AudioSector-chip amp kits, dacs, chassis

[Holty]

Thanks Peter for reply.

[Papa Lazarou]

Hi Peter

I received the DAC yesterday and have soldered the jumper (for 230 volt setting) as below. Can you check that all looks in order please? I am getting no sound from the DAC.

[Peter Daniel]

Hi, Sorry to hear that.

However, you are using previous generation board, with different traces layout and no jumpers marked in a bottom layer (you can see them in top layer though). So you should have consulted me before making any connections, as obviously that board is DIFFERENT than the one from my previous picture.

What you did was connecting live and neutral together and blowing the fuse, that's why no sound from a DAC.

With that board version, you need to jumper the OTHER two pads. If sourcing pcb mount fuse is problematic, use a regular fuse.

[Papa Lazarou]

Thanks Pete. I feel a total spaz.
Will sort it now. A PCB mount fuse should be easily obtainable.
Much appreciated.

[AndrewT]

or use a bulb tester every time you modify a mains powered project.

[Maxhax]

Okey, so I recieved my LM4780 dual mono premium kit, now everything is soldered together.

However when its hooked up to my preamp/dac its producing around 1.1VDC at the output, on both channels.

Without hooking it up and with inputs shorted I get 6.2mVDC on one ship and 4.7mVDC on the other. When measuring DC offset on the pre I get 2.3mVDC/3.3mVDC.

I hooked it up to a pair of shitty speakers, sounds good but it seems to be some HF noise present.

When I hook it up to my iPhone, bypassing the pre its totally noise free and the DC generated at the output is 11mVDC/0,1-0,8mVDC (to low to be measurable with my multimeter)

Lifting the earth solves nothing and gives no noticable change.

Would an AC coupling cap in series with input solve my problems when using it with my preamp?

[AndrewT]

the Audiosector amp is DC coupled.

[Maxhax]

So adding a DC blocking cap at the input wont do any good then?
Then how should I solve this issue!

[Peter Daniel]

Originally Posted by Maxhax

Would an AC coupling cap in series with input solve my problems when using it with my preamp?

It would certainly reduce the offset, although most likely not to lowest value possible like you are getting with iPhone.

The amp offset is also dependent on impedance present at amp's input; if the source's output imp is very low, the offset is minimized as well.

As to the HF noise, try to install 300pF cap between pins 15-16 and 21-22 on LM4780, which would be a similar approach to what I recommended for LM3875: Commercial Gainclone kit- building instructions

[Maxhax]

Originally Posted by Peter Daniel

It would certainly reduce the offset, although most likely not to lowest value possible like you are getting with iPhone.

The amp offset is also dependent on impedance present at amp's input; if the source's output imp is very low, the offset is minimized as well.

As to the HF noise, try to install 300pF cap between pins 15-16 and 21-22 on LM4780, which would be a similar approach to what I recommended for LM3875: Commercial Gainclone kit- building instructions

The Preamp used is the HLLY DMK-IV

I've not found any information regarding the output impedance of the preamp.

Is the 1VDC offset caused by the offset from the preamp, or is there anything else that's likely to cause this?

Is there more measurements that I can do to narrow down my troubleshooting?

Max