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The YARRA Preamplifier/HPA for Melbourne DB Group Buy
The YARRA Preamplifier/HPA for Melbourne DB Group Buy
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Old 25th February 2019, 08:38 AM   #11
mordikai is offline mordikai  United States
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Sweet!

Vunce - 1 board set - USA
zman01- 1 board set - USA
twitchie- 1 board set - Canada
BRN - 1 board set - USA
Roundtoit - 1 board set - USA
Russellc- one board set. USA
mordikai- 1 board set - USA
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Old 25th February 2019, 09:48 AM   #12
poseidonsvoice is offline poseidonsvoice  United States
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The YARRA Preamplifier/HPA for Melbourne DB Group Buy
Iíll cheer you guys from the sidelines. After looking at the number of individuals who wanted 4 boards of the Melbourne GB, I suspect at least 18-20 of these Yarra boards to be gone!

As much as I feel that I am a board hog I will remain a bystander on this one!

Best,
Anand.
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Old 25th February 2019, 11:41 AM   #13
bologna1 is offline bologna1  United States
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The YARRA Preamplifier/HPA for Melbourne DB Group Buy
I just finished building the Aksa Lender. You can't have too many preamps.

Vunce - 1 board set - USA
zman01- 1 board set - USA
twitchie- 1 board set - Canada
BRN - 1 board set - USA
Roundtoit - 1 board set - USA
Russellc- one board set. USA
mordikai- 1 board set - USA
bologna1 - 1 board set - USA
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Old 25th February 2019, 01:30 PM   #14
Mark Johnson is offline Mark Johnson  United States
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The YARRA Preamplifier/HPA for Melbourne DB Group Buy
I think your buyers might welcome a list of officially sanctioned and formally approved replacements/upgrades for the TIP41 and TIP42 power transistors, of course retaining the BCE pinout for compatibility.

Three possibilities that immediately spring to mind are (D44H11 + D45H11) , (2N6107 + 2N6292) , and (MJE15030 + MJE15031) , but you may have different candidates and criteria.

Also I think it might be wise to arrange the PCB layout so it will accept high current diodes in the safety ground isolation leg "V1041" "V1043". Six ampere diodes are available in axial lead packages which aren't ginormously bigger than 1 amp diode axial packages. But of course the 6A attachment legs are much greater diameter. To name one example, the "6A4" diode (dataseet) might offer a lot more peace of mind, at a very low additional cost in PCB area. And if someone wants to stuff their board with 1 amp diodes to save fifty cents, you can't stop them.
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Old 25th February 2019, 03:28 PM   #15
TungstenAudio is offline TungstenAudio  United States
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Yeah, need a place to park two of my Melbourne daughtercards.

Vunce - 1 board set - USA
zman01- 1 board set - USA
twitchie- 1 board set - Canada
BRN - 1 board set - USA
Roundtoit - 1 board set - USA
Russellc- one board set. USA
mordikai- 1 board set - USA
bologna1 - 1 board set - USA
TunstenAudio - 1 board set - USA
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Old 25th February 2019, 03:45 PM   #16
xrk971 is offline xrk971  United States
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The YARRA Preamplifier/HPA for Melbourne DB Group Buy
The 6A diodes is a good idea - depends on if changing the hole size and regenerating post-processor is too much of a pain, given that the rectifiers for each channel are composed of the same 1A 1N4005 diodes, there probably isn't too much of a risk of needing more than 1A of safety grounding path.
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Old 25th February 2019, 04:32 PM   #17
Mark Johnson is offline Mark Johnson  United States
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The YARRA Preamplifier/HPA for Melbourne DB Group Buy
The purpose of the safety ground is to protect anyone who touches the chassis if and when the mains accidentally becomes shorted to the chassis. The current in such a short is only limited by the mains itself, before the house panel circuit breaker (USA) pops or the in-plug-fuse (UK) blows. Which means it could be ten or fifteen amperes for 1 or 2 seconds.

BTW 10A04 axial diodes are in the same package as 6A4 diodes, same footprint. More grunt.

Last edited by Mark Johnson; 25th February 2019 at 04:34 PM.
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Old 25th February 2019, 04:58 PM   #18
xrk971 is offline xrk971  United States
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Let me see if I have this right.

The chassis is certainly connected to mains earth ground for this reason. The actual Yarra preamp is on the electrically isolated (via isolation from transformer primary and secondaroies) low voltage side. The grounding between chassis/earth to the low voltage GND of the preamp board is mostly for purposes of noise reduction. The noise reduction is improved by adding a thermiator between the analog ground and earth ground. We add the diodes to allow a higher current path in case there is a component failure that allows the maximum current from the secondaries, through the rectifier diodes, should they need to, have a path to go from the preamp low voltage ground to the earth ground.

At no point should mains 15A 120VAC ever be present on the preamp board proper assuming the CE/UL certified Talema transformer does its job of isolating the primary from the secondary.

I think the displayed schematic may be an older version because I see two independent ground loop breakers for each channel on the preamp board. Each one has a pair of 1N4004 diodes in addition to an SL15 47003 thermistor (R1042/R1042) rated at 3A for larger currents should the diodes fail. Although I think the value of this thermistor might need to be revised from the one spec’d by JPS64.
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Last edited by xrk971; 25th February 2019 at 05:01 PM.
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Old 25th February 2019, 05:47 PM   #19
Mark Johnson is offline Mark Johnson  United States
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The YARRA Preamplifier/HPA for Melbourne DB Group Buy
Both ends of the safety ground isolation leg, exit the chassis and are present on external I/O terminals. Exposed. Therefore some idiot named Murphy can apply the full mains voltage between those terminals. Murphy's Law tells you that what possibly can go wrong, eventually will go wrong.

Here's a diagram. Flow of undesirability highlighted in magenta.

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Old 25th February 2019, 06:10 PM   #20
xrk971 is offline xrk971  United States
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I think the dual 3A rated thermistors (R1043/R1044) should take care of that even with the 1A diodes removed.

But still not sure what you are trying to show on the diagram? That because there exists a mains wire somewhere in the case, there is a possibility of that wire shorting to the ground plane, and as such a possibility exists due to Murphy's Law, analog grounds must be attached to earth mains by suitable current carrying device. So right now we have two SL15 47003 3A thermistors in parallel for 6A of total current between AGND and PGND. Is that not enough?

The YARRA Preamplifier/HPA for Melbourne DB Group Buy-yarra-schematic-thermistor-png
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Last edited by xrk971; 25th February 2019 at 06:12 PM.
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