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Chip Amps Amplifiers based on integrated circuits

My_Ref Fremen Edition - Build thread and tutorial
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Old 3rd December 2018, 10:12 PM   #4061
Peterma is offline Peterma  Australia
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Join Date: Jan 2009
Location: From London to Sydney Feb 69
Quote:
Originally Posted by Aswin2 View Post
Aliexpress is your friend.

Search: fan temperature controller

yep thanks just ordered them.
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Old 4th December 2018, 05:24 PM   #4062
Aswin2 is offline Aswin2  Netherlands
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Join Date: Mar 2013
Hi,

I've got similar questions for the inrush limiting pcb.

Search on Ebay or Aliexpress for "soft start" and useful items will pop up.

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Old 5th December 2018, 11:10 AM   #4063
wilco87 is offline wilco87  Netherlands
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Join Date: Oct 2015
Location: Haarlem
Hi, back with my second my_ref, but now it's an integrated version. Really like the amp, still amazed it played better than my tube...

Problem is there's a lot of hum from both channels in the integrated one, probably a ground loop I cant find.
-hum increases with volume turned up
-hum stays when inputs are disconnected
-hum stays when selector is set to 3 of the not used positions
-when touching transformers, i hear a 'pop' (softly) through the speakers, also while touching mass of cinch/input
-dc offset is 3mV on right channel, 6mV on left channel.
-music sounds already rather good, even through 7 dollar test speakers

Is the mass from cinch to IN (myref gnd) and from volume to IN (on myref gnd) correct? Took that connection from the audiocreative integrated chipamp. DIY LM3886 Chipamp

See attached photos for drawing of the spaghetti mix of red wires. Still need to clean that up...
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Old 5th December 2018, 12:21 PM   #4064
Luca72c is online now Luca72c
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Join Date: Sep 2013
Quote:
Originally Posted by wilco87 View Post
Hi, back with my second my_ref, but now it's an integrated version. Really like the amp, still amazed it played better than my tube...

Problem is there's a lot of hum from both channels in the integrated one, probably a ground loop I cant find.
-hum increases with volume turned up
-hum stays when inputs are disconnected
-hum stays when selector is set to 3 of the not used positions
-when touching transformers, i hear a 'pop' (softly) through the speakers, also while touching mass of cinch/input
-dc offset is 3mV on right channel, 6mV on left channel.
-music sounds already rather good, even through 7 dollar test speakers

Is the mass from cinch to IN (myref gnd) and from volume to IN (on myref gnd) correct? Took that connection from the audiocreative integrated chipamp. DIY LM3886 Chipamp

See attached photos for drawing of the spaghetti mix of red wires. Still need to clean that up...

Unshielded low level signal wires so close to unshielded 230Vac wires and input plug is not a good idea...
I don't know if that could be enough for the hum you hear, but i'll fix that anyway.
Then try using a proper ground lift (as described in the tutorial) and connecting PGNDs to ground lift chassis GND.
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Old 5th December 2018, 01:05 PM   #4065
wilco87 is offline wilco87  Netherlands
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Join Date: Oct 2015
Location: Haarlem
Quote:
Originally Posted by Luca72c View Post
Unshielded low level signal wires so close to unshielded 230Vac wires and input plug is not a good idea...
I don't know if that could be enough for the hum you hear, but i'll fix that anyway.
Then try using a proper ground lift (as described in the tutorial) and connecting PGNDs to ground lift chassis GND.
Thnx Luca, I'll try that when i have those components.

Decoupled volumepot, selector and cinch from PCB, hum is still present.
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Old 5th December 2018, 11:59 PM   #4066
Panelhead is offline Panelhead
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Join Date: Dec 2002
Location: Houston
Are the inputs (RCA jacks) isolated or grounded?
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Old 6th December 2018, 12:31 PM   #4067
wilco87 is offline wilco87  Netherlands
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Join Date: Oct 2015
Location: Haarlem
Quote:
Originally Posted by Panelhead View Post
Are the inputs (RCA jacks) isolated or grounded?
Inputs are isolated from case and grounded.

Removed all the wires, selector and volume: Just the boards and output. Stil humming. I will remove the boards from the case and report back.
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Old 6th December 2018, 12:54 PM   #4068
Joseph K is online now Joseph K  Hungary
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Join Date: Dec 2004
Location: gran sasso
Wait a minute.. it is my favourite case: You did not connect any way the board PGND references to the case. I see the PE connected to the case but the boards are floating..

This is the typical situation forced around here: all heavy attention to the safety rules - - and zero attention to signal integrity..
Sorry it's not directed to You but the general attitude..

Ciao, George
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Old 6th December 2018, 01:09 PM   #4069
Joseph K is online now Joseph K  Hungary
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Join Date: Dec 2004
Location: gran sasso
That is, to be very clear: these amps are high speed solid state devices. Easily go to the MHz region in their usable bandwith. They have to be treated as such. They are not Toobzz!

For any kind of sensitive high speed electronics : shielding is an all important element.
The case cannot be floating antenna receiver closely coupled to the sensitive parts (like high impedance input pins of LM3886 <> heatsink)

The case must be connected with low ! Inductance, short thick conductor to the metal case / shield & heatsink.

PE earth connection is for safety. It is in clear collision with signal integrity requirements, and would need extra care to resolve properly.

Ciao, George
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Old 10th December 2018, 11:40 AM   #4070
wilco87 is offline wilco87  Netherlands
diyAudio Member
 
Join Date: Oct 2015
Location: Haarlem
Quote:
Originally Posted by Joseph K View Post
That is, to be very clear: these amps are high speed solid state devices. Easily go to the MHz region in their usable bandwith. They have to be treated as such. They are not Toobzz!

For any kind of sensitive high speed electronics : shielding is an all important element.
The case cannot be floating antenna receiver closely coupled to the sensitive parts (like high impedance input pins of LM3886 <> heatsink)

The case must be connected with low ! Inductance, short thick conductor to the metal case / shield & heatsink.

PE earth connection is for safety. It is in clear collision with signal integrity requirements, and would need extra care to resolve properly.

Ciao, George
Hi George, thanks for the tips. Just to be sure, do you advise the same as luca (loop breaker, heatsink connected on zero volt Line)? This breaks the floating design Dario proposes, but listening to that hum is quite a challenge.

The heatsinks seem to be the source of the hum. Just with one channel installed, without anymore extra wires the hum remains.

Hopefully the stuff for the loopbreaker will be here at friday.

Last edited by wilco87; 10th December 2018 at 11:42 AM.
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