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Dx Blame MKIII-Hx  - Builder's thread
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Old 16th November 2013, 07:57 AM   #1931
BV is offline BV  Slovakia
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Attached is relative "blameless" grounding concept for unbalanced stereo amp sharing one common PSU for both channels. R1, R4 should be the same value, R2, R3 too (CMMR..). Other channel identically.
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Last edited by BV; 16th November 2013 at 07:59 AM.
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Old 18th November 2013, 06:33 AM   #1932
lgreen is offline lgreen  United States
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Originally Posted by still4given View Post
Hi LG,

I like it a lot. It has very good clarity and that kind of authority that is tough to get without high power. I want to put in a speaker protection circuit mainly because it has a nasty groan after shutoff as to voltage winds down. I will probably put in a soft start too although I haven't needed it so far.
Thanks for the response. My DX Corp Amp (DX HR II) is fantastic, no problems, ever. Looks good and sounds great but as you say sounds a lot louder with more authority than it should. I like to encourage people to try Carlos' designs but the support and documentation is not the greatest (depending on the project). Anyway, congrats!
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Old 22nd November 2013, 09:12 AM   #1933
destroyer X is offline destroyer X  Brazil
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Default Please, ground your potentiometer case the way shown in this video

Approximately at 06:20

How To Build A Tweed Deluxe Kit - YouTube

regards,

Carlos
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Old 24th November 2013, 01:14 AM   #1934
canonnica is offline canonnica  Canada
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I wonder how many of you used speaker protection circuit for that project?!?

I did, but it creates a problem to my... let me explain.

I have an odd 120HZ buzzing. I just found that I have a ground loop that circles around my rear power transfo.

My amp is built as a dual mono, meaning everything is doubled and completely isolated... except for the star ground. and that'S the gotcha. My line inputs goes one to the far left and the other to the far right. I have a grounding post that is shared for both channels. It's located between the two power transfos. See on the picture that nicely done ground loop.

Of course I need to break open that loop. The thing is I cannot totally separate the two grounds since I have a shared speaker protection circuit that needs to be grounded to the channel it protects, ie both...

So I was wondering if I would prefer to have two speaker protection circuits, or simply get rid of the one that's there...

Here is a pic of the inside of the amp... of course feel free to suggest wiring improvements. I don't plan to redo the whole interior nor to replace the chassis but I obviously lack comme knowledge to properly route the wires.

Regards,
Martin.
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File Type: jpg IMG_2442.jpg (439.0 KB, 273 views)
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Old 24th November 2013, 01:39 AM   #1935
still4given is offline still4given  United States
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I'm planning to install speaker protection. I had a kit waiting for me when I returned home last night. I will let you know if I get any new hum once it is installed.

Last edited by still4given; 24th November 2013 at 01:46 AM.
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Old 24th November 2013, 06:53 AM   #1936
overall feedback is offline overall feedback  Croatia
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Dx Blame MKIII-Hx  - Builder's thread
Quote:
Originally Posted by canonnica View Post
I wonder how many of you used speaker protection circuit for that project?!?

I did, but it creates a problem to my... let me explain.

I have an odd 120HZ buzzing. I just found that I have a ground loop that circles around my rear power transfo.

My amp is built as a dual mono, meaning everything is doubled and completely isolated... except for the star ground. and that'S the gotcha. My line inputs goes one to the far left and the other to the far right. I have a grounding post that is shared for both channels. It's located between the two power transfos. See on the picture that nicely done ground loop.

Of course I need to break open that loop. The thing is I cannot totally separate the two grounds since I have a shared speaker protection circuit that needs to be grounded to the channel it protects, ie both...

So I was wondering if I would prefer to have two speaker protection circuits, or simply get rid of the one that's there...

Here is a pic of the inside of the amp... of course feel free to suggest wiring improvements. I don't plan to redo the whole interior nor to replace the chassis but I obviously lack comme knowledge to properly route the wires.

Regards,
Martin.

Supply wires are not twisted, the loop is between it. Try to turn phase on one transformer also, maybe buzzing decrease.
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Old 24th November 2013, 09:03 AM   #1937
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by canonnica View Post
I wonder how many of you used speaker protection circuit for that project?!?

I did, but it creates a problem to my... let me explain.

I have an odd 120HZ buzzing. I just found that I have a ground loop that circles around my rear power transfo.

My amp is built as a dual mono, meaning everything is doubled and completely isolated... except for the star ground. and that'S the gotcha. My line inputs goes one to the far left and the other to the far right. I have a grounding post that is shared for both channels. It's located between the two power transfos. See on the picture that nicely done ground loop.

Of course I need to break open that loop. The thing is I cannot totally separate the two grounds since I have a shared speaker protection circuit that needs to be grounded to the channel it protects, ie both...

So I was wondering if I would prefer to have two speaker protection circuits, or simply get rid of the one that's there...

Here is a pic of the inside of the amp... of course feel free to suggest wiring improvements. I don't plan to redo the whole interior nor to replace the chassis but I obviously lack comme knowledge to properly route the wires.

Regards,
Martin.
That's the problem with every dual or multi-channel power amplifier that is connected to a source with a common signal ground/return.
It has nothing to do with the speaker protection relays or relay driver circuit.

You have to reduce the currents in the power amplifier loops to such a level that the interference voltage becomes low enough not to be a problem.
This reduction of loop currents, generally requires extra resistors in the loops.
Reducing the imposed voltages generally comes from using low resistance return cabling.


BTW buzzing instead of hum usually indicates an amplifier ground connected to the PSU zero volts. It is the high frequency of the spiky charging currents that are being imposed on the audio ground reference.
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Last edited by AndrewT; 24th November 2013 at 09:14 AM.
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Old 24th November 2013, 11:46 AM   #1938
Vostro is offline Vostro  South Africa
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" BTW buzzing instead of hum usually indicates an amplifier ground connected to the PSU zero volts. It is the high frequency of the spiky charging currents that are being imposed on the audio ground reference."

+1 on a previous amp of mine, I had zzz sound on my speaker, the problem for me was that I had my main smoothing caps on my amp pcb which connected straight to the star ground point on my pcb.

I took out the 6800uF caps and substituted 1000uF local on pcb, and moved the 6800uF caps off board.

Regards
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Old 24th November 2013, 01:55 PM   #1939
canonnica is offline canonnica  Canada
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The buzzing is definitely picked-up by the audio cable that's running from the RCA connectors to the board's input lugs.

With everything connected, if I short the input at the RCA connector's end, it buzzes.

If I disconect the board input cable and short the input at the board, it becomes dead silent.

I do use the lifted ground resistor on the board.

I will try to find a screened two cores wire for the input just like S4G did and ground the screen to the chassis at the RCA connector end. I will put a 10R resistor between the audio ground and the chassis ground (screen) at the RCA connector's end too.

The screened wire should help isolate from noise pickup, and the extra resistor at the RCA end should help send the picked-up noise back to the ground.

I will post results.

Martin.
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Old 9th December 2013, 05:38 PM   #1940
still4given is offline still4given  United States
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Dx Blame MKIII-Hx  - Builder's thread
Hi Martin,

Did you get a chance to address some of this? I still have a very slight hum. It is very low and not noticeable when listening to music but it is still bugging me that it is there at all. None of my other amps do this. I tried attaching a resistor from star to case and it makes the hum worse. I have been working on other amps but I want to get back to this soon. I like the sound of this amp a lot so I really want to get to the bottom of this problem.

Thanks, Terry
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