MyRefC build guide

[tuyen]

Does anyone use myrefC amps with 100db+ horn speakers? I'm getting noticeable noise that I'm not sure if is normal with this design or not? Unlike my class T that is pretty much dead quiet..

[ClaveFremen]

Try grounding the heatsink

[linuxguru]

Originally Posted by tuyen

I'm getting noticeable noise that I'm not sure if is normal with this design or not? Unlike my class T that is pretty much dead quiet..

Check your input-side grounding and shielding setup. PGND is best left floating (isolated) from chassis ground (earth) for minimizing hum. Also, a toroidal or R-core trafo will radiate less mains hum than an EI core. The secondary-side wiring from the trafo should be braided to minimize the AC loop area.

Other things being equal, my MyRefs are quieter at no input signal than my SMSL T-amp, which is also very quiet, but has a very faint background fuzz from its switching power supply.

[ClaveFremen]

Originally Posted by ClaveFremen

Try grounding the heatsink

Obviously the heatsink must be insulated from the LM3886T.

No problem with the LM3886TF

[tuyen]

Thanks guys. I will check those things out. Will report back!

[tuyen]

Heatsink was not grounded. Tried grounding and did help a little. chip is LM3886TF.

Input wiring is shielded, secondary winding is braided.

Doesn't have noticeable noise on my 'normal' Rogers 2-way speakers. But on my 110db goto horns, it is no good. Can hear buzzing non stop.

Also, still pops on startup and big sounding pop on shutdown. Sounds pretty good powering the Rogers... but unfortunately I don't think this type of amp is what I'm after to run my Goto horns.

[bcmbob]

In my setup it is necessary to turn off both FE amps before turning off the DAC that feeds them - no pops - no noise. If that sequence is reversed Iget what you get.

And yes. I turn the DAC on before powering the amps.

[AndrewT]

"fast off" of the protection relay will achieve the necessary speaker isolation @ power OFF.

"slow on" (or speaker delay) should already achieve the necessary speaker isolation @ power ON.

An input mute or source output mute will isolate Source start up noises, IF the mute knows that the Source is started out of sequence. A common power ON/OFF switch solves this fairly easily.

>100dB speakers will require a very low noise value at the amplifier output.
Chipamps do not have that required very low noise value. Peter Daniel developed his implementation that he uses (or used) with 95/96dB/W@1m speaker, I cannot recall if he had reservations on noise.

[bcmbob]

Andrew, is this a situation where a discrete soft start module would help?

[bcmbob]

OT

tuyen, Very interested in learning about your 110 db horns. Can you post a link or PM me with more info?

Thanks