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diyAB Amp  The "Honey Badger" build thread
diyAB Amp  The "Honey Badger" build thread
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Old 14th April 2019, 01:09 PM   #3511
Grendel321 is offline Grendel321  Congo-Brazzaville
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Quote:
Originally Posted by Kay Pirinha View Post
I see 5 pin power devices. What are these? Do they contain temperature sensing diodes (ThermalTracks)? If so, why's there also this BD139 Vbe multiplier?
Best regards!
Yes, they are the NJL3281 thermal track devices. The thermal track transistors diodes by themselves alone proved inadequate for thermal bias stability despite the datasheet claims, therefore it is necessary to use them together with a traditional vbe multiplier (bias spreader) to achieve thermal stability. They are generally placed in series with the traditional vbe multiplier. The tracking diodes introduce the temperature effects of the output transistors, while the vbe multiplier transistor takes care of controlling that part of the bias spread necessary for the predriver and driver transistors.
I am of the understanding that in this method the vbe multiplier transistor should NOT be mounted on the heatsink as it should have nothing to do with thermal bias, so i am thinking that it was a error of the silicon chip design to mount the bd139 on the heatsink.

Bob Cordell talks about this a lot in his book designing audio power amplifiers. I have copied the image below from his book, i hope he does not mind it as it is to show the method.

test.jpg

Last edited by Grendel321; 14th April 2019 at 01:12 PM.
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Old 14th April 2019, 01:28 PM   #3512
Grendel321 is offline Grendel321  Congo-Brazzaville
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Originally Posted by spierdolony View Post
Hi guys,


Would it be correct to do the following:

Speaker return to amp board
Signal return to amp board
Capacitor midpoint on power supply to amp board ground point
Join signal ground to speaker (load ground) and then to local PCB star ground. Local on board PCB decoupling capacitors grounds are joined together and then returned to the local PCB star ground as well. Return the local PCB star ground to the main power supply decoupling capacitors ground.
The best location for the mains earth wire to be grounded with the chassis ground would be the input signal ground.
I see this arrangement in most low distortion designs to minimize ground loops and hum.
Regardless, the only real way to get immunity from ground loops and hum is to use a fully differential input stage.

Last edited by Grendel321; 14th April 2019 at 01:33 PM.
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Old 14th April 2019, 02:21 PM   #3513
Kay Pirinha is offline Kay Pirinha  Germany
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Regarding grounding, both schematics are identical.


Best regards!
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Old 14th April 2019, 09:49 PM   #3514
Mark Whitney is offline Mark Whitney  Netherlands
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Quote:
Originally Posted by spierdolony View Post
Hi guys,

I'm also confused about the correct grounding layout for the HB.

Having a look at Bob Cordells Star on Star diagram 16.8

Attachment 749651

Would it be correct to do the following:

Speaker return to amp board
Signal return to amp board
Capacitor midpoint on power supply to amp board ground point

Then connect TP0 on amp board to safety earth.

This configuration would follow Bobs 16.8 diagram the best and be a star on star ground.

It seems most advice so far to approximates Bobs 16.1 diagram

Attachment 749661

i.e.

Make power supply capacitor junction the star ground point and connect everything to it including safety ground. No one seems to connect signal return directly to power supply star ground. Instead signal return goes back to the amp board and then would eventually connect via the power supply ground and about 5 ohms of resistance through the pcb.

Firstly am I on the right track, does my interpretation of 16.8 make sense?

Why doesn't anyone recommend returning signal return to all the way to the power supply? This would match the 16.1 diagram best.

Which is better out of the two options described?

Is there a good image of the chassis ground wiring that I can just follow so i can finish the amp.....
I believe this is what was intended by the designer.
Attached Images
File Type: jpg HoneyBadger.jpg (198.5 KB, 120 views)
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Old 14th April 2019, 10:02 PM   #3515
Bonsai is offline Bonsai  Europe
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I cover this issue in my ground loops write-up (see link below).

If you run the speaker return wire back to the amplifier module PCB, the important thing is to have good bulk decoupling on the amp module PCB, and it needs to be wide band. That way, you end up with only LF speaker currents in the 0V wire from the amplifier to the PSU star ground - the HF currents are trapped on the module through the bulk decoupling.

If you decide you want to run the speaker return back to the central start ground, just twist it with the speaker hot and then run it (twist if you can) with the 0V supply connection. There will be a short section that will not be coupled to either the speaker hot or the 0V to the PSU, but it should still be ok.


From my experimentation, it seems practically there is not much between the two - if and only if - your amplifier module board decoupling is good, which is pretty easy to do.


Happy building

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Old 14th April 2019, 11:11 PM   #3516
TonyTecson is offline TonyTecson  Philippines
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diyAB Amp  The "Honey Badger" build thread
in my amps, safety ground is connected to the nearest netalwork, i.e. in one of the screws holding the IEC socket screws...

i do not connect the main star grounding of the psu direct to chassis, but where the signal is lowest, via the input jacks and thru a low ohm resistor....

i have done amps using plastic casings, and grounding was never an issue...
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Old 15th April 2019, 05:37 AM   #3517
Mark Whitney is offline Mark Whitney  Netherlands
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This design already has a hum breaking resistor (HBR) R4 and some diodes between power and input ground. My concern connecting the input ground to chassis would be safety.
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Old 15th April 2019, 12:17 PM   #3518
spierdolony is offline spierdolony
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Thanks for the comments and especially to Bonsai your guide is exactly what I've been looking for.
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