted to keep the control) you could use it as the on/off switch position. Although you could mod the loudness switch to serve as the on/off switch I would strongly suggest putting in a 120VAC rated switch for safety.

Here are some old pictures of my switch and Alps mod. I am currently modding it again to improve the loudness section. My Khorns require a good loudness control for listening at low levels, the only major drawback of the highly sensitive horns IMHO.

Note that I have shielded the switch with a lamp socket base and that the cable is also shielded. The switch is right there with very low level audio and without proper shielding would pump 60hz hum into the signal.

My current design has me looking for a tone control with knobs. Anyone got one?
 

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Found a solution for those of you who are interested. I wrote Mark Oppat at Antique Audio about the volume/on/off switch. here is his response.

"I can either fix or make a new control for your set. Price is same either way... about $50 + $3 postage. Send it in a small box with all you contact info and a check. Turn around is usually a week or two.
Mark Oppat
Antique Audio
253 Blanche St
Plymouth, MI. 48170 USA
www.oldradioparts.net
734-20-RADIO 11am-8pm EST"

Price is about the same as you would find if you got a part on ebay from a donor unit. but basically brand new. I like that he can just make a new control if you want, switch and all. I need to make sure that may switch is bad this week. if I find that it is, I'll just get one from Mark. It would need to be done at some point anyway. No point in restoring it half assed. I think he's the only one who does this, that I've found.

Check out his site as well. its small, but some good things for old equipment.
 
Please let me know what you think. I refer to the pins by the numbers I placed on them. :yes: Because I'm embarrassed to say I dont know which side is left and right.

The unit was NOT powered on, volume was set to 12:00, balance set to center (12:00)

I placed a probe on pin #2 and recorded the measurements on pins 1 and 3. Numbers with "L" in front of them mean that it was measured again with the loudness switch on.

Pin 1 62.8 kohm L136 kohm
Pin 3 145 kohm L167 kohm

probe clip on Pin #5. measured pins 4 and 6
Pin 4 75.3 kohm L146
Pin 6 153.8 kohm L175

Measured from pin #1 to #3
136 kohm L151 kohm

Measured from pin #4 to #6
140 kohm L154

I'm honestly not sure what I should be seeing here. what do these numbers mean to you guys?

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You can use the headphone jack and your soundcard to check the volume control linearity (and a bunch of other stuff) on the 500c. Much more accurate than the voltmeter.

Get the RMAA free software: http://audio.rightmark.org/download.shtml

Install the software and set it up for your soundcard using a loopback from the line out to line in. This will usually be a 1/8" to 1/8" stereo cable.

After you are sure you have it set up correctly hook up your Fisher. Be forewarned the original Fisher power cable can be flipped and zap your soundcard. This is due to the computers power supply ground reference not liking the hot chassis ground when plugged in backwards. If your soundcard does not work unplug it from the Fisher, flip the Fisher power plug and give a minute or two to settle and try it again.

Use the headphone jack for the output. I use a 1/4" to 1/8" adapter and the cable used above for the input. For the soundcard output I use a 1/8" to RCA cable and input to the AUX input. Turn the volume down on the Fisher, turn it on and let it warm up.

In this case we are only interested in the test signal screen. You would have already seen it in the loopback setup procedure. Start cranking up the volume control. I usually turn off the speakers since the test tone is so obnoxious. The headphone output has load resistors so this is permissible.

The test signal screen has both numeric and graphic indicators for each channel. I usually watch the db numeric indicator as I turn the volume up. Be prepared for a surprise. Most of vintage units with this switch arrangement are out 6db or more at low volume.
 
Wow. That's pretty seriously involved. I don't have a laptop as of yet to attempt this test either. Do my numbers not really tell us anything? Did I at least measure correctly?
 
sigh.. another strike against me. I'm using an older mac. the hardware and system are not compatible with that program. when I get my new laptop in the next month or so, I can do it, but until then....
 
You could try Audacity. Just feed your heaphone jack to the input of your soundcard and watch the meters in the software.
 
ok, audacity I have. I've never input any audio into my computer outside of a program. I have to find that input. its probably not a standard mini rca. I'll look into it.
 
Would you believe my mac does not have an analog audio in!? unreal. Seriously, I'm not trying to fail here. looks like I may be stuck interpreting the numbers.
 
keithpgdrb said:
Would you believe my mac does not have an analog audio in!? unreal. Seriously, I'm not trying to fail here. looks like I may be stuck interpreting the numbers.
Click to expand...

So it is quite old I guess... Even the colored IMacs had line in jacks.

What's the particular model of your Mac?
 
Patrice B said:
So it is quite old I guess... Even the colored IMacs had line in jacks.

What's the particular model of your Mac?
Click to expand...

It's a g4 powermac tower (quicksilver 2002). Would you believe it did t even seem to be slowing down until about 2 years ago. It's still going strong, but the processor just can't keep up with the new opeating systems. All the ram is maxed out. It is going to be a dedicated music machine when I get a new one. Seriously don't think it will die. Very well built machine.

Anyway, back to the point. I read that they left the input off of these machines. And they did. No mic plug. All USB if you want an input I guess.
 
drewbolce said:
There are several equivalent (free) programs available fot the mac, here is one that should get the job done:

http://www.voxengo.com/product/span/
Click to expand...

my wife agreed to let me use her pc laptop for the test. I tried to download the first program, and it fails while installing every time. I tried to get voxengo, but the download is an extension that you add to another program. what program is that?

EDIT: looks like i successfully installed the previous version of the rightmark program. I'll be back.. we'll see if I can make it work.
 
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