Balanced Volume Controller / Line Stage

[alexcp]

Anything is possible, of course, but I want my DIY gear look a bit nicer than an old Cyrus amp.

 

[aditya]

I like the kinki studio amp and Rotel Michi look but the best is Cambridge streamer amp with the 6” display - just saying

 

[alexcp]

I agree. All of them obviously know what they are doing on the design side.
Another example:

 

[kazuviking]

The BOM for the pot one states 1/2 & 1/4 resistors but looking at your other balanced line receiver that uses 1/6 resistors then i can safely assume that i can use 1/6 or even 1/8 resistors in the signal path since they are easier to find in smaller sizes.

 

[alexcp]

Those actually are compact metal film resistors in the axial 0204 package (i.e. 2mm diameter, 4mm length). The example part numbers are from Vishay SFR16S series, which is rated for 0.5W (see the datasheet).

Still, sorry about the confusion - I will edit the BOM description for clarity.

 

[kazuviking]

No worries. I was asking because on LCSC vishay is never in stock or available and every other resistor that would fit in size and ppm is either 0.25W or 0.16W.

 

[rsavas]

I recently received a EOL notice from Dig-key, on one of the SFR16S parts 4R7, I had in a list, but it was a packaging option EOL, not the SFR16S series being elinimated. I also use MBA0204
LCSC is not very good for specialty passives and even some very general purpose IC's. Hit and miss.

 

[alexcp]

Except for the four resistors in the power supply (R1 R2 in the DC input filter and R3 R4 in zener biasing), there is no real power dissipation or large currents anywhere in the circuit, so 1/6W resistors such as YAGEO MFR-12 series will work just fine.

 

[kazuviking]

While messing around in falstad i changed the zener to 5V, regulator to 12V(just a super simple zener+transistor reg in a subcircuit) and it just barely works from a 19V input(probably made it incorrectly).

 

[alexcp]

The three-pin regulators cascoded by Darlingtons were designed for, and work well with, higher supply rails. They allow powering the board directly from the power amplifier supply. The practical upper limit there is about +/-35V, limited by the power dissipated by the regulators and transistors.

With lower supply rails, there are several way to configure the onboard regulators:

1. If the supply rails are within opamp's power supply ratings (e.g. +/-18V max for the LM4562), you can omit both the transistors and the regulators by just shorting the appropriate pads on the board. Obviously you don't need the zeners and their associated resistors in this case. For example, I have one board running like this from an SMPS that has a separate low current +/-15V output.
2. You can omit just the transistors and the zeners and keep the three-pin regulators. This works as long as the regulators drop at least 3V input to output.
3. You can keep both the regulators and cascodes, choose appropriate zeners and recalculate their resistors.
   You want +/-12V on opamps. At the input of the regulators, you'd need +/-15V. On the bases of the Darlingtons, you'd need +/-(15V+2×Vbe) = +/-16.5V or so. Therefore, the minimum appropriate zener voltage would be 16.5V-12V=4.5V. Choose 4.7V as the closest standard value. Now calculate the resistors (R3 R4). If your supply is +/-19V and the bases of the Darlingtons are at +/-(12+4.7)V, each resistor drops 19-(12+4.7)=2.3V. The current through each resistor needs to be sufficient for the zener to operate; 5mA would be ok. Choose R3 and R4 to be 2.3V/5mA = 460ohm. The standard value of 470 ohm will work well.

 

[kazuviking]

Wow you even explained how to get there without asking, what a legend. Tried making my own boards but JLC said the tolerances are not good so i'm redoing the board with 0.127mm instead of 0.2mm signal traces.