[MrMajestic2]

Quote:

Originally Posted by Russ White /img/forum/go_quote.gif Hey Folks, I am only posting here because someone asked me to. IVY certainly can be used as a SE to Balanced converter. You would just omit the BAL/SE part of the cct, and tie -IN to GND. The setup would be similar to the Opus setup, in fact you could use that setup sans the BAL/SE part. You might adjust the input impedance to 2K. Its a pretty simple mod. The output will be a nice clean balanced signal. Cheers! Russ

Hi Russ,
Could you be more specific about this mod? Exactly what parts should I omit and change? Would be really helpful as Im planning on using the IVY in a b22 build.

 

[tenorsaxophone]

Hello!
To those who they have already built β22 amplifier:
Is it better (or more easy to work on PCB) to use 1/8 or 1/4 watt resistors?
Many thanks.
Davide.

 

[Ferrari]

Except for the 0.47Ω power resistors, all resistors on my β22 amps are Vishay-Dale RN55D 1/8W.
Resistors from other manufacturers like Xicon, BC, Panasonic... (1/4W) with the same dimensions as Vishay-Dale RN55D 1/8W will work fine but not necessarily better.

 

[MrMajestic2]

Quote:

Originally Posted by tenorsaxophone /img/forum/go_quote.gif Hello! To those who they have already built β22 amplifier: Is it better (or more easy to work on PCB) to use 1/8 or 1/4 watt resistors? Many thanks. Davide.

I though the recommended 1/8W was easy enough to work with. I dont see any benefits in going 1/4W unless you have trouble finding the 1/8W. There is space for slightly larger resistors on the boards though.

 

[Crow]

Hi amb (or anyone who knows for sure):

I will have a Dantimax relay attenuator between the input and my 3 B22 boards (AG config.)

Should I connect the ground channel to the RCA jacks (at the signal grounded case) or to the output of the attenuator?

What type of cable is best to use for the ground channel's input--shielded (shield connected to what?!), or would simple hookup work for this (~7")?

Thanks for your support. My build is going quite well thanks to all the posts here and elsewhere.

Scott

 

[amb]

Crow, see the β22 website's "Parts list" and "Wiring and ground" sections. You'll note that the active ground channel board's input is already grounded via its own R2 resistor. The diagram shows a ground wire only, connected to the input ground (same place as the left and right channel board's input ground -- at the volume pot). Since it's only one wire, there is nothing to shield.

 

[Crow]

Got another one for you guys. On my B22 Left channel, both 2sj74 jfets measure a short across D-S. Indeed, my input is short circuited; my 170's are both ok (4.5v across R9), and during the initial setup all the procedures went ok--the board still powers up and biases (output at least) correctly.

So my 74's are blown. I don't know how this happened, but I have a couple guesses:

1) As I recall, I did not have my inputs shorted while adjusting the bias of the input transistors (dumb mistake), but did so right after, and the setup still went as expected.

2) Heat: Should I have used alligator clips on the transistors to keep heat down? I did not have the (40w) iron in contact for more than a second though, and I already have built one healthy board w/o clips...

What else could have caused this?

Thanks...

 

[amb]

Testbench accident (whether you were aware of it or not)? DMM probes and other objects, useful tools as they are, could also cause damage in the most inopportune moments.

 

[Crow]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Testbench accident (whether you were aware of it or not)? DMM probes and other objects, useful tools as they are, could also cause damage in the most inopportune moments.

Hmm.. my voltmeter thought 30 ohms was a short across S-D of the 74's. It turns out that all input jfets have sane G-D and G-S resistances. Inspection of the board seems not to reveal any solder bridges/etc. Still operates normally.

In light of this, would you think that there must be some bridged connection hidden somewhere between the input jumpers and the transistors? If not, what other components could cause a short between input and ground? Or are my jfets still dead?

Just wanted to double check before I really start ripping stuff apart to check for shorts...

Thanks so much

 

[amb]

Crow, how about a careful visual examination of all solder joints and traces (under magnifying glass)?

 

[Crow]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Crow, how about a careful visual examination of all solder joints and traces (under magnifying glass)?

Progress. The short is between the input pad and R1. I have connected a wire to the input side of R1 and disconnected it from the board there. I now have sound. Inspected all around the jumpers, and elsewhere--can't find the short. I'm thinking it may be inside the board, wish I'd checked it before I populated it.

Thanks for your patience!

 

[amb]

It's possible the short is on the board, but not inside the board as these are two-layer boards. Sometimes a manufacturing defect (under-etched spot) could cause such a short. You should look very carefully at the trace between the input pad and R1 (under magnification) to see if you could locate it. Then, it's a simple matter of scraping/cutting the short away with an X-acto blade.

 

[Crow]

So I found the short. Connected the dmm to the input and put it in continuity/beep mode. Started slicing around the input trace with an x-acto blade, and when the beep stopped, problem solved.

Ti, this short escaped a 16x loupe and a bright flashlight. There was no reasonable way to visually find it. The moral of the story for prospective builders out there: check for shorts before you build.

I know that having the manufacturer not do this step makes these boards affordable, etc, but this point is still important.

Another B22 is born, and it's sounding fantastic. It has a spacious and mature sound that I won't soon grow tired of. I'll post some photos eventually.

One quick Q amb, as I am plugging in the 'phones (volume at minimum), there is a quick, semi-loud squeal until the plug is fully seated. Hopefully this is harmless oscillation caused by a temporary short condition? Otherwise, the amp is behaving as spec'd (offset, bias, etc) and sounds excellent.

I appreciate your support and may not have started this project without your presence here and elsewhere. Thanks for bringing so much perfection into DIY audio.

Cheers,
Scott

 

[amb]

Crow, do you have a 3-channel active ground configuration? Check that you used the correct C2-C5, R2, R3 and R4 values on the ground channel (they're different than the left and right).

If those are correct you might want to try adding the zobel network to the output as described at the β22 website.

 

[fault151]

Hi guys, im thinking of getting an alps rk27 balanced control for my balanced b22 until the joshua tree becomes available again.

Which should i go for, the 10k or 100k?

What difference would it make to the amp?

Cheers