Tag Archives: BCF

DN2540 + LM317 Cascode CCS

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I’m doing the DN2540 cascode with LM317 so that i can set the current to exactly what i want. In this case, it is to load the RCA 5691 red base tubes with just 1.2mA of current per tube. This should be sufficient for voltage gain from the Bufallo DAC into the BCF, more importantly, I can draw from the same B+ rails that powers the BCF.

With the previous MJE350/BC557C and LED version, I could not get the resistors for the B+ correct. Quite frustrating when this has worked for me before…

Schematic is the same as Figure 13c from Jung. Rset is 1k to give 1.25mA.

 

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Dremel Versatip 2000

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Got a new toy from Sgtooling.com. This interesting store sells CNC mills and lathes. Quite interested in the mills, but it’s definitely something that will have very low ROI… I will need to justify a purchase by building more projects. 🙂

Anyways, I used the versatip for soldering of a pair of CCS for the red base 5691 tubes that i’m gonna try using in the BCF for my sabre32 DAC implementation. It’s a very nice tool. The sound of the butane flame reminds me of my secondary school chemistry lab days with the bunsen burners. One side of the solder tip has a circular hole for the flame to burn. This causes lots of heat to be released from that area. Best to solder with that hole facing up, else the work piece will become hot.

Heat up time was quite quick. The literature listed a +/- 25 seconds duration. It took around 10 – 15 seconds to heat up at the minimum heat temperature. This setting is enough for soldering. Turning up the gas a little more and the versatip had no issues with desoldering speaker terminal connections. This normally takes a long time to heat up with my electric soldering iron.

The easy on and off feature of the versatip also suited my work style. I had to alternate between laying components and soldering. The ease of using the versatip made it quick for soldering jobs anywhere. Why didn’t I get this earlier…

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I/V for Sabre32

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I ordered the Twisted Pear Buffalo32 version 2 DAC some time ago. It’s quite a different order process from other stuff in that I had to queue to register my interest and pay for it first. It’s like queuing up for new condominium launches in Singapore…

Anyways, there is the need to do up an I/V stage for this DAC. There’s so many choices out there… and coincidentally, John Broskie had a newish Broskie Cathode Follower design on his site. I then built the BCF for 6H30 tubes. The tubes will be powered by a Salas High Voltage Shunt regulator, which would be recitified by my Telefunken RGN1064 mesh plate globe tube. All great stuff in their own right. 🙂

I was checking TubeCad today and Broskie had an update to the BCF in the form of The Unbalancer. An input differential voltage gain stage is added to convert the lowish voltage swing into something more usable for an amplifier. Well… this made sense. I was just hoping that the BCF alone will be able to do the job… Seems I will need to put something here. I’ve got 5 stars GE 6072, but the gain (44, i think. The Unbalancer circuit used a 12AX7 – gain of 100) may not be enough. I’m thinking of using my red base 6SL7 (gain of 70), which would be a better candidate. Or maybe I should buy some 12AX7…

Just over the weekend, we had a Sabre32 mini shootout with 3 different implementation of this chip. My EE MiniMax DAC, Nick’s Amplidac, William’s UTS. We played some very nice cds. I especially liked the Sara K & Chris Jones – Are we there yet? and a Koji Tamaki cd.

You’re gonna ask me which implementation won… Well… it’s down to personal preference. The Sabre32 signatures of better resolution, imaging and soundstage are definitely there. For DIY guys, this is an avenue to custom build a Sabre32 DAC to their liking that matches their system.

Guess I can only pursue this after my reservist which starts tomorrow… In the meantime, enjoy your music!

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RCA 834 Tubes

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Went to the post office to collect the 2 pairs of RCA 834 tubes. While collecting the B4 sockets for the Telefunken RGN1064 from Joh, he mentioned that the top pins would need to be “heat sinked” in order to dissipate the heat otherwise the glass would crack. One of his friends encountered this issue with a similar tube. I remembered coming across a site somewhere on the web where a DIY guy can help machine those top caps meant for the 833 tube. Need to do some searching…

Anyway… this will be a build that I’d attempt only after I managed the RCA 808, which has been in the pipeline for a long time. I need to finish up the 1626 first (some adjustments need to be done on the aluminum plate so that the top plate can be accommodated. need to get a few short standoffs as well), then build the Sabre32 DAC with Broskie Cathode Follower with a Salas High Voltage Shunt regulator, before the 808 project starts.

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