[L0rdGwyn]

Here are some random parts that are going in the PCM56 DAC. I know these posts are kinda dumb but it helps me cope with the wait.

Talema 7XXXX series toroidals. Had to order these from the UK, one for each channel, one for the digital supply.



Medical grade dual primary dual secondary toroidal, has an electrostatic shield and hum band, this will be my balanced isolation transformer for now.



Rubycon Caps, more of these to come, but this is the bulk, ZLH series low ESR long-life types.



Some transistors that will be used in the power supply positive rails.



DIP-16 socket for the PCM56 chips.



More stuff should arrive today, will probably start doing some prep work today and tomorrow, mostly around the 12B4A output stage. In chemical kinetics terminology, the rate-limiting step is the PCB production, I am expecting those to arrive middle-to-late next week. Will get everything else I can done in the mean time so it's simply a matter of stuffing the boards and testing!!!

 

[triod750]

Medical grade prevents headache...

 

[L0rdGwyn]

Medical grade prevents headache...

Unless you are in medical school

 

[triod750]

Unless you are in medical school

Absolutely - didn't think of that.

 

[Zachik]

Being in high-tech all my life, I have to admit I was never exposed to medical jokes
(hopefully, my pun is an acceptable medical joke... )

 

[triod750]

Being in high-tech all my life, I have to admit I was never exposed to medical jokes
(hopefully, my pun is an acceptable medical joke... )

At least you are .

 

[L0rdGwyn]

I did a lot of boring DIY stuff today, but it needed to be done for DAC preparation.

I put together CCS loads for the 12B4A output stage.



I determined snubber component values for all of the DAC transformers as well as the output stage transformer.



I reconfigured the digital front end module for PCM56 (it was originally set up for TDA1541A in Philips simultaneous mode). I crimped power supply and digital data output leads. Will crimp and terminate the other ends when most everything is set up and the lengths are determined.



I put together the final part lists, one more parts order and we are all set, will arrive before the PCBs.

Getting this stuff out of the way, the prototype should come together pretty quickly! First step will be testing the power supply, if that checks out we should be in good shape

 

[L0rdGwyn]

More boring DAC stuff.

Wired up the bottom of the 9-pin tag boards for the 12B4A.



Here are the major components of the output stage. Sowter I/V transformers, 12V A23 battery between the transformer secondary and ground, aka battery (fixed) bias. CCS active loads, plate current at 30-35mA, plate voltage will be somewhere between 100-130VDC, which will put the output impedance of the stage at 750-800ohm. Heaters will be AC, elevated 40VDC above ground.

Will use some Clarity Caps I have around for testing, but will swap to some fancy type cap once all is finalized, maybe a 2.2uF 400VDC Jupiter copper foil, TBD.



Really nothing stopping me from putting this output stage together and testing it while waiting for parts and PCBs, will probably do that next.

 

[L0rdGwyn]

Okay, bias of the output stage is set up and tested.



Based on the measurements, decided on a 30mA / 110VDC bias point with -12.5V on the grid provided by the batteries.

I didn't bring the I/V transformers into the mix, just the secondary resistor, will need to add the output caps as well, but this was only for biasing purposes. Just need those dang PCBs now.

 

[L0rdGwyn]

That's all for now, not a whole lot else to do until PCBs are here.

So how about some music! Without a top end DAC around, vinyl it is vacant space in the rack for Audial S5 and/or DIY DAC when it is complete.

 

[UntilThen]

Nice Keenan. Vinyl with that Sowter amp with that menacing mains transformer looks the works. Speakers looks good too.

 

[Zachik]

Based on the measurements, decided on a 30mA / 110VDC bias point with -12.5V on the grid provided by the batteries.

So... how long do you expect the batteries would last?

vacant space in the rack for Audial S5 and/or DIY DAC when it is complete.

I thought the S5 should be on its way by now... Anxiously looking forward to your impressions

 

[bcowen]

More boring DAC stuff.

Wired up the bottom of the 9-pin tag boards for the 12B4A.



Here are the major components of the output stage. Sowter I/V transformers, 12V A23 battery between the transformer secondary and ground, aka battery (fixed) bias. CCS active loads, plate current at 30-35mA, plate voltage will be somewhere between 100-130VDC, which will put the output impedance of the stage at 750-800ohm. Heaters will be AC, elevated 40VDC above ground.

Will use some Clarity Caps I have around for testing, but will swap to some fancy type cap once all is finalized, maybe a 2.2uF 400VDC Jupiter copper foil, TBD.



Really nothing stopping me from putting this output stage together and testing it while waiting for parts and PCBs, will probably do that next.

Sweet! One question though: how do you know when the batteries need replaced? I'm guessing that losing the negative bias voltage would be a not good thing? Or will they last long enough you just replace them once a year when you do your smoke detector batteries (being silly, but actually a serious question)?

 

[bcowen]

So... how long do you expect the batteries would last?


I thought the S5 should be on its way by now... Anxiously looking forward to your impressions

Quit posting while I'm posting the same question. Sheeez.

 

[L0rdGwyn]

So... how long do you expect the batteries would last?


I thought the S5 should be on its way by now... Anxiously looking forward to your impressions

The lifetime of the battery, so 5 years according to Duracell!

When using battery bias, the battery will not be drained, assuming the grid of the tube draws little-to-no current, which is the case in this circuit (and most class A1 gain stages). Probably will check once a year to ensure the voltage hasn't drifted significantly.

The S5 is on its way! International express, doesn't have a delivery date yet but my guess is Monday or Tuesday.

LOL @bcowen please see above