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Black Lace - 6V6 power amp, direct mains, old school
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4623
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Author:  mwhouston [ 01 Aug 2016, 08:21 ]
Post subject:  Re: Black Lace - 6V6 power amp, direct mains, old school

Part II.

I got to enjoy Black Lace with my DIY Pi3B music server and DIY XMOS DSD64 DAC. It took a full hour before Black Lace got warmed up but boy did it finally perform. I played one whole album (all 24/96) after another and couldn't believe just how good it all sounded. The only issue is the low -3db point is 60hz but for most of the classical music I listen too that is really low enough.

Author:  mwhouston [ 03 Aug 2016, 21:18 ]
Post subject:  Re: Black Lace - 6V6 power amp, direct mains, old school

This is how the PS finished up and shows where the dual rails start except the last electro is 470uf.
Attachment:
6V6PS.jpg

Author:  mwhouston [ 06 Aug 2016, 21:21 ]
Post subject:  Re: Black Lace - 6V6 power amp, direct mains, old school

Here is the latest drawing of the dual rail PS for Black Lace. Corrections to last drawing are last cap is 470uf and the CT for the power tranni secondary has been added.
Attachment:
6V6PS.jpg

Author:  mwhouston [ 10 Aug 2016, 19:27 ]
Post subject:  Re: Black Lace - 6V6 power amp, direct mains, old school

I have had the amp in play for a while now since the PS mods. This amp is virtually dead silent. I think the big twin electros have settled in. Only by pressing my ear to the 15" bass cone of my high efficiency Beymas can I hear even the faintest hum. It's not really a hum it's just an "on" sound. Vey happy with the little amp now.

Author:  Peter W. [ 11 Aug 2016, 08:01 ]
Post subject:  Re: Black Lace - 6V6 power amp, direct mains, old school

YIKES: RANT WARNING!

From about 1935 until well into the 1960s, many radios were transformerless - the tube filament string matched line voltage (with or without a dropping resistor, c.f. "Curtain Burner"), and were made in their uncounted millions all over the world. In most cases, the chassis would be "HOT" as long as the radio was plugged in, whether running or not. These radios would be in plastic, Bakelite, Catalin, or wooden cases, and rely on the insulating knobs and hidden screws to protect the user from shock. So, the concept is not new. Commonly and in the US, these were called AA5 (All American Five) radios. Over 300,000,000 (yes, that is a correct figure) radios were made in the US alone between 1911 and 1963. The bulk of them were AA5/6 models.

Today, we have some protective options that can reduce the risk from such a device - GFIC devices are one. As I am a collector of vintage radios, I have my share of AA5 radios. I feed them with an outboard extension box fed with a three-wire cord to a switch to a GFIC receptacle. Such a precaution would be a reasonable option for the proposed amp. It could even be included within the chassis rather than as an outboard device.

Pretty much every switching power-supply out there *STILL* uses a transformer, but by switching at extremely high frequencies, the transformer is now not much bigger than an M&M Peanut candy. And THAT goes back to WW-II when aircraft electronics had to be light - so they used 400 Hz current, allowing for much smaller transformers. So, don't think that tiny little wall-wart is not isolated. It is.

Bottom line: The idea is not new. There are ways to make such a device reasonably safe. And for the very same reason that AA5 radios have no power-transformer (cost), there is a legitimate place for investigating this with audio equipment. BUT WITH ALL DUE CAUTION. We have cats, dogs, and grandkids running through our house. So I have an overly cautions approach to these things. But at the same time, I grew up with AA5 radios, and other appliances such as single-insulated. two-wire cord all-metal drills... Remember those? We know much more now, and are better prepared to deal with what we know. Accordingly, we are obligated to use that knowledge when dealing with potentially deadly devices. When I do repairs and restorations of vintage stuff, I will do things like use polarized line cords, make sure that the 'hot' side is switched and so forth. Also I will explain to a non-expert the issues and dangers of an AA5 ,or an amplifier that has 500VDC and extremely hot surfaces exposed if the cover is not in place. My expression for these things is "Preparing them for polite society". If I would not let my grandkids around it when in use, it will not be in the house. Ah, well!

End Rant.

Author:  mwhouston [ 11 Aug 2016, 08:04 ]
Post subject:  Re: Black Lace - 6V6 power amp, direct mains, old school

I used a trannie.

Author:  mwhouston [ 14 Aug 2016, 08:10 ]
Post subject:  Re: Black Lace - 6V6 power amp, direct mains, old school

Finally got my new digital CRO working and measured the noise - 955uV. That's right folks less than 1mV. That is bloody quiet. 2.5mV is bloody quiet this amp is dead silent. But here is the thing when I turn on the LED lighting above my work bench it jumps to 12mV. Easy to see how noisy LED light are and should be around hifi gear.

Author:  famousmockingbird [ 14 Aug 2016, 11:24 ]
Post subject:  Re: Black Lace - 6V6 power amp, direct mains, old school

I have an LED light above my bench and it doesn't emit any noise into any of my test gear, it is plugged in the same branch circuit as my test gear too. I wonder if in Australia the restrictions are more relaxed on electronics polluting the power grid. I feel confident saying that the filters found before SMPS in modern gear isn't just for keeping noise from the grid out but it's actually to keep noise from the SMPS from going into the grid. You could whip up a small filter box fitted with common and differential mode filters to plug the LED fixture into.

Why do you have 6.3v on the 5U4GB filament/cathode?

Author:  Suncalc [ 14 Aug 2016, 11:46 ]
Post subject:  Re: Black Lace - 6V6 power amp, direct mains, old school

famous mockingbird wrote:
... the filters found before SMPS in modern gear isn't just for keeping noise from the grid out but it's actually to keep noise from the SMPS from going into the grid.
Very true.

If you are really interested in power system noise, pull up a copy of MIL-STD-461E and run the following four tests: conducted emissions 01 (CE01), conducted susceptibility 01 (CS01), radiated emissions 01 (RE01), and radiated susceptibility 01 (RS01). This is the set of tests covering the lower frequencies for power leads. A good set of tests for amy piece of equipment be it lights or audio gear. Much better than guessing.

Author:  famousmockingbird [ 14 Aug 2016, 14:54 ]
Post subject:  Re: Black Lace - 6V6 power amp, direct mains, old school

Suncalc wrote:
If you pick up the driver B+ after the second choke, then variations in B+ at that point due to the heavy load of the power stage get inserted back into the driver.


The PS isn't regulated so there is going to be B+ variations regardless (mains fluctuations). Besides that what heavy load do you speak of and how does it get back into the driver? From a DC standpoint the power stage should have very little current variation unless the amp is being run into clipping.


Suncalc wrote:
And because the power stage load is highly inductive, i-v phase offsets can cause all kinds of headaches to the driver stage.


Care to explain?

The inductive load means at low frequencies when the reactance in the OPT dominates, the current through the inductor lags by 90 degrees. At higher frequencies the speaker load dominates. I can't see how this would effect the driver? AC current at the plate passes through the power supply and back up through the cathode bypass cap back to the tube. Since ESR is dominated by Xc at frequencies we care about then use a big enough cap and there will be a low impedance current loop. 470uF @ 20Hz = 16R


This was from way back on page 3 and I found it very interesting, any information shared is much appreciated.

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