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Vaccum tube Equalizer schematic?

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Joined 2011
Jack's Photos: The Blonder-Tongue Audio Baton
blonder tongue audio baton eq - Google Search

Here's a classic one. Jack's Photos: The Blonder-Tongue Audio Baton

9cf12c0bd999bd784a628b940fb7a8e8.jpg
 
Why?

OLD SCHOOL equalizers are a pain in the âhrse to do right. You need band-pass AND band-notch. Your band-to-band roll-off needs to be really accurate so when all the bands are remixed, the output "at all-zero" is indeed almost exactly unmodified from the original coming in the front.

OLD SCHOOL would have 4 pole or 6 pole band-pass/cut filtering. Each with its own accurately matched either linear or coaxially mounted pair of potentiometers. Ideally, "old school" would have you pouring thru dozens of then-popular commercial designs, as the "commercial boys" more or less worked out all the poles-phases-and-values magic.

There is a reason why OLD SCHOOL was at first - and for a long time - entirely semiconductor. And rapidly migrated to low-noise op-amps for more compactness, higher reliability and better passband-to-passband matching. And to move to 6 pole or 8 pole designs. With one or more of them being Bessel filters instead of Butterworth. Or even Chebychev-Bessel combinations.

Most recently, almost all this now fits in "a chip". But still … there is the OLD SCHOOL:

http://www.elektropage.com/images/ic/TL074_10_band_Equalizer_ZF33B.gif

That's kind of MIDDLE school. Using op-amps to reintegration all the bandpass filters back to the bus.

So, at the very least, you'd need about 20 competent triode-stages per stereo channel. Could use 12 AX7's, or perhaps higher current devices. But in the end you'd need a lot of tubes.

With "a lot of tubes" comes "a lot of heartache". Matching problems, tubes mysteriously going stupid on you, capacitors shorting, and pretty stiff power supplies.
_______

Are you SURE you want to do this?
If so, start searching for schematics.

GoatGuy
 
Simple and Recommended

Built two of these. Work and "sound" very nice.

Recommend the same center frequencies as in the Cello Audio Palette: (around) 20, 120, 400/800; 1K/2K, 5K, 20K. Added switches to vary two of the mid-frequencies. This design will give you around 3-4db of Boost/Cut which I've found is all you need at the mids. More in the lows is nice - especially for early LP's.

Now use my own version of the Palette Preamplifier - with an umbilical so I can control "things" from my listening position.

Charles
 

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I've had a perverse desire to build something similar to this for years, and can already see some ways to improve on this... Higher supply voltage, current sources in the LTP and cathode follower load resistors (which will allow for much, much lower negative rail voltage) and maybe a DC servo on the output with a mute/dethumper circuit... Could borrow some aspects from Sy's Heretical preamp to make this super fancy....

Hmmmm.

Also, now that I think about it more it would be fairly simply to use the 6N2P in lieu of the 12AX7 to save some cash, and that would let you buy a few extra sets of tubes to be able to pick the ones that have better parameters for equal effect in each channel... It would be also pretty good to replace the 12AT7 with a 6DJ8 for lower output impedance, and higher available drive current, which would make it overall a pretty useful preamp for the guy who wants it all. Distortion of .0001 at 1V is pretty good already, but with a few tweaks you can have a pretty affordable EQ that is pretty decent performance.
 
Built two of these. Work and "sound" very nice.

Recommend the same center frequencies as in the Cello Audio Palette: (around) 20, 120, 400/800; 1K/2K, 5K, 20K. Added switches to vary two of the mid-frequencies. This design will give you around 3-4db of Boost/Cut which I've found is all you need at the mids. More in the lows is nice - especially for early LP's.

Now use my own version of the Palette Preamplifier - with an umbilical so I can control "things" from my listening position.

Charles

Hi Stellavox,

so did you build the 10 band eq by the magazine picture? I am asking because I want to built one too, I was just surprise using a simulator that there a big attenuation on the output, but of course simulator can make mistakes that's why I need some confirmation from somebody already build it....best regards
 

PRR

Member
Joined 2003
Paid Member
> This BBC AM1/11 equalizer looks a lot like the Blonder Tongue Audio Baton.

It is nearly exactly the same except for "Pro" input and output interfaces (extra tube for pro output level) and minor addition in the power supply for the added output stage.

I wonder if it really IS a Blonder but modified in the UK for Pro use? (It was also used in US "Pro" work, but the BBC paper shows 8D3 output valve, which is not how we number that type.)
 

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I am at home for 30 days for this virus so lots of time, so I decide to give it a go to the Rickard Berglund design show here by Stellavox.

I already order most of the components moths ago, still waiting the power transformer from Antek and the 3U rack mount cabinet all bought in US so I really do not know when they will arrive here in Philippines with this crisis, so with all I have and using a power transformer used for a tube amp I start the project.

I finish the project on paper and assembling all components, this became also more complex because I add to the Berglund design a led display for every single frequencies so when finish I will have the exact idea of the equalisation.

I used 6N2P instead the 12AX7 but when finish I will replace with 6N2P-EV, also on the way, so I put all on a wooden board connect everything unfortunately with a not really good wire but is the only one available at the moment, so I was expected a not so good result or some not pleasant noise but with surprise when I put on the EQ all work very good and the sound is really amazing, no oscillation at all, just a little hum at the max vol of the amp, so I am extremely happy with the result so now looking forward to receive the missing component and cabinet for finalise this project, I still do not know how I will be able to do 100 perfect holes on the front panel of the cabinet but well will see :).

The sound test was very good so next I will make some serious test with generator and scope and Rew, for the main time some pic of the EQ.

All the best to everyone and thanks to the useful information received from other members.
 

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i would love to build a tube eq and or active crossover but alas I am no 300v pioneer more of a 300v dreamer, I would like a very simple 3-5 band eq (all bands above 120hz) with an active variable subwoofer crossover and output for below 120hz, if a lego master builder wants to design/test/produce a board I will take 2
 
I am at home for 30 days for this virus so lots of time, so I decide to give it a go to the Rickard Berglund design show here by Stellavox.

I already order most of the components moths ago, still waiting the power transformer from Antek and the 3U rack mount cabinet all bought in US so I really do not know when they will arrive here in Philippines with this crisis, so with all I have and using a power transformer used for a tube amp I start the project.

I finish the project on paper and assembling all components, this became also more complex because I add to the Berglund design a led display for every single frequencies so when finish I will have the exact idea of the equalisation.

I used 6N2P instead the 12AX7 but when finish I will replace with 6N2P-EV, also on the way, so I put all on a wooden board connect everything unfortunately with a not really good wire but is the only one available at the moment, so I was expected a not so good result or some not pleasant noise but with surprise when I put on the EQ all work very good and the sound is really amazing, no oscillation at all, just a little hum at the max vol of the amp, so I am extremely happy with the result so now looking forward to receive the missing component and cabinet for finalise this project, I still do not know how I will be able to do 100 perfect holes on the front panel of the cabinet but well will see :).

The sound test was very good so next I will make some serious test with generator and scope and Rew, for the main time some pic of the EQ.

All the best to everyone and thanks to the useful information received from other members.

Unexpected arrival of shipping from US during lockdown of remaining parts necessary to finish this all tube graphics EQ by Rickard Berglund, then again extended quarantine until May 15 so perfect for give a finish to this project.

Big task has been find a way to avoid to much cable connections, so I made this kind of "guitar string" for connect the all 10 modules, this workout very well avoiding bundles of wires and unwanted oscillations.

I just tested musically and sound and work very very well, no oscillation whatsoever and even the little hum on the wooden board test is gone, max vol on amp and no noise at all.

I still need nice knobs and somehow some print for the front panel.

I will test now the EQ with generator, scope and Rew for see the real performance.....all the best
 

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