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The YARRA Preamplifier/HPA for Melbourne DB Group Buy

jwjarch

Member
Paid Member
2017-03-23 6:19 pm
Denver, CO
For the original Yarra CapMx based PSU, would increasing R155, 156, 175, 176 be an option in order to bleed off a little more voltage before the CapMX? I'm going to run the 22V Talemas and I'm still a bit squeamish about approaching the voltage threshold of the daughter boards. Yes, I read through the entire thread before posting this. Still squeamish. ;) Could one use, say a 5W 20R resistor? That should be able to drop 1.5volts or so at 80mA according to my non-EE based calculations. And stay within safe dissipation of the resistor. I know it's a shame to burn up power into a resistor but I'd rather use the 22V Talemas than pay for, and wait for, new ones. Plus I would still have more headroom than 18V secondaries, even after the voltage drop. I'm planning on pre-amp duty only, no headphone use.
 
KOA BPR’s are great. They are non inductive and handle 5W. I got some fake Chinese ones and they work fine for PSU CRCs but not good for source resistors due to use of steel legs. That reminds me, a member bought me a set of genuine ones to test as a low distortion dummy load resistor. I need to test it out. For CRC PSU, Vishay Sfrenice green porcelain wire wound 3W axial are good too.
 

jwjarch

Member
Paid Member
2017-03-23 6:19 pm
Denver, CO
Good to know X. I have some experience with the green Vishay's (The AC03 series, if that's what you're referring to) in an F7 clone. They sound good too! ;)

I see the KOA BPR's only range up to 1.0 ohm though. They definitely get the job done in the SLB's I have running in Babelfish J2 and Singing Bush amps. Great PSU's again, X!
 

jwjarch

Member
Paid Member
2017-03-23 6:19 pm
Denver, CO
Another Yarra PSU up and running. I can’t say how amazing it is to have the case done before the boards are soldered up. Thanks again especially to JPS and Gianluca on that! Voltages are at about 30.5 across the board with 5.1R 1W resistors in front of the CapMx. I have a bunch more on the way to test, as well as the correct snubber components that I forgot to order on the last round.
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jwjarch

Member
Paid Member
2017-03-23 6:19 pm
Denver, CO
First sound! Sort of…..
So I got a pair of Haikun boards soldered up today. I plugged them in and fired up the Yarra. I measured 24.4v at the Toshibas. Perfect! Using my usual little Bluetooth source I plugged into the Yarra and plugged outputs into my Lufo-Lite. No sound at all. I was a little perplexed. After switching inputs. Adjusting volume. Double checking source and amp we’re working by plugging the source directly into the amp. That worked. So back to the Yarra. I bypassed the I/O section and went in and out of a Haikun board directly. Sound! Great sound in fact. A little more fiddling around. I took the ribbon cable from the I/O board and flipped it upside down. I got sound out of both channels but the volume pot doesn’t do anything. What could be going on here? I’m out of brain power for tonight.
 

jwjarch

Member
Paid Member
2017-03-23 6:19 pm
Denver, CO
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Please ignore my previous stupid post. 😝

My brain wouldn’t let me quit so easily tonight. I was thinking it should be a very simple solution if the Haikun boards are working correctly. Sure enough it was. In my haste to get the main board soldered up yesterday I forgot the most obvious and important signal path in the amp. I forgot the jumpers at X123 and X133. Doh!!! Jumpers are in and the Yarra with Haikuns is playing sweetly. Sounds really good so far. More listening to come tomorrow in the main system.
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jwjarch

Member
Paid Member
2017-03-23 6:19 pm
Denver, CO
Thanks X! I've been looking forward to this for a LONG time. :)

Another note about my Haikun boards, one has a genuine Toshiba 2SA1837 and the other has a 3CA1837. I came across these, and their complement, on LCSC.com when ordering some other parts back in 2019 (see below). They were made under the Foshan Blue Rocket Elec company, which I suspect was an alias that re-badged genuine Toshiba parts. Or something along those lines, maybe. They appear to be VERY similar in the appearance of the case and leads. And so far the 3CA1837 seems to be performing as well as the genuine Toshiba part in terms of general listening. I'll see if I can perform any other measurements on these in and out of circuit. I may wish I would have bought more as they have been discontinued since.

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jwjarch

Member
Paid Member
2017-03-23 6:19 pm
Denver, CO
Been listening to the Yarra and Haikun boards for the past week and a half or so and I am loving it. My system has never been so quiet. My speakers are about 96db so it’s been tough to get them quiet. The Yarra has pretty much solved that. Such a great design.

I have a question regarding the Yarra as a buffer or zero gain pre. I am collecting parts for a Baby Huey EL34 mono block build. The BH does not require a preamp but I would like to retain the input switching and not have to swap in a separate passive preamp when I hook up the BH amps.

So what are my options here. Is it as simple as jumping the in to out screws without a daughter board? Or is it best to set up an existing DB for low to no gain?
 
You could put some DPDT switches (or a small signal audio grade relay operated by front panel toggle) to bypass the signal path through the daughter boards for a “passive pre” mode. It would still use the pot etc. not easy, but doable as there are some on board circuit path jumpers for the signal as you recall that had to be enabled for sound to play.