Pontus turn on “thump”

[Wolf11Man]

Inverting or non inverting has nothing to do with the voltage supply. It only depends on the OP-amps input that is used.
A typical OP-amp has positive + and negative - voltage feeds, but no ground. This makes the output DC free.
If you only use the positive voltage and keep the negative at ground level, the output has a DC component. It needs a coupling capacitor to remove it from the output signal. A dual supply doubles the possible headroom.
Just as a reminder.

 

[gjpmho]

Inverting or non inverting has nothing to do with the voltage supply. It only depends on the OP-amps input that is used.
A typical OP-amp has positive + and negative - voltage feeds, but no ground. This makes the output DC free.
If you only use the positive voltage and keep the negative at ground level, the output has a DC component. It needs a coupling capacitor to remove it from the output signal. A dual supply doubles the possible headroom.
Just as a reminder.

Inverting or non inverting has nothing to do with the voltage supply. It only depends on the OP-amps input that is used.
A typical OP-amp has positive + and negative - voltage feeds, but no ground. This makes the output DC free.
If you only use the positive voltage and keep the negative at ground level, the output has a DC component. It needs a coupling capacitor to remove it from the output signal. A dual supply doubles the possible headroom.
Just as a reminder.

Yes doesn’t this DAC look like the one described in the AI overview? At the output there are two opamps per ladder, one inverting and one non-inverting, correct? Each with GND for one voltage feed is non-inverting or inverting op-amp, right?

 

[Wolf11Man]

If you can identify the OP-amp, have a look at the data sheet. There should be some examples how it can be used.

For the DAC output you can use different configurations. Should be standard use of OP-amps or discret output stages.

 

[gjpmho]

If you can identify the OP-amp, have a look at the data sheet. There should be some examples how it can be used.

For the DAC output you can use different configurations. Should be standard use of OP-amps or discret output stages.

Yes that’s what I’m trying to show is the OP-amps mentioned before are OK and based on the AI overview I sent, it appears their configuration (non-inverting and inverting - one voltage supply is connected to ground) has already been used in balanced R2R ladder DACs, which the Pontus is.

 

[gjpmho]

I replaced IC29 with an extra LT1763 I forgot I had from a few years ago, sourced from mouser.com. IC29 is in the Standby circuit. Vout is now much closer to 0 Volts, still thumps, oh well.

I did some searching and although I don’t have EE fundamental knowledge or really much solid knowledge to anchor my understanding… this could explain the op-amp configurations above:

Google AI Overview produced this result. I can’t vet the overview through the linked source material… yet it does make sense at least, and it doesn’t seem like a coincidence there are inverting and non-inverting op-amp circuits in the Pontus.

“A truly balanced R-2R DAC uses
two R-2R ladders, one for inverting (LSB-driven V_ref/2/4...) and one for non-inverting (MSB-driven V_ref/2/4...) with switches connecting to +Vref and -Vref, feeding a differential op-amp buffer(like a Fully Differential Amplifier) or two separate single-ended op-amps(inverting for one ladder, non-inverting for the other), summing their outputs for true bipolar/balanced output, achieving better linearity and common-mode rejection than single-ended designs”

Update: I was wrong about IC29. It is not part of the Standby circuit (I jumped to that conclusion after accidentally shorting VIN pin to GND pin which apparently triggered a fault condition, and put the DAC into Standby). Then, while replacing IC29 (which was not faulty after all) I shorted one of those capacitors next to it. A nearly invisible strand of solder! I should have checked all the components for shorts and connections to the IC29 pins. After powering up the DAC USB input stopped working! USB input is working after removing the short, and IC29 Vout=3.4V when USB is On, and Vout=0.14V when USB is Off. IC29 is part of the USB circuit. This all is just an illustration of how things can quickly go wrong if you’re not careful and thorough. Double check your work before pushing the power button. I got lucky.

 

[gjpmho]

Good news I replaced all electrolytic capacitors, relays, and AC/DC convertor on the power supply board. The thump is virtually gone, barely audible at rather high volumes! Yay! I know it was overkill but this shotgun approach is an option when you can’t probe the power supply board while powered, don’t have schematics or ability to fault trace, and it’s a pain to dissemble and re-assemble the DAC. I left the DAC board alone, those Rubycon XYG/H capacitors will last a very long time.

If anyone else is interested here are the components I installed. FWIW absolutely no change in sound signature with lower ESR capacitors.

Manufacturer part numbers I bought on mouser.com

EEU-FS1V272 ( 2 )
UHE1E102MHD6TO ( 61 )
UHE1V221MPD ( 6 )

IRM-20-5
ORWH-SH-105D1F,000
G2RL-2A-HA DC5 ( 4 )

Photos of before and after, and heatsinks mentioned earlier for the MOSFETs. These need to be 5mm height max for clearance with the case. Found on Amazon.