new gain is born

[sith]

Hi folks....
New baby is born, LM3875, 36-37V on rails, 11-17mV dc-offset (no dummy-load).Everything worked from the start, no smoke no water;-))). Design, Joe Rasmussen 'sans-tube'. Now I need to find nice cradle for newborn since everything is still on bench, lol. Tested with crappy speaker no hummm at all.
Question, I plan to use it with preamp, so do I need to put resistor in place of volume pot or just bypass wire from input?
Do I have to run some additional tests before connecting speakers, until speaker protection is on the air.

[sith]

one more

[Nuuk]

I plan to use it with preamp, so do I need to put resistor in place of volume pot or just bypass wire from input?

Use the resistor to ground. It won't do any harm and is good insurance if you power up without the preamp connected.

If you are happy with those DC offset levels (and they are fine), and the test speaker was OK, I would say try it with your 'good' speakers.

PS- do be careful with that mains connection to the transformer!

[budwiser]

I built mine without volume control, I use a preamp. Should I have a resistor to ground? If so what value? I built mine using Brians v2 boards

Thanks

[Nuuk]

I built mine without volume control, I use a preamp. Should I have a resistor to ground? If so what value? I built mine using Brians v2 boards

AFAIK, the resistor to ground is only required with the IGC. You have built an NIGC.

[joensd]

Hi Sith,
which transformer (AC-voltage and VA) do you use?
Just curious as I´d like to hear results from people using the LM-chips at their maximum voltage rating (I´ve got this 30VAC lying around...)

Cheers

[Nuuk]

[QUOTE][which transformer (AC-voltage and VA) do you use?
Just curious as I´d like to hear results from people using the LM-chips at their maximum voltage rating (I´ve got this 30VAC lying around...)
/QUOTE]

That would be just about OK with an LM3886 but too much for the LM3875 (unless you regulated).

[joensd]

That would be just about OK with an LM3886 but too much for the LM3875 (unless you regulated).

I have got Brians kits on the bench so LM3875.
But why OK with the LM3886 ?? as both datasheets give max. 84V total (with input signal, 94V without).
I´ve tried it and the rails drop down to ~40V with quiescent current of 4 channels. Transformer is 330VA.
Probably will give it a try anyway as the chips are not that easy to "shoot".

[ofb]

30vac puts you right on the edge to trigger the lm3875's protection circuit. another member reported his 30vac gc getting quite warm and cutting out at high volume. also consider your house power may fluctuate a bit, pushing your voltage even farther up some days.

but it might be okay for low volume listening. i'll be trying it myself.

don't know about 3886. perhaps it has different behavior at max and merely distorts?

[sith]

which transformer (AC-voltage and VA) do you use?

HI joensd
2x28V ac, It was 2x30V ac but I've read over here it would be too much for 3875, so I unwound few turns to get this voltage.

My advice is, do the same or try regulate rails...