"The Wire" Ultra-High Performance Headphone Amplifier - PCB's

Jump to Latest
A

AndrewT

R.I.P.
Joined 2004
If your cable is screened/shielded, then connect the screen/shield to Pin1 and that connects the shield/screen to the Chassis.

If you cable is unscreened twisted pair, then use the two signal pins (2 & 3) and leave pin1 unused.

For a 2 core unscreened cable, you don't need a 3pole plug and socket.
A 2pole plug and socket is sufficient.
 
W

wendell c

Member
Joined 2006
IanAS said:
Seems that to certify for the CE mark in 1997 we had to connect the incoming RCA grounds to chassis only via a capacitor, 0.01uF in that case. Is it different for XLR?

What would be the point in chassis'ing pin 1 if you're only using pins 2 and 3 for (headphone) speakers leads? Especially if they are, like most after market high quality leads, un-screened. Or you used a 4 pin connector? :) Maybe if you want to make your home built headphone amp compatible with industry standards for dual 3 pin XLR headphone leads?

I only presume that balanced headphone amps use, for speakers leads, pins 2 and 3 for the two hot wires and don't bother with pin 1.

I've just checked a few bits of very old Hi-Fi laying around here and none have pin 1 grounded at the chassis, for input nor speakers leads; input done on the PCB and speaker leads direct back to earth star, though that power amp, for speakers leads, still does use pin 1 for earth and 3 for hot wire, but it's not a balanced output. Perhaps things have moved on in that regard since the '80's and '90's?
Click to expand...
.

AndrewT said:
Pin1 has been wired many ways and the "professionals" were just as bad as the amateurs in getting Pin1 wrong.

Around about 1995, after decades of seeing it being done wrong, by so many, there was an article telling everyone how to wire Pin1 properly. I think it was by Neil Muncy.

But since then there are still many that get it wrong. Even equipment manufacturers are still wiring Pin1 incorrectly.

The audio standards authority in the USA (AES) has even changed the test so that measurement can prove that Pin1 is wired incorrectly.

There are dozens of articles and AES guidance to show how to do Pin1 correctly.

There is no excuse for any informed builder to wiring Pin1 incorrectly. It would be simple incompetance.

We need the context of this.
On the face of it, I consider the information to be incorrect, but there may be some operational circumstance where it would be mandatory to add an RF attenuating capacitor at the input RCA.
As far as I know the RF attenuating capacitor is optional.
This capacitor is one I have been recommending for years. And on the speaker cables and on the mains cables. Every cable entry to the enclosure can have an RF attenuating capacitor to the enclosure.
Are any of them mandatory?
Click to expand...


Sent from my Nexus 6P using Tapatalk
 
A

aive

Member
Joined 2013
Hey Owen - Just want to confirm, will there be any issues with feeding my dual-mono MPUHP a SE signal (via XLR connector with ground connected to -'ve input). I'm planning on building a DAC soon in a SE arrangement and plan to connect it to the amp.

Thanks mate :)

Edit: I think it's fine based on earlier posts but just wanted to confirm specifically for this amp :)
 
Last edited:
P

pwh

Member
Joined 2012
Hello... looking for some advice. I was just about done with my amp when I accidentally shorted the PSU's 15V rail to its ground and got a wonderful zap/acrid smoke from its regulator. Fortunately it wasn't directly connected to the amp board at the time so that end is fine.

For shorting one half of the PSU, are there any parts besides the regulator that should be automatically replaced? The board/parts look fine except for the poor TPS7A3001
 
I

IanAS

Member
Joined 2004
Perhaps check the bridge or bridge diodes.

If the short damaged the bridge and it went closed circuit, then check the transformer windings are what they should be and not shorted.

If the earth rail then failed and the entire ± peak to peak voltage went across the non shorted sides capacitors, check those too if they're voltage rating was less than the total of the ± rails.

Also clean any carbon residue off the PCB.
 
P

pwh

Member
Joined 2012
I've checked the transformer windings and they're good, as is all of the non-shorted side. Would I need to check the diodes individually beyond that? Also, for BamboszeK's suggestion, how should I check the caps? I'm still pretty raw with handling damaged circuits, not terribly familiar with the process.

Thanks both of you!
 
I

IanAS

Member
Joined 2004
Depending on the severity of the short, I probably would take the diodes off if necessary to use the diode tester across them, on my multimeter, or maybe just swap them for new.

If the earth return track is OK then the caps probably are as they will not have had an excessive voltage across them.

The shorted side caps will simply have discharged through the short. It's reverse or excessive voltage that damages them. Though some electrolytics sometimes don't tolerate well being shorted out.

Caps; visual inspection, any bulges or leaks? If required, take them off, measure them with a capacitance meter.

:)
 
P

pwh

Member
Joined 2012
I checked that the diodes were OK and replaced the blown regulator and now the PSU is giving a rock steady +/- 15V, so that's great.

Unfortunately, now my amp board is giving me 2.7V DC offset (!). I'm a little puzzled since the amp board wasn't connected when I blew the regulator, and I don't remember touching it since it last worked. Any suggestions? Unfortunately the wiki hasn't been up for a bit so I'm not able to load the schematics and other docs :X

Edit: A few more checks shows that the new regulator isn't properly insulated from the heatsink. I know I checked that several times, alas.
 
Last edited:
P

pwh

Member
Joined 2012
I have a grounding question... the mounting holes of the PSU are connected to the PSU's output ground, so if I mount the board to the chassis through aluminum standoffs I have them electrically connected. I know Earth Ground should also be connected to the chassis, but then EG and PSU ground are tied together and that doesn't seem right. What's the best approach to grounding? And apologies if this was answered elsewhere on the thread or on the site... lots of information to take in.
 
A

AndrewT

R.I.P.
Joined 2004
For Audio, your circuit can float. It does not need a connection to Earth.

For Safety your mains powered equipment must meet the rules for ClassI and/or ClassII equipment.

Do not mix up these two very different requirements.
Sort the Safety and get it right.
Never compromise the Safety of your mains powered equipment.
 
You must log in or register to reply here.
Top Bottom