• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

The YARRA Preamplifier/HPA for Melbourne DB Group Buy

Vunce

Member
Paid Member
2014-01-26 8:20 pm
LI, NY
Hehe, I knew that idea would get the wheels turning.

Unfortunately, I never did get EL34 BH built. I have all the parts and transformers to build sitting in a bin for the past couple of years. But now I see there are updated amp boards and psu pcb’s and I’ve lost track. The thread is HUGE!!
 
I would get a Yarra prototype DB with vero board holes and opamp pads (someone posted Gerbers) and use an OPA1655 (or even 5532) wired as a buffer and call it a day. :)

The H2 is indeed a unity gain buffer but adds a lot of H2. If you are ok with that it is a good choice as a zero gain preamp. If you are willing to swap out daughterboards then simply jumper the input to the output bolt pads. That’s about as easy as it gets. You could even use HiFi single crystal copper wire dipped in Unicorn tears for better sound. :)
 
Last edited:

jwjarch

Member
Paid Member
2017-03-23 6:19 pm
Denver, CO
I’ll certainly give the crystal copper wire a try. I think my daughter has some unicorn tears laying around too! ;) But seriously, you’re right X, this is the easiest potential solution ahead of replicating the B1 Buffer.

I quickly thought about the Melbourne as unity gain but seems like such a huge amount of work for no gain. Pun intended. :) Not to mention the possible instability. I’m making the Melbourne as designed to compare with the Haikun, PCA and ACP+.

I reached out to puijkh about the experimentation boards but he hasn’t been on the forum in a while. I couldn’t find any gerbers from his boards either. We’ll see if he responds to my PM.

Vunce, I’ve read through almost all the BH thread at this point. The consensus seems to be that the boards you have are certainly worth building for the EL34. The newer boards (MK2) can handle the KT88 better. I have the MK2 boards and I think I have a fair amount of the info needed to populate them properly. I’ll be posting about it for sure.
 

jwjarch

Member
Paid Member
2017-03-23 6:19 pm
Denver, CO
Hi X,
I actually bought most of the parts back in August of 2020 and had them sitting until recently. I think the 2019 BOM is still the best starting point one can use. I also substituted some parts in my build which may not exactly align with the BOM. I re-read the ENTIRE thread before starting my build as well. Something I recommend that everyone does.

For the Yarra PSU board, keep an eye out on the transformer discussions, 18v vs 22v secondaries etc., as well as snubber values if you're using the original PSU board design. It goes without saying now that there will probably be parts that are out of stock due to supply shortages. If anyone is building and has questions go ahead and post here, of course.
 

hirscwi

Member
Paid Member
2014-03-06 2:18 am
Indianapolis, IN, USA
I'm late to the game and just completing this Yarra preamp and have what is probably a dumb question. I'm using the Melbourne daughter board. I've read most of the threads, but may have overlooked something. It appears that the Melbourne wants +/- 24VDC rails. I'm using 22 volt transformers and hence getting 32VDC from the Yarra PSU. I assume that I should be using 15 or 18 V transformers instead, but wanted to check here first. Thanks.
 
I have a question regarding running the Melbourne / Yarra DC coupled vs capacitor coupled. I think I originally built mine capacitor coupled. What should be removed or jumped on the Melbourne and Yarra boards if I want to try running mine DC coupled, and what is the crucial resistor on the Melbourne boards that needs to have really tight tolerance to avoid DC offset?

Thanks,
Alan
 
Just replace C126/128 C136/138 with wire jumpers. There’s nothing to change on the daughter boards themselves. The DC offset should be naturally low due to the design. It should be in the range under 5mV or so. You still need to keep the input coupling cap (C1022/1023 etc) though.
1658869654092.png
 
  • Thank You
Reactions: 1 user