B1 with Korg Triode

[MEPER]

Ok.....I have a lot of common mode chokes "in stock". It could be combined with the small ferrite chokes. Will a HF noise signal always be a common mode signal? …..if not the common mode choke would not filter it?

 

[6L6]

The current has to flow out and flow back, hence "Circuit".

(Yes, a common mode choke, made for filtering RF junk, will filter RF junk...)

 

[MEPER]

Ok.....I was trying to understand how a common mode choke works and what signals will generate a magnetic flux etc. The DC current flowing through it will not generate a flux as it will be zeroed out defined by the way the windings are of the two chokes. I think I understand it a bit better after thinking a bit more...…..

 

[Nelson Pass]

Or you can employ a FET CxMx and get rid of all the HF noise.
Very elegant and very simple.
I use a SMPS for a Pearl phono pre, followed by a CxMx and it's dead quiet, with no sharp edges and all that, just silent.

You will want to have the 24V coming out of the filter unless you want to
adjust the Nutube yourself, as the performance is voltage dependent.

 

[Nelson Pass]

I have not heard any microphonics from the Nutube in this B1 build. I haven’t gone around tapping or anything, but in normal application it seems to be a dead quiet tube. I did apply foam tape under the nutube on the board before soldering — definitely recommend that, as it actually sits better with a little elevation underneath.

If you tap on the Nutube you will hear a decaying tone at about 5 KHz,
which appear to be mechanical. Apart from that, I haven't seen what I
would call significant microphonics.

I wouldn't put the circuit on top of a loudspeaker though...

 

[avdesignguru]

Sounds great BTW! Testing it out at 9.4v at T7, T8.

Nice knobs, can I ask your source? They go well with the Galaxy chassis. Also, for the Bulgin switch (also nice) couldn't one just add some more external series resistance to the resistor built into the switch? 5K - 10K? Amazon only sells the sub-$2 buck converters as a 6 pack.

 

[MEPER]

It the voltage drop over the 10 ohm resistors in the filter insignificant? …..so it is ok just to have 24,00 V at the input or is it better with 24,20 V or so? …..it seems the preamp only consumes a few mA's? you want to have 24,00 V at +F in the schematic?

 

[Gyuri]

I think, I will use something like this:
http://www.meanwell.hu/userfiles/webshop/products/attachments/RS-25-3.3-5-12-15-24-48.pdf
You can set its output voltage between 22-27.6VDC.

 

[jphabc54]

Nice knobs, can I ask your source? They go well with the Galaxy chassis. Also, for the Bulgin switch (also nice) couldn't one just add some more external series resistance to the resistor built into the switch? 5K - 10K? Amazon only sells the sub-$2 buck converters as a 6 pack.

Thanks! Knobs are from Parts Express — very nice quality:

Large Aluminum Receiver / Amplifier Knob 1.58" - Matte

I couldn’t find LED specific specs in the Bulgin data sheet for that switch, but Bulgin sells panel mount indicators with blue LED. Fwd voltage is 3.8v; fwd current is 25ma. Not sure what’s already in the switch for resistance, but even adding 1k at .5w could be enough at 24v. I would imagine the indicator vs switch LEDs are pretty close in spec, if not identical.

https://www.bulgin.com/products/pub/media/bulgin/data/Indicators.pdf

 

[Nelson Pass]

It the voltage drop over the 10 ohm resistors in the filter insignificant? …..so it is ok just to have 24,00 V at the input or is it better with 24,20 V or so? …..it seems the preamp only consumes a few mA's? you want to have 24,00 V at +F in the schematic?

It's been figured in. I think you're OK with 250 mV volt tolerance.

Draw is about 65 mA, so you can figure a .6V drop across each of the
10 ohms resistors, resulting in about 22.8V at F+.

If you are capable of measuring distortion as described above, you can
put up with a several volt supply tolerance.

It doesn't necessarily get better with more or less supply voltage.

 

[Stanislav]

You will want to have the 24V coming out of the filter unless you want to
adjust the Nutube yourself, as the performance is voltage dependent.

Yes, I use a SMPS with 48V out, dropping a lot of voltage through a RCRC filter before the CxMx.
The output of the filter is 28V and then 24V out of the FET CxMx.
It's not the only way to do it, simply one way of using what one has on hand.
Passive with chokes is a valid option too but way more expensive.

 

[bk856er]

Thanks to Papa for his generosity this Christmas!

Thanks to soundhappy for taking the initiative with list organization!

Finally, thanks to the 38 USA participants, who collectively scraped together $177.06 to donate back to diyA, and also paid for shipping to 6L6 as a token of appreciation for his build guides!!

Wonderful acts, and an example of what a great place this is.

BK

 

[tsmith1315]

And thank you Bob, for taking on the headache of distribution, dealing with 38 of us, taking care of Jim and helping us out with the tube purchase!

 

[MEPER]

It's been figured in.
Draw is about 65 mA, so you can figure a .6V drop across each of the
10 ohms resistors, resulting in about 22.8V at F+.

Thank you. I go with 24V PSU as specified so there is a little less at F+. Then we will see what happens. First I have to finish BA3-Pre. There I will get some experience with distortion measurement.

 

[Jason]

Donation received - thank you very much for organizing things Bob

 

[jphabc54]

For all who want to see the phase of the second harmonic use Diana distortion software, discussed here

DiAna, a software Distortion Analyzer

I used it the last months to measure the k2 phase of F4 beast, DEFSIT, SIT-2, Aleph 3 and, and...
works like glue....!

Any recommendation for a cheap USB sound card to use for Diana measurements? Behringer UCA202 or UCA222 okay or something higher spec? I know these work with ASIO.

 

[jphabc54]

It's been figured in. I think you're OK with 250 mV volt tolerance.

Draw is about 65 mA, so you can figure a .6V drop across each of the
10 ohms resistors, resulting in about 22.8V at F+.

If you are capable of measuring distortion as described above, you can
put up with a several volt supply tolerance.

It doesn't necessarily get better with more or less supply voltage.

22.8v is exactly what I’m getting at F+ with the Meanwell 24v SMPS.

 

[gary s]

Thanks again for all of this Nelson, the Oz /NZ kits were delivered here this morning - only took 8 days, so quite quick. To the 3 forum members in Oz and NZ, I will post these out to you tomorrow and get back to you by email, thanks.

Once again a big thanks to Nelson!!

 

[Dennis Hui]

Christmas in January

The parts have arrived in Canada. Thank you Papa!

 

[tubesguy]

Pro tip: If you didn't order the NuTube because you thought you'd unsolder yours from one of Pete's boards, one that you had dutifully affixed to said board with the type of double-sided tape ordinarily used for decoratively mounting anvils on walls, you should just, right now, give up and order a new one.