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The YARRA Preamplifier/HPA for Melbourne DB Group Buy

Founder of XSA-Labs
Joined 2012
Paid Member
Edit Apr25, 2020: Here is the current Yarra Preamp Family
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More info on which is which here.


Edit Nov 29, 2019: Note that the Yarra is a true dual monobloc design. That means that the ground from the left channel never mingles with the ground from the right channel, except via the two ground loop breakers (either NTC or 10R resistor and 22nF caps). So if your audio input only has one side grounded, the other side won't work. Also, there is an error on the I/O board, there are a few RCA ground pads that are orphans (not connected to ground). More info here:
The YARRA Preamplifier/HPA for Melbourne DB Group Buy

Edit Oct 12, 2019: Korg 6P1 preamp modules described here
The YARRA Preamplifier/HPA for Melbourne DB Group Buy
Verification build shown here: https://www.diyaudio.com/forums/gro...fier-hpa-melbourne-db-buy-87.html#post5942424

Korg 6P1 preamp data including schematic, stuffing guide, photos, and BOM here:
The YARRA Preamplifier/HPA for Melbourne DB Group Buy

787419d1570917320-yarra-preamplifier-hpa-melbourne-db-buy-korg-6p1-yarra-test-build-02-jpg

Edit June 12, 2019 - due to the huge logistical and time commitment issues of providing large GB’s via my old PayPal invoice method, I will be switching to using Etsy for handling GB orders. Yarra is now available here:

Yarra Class A modular preamplifier PCB | Etsy


This is the integrated preampflifier/headphone amplifier based on the Melbourne daughterboard which uses the Aksa-Lender topology. More on the Melbourne here. The Yarra river runs through Melbourne, so it seemed like a fitting name for the daughterboard the resides on it. The Yarra will provide a power supply based on a BJT capacitance multiplier fed by a linear toroidal transformer. The output of the capacitance multiplier is further smoothed by the built-in CRCRC aboard each Melbourne DB. The Yarra also provides for extra room for boutique coupling capacitors, your choice of volume pots (4 different formats), an input selector switch and double RCA outputs plus a HPA jack output. The nice thing about the Yarra is that you can switch out the Melbourne modules easily if you want to try different gains, or even different bias currents etc. They are easy to make and cost effective little core units that are available on a separate GB here. the Yarra is a dual monoblock design with separate power transformers and separate capacitance multipliers for the lowest noise, and highest channel separation, and it helps to eliminate ground loops.

Thanks so much to JPS64 for yet another masterpiece in layout design!
And of course, thank so much to Aksa for the Aksa-Lender core circuit!
And thanks to Prasi for the design of the BJT capacitance multiplier which was the inspiration for the one used here!

Here is the 3d render of the Melbourne DB (v2):
734405d1549477964-aksa-lender-pass-hybrid-m2-alph-m2-amp-melbourne-th-v2-top-1-png


Here is the schematic for the Yarra:
738798d1551063707-yarra-preamplifier-hpa-melbourne-db-buy-melbourne-schematic-v1-image-png


Here is the 3d render with the components mounted:
738795d1551062651-yarra-preamplifier-hpa-melbourne-db-buy-melbourner-mb-3d-01-png


Here is the render of the PCB showing JPS64's trademark via stitching:
738796d1551062651-yarra-preamplifier-hpa-melbourne-db-buy-melbourner-mb-3d-02-jpg


Here are how the parts are placed on the board. The toroidal transformers are 20W Talema's.
738797d1551063449-yarra-preamplifier-hpa-melbourne-db-buy-melbourne-top-placement-png


So i am trying to determine interest in this project. The boards will probably be 1.6mm thick and 1oz copper but with ENIG finish and blue color solder mask. These are rather large boards at 299mm x 227mm so will probably end up being about $40ea.

Edit Mar 2, 2019 - changes to shipping costs:
If you are interested, please add your name, qnty of boards desired, and country to ship to below. Shipping will be $8 in CONUS, $18 CAN, and $23 everywhere else for up to 1 board plus up to 4 Melbourne DB's should you order those in this GB, and additional boards will be extra (TBD).

Edit Feb 25, 2019: If you want to get the Melbourne DB that is goes with the Yarra, you can add it to your order here at $10ea with no extra charge for shipping.

Thanks,
X

Example of sign-up list:
DIYA_Johndoe - 1 Yarra - USA
DIYA_Janedoe - 2 Yarra, 4 Melbourne - UK

etc...

Edit Mar 2 2019, Yarra BOM here:
https://www.diyaudio.com/forums/att...er-hpa-melbourne-db-buy-yarra_bom_v1c_raw-zip

Edit Mar 5, 2019: What parts on Melbourne can be left off if using on Yarra?
740660d1551758605-melbourne-daughterboard-m2x-melbourne-sch-yarra-mar-5-2019-png


Edit March 24, 2019: HPA centric schematic for driving low impedance headphones.
745102d1553442451-yarra-preamplifier-hpa-melbourne-db-buy-3ed7cf39-328d-4152-9f07-41465bd293f5-png


Edit April 14, 2019: Final Production Layout Schematic and Placement Guide:
The YARRA Preamplifier/HPA for Melbourne DB Group Buy

Edit May 3, 2019 - pricing on Yarra custom case is 101Euro ea for minimum order of 20.
Please sign up for GB in list here (and beyond):
The YARRA Preamplifier/HPA for Melbourne DB Group Buy

Edit July 12, 2019: Schematic for PCA daughterboard:
763297d1560673060-yarra-preamplifier-hpa-melbourne-db-buy-pca-yarra-schematic-v1-jpg


Edit Nov 7, 2019: updated Mouser shopping cart for BOM, courtesy of Vunce (thanks!):
The YARRA Preamplifier/HPA for Melbourne DB Group Buy

Edit Nov 18. 2019: change R126/136 from default 47k to 1k in order to reduce the output DC offset decay time when using cap coupled (not DC) output. Also, make sure you power the Yarra on first before the power amp. And when shutting down, power off the power amp first before the Yarra. This will prevent turn on/off transients from reaching your amp.

Alternatively, if using Yarra as purely a preamp (no headphone amp use), replace C126/128 and C136/138 with 22uF each. Leave the bleed resistor at 47k and this should provide adequate bass response and only a 0.3s time constant.

Edit Nov 22, 2019: Tips by Meanie on how to make sure you ground the Yarra properly while building up.
The YARRA Preamplifier/HPA for Melbourne DB Group Buy

Version 001c schematic with some minor updates to the BC560 transistor and 1A10 diodes on the GLB:
The YARRA Preamplifier/HPA for Melbourne DB Group Buy

Update Feb 6, 2020: Slotted test points to mount elevated resistors to change gain easily.
https://www.mouser.com/ProductDetail/Keystone-Electronics/1036?qs=sGAEpiMZZMvNHPdpUdAofAhWaMwDlhEy

Buerklin slotted posts:
https://www.buerklin.com/en/Product...inals/1001-11-tinned-solder-terminal/p/12H566
 

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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
 
Member
Joined 2011
Paid Member
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.
 
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
 
Member
Joined 2011
Paid Member
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.
 
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Founder of XSA-Labs
Joined 2012
Paid Member
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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Member
Joined 2011
Paid Member
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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Founder of XSA-Labs
Joined 2012
Paid Member
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?

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