The M2 Output Stage in Class A/B, and maybe a Power WHAMMY?

[Dan K]

Perhaps a stupid question.. Is there a way to bypass C2 wbst using the 'mixed' feedback layout?

Thanks

 

[Dan K]

Mine are fed +/-23V5

You could increase the Rs resistors to drop a bit of voltage feeding opamp.

Thanks Vunce, is that the voltage at the 604's legs? I'm guessing that you don't see any switch on/ off spikes, due to the Rs resistance and the local cap

I'd also like to know why everyone is using large(ish) local psu caps on their boards. Thanks

 

[Dan K]

If anyone is reading this and wants a set of 4 Mills MRA 0R56 5W bias resistors, 4-off 470R 0.5W Audio Note Niobium gate stoppers and a pair of 22pF Charcroft silver mica caps then PM me.

 

[Dan K]

Does anyone have any views / preferences for either of the following as local power decoupling caps:

Pana FM 1500uF 35V, ESR ~8Ohms 3.7A ripple, 12.5mm*35.5mm. £2.32 each

Nichicon UHW 5600uF, 25V, ESR ~8Ohms 4.2A, 16*35.5mm. £3.49 each.

thanks 😁

 

[Vunce]

8 ohms??

 

[Dan K]

Milliohms 😆

 

[Vunce]

🤣👍🏻

 

[TungstenAudio]

Motor run polypropylene in oil

 

[Dan K]

The 50uF Ducati ones?

I don't think I have enough space, max diameter is 16mm

 

[TungstenAudio]

They won’t fit on the board. Best installed as separate pairs for each channel, on top of or alongside the main PSU board as space demands.

 

[Dan K]

This does beg the question; Is ESR the absolute concern for a power amp OPS local decoupling cap? Ie what is the point of placing huge capacity/ ave ESR caps on the board (Wurth 10,000uF, etc).

To my mind the larger metal cans will pick up more radiated noise from the transformer. Just trying to understand what people were thinking here.

 

[TungstenAudio]

The question is “what issue is a set of local decoupling caps trying to solve?”
There are different approaches depending on whether one is using a shared supply or dual-mono.

 

[Dan K]

Fixing physically large lytic de-coupling caps to the boards/ legs of output devices is a means for noise injection.

 

[Dan K]

Did anyone else building this amp detect any instability at all with the OPA604 and mixed feedback? Shouldn't be the case