I think it's better to have low distortion signal sources, then add tube flavor later down the line. A BAL/SE on the DAC only adds tube sound to the DAC. A preamp is probably ideal place to add the tube because it lets all sources share the same "house sound," and there is a well established art in creating wonderful sounding tube preamps, and there are some good DIY kits and designs, as well as lots of used commercial preamps available for sampling at modest cost.
Edit: If you go forward with the Unbalancer, choose tubes that give you the correct gain to work in your system. The product description's example tubes provide 20dB of gain to the Opus' 2Vrms differential output voltage. Maybe the unbalancer can adjust the gain with different resistors?
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Ya, sim makes nice stuff!!!
Broskie is a good designer, it will work. Follow your heart. You can get help from people here if it hums. Follow Broskie's instructions carefully and it shouldn't hum. Be prepared for it to add some noise compared to the Sim alone. Use the lowest gain configuration possible with the Unbalancer to minimize noise. If you want luscious tube decadence, use 6SN7.
I think the complaints of hum from unbalancer are combination of its high gain plus noisy heater PSs, or bad wire routing, bad grounding, etc. The usual suspects.
Make sure your Sim's input impedance is high enough for a tube stage to precede it, like 47kOhms or more?
something like this
Oh ya! You know how to crank up the sweetner! Steel lam coil has nice magnetic hysteresis too! Maybe you should just go all the way for SET amps!
My suggestion? Buy a 1:1 transformer from Jensen or Cinemag. I use them and love them.
That will take you from balanced to unbalanced, provide isolation, reject common mode noise from the DAC and not have a "Transistor Sound". Passive, easy, not too expensive.
FWIW, I often define "Tube Sound" as an absence of "Transistor Sound". Your tastes may vary. In any case, transformers will mostly likely give you the sound you want.
That will take you from balanced to unbalanced, provide isolation, reject common mode noise from the DAC and not have a "Transistor Sound". Passive, easy, not too expensive.
FWIW, I often define "Tube Sound" as an absence of "Transistor Sound". Your tastes may vary. In any case, transformers will mostly likely give you the sound you want.
Ya, sim makes nice stuff!!!
Make sure your Sim's input impedance is high enough for a tube stage to precede it, like 47kOhms or more?
Bummer input impedance 11kOhms
Hello,
i catch your words so!I built an Unbalancer as I/V stage for my Buffalo III DAC and the result is a really outstanding sound. I'm very happy about its SQ.
BUT there's a small issue: a slight hum in one channel (sometimes in both channels) that i can't get rid of, no matter how i try. The hum is not loud and it disappears when music is playing, but when silence is absolute i can hear it from 2/3mts distance. Its frequency is clearly around 50/100Hz and it is volume independant. That's a pity, as it ruins an otherwise perfect system.
I use a Janus shunt psu to power Unbalancer, so B+ is tube-rectified and tube-regulated and heaters are DC powered and elevated to 1/4 B+.
Grounding on Unbalancer is based on a star point (that is GND input point from Janus psu), where all signal and power grounds converge. That is attached ONLY to Janus GND output.
On Janus psu, B+ ground line is connected to chassis via a PCB standoff; chassis connects to house ground via a small resistor and a cap in parallel. I tried non connecting Janus to chassis, but that didn't affect the hum. Heater supply section ground connection is ONLY in H- being connected to B+ ground line via a 0,33 uF cap. Both B+ and Heaters transformers are not CT.
On Unbalancer there is another elevation circuit, similar to that found on Janus psu. I tried not using it, but that didn't affect the hum (to be honest, it made it a bit worse).
I increased 150uF RC filter caps on the Unbalancer (not filter caps on Janus) to 670uF, but it had no effect on the hum. Nor did filtering B+ using 2 chokes in R12 positions.
All the following things i tried had no effect on hum:
- changing rectifiers (some rectifiers affect hum tone, but not its presence);
- changing tubes (some tubes worsen it a bit, but no tube does eliminate it);
- referring heaters to 0V instead of elevating them;
- changing heaters supply configuration from full-wave bridge to full-wave voltage doubler;
- replacing ultrafast diodes with schottky diodes;
- using better resistors on Janus psu;
- removing connection to any other system component (inputs and outputs);
- using a ground screened B+ toroidal transformer;
- placing Unbalancer outside the chassis to avoid interference from other components (transformers, psu, etc...).
I asked other experts' help but i couldn't obtain to fix the issue.
Anyone between you can help me?
I use E88CC as input tubes and 6CG7 as output.
I also tried 12AU7, 12BH7, ECC88, 5963, 6N23P as input and 5965 as output. I had some worsening of hum with certains tubes (especially 5965), the configuration i currently use has the lowest hum. But it's still audible.
The really strange thing is that quadrupling Unbalancer RC filter caps values doesn't minimally affect the hum. So the problem should be in heaters supply/referencing...
Do you use Janus psu as well?
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Hello, i don't think pics of my build would be of any use, until it's fully assembled.
I just raised input tubes grid stoppers to 4k and cut some traces between resistors R9, R10, R11, R12 and grids to insert 1k grid stoppers.
Values to use depend on the four resistors value and amount of oscillations in your system. In the worst case, you should be able to go up to 20k, using most preamp input tubes, without loosing too much of HFs. For output tubes a lower value is needed.
Also, i have to say that i had to assemble the dac with transformers on a lower floor, just below Unbalancer board, and that led to a large amount of very high frequencies noise.
Then any ground loop has to be broken and Buffalo grounds have to be connected to Unbalancer ground or to a common star ground - no floating.
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