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Old 6th July 2007, 06:47 AM   #1
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Default Graphic 1/3 Octave Tube Equaliser

I want to convert an old ADC soundshaper into a tube equalizer. I figure on using 6n1p's.
One side for high pass and for low pass. That would mean i would need 62 for a stereo equalizer. Using 400watts of heater power. Double that for fourth order.

1) Bad idea?
2) If 1 is no then what order/type of filter should i use?
3) Should i do parametric?

P.S. Biamped, electrostats, not flat response at all. Really needs work.

thanks
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Old 6th July 2007, 11:56 PM   #2
kevinkr is offline kevinkr  United States
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Probably even more than the 62 you cited.

Where tuning flexibility is needed I would use them in active gyrator based filters, otherwise I would use passive rlc filters to set the center frequency of most of your bandpass filters.

Generally these are second order series resonant filters. (Notch filter) Usually there is a pot across the inverting and non inverting inputs of an op-amp (slightly over simplified) to cut the filter appears somewhere between the center of the pot and the end connected to the non inverting input, the reverse would be true for boost. Right at the center of the pot if everything is properly balanced there is no audio present and the resonant circuit is effectively out of the circuit. Some equalizers have pots with taps on the center which are grounded to assure this is absolutely the case.

Look for some examples of transistorized gyrator circuits, conversion to tube is relatively simple.

The op-amp could be all tube of course.

There were tube based graphic equalizers in the past, I had schematics for a commercial half octave design at one point, long lost now. Not too practical in my estimation.

A couple of channels of parametric equalization might be more effective if you have some sense of what you are dealing with.

Better to measure the system response in the room and design a combination of passive and active filters to correct any response anomalies you can't live with.

http://www.4qdtec.com/graph.html for a transistor gyrator circuit.
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Old 7th July 2007, 01:19 AM   #3
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He could always use pencil tubes or even get PC mount sockets for nuvistors
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Old 7th July 2007, 01:47 AM   #4
agent.5 is offline agent.5  United States
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I would definitely consider para eq.


For the mid-bass and bass, you can just buy and use a pro para eq for not much money.

Then. all you have left are 2 or 3 channels of tube eq for higher frequencies.
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Old 7th July 2007, 01:50 AM   #5
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I agree with Kevin;
active filters in EQs were used to eliminate coils and save on costs as soon as opamps became cheaper than coils. No needs to reproduce on lamps what was made to save costs replacing coils by semiconductors.
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Old 7th July 2007, 09:04 AM   #6
ulibub is offline ulibub  France
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Hello!

Have a look here:

http://www.jogis-roehrenbude.de/Vers.../Equalizer.htm

Its an octave tube EQ, but with recalculating the capacitors I think you could change it quite easily to your needs.

The german text doesn't contain much special information, supply voltage should be aroundf 340 V, stabilised and well-fiiltered. DC heating highly recommended.

Uli
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