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Zero volt connections - using Minicap6

G

grahamdocman

pfm Member
I just want to check: as I'm installing a Minicap6 and Qudos board to my Mono 110:

Does is make any difference which end of the Minicap 6 the zero volt connection to the speaker out (Black speaker terminal) comes from.

In some builds it appears be attached to the Minicap6 Power input end where the transformer connects, ("front end") in others I've seen the connection is made to Minicap6 output end where the amp boards are connected ("back end").

To my simple mind, the zero rail is large and runs as a single rail from 'front' (transformer end) to 'back' (output end), so shouldn't in theory make any difference.

However, I think I read the the amp (QUDOS) boards should always be connected to the 'back' end, so shouldn't the zero rail to the speakers be connected from this 'back' end also ?

Any guidance or explanations gratefully accepted.
 
The correct way is to connect the speaker to the opposite end to the transformer centre tap, this is to keep charging currents out of the amplifier circuitry.
However there were people on here who said their amps sounded better with the speaker return connected at the "dirty" end.
I went the opposite way with my NCC300s and moved the speaker return (i.e. the power star) to the PCB.
 
Thanks, I'll do it your way.

Did you notice any apparent difference ?

I'm a little surprised that simply moving this connection to 10cm further along the same rail (from the 'dirty' to the 'clean' end) should make a difference.

Can anyone offer an explanation ?
 
grahamdocman said:
Thanks, I'll do it your way.

Did you notice any apparent difference ?

I'm a little surprised that simply moving this connection to 10cm further along the same rail (from the 'dirty' to the 'clean' end) should make a difference.

Can anyone offer an explanation ?
Click to expand...

This is one of the most common mistakes people make IME ie assuming that things which connect together can do so any which way. That "10cm further along the same rail" MUST be viewed as a resistor and an inductance. Worst case an amplifier can be turned into an oscillator and can blow up. Even 1cm of thick wire can have a right and a wrong end!

The above is generic and does not in any way refer specifically to the amp being discussed BTW.
 
Mynamemynaim said:
Really?
If true... you learn something new every day
Click to expand...

Yep really. Most extreme example not in audio but at UHF RF frequencies a 1cm wire between emitter and ground plane in a power amp would likely turn it into an oscillator. In audio check out distortion mechanism 7, negative feedback take off point, in Doug Self's list of distortions. Similarly, the wrong take off point/'s from PSU smoothing caps can increase hum (charging spike buzz really). In some big amps a copper or aluminium plate of up to about 5mm thick is used to connect the smoothing caps ground centre point together and even with this low a resistance care is taken over the correct connection points for various return grounds and a star ground often used. It is often forgotten that solder has much higher resistance than copper as well!
 
As ever thanks for your patience with my lack of knowledge and expertise, but I am learning all the time and have learned a lot from PFM. I most certainly would not have embarked on my various DIY projects without much of the support and help I've received here.

So: Arkless, if I've understood your comments correctly, connecting to the 'clean' end is potentially - forgive the unintended pun - theoretically better.

Is the 'clean' end the same as the "the junction of the pcb decouplers" in S-man's reply, as I say I'm trying to learn all the time.
 
So in layman's terms what end should the speaker output 0v come from then? The transformer end as per Les diagram or the opposite end of the cap 6 that feeds the ncc200 or where ?
 
S-Man said:
Take a look at slide 56 here:
http://hifisonix.com/wordpress/wp-content/uploads/2019/02/Ground-Loops.pdf

The "dirty end" is point 1
The "clean end" is point 4
The "junction of the pcb decouplers" is where the green speaker wires go

The NCC amps will not self destruct if you connect your speaker returns at any of the locations above.
Click to expand...



Thanks, I've read the whole document, understood quite a lot of it and found it really helpful - also the video you linked your previous answer to, though I understood a lot less of that !
 
UPDATE: OK guys, not necessarily the definitive statement, but from Les W himself - I had to contact him about something else so asked about this at the same time: I have paraphrased Les' comments, but believe I have assimilated the core of what he advised.

Apologies in advance: any errors are MINE. e.g. if I've mixed up which are the 'cleaner' and 'noisier' ends of the Qudos.

The advice applies to both the QUDOS and NCC200 amp boards, Minicap6 and Cap6 boards.

1) Which Zero volt connection for speaker output
"lots of different opinions and it can be amplifier dependent, the theory is sound ....... but there is no definitive answer ....... experiment: use a lead from the zero speaker output long enough to reach both the Zero connections on the Minicap6 and then experiment by listening connecting to the front and back end zero points ........ decide what's best for you ........ its possible you may not even notice any difference".

This fits in with S-man's comments - post #2

2) Can you daisy chain the zero connections on the Qudos board together and thereby take a single lead to the 'clean' Zero connection on the Minicap 6
"NO - each of the Zero connections on the Qudos MUST be separately connected to the Minicap6. The output (back) zero end of the Qudos can be quite noisy and dirty, if you connect both these connections directly to each other, you can feedback this noise (dirt) back into the front end.
But connecting each separately to the Minicap6 (even though it's the same pad on the Minicap6) the Minicap6 sorts it out and avoids noise getting fed back to the front end".

Please note: if I've mixed up the 'cleaner' and 'noisier' ends of the Qudos, the principle and rationale of wiring the front and back ends separately to the Minicap6 back end, remains the same

3) I accidentally bought 16AWG cable for all the internal wiring, is this too large as I have read that thinner gauge cable can have a beneficial filtering effect
"Don't worry about that"

For the less expert and numpties like me:
  • The 'front' end of the MINICAP6 or CAP 6 is the end where the transformer terminals go IN (i.e. A/C 240v input the 'back' end is the DC out end)
  • The front end of the QUDOS (or NCC200) is the end where the signal leads from the pre-amp go in, teh back end is where the leads join the board to the Minicap6
Finally: two bits of safety advice: often and sensibly repeated on PFM threads:
You are dealing with potentially lethal voltages - always disconnect from the mains when working inside the amp - if you don't feel confident about what you're doing: DON'T DO IT

NEVER disconnect the power (+ve and -ve connections between the Minicap6 and Qudos boards) until the capacitors on the Minicap6 are fully discharged,
Doing so no only risks giving yourself a very very nasty shock but will almost certainly blow the and output transistors of your boards and possibly do even more damage - its a very easy mistake to make (if you follow my drift........) :(​
 
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