mwl168

On my builds, which are all balanced inputs with Neutrik XLR connectors, I tie PSU ground to the chassis ground (star ground) which is then tied to the AC ground. No ground connection between the input XLR and the amp's input. The input XLR ground pin is tied to the chassis as is suggested by the white paper "pin 1 revisited" by Rane. For my Carbon which has the GR LV and GR HV PSUs, I run a heavier gauge wire between the ground of the two PSU and run one of the PSU's ground to the star ground. Seems to work very well for me.

Received the US/CA destined pots from MLA yesterday. The pots and boards fit perfectly as can be seen in the pic below. Many thanks to Pars and MLA for their great work! Still waiting for a few board payments but soon as MLA and I figured out the shipping charge I will notify the US/CA GB participants of the final shipping cost and start sending pots/boards out. The shipping charge from MLA to me will be evenly spread between each pots I received. So far, we have one participant who did not respond to multiple payment reminders for pots and boards and will be stricken from the GB.

Since the input to the two channels' tail current sources are on the same connector on the amp board marked as -20VDC input, how do you recommend wiring the two 220K ohm resistors from B-? Also, I assume the 220K resistors would need to be 1W or higher given the voltage drop across them?

Where are the pics? It's your own rule

If you turn the volume pot all the way up wouldn't that serve the same purpose as bypassing the pot?

for V+: (R8 + R7) / R7 x 10 (reference voltage of D5 - LT1021-10), R7 = 1.5K, R8 = 750 for + 15VDC for V-: (R9 + R10) / R10 x 10 (reference voltage of D7 - LT1021-10), R10 = 1.5K, R9 = 750 for -15VDC On the goldenreference4 board silkscreen, R7, R8, R9 R10 are all 1.5K. R7 and R8 are connected and R9 and R10 are connected. R8 and R9 are the 1.5K resistors closer to the DN2540 on each side of the board.

I tested the GRLV drop out voltage when I built one for +/- 20VDC output and it was about 3VDC. the 16-0-16 secondaries should be plenty for the desired 15 VDC output as Pars has stated.

I agree. As an example, years ago I read a review from a prominent reviewer on a prominent audiophile magazine. This guy went on to rave about a front-end gear asserting its outstanding bass extension and quality and this all through using a pair of mini-monitor speakers that barely reach beyond 40Hz if that. So much for a rave review...

I also think it's not necessary to separate the AC filament wires from the regulated DC wires. I did it my way because it actually simplifies the wiring and keep the cost of the connectors down.

Re: the servo; I believe you need to engage both servos to have the opto servo working. It works very well by the way.

@ nopants: the Galaxy has what is referred to as "quasi heatsink" which the GR HV is attached to. I can barely detect a temperature rise after a few hours running in 70 F ambient temperature. My Antek trafo has 325vac secondaries (IIRC) that is regulated down to 400VDC so the voltage drop on the pass transistors is not too severe. @ JoaMat and UFN: yes, no volume pot I rely on the digital volume on my TPA Buffalo DAC. It's a controversial topic I know but it does save me a bundle of $$$ @ GeorgeP, Birgir and Kevin: yes, I don't like the idea of using male connector on the chassis end either but that's the only way this Y2M-7TK connector comes to my knowledge. I have been searching for some connector covers to use for this reason but have yet to find any that fits. May have to bite the bullet and sprint for the Ampheno connectors some day.

Finally finished casing my Carbon. Apologize for the quality of the photos, the lighting condition isn't ideal. I went a different route - have the amp and PSU in separate chassis and set up the PSU as an "universal" PSU which I plan to use for the Carbon, the KGSSHV, the Blue Hawaii and, in the hopefully near future, the Grounded Grid. I used two off-the-shelf Antek transformers. The secondaries for the HV and filament are on the same 300VA transformer. The toggle switch acts as my manual HV delay and switches the HV secondaries which also have thermistors in series. The 7-pin connector houses the +/- 400VDC, +/- 18VDC and Bias supply. The 4-pin connector houses two sets of 6.3vac filament supply, each set has a 0.15R/5W resistor in series to lower the filament supply to around 6vac to help preserve the EL34 tube life. The amp chassis is a Mini Dissipante 3U and the PSU is a Galaxy 3U. Both with all aluminum panels.

Those .22uf/1000VDC caps are coupling caps between stages and directly on the signal path. Quality of the capacitor does matter in that position IMO. I started out with some Wima MKP and later changed to Teflon caps that I happen to have on hand. Good luck and looking forward to seeing pics of your build and your impression of its sound.

Beautiful build Soren. Congrats!

Congratulatrions!

Fees paid. Thanks!

The 2 x 20 should be sufficient for +/- 20VDC output. I tested it when I built my 20VDC GR LV and the dropout voltage is about 3VDC.

Good to know. Thanks! I'll look for a smaller washer to use and maybe cut a piece of sobathane to fit underneath the washer. The mis-aligned chassis happen to be the one my friend used for me to build him a Buffalo III DAC. It's the larger AL421B. I managed to get the pieces somewhat fit together but the cover is a lost cause. Below is a photo of this Buffalo III in the AL421B chassis. The module in the front is a Rev C Dynalo. I'll be interested in those PCBs if you can find them. I can probably use them in the PSU I am building for my KG ES amps.

^ that, the AL316S. Be forewarned though, a friend and I ordered 4 chassis together. Three of them turned out great. One of them the panels were badly mis-aligned, the top cover was not even rectangular in shape. An inquiry to the mechant received no response.

I have been using my Twisted Pear Audio Buffalo II DAC with a Volumite digital volume control for a few years. Earlier this year I decided to expand it to a dual-mono setup. In the process I also added the Amanero/Hermes/Cronus/Rhea USB-i2s adapter with isolation and re-clocking. I used two chassis I have purchased some time ago and house the PSU in its own, separate chassis. A Placid HD powers the digital section and GR LV powers the Legato I/V converter and "The Wire" balanced headphone amp (the small module on the left side of the chassis).

As promised, here are photos of the three boards. @pars: no, unfortunately I do not have any pots to test the fit yet.

Or the DIY mulitamp, aka SuSy Dynalo.

Boards came in yesterday. I am happy to report that the rectangular plate-through slots come out as intended. Will take and post a photo when I get home early enough from work to catch some daylight. We still have a few GB participants that have not made payments yet. Please PayPal to .

Thanks JoaMat. This is an area I have much to learn before I build the digital attenuator. And yes, you are exactly right about the supply voltage. The Volumite can operate on 2.7VDC - 5.5VDC. It has an on-board, optional LDO 3.3V regulator which enables use of any 3.5VDC - 20VDC supply.

Just making a general comment on measuring and setting DC offset on the output on amps, not specific to the transconductance amp.