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THE BALANCED BETA 22 BUILD LOG

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Re: THE BALANCED BETA 22 BUILD LOG

Postby amb » February 11th, 2018, 10:41 pm

Energy wrote:Thanks. I know that ladders have 2 switches and 2 resistors that the signal must go through and much more resistors are used on series type (for the appropriate volume), but how many switches/relays and resistors does the LCDuino-1+δ1+δ2 system go through for it's attenuation?

This should be obvious if you look at the δ1 schematics. The number of series resistors is between 0 and 8, and the number of relay contacts is 8. But these are highly reliable telecom grade relays with hermetically sealed and quality contact materials (better than any open-frame switch).

Also is it possible to replace the VR1, VR2, and VR3 with a fixed resistor after the initial setup is done?
I believe a simple measurement of resistance from pin 1 and pin 3 should be enough to substitute for a fixed resistor with the same value of the measured resistance?
It seems VR3 will take 2 resistors since it has two varied resistances. One resistance value from the pin 2 to pin 1 and the other from pin 2 to pin 3?

Why? Doing so gives you no performance benefit, and prevents you from making adjustments again. The optimal settings of the trimpots is likely not a standard resistor value, and sometimes "closest value" is not good enough.
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Re: THE BALANCED BETA 22 BUILD LOG

Postby Energy » March 16th, 2018, 6:01 am

Thanks for the information.

I was looking into purchasing a JCAT NET Card FEMTO and it's requirements for optional PSU is 5V/1.5A min. http://jplay.eu/ml_post_slider/jcat-net-card-femto/

I believe this is too high for an σ11 to handle. Would a σ22 be sufficient? What is the max total current in amps can the two PSU's supply continuously given the fact that the two are using it's parts list's heatsink?
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Re: THE BALANCED BETA 22 BUILD LOG

Postby amb » March 16th, 2018, 4:20 pm

The σ11 can handle 1.5A continuous if you beef up the heatsinks. See the "Board & heatsinks" section of the σ11 website to make some calculations. The σ22 is a dual-rail (positive/negative) version of the σ11, and has the same current capacity. If you don't need a negative rail, then it makaes no sense to use a σ22.
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Re: THE BALANCED BETA 22 BUILD LOG

Postby Energy » May 22nd, 2018, 3:04 am

Understood. Thanks.

I've never installed the Zobel network to my balanced Beta 22 before so I have a question. Rz and Cz is connected in series and is connected to the load. Is this at the output or input end? Since you talked about headphone and speaker loads under the Zobel Network section, I'm guessing it's the output. If the output is a balanced 4-Pin XLR, then would I need two of these networks in total? One in between Pin 1 & 2 (L+/L-) and another between Pin 3 & 4 (R+/R-)?
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THE BALANCED BETA 22 BUILD LOG

Postby amb » May 22nd, 2018, 4:08 am

The best/easiest place to install the zobel network is at the output jacks. For balanced output, install across pins 2/3 on each channel (two 3-pin XLRs) or across pins 1/2 and 3/4 (one 4-pin XLR). Yes, you need a zobel network per stereo channel ("channel" in this case is not synonymous with the number of beta22 boards).
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Re: THE BALANCED BETA 22 BUILD LOG

Postby Energy » May 23rd, 2018, 12:20 am

Would a higher or slightly lower capacitor do it or is having the 0.047μF completely necessary? I could only find some 0.022μF and 0.22μF WIMA MKP2's left over. Also, I read here on how zobel networks work : http://www.wavecor.com/html/zobel_networks.html. Was the resistor & capacitor values you picked out the best in terms of overall compromise?
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Re: THE BALANCED BETA 22 BUILD LOG

Postby amb » May 23rd, 2018, 12:29 am

Indeed the resistor and capacitor values were chosen to optimize the zobel, so that it's effective against load/cable-induced instabilities, but not too much so that it would affect the high frequency performance of the amp. While small changes in values are fine, 0.022uF is less than half the recommended capacitance whereas 0.22uF is almost 5x. That's not a small change!

P.S. In the article you linked, the purpose of the zobel there is to linearize the driver's apparent impedance (to counteract against the voice coil inductance) in the midrange of the audio frequencies and up. That is why the capacitor values used in the table are so large, and why the zobel must be "tuned" for each driver. For the zobel in the amp, the purpose is to maintain the amplifier's ultrasonic stability, so the capacitor value is small, and would never cause any ill effect across the audio frequencies.
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Re: THE BALANCED BETA 22 BUILD LOG

Postby Energy » May 23rd, 2018, 2:13 am

I appreciate the thorough explanation.

Does the dielectric of say capacitor or resistor have a big influence on how the zobel network performs. For example, is it fine to get either metalized polyester or metalized polyethylene as long as the 0.047μF is achieved? I know some multilayer ceramics work better with oscillators for controlling certain RF frequencies, but if you state either or, does this mean the main importance is the capacitance? Would an electrolytic not be suitable?
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THE BALANCED BETA 22 BUILD LOG

Postby amb » May 23rd, 2018, 4:13 am

You should use capacitors with good ultrasonic performance. This means either a good film type (polypropylene, polyester, etc.) or multilayer ceramic.

Electrolytic types are not applicable as they are neither known for extended ultrasonic performance, nor are they available in small capacitances like 0.047uF.
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Re: THE BALANCED BETA 22 BUILD LOG

Postby Energy » June 3rd, 2018, 3:02 am

I am building a new unit right now and have some WIMA FKP2's on hand in values 33pF and 220pF. Is it possible to use those to substitute for the multilayer ceramic capacitors on the B22/O22? Would there be any performance hit or would both perform about the same?
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