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Wayne's BA 2018 linestage
Wayne's BA 2018 linestage
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Old 28th May 2019, 11:35 PM   #731
Mod Man is offline Mod Man  United States
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A 25-30 VA transformer with two 18 vac secondaries is plenty. The Broskie power supply set up for 18 volts dc works great. Can’t recall how much voltage swing the output has but should go close to the rail voltage.
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Old 11th June 2019, 03:57 PM   #732
PJN is offline PJN  United States
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Well I finally started my build of the purple boards that Jim was so gracious to make available. Had a rainy day this weekend so I was able to populate both boards, and what busy little boards they are. I haven't finished hooking them up yet though, hopefully later this week. I made up a case out of some left over 1/4" plywood and scrounged around in my parts bin for the other stuff I needed. Here are a few pics of where things stand so far. The mouser BOM was perfect, many thanks to Jim and Wayne for everything they do for the community. The only thing that I'm nervous about is the PSU voltage, it's 29 vdc instead of 24 vdc, I think I'll contact Peranders to see why this build is higher than the BOM for the 24 vdc build should make it. Hopefully I'll get is singing soon.
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Old 11th June 2019, 04:26 PM   #733
xrk971 is offline xrk971  United States
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Wayne's BA 2018 linestage
I love the wooden box look, PJN. Nice!

Btw, I just got my verification build PCBs for the WBA18 in Yarra/M2X format yesterday (the ones on the left). Will be populating soon and hope to have first sound by this weekend. If successful, will order production boards with ENIG.

Click the image to open in full size.
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Old 11th June 2019, 05:01 PM   #734
PJN is offline PJN  United States
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Hi X,

The Yarra is on my build list. I want to build it as a gift for my son, he needs an upgrade to the mediocre pre he's using now.
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Old 13th June 2019, 11:45 AM   #735
xrk971 is offline xrk971  United States
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Wayne's BA 2018 linestage
Hi PJN,
The Yarra GB2 is now starting up again and pre-orders are now being taken.

You can use the Yarra to run the WBA18 amp core modules. I just tested them last night for bias current and DC offset. I was getting 13mA bias and the revised pot is given g pretty good adjustment range and resolution to get circa 10mV output offset. The temperature sensitivity of the offset is rather high. Just breathing on the circuit makes it drift by tens of mV. I wonder if the transistor pairs should be thermally bonded and covered with a shrink tube?

Click the image to open in full size.

Click the image to open in full size.

I am testing them at +/-15v rails. Does anyone know if this preamp can safely run from +/-30v rails? I have an extra high rail voltage on my Yarra in order to drive a 50w 0dB gain Class A power amp.
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Last edited by xrk971; 13th June 2019 at 11:50 AM.
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Old 13th June 2019, 12:00 PM   #736
6L6 is offline 6L6  United States
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Wayne's BA 2018 linestage
+/-24v is as much as I've used on the circuit, and it works fine.

The KSA1845 and KSA992 are 120v parts, and the TTA004 outputs are 160v, I can't imagine there would be much issue with 30v unless one is carrying too much bias and dissipation becomes the limit...
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Old 13th June 2019, 12:37 PM   #737
xrk971 is offline xrk971  United States
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I’m actually using 2SA1837 and 2SC4795 (flipped around). They don’t feel too warm. At 30v and 0.013A each they will be 400mW - well within their operating safe limit. Might need a small flag heatsink? Will give it a try quickly and hope magic smoke doesn’t fly out.
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Old 13th June 2019, 12:38 PM   #738
PJN is offline PJN  United States
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Thank Jim, that make me feel better.


Hi X, I'll check out the GB
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Old 13th June 2019, 02:17 PM   #739
Centurion53 is offline Centurion53  United States
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Default Volume attenuator

I'm finishing up my line stage and want to add a volume control. Was thinking of using an Alps R27. I have never used one before so was wondering if anyone could recommend a particular one for this application or other viable options.
Thanks
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Old 13th June 2019, 02:18 PM   #740
6L6 is offline 6L6  United States
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25 or 50k
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