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Old 3rd December 2012, 01:04 PM   #1011
tuyen is offline tuyen  Australia
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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..
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Old 3rd December 2012, 01:19 PM   #1012
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Try grounding the heatsink
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Old 3rd December 2012, 01:39 PM   #1013
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Quote:
Originally Posted by tuyen View Post
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.
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Old 3rd December 2012, 01:47 PM   #1014
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Originally Posted by ClaveFremen View Post
Try grounding the heatsink
Obviously the heatsink must be insulated from the LM3886T.

No problem with the LM3886TF
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Old 4th December 2012, 01:50 AM   #1015
tuyen is offline tuyen  Australia
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Thanks guys. I will check those things out. Will report back!
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Old 4th December 2012, 11:06 AM   #1016
tuyen is offline tuyen  Australia
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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.
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Old 4th December 2012, 11:11 AM   #1017
bcmbob is offline bcmbob  United States
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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.
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Old 4th December 2012, 11:30 AM   #1018
AndrewT is offline AndrewT  Scotland
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"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.
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Last edited by AndrewT; 4th December 2012 at 11:33 AM.
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Old 4th December 2012, 11:34 AM   #1019
bcmbob is offline bcmbob  United States
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Andrew, is this a situation where a discrete soft start module would help?
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Old 4th December 2012, 11:37 AM   #1020
bcmbob is offline bcmbob  United States
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OT

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

Thanks
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