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PostPosted: 12 Jan 2017, 19:42 
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I have replaced Ck with 470uf 63V and moved the 100K input resistor to where it should be. On my 99db efficient Beymas there is hum. I have to get close to the speakers to hear it. On lesser efficiency drivers it may not be a concern.

Also because I am playing music from a Pi running on a battery pack if I touch the ground of the RCAs I get a buz and hum through the amp.

As stated earlier only the frame of the filament tranni is connected to mains earth. What if I connect mains earth to the PS negative? I can check with a meter if there is any voltage differential before I do it and do it with a alligator lead.

Should I try this or not?????

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PostPosted: 12 Jan 2017, 19:58 
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Without isolation and with a full wave bridge, it's dangerous. You'll likely fry your diode bridge. Check the voltage difference and report back.

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PostPosted: 12 Jan 2017, 20:10 
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Suncalc wrote:
Without isolation and with a full wave bridge, it's dangerous. You'll likely fry your diode bridge. Check the voltage difference and report back.


Do you think though it will help hum and incompatibility issues? Or am I just best to build an external PS?

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PostPosted: 12 Jan 2017, 20:13 
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Another thought is a mains isolation tranni.

Just checked pricing - big, ugly and expensive.

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PostPosted: 12 Jan 2017, 21:06 
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The voltage difference between mains earth and negative of the PS is 120V. This is half mains voltage. No way am I earthing the negative of the PS.

I'm now thinking an external PS. I like the amp but cant try it with my better DACs etc.

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PostPosted: 12 Jan 2017, 22:36 
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This amp is out of action until I can fix the PS issue. Just thinking about it; 120V between the earth of the RCAs and mains earth means had I have had my hand on the RCA earth my other hand on the chassis of an earthed amp, player or whatever I would have been electrocuted. Only 120V but at my age and across my chest may have left me dead.

Not ruling out direct mains but there is all sorts of problems associated with it. Not for this amp.

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PostPosted: 12 Jan 2017, 22:45 
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I just want to make it clear, Suncalc (Matt) had nothing to do with the PS design. His part in this project was to design an amp around some old metal 6L6s and new 12AT7. And for this I'm very greatfull. The PS problems are my own folly but Matt has been most helpful with suggestions.

This amp is not finished yet. It will be perfect, lol.

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PostPosted: 15 Jan 2017, 01:08 
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Long story short, I have installed four diffent PS configurations. The last one works.

This PS has a 160VA toriodal external tranni. The two 12V winding are parralled to provide 13A. I'm probably using half of that but at least nothing is getting red hot anymore. The toroidal is the step down for 12V heaters and a internal 5A step down is stepping up to 250V. I know this is down from what has been designed but I want to try this for a while. If the 5A 12V step up does not get too hot I'll try it on the 9V taps. I have parralled the 12V secondaries (now the primaries) to handle the current.

Here is where a shocking admission is made. This amp has been a real ass. But it was my fault. I had the RCAs wired wrong. So ground was signal. This is why the amp only worked with battery media players. Also three bad solder joints. I only highlight this so others may lean from my mistakes.

Amps going now but may recieve yet another mod to the PS to see if I can up the HT without burning out a big tranni.

Initial sound; heavy, solid and grounded.

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PostPosted: 19 Jan 2017, 07:10 
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Wow! Im quite shocked just how good this amp is. The Class D monoblocks aren't getting a show in my system.

This little amp, built in a $9 wooden box, is extraordinary. I have mainly been listening to classical and opera. It excels at opera.

I'm so impressed I've started second. Not sure weather it is the 6L6s or the 12AT7 tube which is holding the magic but the sheer grunt of this amp is astonishing.

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PostPosted: 19 Jan 2017, 15:30 
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Good to hear.

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