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BA-3 Amplifier illustrated build guide
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Old 24th November 2020, 09:08 PM   #601
andynor is online now andynor  Norway
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Btw: Can any of you guys using rectifier ground loop breakers post a pic, explain a bit how it works, and possibly best of all, how my build possibly could be helped?

Regards,
Andreas
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Old 24th November 2020, 09:08 PM   #602
Dennis Hui is offline Dennis Hui  Canada
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BA-3 Amplifier illustrated build guide
New fets? I seem to recall something about some fets running cooler than others. Is
that what the replacements are for? (Or are you already planning to build another
amp? )
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Old 24th November 2020, 09:12 PM   #603
andynor is online now andynor  Norway
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One of the N channels on the left sink biases much higher than the others. 30%. ZM says that those three N channels definately have a matching issue. But the store don’t buy it, since, it appears, Papa matched them himself! (!!)

So they asked me to do some tests for which I do not have the equipment, knowledge or time for. So instead I ordered another matched set. But who knows? I now have two transformers, three heatsinks, two sets of boards for BA-3, three sets of MOSFETs (2xBA-3 and one for F5T), and boards for F5t. The future is bright? Or maybe just busy... haha

Three sinks: do you think it is possible to build half an amp?

Last edited by andynor; 24th November 2020 at 09:15 PM.
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Old 24th November 2020, 09:19 PM   #604
andynor is online now andynor  Norway
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Quote:
Originally Posted by cubicincher View Post
Hello Andy,


I make my connections the same way like you did - one exception:


I go from mid PSU (0 V = audio ground) over the groundloopbreaker
(35A bridgerectifier+CL60) to IEC-inlet ground/case.
So, my audioground is slightly floating.



I have added a sketch....


Don't ask me if this is the right way???



Greets
Dirk
Quote:
Originally Posted by Dennis Hui View Post
New fets? I seem to recall something about some fets running cooler than others. Is
that what the replacements are for? (Or are you already planning to build another
amp? )
Most specifically, since the amp if working fine now, the replacements are intended to let me bias high enough to really keep them sinks warm. 200 wata dissipation apprently doesnt overheat them. Some advantages of living in a cold country!
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Old 24th November 2020, 09:19 PM   #605
cubicincher is offline cubicincher  Germany
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Good night for today!
Dirk
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File Type: jpg PSU_art_ba1 pdf(1).jpg (96.0 KB, 65 views)
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Old 24th November 2020, 09:20 PM   #606
andynor is online now andynor  Norway
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Thanks, Dirk! I have seen that. But can’t say I ever understood it. Will get back to the schematica for everything I do wrt gnd from now.
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Old Today, 08:55 AM   #607
cubicincher is offline cubicincher  Germany
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Hello Andy,


I had to search a little bit - but there are many articles and pics about groundloopbreakers on the web.....
A good article is on the website of Elliott Sound Products:


Earthing (Grounding) Your Hi-Fi - Tricks and Techniques


Perhaps you know it?



Greets
Dirk
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Old Today, 09:16 AM   #608
andynor is online now andynor  Norway
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Good morning, Dirk!

I will check that one out. I am currently reading and rereading Bonsais article on the subject:

http://hifisonix.com/wordpress/wp-co...ound-Loops.pdf

As I see it, my NTC to chassis does that job for me right now. Mostly, I am just curious on the physics behond the extra rectifier. Maybe try it? =)

However, since my hum does not go away when i connect the amp to an ungrounded outlet, I believe the error is elsewhere, like you expressed might be the case. I am currently thinking it is either a cross channel loop, capacative coupling between secondaries and primaries of the tranny, or a common impedance loop. I will in time try to falsify those hypothesis. But will still explore improving my gnd scheme.

Btw, do you have a Mouser link for those rectifiers you use in your beauty of an amp? My fast rectifiers make quite some noise, so I am hesitant of moving them closer to the PSU and FE.

Regards,
Andy

Last edited by andynor; Today at 09:19 AM.
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Old Today, 06:10 PM   #609
Bonsai is online now Bonsai  Europe
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Hello Andreas,
I'm not an expert in these things, but let’s try to improve it. You will need to do some tests to determine what kind of problem it is.

1. Unplug the amp from the mains and remove any input cables and disconnect from the speakers.

2. Disconnect the thermistor (TH1 in post 605 circuit diagram). Measure from the amplifier 0V and input socket signal ground to the chassis to confirm it is open circuit (use high resistance mode, not diode mode). You should be measuring 100's of k Ohms or higher. If you measure a short or very low Ohms, you will have an earth loop problem in your amp and need to resolve it. Reconnect the thermistor (for safety) after you have fixed it.

3. The next test is for common impedance noise. Make sure the input connector signal grounds are NOT joined together inside the amp. Short each input, connect the speakers and re-apply power. If you hear hum, there is a good chance you have a common impedance coupling problem and this means you should look carefully at how the grounds are connected at the PSU side - I assume since this is Nelson Pass design amp board, there are no problems on the amplifier module side. If you hear no noise (or very low noise), then there is a good chance you do not have a common impedance coupling issue, or that it is not your biggest problem at this stage.

4. If there is no noise in step 3, the next test is for a cross-channel ground loop. In a typical cross channel ground loop, the amplifier is quiet with only one input channel connected, or no inputs connected, but when you connect BOTH input channels, then you get hum. To test for this, take a standard 1 metre phono cable and connect it from one input to the other so it forms a loop outside the amplifier. You should hear no noise on a good amp. If you get hum (but none with the cable disconnected both ends), its likely a cross channel ground loop and it is arising inside your amp due to the transformer mag field intersecting a loop formed by the signal ground connection from the one input, through the module, through the 0V power connection to the PSU, out to the other module via the same route and around the external cable. To overcome/reduce this issue, check you using hum breaking resistors (HBR) - see pages 30-41 in the Ground Loop presentation (link below in my signature) and then check point 5 below.

5. Have you routed the input connector to amplifier module cables correctly? The shortest connection is not always the quietest (See pages 61-64 in the Ground Loop presentation). I usually mount these next to each other not separate on either side of the rear panel (although I did this on my earlier amps). You do this to minimize the loop area between the channels. If you join the grounds together where the connectors come into the amplifier, you trap cross channel ground loops inside the amplifier. If your input connectors are on either side of the rear panel and you are running the input cables directly to each amplifier module, you will be creating a very large cross channel ground loop area and you will not help the situation by joining the grounds together on the input sockets in that case. Only bond the input grounds together if the connectors are located right next to each other.

6. This is a class A amplifier with a heavy constant current draw. The transformer will be radiating big magnetic fields compared to a class AB amplifier even with no input signal. If you are still getting hum and all the above is correct, I would lift the transformer out of the chassis a few feet away and run twisted cables to the rectifiers to see if it solves it. If it does, it’s a general mag field problem and you then need to consider a better transformer - hopefully you can avoid that though. For class A amplifier, I always recommend an oversized toroid, with a GOSS band and a pri-sec screen for the reasons I mentioned above.

7. Ground lifter: I usually use a 35A chassis mount rectifier - see page 25 in the 'Ground Loop' presentation. I have not tried the thermistor method, but suspect it works more like an HBR than a true ground lifter. Note on my commercial products I do not use a ground lifter. The amplifier 0V goes straight to the chassis and is bonded to the incoming power safety earth (I do this for safety reasons).
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