Tube Tone Control Project

[skidave]

I thought I would share a project I have been working on for a while. This is a tone control circuit based on the Baxandall circuit.

A few years ago I built a preamp without tone controls and I decided to build a stand alone tone control to go with it. Attached are some pictures.

The circuit uses both halfs of a 12AX7. B+ is about 260V and I used an elevated DC heater supply. Those are the biggest Hammond enclosures in that series, and space is limited. I ran some frequency plots on an old Sound Technology unit, but I have no way to export the data (and I have no time to manualy graph them in excel). Response is relatively flat when in the circuit and noise floor is low. Distortion is low with a standard 2 volt signal.

Attached are pictures of the insides and then a picture of the units in my system. The front left is the preamp, the right is the tone control and then the unit in the rear is a re-packaged Bottlehead Seduction phono preamp.

Dave

[Geek]

They look great!

Cheers!

[Shannon Parks]

It is so satisfying to cram a tube circuit into a small chassis. Very nice work, indeed.

Shannon

[skidave]

Thanks guys. I wish Hammond made this series of aluminum enclosures larger. I'm not much of a 'metal worker', so I stay away from steel enclosures if possible. The transformers just clear too!

Next time I plan a preamp, I'll probably put everything into one larger enclosure!

Dave

[dhuebert]

I'd love to see the schematic!

Don

[msmpe]

I'm tempted to call your system a sweet suite..
Really nice!
We all love to look at schematics!

[skidave]

Attached is the schmatic. Yeah, excuse the hand drawing of some of the power supply. I don't have time to play with the schematic drawing software that is out there.

The power supply is from Bruce Rozenblit's book 'Beginners Guide to Tube Audio Design'. I added the LED and relay portions (can you tell by my drawings!).

The tone control circuit is from: http://www.angelfire.com/electronic/fun ... one-A.html
I prototyped this circuit and tested it on my bench before building it...and it measured much like the article stated. I also listened to the prototype connected into my system. When I built the actual unit, it was just a bit better than the graphs showed. I found this circuit the most adaptable for a 'stand alone' tone control. I love the tone control on the Audio Research SP-3 series. However, trying to make that circuit a stand alone tone control was not that easy.

Thanks,

Dave

[Rockinrob86]

are you using this like source - preamp - tone control - amp?


I am thinking I might add this to the preamp I just built. I purposely used a large 16x16x5 chassis so I had room to experiment with a built in headphone out, possibly tone controls, and possibly one day a remote...

I built the VTA SP8, and the detail sounds amazing, with my best recordings sounding better than ever, but I am finding some lesser material (really only the most lo-fi and less pro stuff in my collection) is sounding a bit harsh. It would be nice to have the capability to slightly fix that stuff

[skidave]

The source feeds the preamp directly. When I built the preamp, I built it with a loop output / input setup. Specifically so I could add an external tone control or EQ. Obviously, with the small enclosure, I could not add anymore.

Source-preamp (loop to tone) - out to power amp.

The tone control has a bypass so it can be completely out of the circuit.

Dave

[gazzgary]

Hi Dave,

I really like your tone control unit, I also am looking at builing this circuit and i have been playing with Diptrace for a few days with view to pulling more hair out and hopefully making a stereo pcb version of it.

I know it has been quiet a while since you built this unit but i have a question, do you remember the type and voltage ratings of the caps you used in it.

I have built a few of shannons wonderful projects on here and have some experience with the assembly of tube based electronics but trying to figure out capacitor voltage ratings and suitable types are a little beyond me at the moment.


This is my first post in a very long time and i hope everyone is well, and im really looking forward to getting back into my hobby.

Gareth

[dcriner]

For all its elegance, isn't that tone control just using caps to shunt or pass audio freqs?

My main amp & preamp have no tone controls. I was sold on the idea that "real" hi-fi amps should not have them - maybe because they are supposedly a kludge to artificially tamper with the bandwidth of the original source? Best to leave them out of the signal path?

[nyazzip]

i spent my life using solid state amps and low grade speakers, so i was skeptical/incredulous when i built my st35 that there were no tone controls- but the fact is, if you are sourcing professionally produced recordings and you have good speakers, then there is no need to play with EQ- the studios who mixdown and master did it right (and with better equipment)the first time, in %99 of cases.
i'd focus on speaker selection and speaker placement/room acoustics...

[skidave]

The power supply is from Bruce Rozenblit's book 'Beginners Guide to Tube Audio Design'. I added the LED and relay portions (can you tell by my drawings!).

The tone control circuit is from: http://www.angelfire.com/electronic/fun ... one-A.html

B+ is around 265V.

I hope this helps...

It is a Baxandall circuit.

My image hosting site changed everything, so you might not be able to enlarge the pictures.