Raw B+ voltage test issue (600+ volts..)

[Bjorkvald]

Hey all.
I cant seem to get out of a issue getting 600+ volt in the raw b+ voltage test..
235 volts in the walls, so I chose 230+ volt setup.
Seems correct wiring on the transformer, with 8,2v terminal 6-7 and 112v terminal 9-10. Tubes glow.

Soldered to page 38. Got 600+ volt in raw B+
Took a few steps back (i am a rookie for sure), checked all, found nothing wrong, figured it must be my lack of sondering skills. Re-did the joints, measured resistance around all, checked for not functional components (there was a uf4007 that seemed bad so i got new one). (Have not cut off ends yet as i am in trouble)

Hooked it up again, and same result
Any ideas? There are only a few connections in there so it must be obvious, but i cant see it and do not feel like playing with 600+ volts..
KR Henrik

 

[Kris]

You have your meter set to VAC.
B+ is a DC voltage. Just switch your meter to VDC and remeasure.

 

[Paul Birkeland]

You'd also be well served by spending a few bucks on a pair of side cutters so you can trim those leads back. I recommend the CHP-170.

 

[Bjorkvald]

Ah stupid mistake then, hopefully I’ll test again when i can, and will clean up the ends as soon as it works. Thanks!

 

[Bjorkvald]

Late thanks for the help, you were right, there was no problem there, with the correct settings for the meter. The rest of the build was straightforward and the change of dynamics is quite substantial, compared to using a MiniDSP Flex as pre (now there is a 100% analog path for vinyl and the flex acts as dac). Finish of wooden sides to be done, Will try to sort of match the walnut plinth.

Surprisingly my line level analog crossover still works, even though it seems to work better at lower volume compared to when volume pot is above 9 (output impedance to high? 9 is pretty high though…).
It does feel like something I can’t ”fix” as of not fixed output impedance (?), so I will try to get the Nelson Pass active cross up and running unless anyone think I can remain passive (the line level cross worked great otherwise, with the constant output impedance of the flex).

System is:

Thorens Td-124 - sut transformer - Ear clone -
Elekit 8600 (300b, 50kOhm). - FaitalPro/Fostex Horn
Bottlehead Moreplay. - diy cross (line level, analog or active)-
FirstWatt F7 diy (10 kOhm) - GPA 416 DIY
Eversolo a6 - MiniDsp Flex (as dac / eq) -

Thankful for all input/suggestions

 

[Paul Birkeland]

What is the input impedance of your active crossover, and what are your obervations?

 

[Bjorkvald]

Bear with me on this one, I took inspiration of hifihaven on a similar cross and used ears and measurements to tone it in, including eq for mostly the faital pro hf10ak.

With the flex this actually to me sounds better than both MiniDSP cross and analog crossover. I never figured out how to simulate this so I have a testboard and just switched parts until it made sense. I could not run it propert using my Ear phono directly (very dark sounding, I have up quickly and went through the Flex), so I was expecting something similar with moreplay but with the moreplay it sounds great even without alternativ any values.

High is 2 times 330nF with 1,5kOhm to zero + a notch (?) eq consisting of 1kOhm, 220nF and 100mH in serie to zero.
Low is 2 times 125Ohm with 470nF to zero + a notch (?) eq/fix of 1kOhm, 6,8uF and 100mH in serie to zero

Not sure if this means it is 125+125=250Ohm for the low frequency?

This measures well with a slight slope down, maybe 8dB or so from 600 hertz (which likely is the cross figure) to 20k.
I havent tried measuring with the moreplay, but it does feels more dynamic and I would be surprised if it degrades things even as is, but it could also be more focused on low frequencies, perhaps changing either the cross frequency or attuneation.? If I have your internat in the subject I promise to measure it up tomorrow, to see if and how it measures (by reading, I guess it should change quite a bit somehow)

KR Henrik

 

[Paul Joppa]

Yeah, that's way too low an impedance to drive with a tube preamp. Even Crack would struggle. Something like a S.E.X.4 should work well ... :^)

 

[Bjorkvald]

Still works, maybe as it only is running up to 600 hz or so? If my cross has 250 ohm for the low (not sure about this, but sure of the parts used) i guess that should be more of an issue for moreplay than the FirstWatt (10000/250 is 40 times) ?

But I have a almost build Nelson pass Lxmini active cross, and have been toying with the idea of a buffer a bit. (Pass mosfet or musical fidelity tube buffer perhaps). I’ll likely give it a go to use a normal speaker cross for the low as I do have the parts and possibility to do this, to see how it affects it.

The plan to begin with was to use the moreplay with the active, but I tried the passive before getting the moreplay going and it does sound great.
So I guess your comment will push me to finalizing the active (same box, different PCB sort of) - thanks.

Would it with a SEX4 or other more ”normal” input impedance make sense with the moreplay - or would it still be a no-go as of the output impedance of the pre messing it up for me? I am on a long journey of trying stuff out, so who knows, the more tubes the merrier..
This also as I am quite impressed of the sound, ease of build, low cost of good parts etc. of the passive..

KR Henrik