Sneak Preview: 9 Band Active All Tube EQ

[HideawayStudio]

After much toil the beast lives!! This is the first prototype assembly of my 9 band (1 octave / band) all tube active EQ (codename TEQ-9B). This is partially based on the very first gyrator based tube EQs from the late 50's whereby each band is handled by a discrete tube gyrator providing +-12dB of boost/cut. All five 12AX7 tubes very much play an active role in shaping the sound - ie. this is not simply a passive EQ with tube output buffers.

I have taylored the EQ for use in studios specifically as a colouration device for use with single sources. It will be housed in a bespoke 2U rackmount chassis and features balanced I/O on both XLR and TRS jacks with an overdrive facility to permit the EQ stages to be pushed into as much non linearity as you wish

Here is a sneak preview of the first bare pcb assembly in action:

Download D.A.Wilson_TEQ-9B_Active_9_Band_Tube_EQ_Demo.wav from Sendspace.com - send big files the easy way

All A-B tests: A = bypassed audio B = EQ'd audio. Please note that in bypass mode two triodes in the output amplifier and the NE5532 based preamp and balanced line drivers are still switched in.

[athos56]

ohhh, that looks neat... Are you going to sell the PCB or finished units?

Athos

[HideawayStudio]

Originally Posted by athos56

ohhh, that looks neat... Are you going to sell the PCB or finished units?

Athos

It will be a finished unit housed in a 2U custom rackmount chassis which is currently in fabrication. The prototypes require calibration and a significant degree of auditioning and field testing before release.

Despite it being aimed at the studio gear market, there has been some suggestion that guitarists may also show an interest in this unit. The EQ does indeed sound very sweet with bass and lead electric guitar.

[HideawayStudio]

A quick addition to the basic spec:

The heaters rails are regulated DC and the anodes are fed from a regulated 220 Volt B+ rail - ie. not a starved plate in sight!

[leadbelly]

Are you going to be sharing anything with us, or is this just advertising?

[Rodeodave]

I happen to have a couple of questions:

Is this thing mono? Well I think it must be, since it seems to use gyrators with ECC83 and R-C networks, and there's only five 12AX7/ECC83. Also the pots (log/lin?) look like mono. What about the tenth triode system, is it used to generate the output signal by mixing the input with the eq'ed signal?
What do you use for an input-differential, opamps? I hope not...
Or is the cicuit more like this one: http://www.triodeel.com/images/b9b.gif?
What does the 11th pot do?
Why are there some electrolytic caps so suspiciously close to the XLR connectors?
And finally, how do you keep the circuit's output balanced? Opamps?

[SY]

Originally Posted by Rodeodave

And finally, how do you keep the circuit's output balanced? Opamps?

He said NE5532. The idea of driving a line with 12AX7/ECC83 is chilling.

[Rodeodave]

Oops, I completely missed the last sentence.

[HideawayStudio]

Originally Posted by Rodeodave

I happen to have a couple of questions:

Is this thing mono? Well I think it must be, since it seems to use gyrators with ECC83 and R-C networks, and there's only five 12AX7/ECC83. Also the pots (log/lin?) look like mono. What about the tenth triode system, is it used to generate the output signal by mixing the input with the eq'ed signal?
What do you use for an input-differential, opamps? I hope not...
Or is the cicuit more like this one: http://www.triodeel.com/images/b9b.gif?
What does the 11th pot do?
Why are there some electrolytic caps so suspiciously close to the XLR connectors?
And finally, how do you keep the circuit's output balanced? Opamps?

So Many Questions

Yes - the unit is mono, as it was aimed at processing single sources prior to mixdown in the studio eg. bass, vocals etc as a means to add colouration rather than it being a super accurate mastering device. There is a dual channel unit in the pipeline.

The gyrators pass the full audio signal ie. there is no mixing of dry and wet signals.

The electrolytics are there to decouple the rails (there are no electrolytics in the audio path) for the op-amps used to implement the balanced line I/O using NE5532's (a popular choice in studio gear).

The 5th triode is used to implement a post-amplifier and buffer stage, as in the B9B, for gain control and buffering as the mixed output from the gyrators is very high impedance.

[HideawayStudio]

Originally Posted by SY

He said NE5532. The idea of driving a line with 12AX7/ECC83 is chilling.

It's not impossible though (I was tempted!) - I have vintage gear in the studio using triodes driving balanced line output transformers.