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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 18th April 2019, 03:05 AM   #251
TboneAK is offline TboneAK  United States
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Wow JP! Had to print it off to put it on the shop wall to drool over. I think it is truly amazing how this all came together. Can’t wait until I’m building it!
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Old 18th April 2019, 05:30 AM   #252
xrk971 is offline xrk971  United States
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The YARRA Preamplifier/HPA for Melbourne DB Group Buy
Very cool. How many other DIYA projects have a professionally made exploded view diagram?

Thank you, JPS64!

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Old 18th April 2019, 08:19 AM   #253
xrk971 is offline xrk971  United States
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The YARRA Preamplifier/HPA for Melbourne DB Group Buy
Just wanted to give an update on the Yarra PCB. I ran into a couple of delays with the production because it is such a complex layout with lots of vias and cutouts for sub boards. The fab house had many questions and emails back and forth before production actually started. The 12 hr time difference sort of added a delay to emails back and forth. The PCB is now truly in production. Hopefully will be done in 2-4 days.
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Old 18th April 2019, 08:40 AM   #254
Oracle1 is offline Oracle1  Greece
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Thanks for the info. About the trafo? 2X12V or 2X15V. I dont want it for HPA, only as pre!
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Old 18th April 2019, 11:02 AM   #255
xrk971 is offline xrk971  United States
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The YARRA Preamplifier/HPA for Melbourne DB Group Buy
Go with 2x15v - you will have headroom and be able to dial down voltage drop with cap Mx if needed. Even 22v is good choice as that gives you a Preamp capable of driving F4 to 25wrms info 8ohms (40Vpp).
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Old 22nd April 2019, 12:57 PM   #256
yourownbuzz is offline yourownbuzz  Australia
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So.. let's see if I understand this correctly (have been jumping across a few threads to try and work out what this one is about)

1) This is a mainboard to use the melbourne daughterboards from another project, and it's essentially a PSU and input/output caps?
2) The melbourne board schematic in post 1 looks very similar (identical?) to Aksa Lender preamp/hpa except its running of dual rails? [and the HPA uses a current transistor rather than the discontinued part]

If that's correct... then.... what's the difference between this and the aksa lender preamp/hpa (more interested in the hpa aspect)? Or is this just a slightly different take on the same thing?

Would this work with the PSU from the Simple DC Coupled HPA?
(Simple High Performance DC Coupled Class A HPA with sub PPM THD)


Just trying to gauge if I should jump on this as well haha

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Haha, the Aksa fan club returns!
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Old 22nd April 2019, 01:48 PM   #257
xrk971 is offline xrk971  United States
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Hi YOB,
Glad you found this in your perusals.

The Melbourne is indeed similar to Aksa Lender Preamp but dual rail, more importantly, is DC coupled, if you wish. It also has a topology tweak on the output - it has a mu-follower which enables it to drive lower impedance loads at lower distortion. This was needed since the 600ohm Edcor on M2x was quite a difficult load for the regular Aksa Lender. Maybe the HPA version would have faired better - but I needed dual rail to be compatible with M2X.

You can indeed use same awesome PSU from the ppm distortion HPA project. However that’s a 18v supply and the Melbourne likes 24v to 30v dual rail.

It’s got a lot of SMT though so the YARRA is pretty much all TH, which works well for a lot of folks. The use of linear trafos and cap multipliers also makes this PSU one of the best around. It can handle loads in excess of 1A depending on your trafo and diodes.

Jump on in if you want. Get the Melbournes at least and play with them.
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Old 22nd April 2019, 02:23 PM   #258
yourownbuzz is offline yourownbuzz  Australia
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I won't pretend to understand what a mu follower is but I'm on board with the improvements you say it brings

Quote:
However that’s a 18v supply and the Melbourne likes 24v to 30v dual rail.
I'm just mainly interested in using it as a hpa, the hpa schematic on first post had +/- 15v? or is 24-30V still the preferred voltage?
Would prefer to stick with that PSU if it works since it's a handy get out of jail card for avoiding mains wiring

Quote:
Get the Melbournes at least and play with them.
Will the boards work without a mainboard / would I lose anything (aside from tidiness haha) from just wiring it up like you did with the wooden board prototype I saw on one of the threads?


My initial trepidation of soldering SMD when I started with the PCA has passed after making several PCAs and the ppm hpa
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Old 22nd April 2019, 03:40 PM   #259
xrk971 is offline xrk971  United States
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It will work fine without the Yarra (but kind of messy), and you will need a clean dual rail PSU. 18v should be ok for a HPA - you will need to adjust the resistors on the CCS to get the current up to, say 80mA to 100mA for driving lower impedance phones. I used mine with only 42mA bias and they worked surprisningly well on 55ohm headphones.

Maybe just get a set of Melbournes to play with? They are TH.
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Old 22nd April 2019, 07:47 PM   #260
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by xrk971 View Post
This is going to be a sweet preamplifier. Can't wait to see the case in real life. JPS64 made this look probably as good or better than many big name professional products. Vunce tells me the populated PSU board alone weighs 3.1 lbs. Still waiting to hear from JPS64 regarding manufacturer's quote.

I have made SW assemblies before, but never anything with this many parts - it is an incredible amount of work to see that it all fits a-priori. I think we also have JPS64's significant other to thank for the SW model. What a lucky guy. I do not know another guy on DIYA whose spouse does audio with him on the same projects!

Click the image to open in full size.
Hi JPS64,
Any news on the quotation for the custom case yet? These HiFi2000 guys take their time!
Cheers,
X
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