DIY Audio Projects Forum

Simple Passive Tone-Control
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Author:  roggom [ 05 Jan 2009, 22:07 ]
Post subject:  Simple Passive Tone-Control

I have built up quite a collection of headphone amps and now venturing into higher voltage/wattage amps. My workbench/home office now has a variety of sources and amps, but one DIY item that was missing was an EQ of some sort. I have a few preamps, but I really did not want to add any more gain and noise to an already congested system. I found an answer in a simple but genius tone-control by Tony van Roon ... xtor5.html.

I drew the amp up in Tina and sim'd the outputs and made only a few minor changes. I replaced the electrolytics with Poly film, R5 to 1K, and C2 to .068u for a little more bass.

The tone control sits in between two switch boxes (back to back) so that I have three sources to a switch box, tone control, switchbox, the amps. This gives me max flexibility to listen to any of the sources on any of my amps.

Since the control is passive it will attenuate about -20db at the baseline and the pivot point is around 800Hz. I get about +15 db of boost and -10db of cut. Now all I need to do is get through a song without knob tweaking :).

BTW: The volume pot is 50K (audio) and is before the input. Both bass and treble pots are (audio) log, radio shack 271-1732

Author:  Gio [ 05 Jan 2009, 23:54 ]
Post subject:  Re: Simple Passive Tone-Control

Very nice Rogers. Looks like a Radio Shack enclosure and board.

TINA TI is very handy and I am staring to get the hang of it. I have been using the software to look at line level BSC. The advantage of the line level BSC over a speaker level BSC is that you don't need an inductor and a large wattage resistor.

Author:  RiGuy [ 06 Jan 2009, 00:03 ]
Post subject:  Re: Simple Passive Tone-Control

I have so many projects I want to do. One is to build tone controls. This one is really nice. Minimum of parts to get the sound dirtied up.
Does it sound pretty clean? Can you tell its there if everything is set flat?

Author:  roggom [ 06 Jan 2009, 12:44 ]
Post subject:  Re: Simple Passive Tone-Control

Very clean, the only thing is the -20db loss, not a show stopper considering my RIAA stage and pre stage in the Magnavox can make up for the loss. I made a small change that raises the bass a little, but the original design would be completely flat. The controls will raise the high and low rolloff, the mids remain unchanged to an extent.

Gio, this is another Radio Shack project, Caps were sourced at a local electronics shop, as they have some obscure but not unobtainable values.

There is an active version that has a transistor and I played around with changing the transistor with a 12au7 and it is promising, but I will stick with the passive version.



Author:  CrazzyAbtTubes [ 06 Jan 2009, 18:37 ]
Post subject:  Re: Simple Passive Tone-Control

I like that design, it is the simplest one I have ever seen, and best of all it does not use any transistors to boost the signal, so audio quality will stay unchanged with high quality components.

Author:  roggom [ 06 Jan 2009, 18:47 ]
Post subject:  Re: Simple Passive Tone-Control

One note on using the Tina-Ti sim, I believe the pots are linear in the simulation vs. log audio, so 50 percent is not flat. The passive 9% is flat 1% is max cut and 99% is max boost.I will look online for a log pot model.

Author:  roggom [ 07 Jan 2009, 01:34 ]
Post subject:  Re: Simple Passive Tone-Control

One more addition, if -20db is too much attenuation I added a 2k feedback loop to bump the gain up to baseline -10db and the curve remains stable. If you use a volume pot the loop goes between the center pin and the output.

Author:  billnchristy [ 08 Jan 2009, 22:39 ]
Post subject:  Re: Simple Passive Tone-Control

Here are a few more tube types:

Author:  roberts67 [ 04 Jul 2009, 08:29 ]
Post subject:  Re: Simple Passive Tone-Control

Hello! Am I right to assume this is for 1 channel and you would build 2 of these for a stereo tone control network? Peace. Robert

Author:  roggom [ 04 Jul 2009, 16:09 ]
Post subject:  Re: Simple Passive Tone-Control

Yes that is correct, most DIY schematics are drawn with one channel and you just repeat for second channel. One the same pcb or by making dual mono pcb's.

I have been using this as my primary passive pre/tone control for abour 6 months. It is controlling a magnavox 6v6 tube amp. Not super fancy but simple and sounds good. Here are some more pics as I had issues with my flickr account.

Remember this a passive pre so the overall volume will be less, but you can definatley tweak the highs and lows. I added an almost defeat switch for rocking out. :headphones:

The only change I would do is use a Blue velvet volume pot as the radio shack pot gets dirty sometimes, just have to cycle the pot a little, will hit it up with some faderlube someday.


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