BUILD THREAD - A New Take on the Classic Pass Labs D1 with an ESS Dac

[glt]

Thanks, qusp. The Edcor looks very reasonably priced...

[qusp]

no problems, edcor have a lot of models, so you might need to do some searching for something appropriate, but the spec is reasonably good overall and very good for the money.

the O-netics I know more about, windings are tightly enough matched that they will cope no problems with direct connection to the dac, no caps needed to null AVCC DC current (they wont saturate) and the gandwidth is pretty good really, much better than some. nothing on a good solid state circuit such as this (for THD etc) but there is something to be said for the simplicity of the connection

something similar from Audio Note, Sowter, Lundahl, or heaven forbid the exotic Feastrex/Teramoto/Suzuki Finemet transformers will set you back MANY times more

[glt]

I am talking $99 DAC to $99 Amp and likely a $99 full ranger :-)

[opc]

Are you targeting 99% perfection?

I like your concept... I would imagine with the right choices you could get a whole lot of bang for your $297.

hmmm... $99 would get you a pair of Fountek FR-89 drivers.

But I digress... It's OT.

If you're really looking for low price, Hammond also makes some 600 ohm telecom transformers that might fit the bill. I don't know the P/N off hand, but I'll check tonight. I ordered a few to see how they would work direct coupled to the output of the NTD1, but never got around to it.

Cheers,
Owen

[glt]

Thanks for the info on Hammond.
Have a pair of Wild Burro Betsy-Ks. Just need to build the cabinets

[bigpandahk]

Lot of discussion in just one day

I will try BAL-SE converter and compare it with direct connection with one phase and report the result. Transformer will not be considered at this stage.

Thanks for all the suggestion.

[analog_sa]

Originally Posted by glt

But I agree, transformer is probably the simplest solution. Way, way back there were some recommendations for low cost (and good for audio) transformers. Anyone remembers?

Powered the monstrosity up and, no big surprise, direct connection of a summing transformer won't work. It is probably easy to trim most of the dc imbalance at the operating point by applying a parallel resistor to one of the source resistors, but that isn't the problem. As the circuit heats up the imbalance covers a range of 30-40mV, probably because the fets are only matched at the o.p.

I am certainly not an expert on cores but somewhere in the back of my mind there is some info that at least some of the more exotic cores do not take well to magnetization which can permanently alter them. So, any of the worthwhile transformers i can think of won't be too happy.

That leaves parafeed of course, for those who like it

[analog_sa]

So, as promised i did compare the SE output to a bal to SE using a Lundahl 1676 connected as 1+1:2. In both cases no preamp was used and the following non-balanced power amp had 80k input impedance. Coupling caps were 3.3uF of Clarity MR. Due to unbalanced and unstable dc at the outputs, the transformer primary was fed through a cap as well.

In short, the SE cap only coupled output sounds much better than the transformer summed output, especially at the frequency extremes. Obviously i was biased towards this outcome and in any case it only proves that this particular Lundahl transformer is not so great in this application.

The I/V sounds very impressive - bass, dynamics and surprisingly - warmth. I am genuinely surprised that something powered from crappy 317/337 regs can sound so good. Btw, the regulators occasionally do not fire up on power-on - not sure if it's because of the large caps following them, or the high incoming DC voltage. Will replace them with 1085/1033 at fist opportunity.

[Nikola Krivorov]

Originally Posted by analog_sa

...Btw, the regulators occasionally do not fire up on power-on...

That was a huge problem for me too, the only thing that wasn't expected... We can discuss what was done in my version, might save you some time.

[opc]

Hi Guys,

I've never had this issue before with the regs. Can you elaborate on the conditions under which it is happening?

- What is the input DC voltage?
- What is the output DC voltage?
- What is the input capacitance?
- What is the output capacitance?
- What is the bypass capacitance?
- What 317/337 brand / type are you using?

Hopefully we can get to the bottom of it.

Regards,
Owen