Beta Bass

[gbono]

Hello,

I need one of the spider pots for a Beta Bass level control. Does anyone have a spare (used of course) they would like to sell?

THX

[Enzo]

If you find one, great.

When I need a spider pot like those, I make them. I get a plain old vanilla pot and solder stiff wire extensions on the solder tabs. Then those go down to the board. All it needs to do is hold the pot more or less in place until you can get a nut on it.

When I install resistors and caps and such onto circuit boards, I keep the trimmed off excess wire leads in a jar. I then use them for this sort of thing - or for patching over cracked pc board traces or destroyed pads under jacks. The heavier ones like from 2w resistors are perfect for this. Of course you could also just strip an inch or two of solid insuated wire

[gbono]

Beta Bass

Hey Enzo,

Thanks for the reply. I also keep lead trimmings - just can't throw anything out. I think I have a solution. I disassembled the pot and found a suitable shaft from anothet "donor". Seems to work - now to find out why the red/green leds on the front panel don't light up.

THX

[trevorus]

mouser.com has nearly everything!

[Enzo]

Not generally spider pots. In fact not most amplifier pots. The issue is not resistance, it is the mechanical shape of the part. Pots are almost always custom made for the amp OEM.

A 50k pot is easy to find, but one on a spider is not. And even then finding one with the right shaft is even harder. Other than finding the original in someones bin here.

Yes, I often take apart pots and swap shafts. Not all can do that of course, but many are made so you can.

[gbono]

Beta Bass Again

Enzo,

I finally took your advise and "spidered" a plain Jane 100K linear taper pot. worked fine. I had previously rebuilt the pot but the saft length didn't work out correctly.I have the amp up and running, since the problem was related to some very bad solder joints in the -15 regulation circuit. I replaced the BJT and resoldered everything.

I'm getting a differnce in standing (idle) noise between channels A & B. The noise is what I call 1/f or "white/shott" noise. I thinks it is the JFETS or the op-amps in the final drive stage on the A channel. A simple low cost fix since all the components are available from Digikey. Have you seen this problem as well?

THX

george

[Enzo]

Have I seen a noisy channel in a solid state amp? Yes, of course. Is it more likely in one brand over another? No. They all use the same stuff, and a 4558 is no more or less likely to go noisy in one model than in another. Or a JFET, or a bipolar. or, or, or...

Turn the controls up and down. ANy that have an effect on the noise are after the source of the noise. ANy that have no effect are before it. Betwen that and a scope, you ought to be able to isolate the noisy part.

[gbono]

Beta Bass

Sure, solid state devices are going to be a source of noise. I was specifically asking about the Beta design and if you knew of any issues - just trying to prune the tree.

THX

[Enzo]

I am sorry for not being clear. There is no reason in my experience to expect one part over another in there. SInce the Sunn Beta was made with the same stuff all the other amps were made of, this would not be surprising then. I would suspect an op amp before a JFET myself, but not by a whole lot. ANy individual transistor can come up noisy, and op amps are full of transistors too. So I would have to say for the most part ANY semi in there has about as much chance as another.

SInce these are SS they run on low voltage, so noisy resistors are far less likely than on tube amps.

A very loose rule of thumb on most circuits, well SS circuits anyway, is when one fails it is more likely a chip that interfaces to the real world than one in the middle of the circuit. More opportunities to encounter high static discharges or other odd voltages. An input or output IC instead of oh the tone stack driver. But that is more about out and out failures than just noisy. Certain Marshall amps with mostly SS preamps tend to lose an IC and it is almost always the second on in from the input - I have no idea why.

There are not that many stages in a channel here, so between turning the knobs and scoping, the tree should prune readily.