Roll Call: Who's building, built, or thinking of building a beta22? - Page 184

I haven’t heard or read about any kind of audio degradation from a one box build, only the inherent issues you’ve pointed out.
I use two par metal cases stacked, the psu has 2 unshielded 50VA transformers and I’ve had no noise, hum or RF issues, but of course there’s no insurance.
If it was me I’d put the transformer in a small box away from the amp and psu, that way you could still have the convenience of one box on display and the transformer tucked away out of sight. 

Originally Posted by johnwmclean 

I haven’t heard or read about any kind of audio degradation from a one box build, only the inherent issues you’ve pointed out.
I use two par metal cases stacked, the psu has 2 unshielded 50VA transformers and I’ve had no noise, hum or RF issues, but of course there’s no insurance.
If it was me I’d put the transformer in a small box away from the amp and psu, that way you could still have the convenience of one box on display and the transformer tucked away out of sight. 

Thanks for the info. I have considered the small transformer box option, but I want to have some uniformity in the casing and use a nice power switch (epsilon 24 & Bulgin switch), so I'm either going to use a single box for everything or one box for the transformer, sigma 22, and power switch circuitry and another box for the beta 22 boards.

In that case, if your chassis is aluminum then yes it’s definitely a good idea to use a shielded transformer in a two box build.

I have been told that I will need about 20 feet of 18 awg wire for the power runs and about 20 feet of 22 awg wire for everything else.  Will this change now that I am using an epsilon 22 backplate?

By the way I am housing only my transformer in a separate chassis and my omega 22 board and three beta 22 boards are in a separate chassis.

Thanks

mgrewe, look at option 2 on AMB’s website under wiring and ground.

20 foot will be over considering your using an ε22 backplane board which saves internal wiring, you could use the remainder for another project?

omega 22? I think you need do a little reading. Good Luck.  

I recently built an enclosure for my beta-22 so I wanted to verify adjustments to make sure my output stage current wasn't so high that anything would burn up since it seemed to be running pretty hot in there. I got to checking the DC offset on my meter and the meter reads somewhere between 250V and meter-out-of-range (1kv). Obviously this can't be accurate, must be some sort of oscillations fooling the meter? The volume knob is zeroed so the inputs are grounded. Any thought what is going on? I don't have access to a scope at the moment so I can't just use that to set the dc offset. This is a nice Velleman meter, not sure why it's acting up in this manner.

Quote:

Originally Posted by dude_500 

I recently built an enclosure for my beta-22 so I wanted to verify adjustments to make sure my output stage current wasn't so high that anything would burn up since it seemed to be running pretty hot in there. I got to checking the DC offset on my meter and the meter reads somewhere between 250V and meter-out-of-range (1kv). Obviously this can't be accurate, must be some sort of oscillations fooling the meter? The volume knob is zeroed so the inputs are grounded. Any thought what is going on? I don't have access to a scope at the moment so I can't just use that to set the dc offset. This is a nice Velleman meter, not sure why it's acting up in this manner.

Clearly that's not possible as there is not that much voltage in the amp.  Is that supposed to be mV instead of V?

You can sanity-check your meter by measuring a battery.
 

Agreed it's not possible... just checked, the meter is in auto-scaling mode, tested it on the main rails and it reads +-28V properly, then in that same mode hook it up to either channel's output and it reads >1kv with overload signal.

Quote:

Originally Posted by dude_500 

Agreed it's not possible... just checked, the meter is in auto-scaling mode, tested it on the main rails and it reads +-28V properly, then in that same mode hook it up to either channel's output and it reads >1kv with overload signal.

Does it do that on all channels?  Or only on one of the boards?  Maybe there is indeed an oscillation that's confusing the meter.

I have two Goldpoint stepped attenuators that I am planning to wire in series for my beta22 volume control. They are rated as 10k, so I'm guessing doing this will result in an overall 20k resistance. This should still be fine, right?

I will be using the amplifier with a number of different sources, so I want to have a good amount of play in the volume control. In other words, I plan to use one control just to get the volume in a decent range and the other for fine tuning.

Quote:

Originally Posted by chronomitch 

I have two Goldpoint stepped attenuators that I am planning to wire in series for my beta22 volume control. They are rated as 10k, so I'm guessing doing this will result in an overall 20k resistance. This should still be fine, right?

 

I will be using the amplifier with a number of different sources, so I want to have a good amount of play in the volume control. In other words, I plan to use one control just to get the volume in a decent range and the other for fine tuning.

Please post a diagram of exactly how you could wire the two attenuators.  "Series connection" could be interpreted in one of two ways -- literally stacked, or cascaded (one after another).  The equivalent resistance of the combination is not the same between the two, and the adjustment range also differs.
 

They would be cascaded. In other words, the output of each channel from the first attenuator would be fed into the inputs of the second attenuator.

I am building a three channel beta22, and these are stereo attenuators.

Quote:

Originally Posted by chronomitch 

They would be cascaded. In other words, the output of each channel from the first attenuator would be fed into the inputs of the second attenuator.

 

I am building a three channel beta22, and these are stereo attenuators.

OK, in this case the total resistance of the two would be 10K when the first one is in the minimum position, or 5K when both are max.  Also, the two will each have the same (large) adjustment range down to "-∞" dB

Quote:

Originally Posted by amb 

OK, in this case the total resistance of the two would be 10K when the first one is in the minimum position, or 5K when both are max.  Also, the two will each have the same (large) adjustment range down to "-∞" dB

Thanks. I take it that when you say they will have the same (large) adjustment simply means that wiring the attenuators in this way will not make the volume steps any smaller.

Quote:

Originally Posted by amb 

Does it do that on all channels?  Or only on one of the boards?  Maybe there is indeed an oscillation that's confusing the meter.

It did it on all channels... solve the problem by putting a 100 ohm resistor between the output and ground and probing the drop across that, not sure why it mattered but it fixed it, I guess that was able to lower whatever no-load oscillations were occuring