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 Post subject: Baxandall circuit
PostPosted: 03 May 2015, 13:33 
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Joined: 01 Feb 2015, 13:41
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Location: Athens-Greece
Is it recommended to use the attahed Baxandall circuit, to control bass & tremble?

The idea is to insert this circuit between pre-amp, eg 4S Universal preamp and my amp 6SN7 - 300B SE

Has someone tried something similar


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 Post subject: Re: Baxandall circuit
PostPosted: 03 May 2015, 13:36 
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Location: Athens-Greece
The circuit ...


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 Post subject: Re: Baxandall circuit
PostPosted: 03 May 2015, 14:08 
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Joined: 06 Apr 2009, 10:08
Posts: 1467
Location: US Pacific Northwest
Yes. However, it will work much better with a buffer on the input and the 4S without an output volume control on the output. This way it's virtually impossible to overdrive the input, the input impedance is very high (a good thing), you have the default insertion gain of the tone stack before the gain stage (so gain stage overdrive is usually not a problem), you eliminate one signal capacitor in the signal chain, and the output impedance is fixed and much lower than the 4S.
Attachment:
Schematic (CF Input - 4S output).jpg
I suggest you approach it in this fashion.

Matt


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 Post subject: Re: Baxandall circuit
PostPosted: 04 May 2015, 03:32 
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Joined: 01 Feb 2015, 13:41
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Location: Athens-Greece
Thanks Matt

Just a few questions for final clarification

1. In the attachment you sent me , you mention 300V; that means I have to change the power supply? In 4s Universal pre-amp you have lower voltage

2. Most probably I will stay with 4s only, in order to connect my cd player. I have already a commercial pre-amp for the MM phono. However, I have some difficulties due to Europe versions:

- Mains are 220V so I have to manufacture the power transformer. I did it in the past. Are there any special consideration?
- In 4s power supply choke is 2H (154M), but I can find in Greece the 3H (193N). Is it ok or I have to buy from US?
- Last, could I used copper chassis 3 mm ? I have the general impression that copper is better. Also connection to chassis can be done by soldering instead of bolting.

I have already ordered remaining material and am very keen to go ahead with this device.

Cheers
Dimitris


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 Post subject: Re: Baxandall circuit
PostPosted: 04 May 2015, 08:37 
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dimitris1811 wrote:
1. In the attachment you sent me , you mention 300V; that means I have to change the power supply? In 4s Universal pre-amp you have lower voltage
I just like the way the circuit performs at 300v better than at 250v. It also provides a little bit lower distortion. The circuit will still work fine at 250v.
dimitris1811 wrote:
Mains are 220V so I have to manufacture the power transformer. I did it in the past. Are there any special consideration?
I haven't wound a transformer in over 30 years. I would think that you should be able to find one commercially produced that meets your needs. Perhaps some of the other forum members could help.
dimitris1811 wrote:
In 4s power supply choke is 2H (154M), but I can find in Greece the 3H (193N). Is it ok or I have to buy from US?
The 3H choke will work fine.
dimitris1811 wrote:
Last, could I used copper chassis 3 mm ? I have the general impression that copper is better. Also connection to chassis can be done by soldering instead of bolting.
Yes. Copper is a great material to work with. It won't provide any better performance than steel or aluminum, but it is easy with which to work and looks nice. It's just kind of expensive.

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 Post subject: Re: Baxandall circuit
PostPosted: 26 May 2015, 08:56 
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Location: Wales, UK
This is an interesting topic. What frequencies does the above circuit atenuate and also how much cut and boost?

Phil


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 Post subject: Re: Baxandall circuit
PostPosted: 26 May 2015, 18:20 
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philip davies wrote:
This is an interesting topic. What frequencies does the above circuit atenuate and also how much cut and boost?
Here are the characteristics curves representing the various nominal and extreme control settings. These are spice simulations based on the various circuit impedances at the tone stack interface.
Attachment:
Tone Curves.png
If you have any questions, just ask.


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 Post subject: Re: Baxandall circuit
PostPosted: 28 May 2015, 07:40 
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Matt, love the idea but how about a defeat switch?

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 Post subject: Re: Baxandall circuit
PostPosted: 28 May 2015, 20:37 
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mwhouston wrote:
Matt, love the idea but how about a defeat switch?
You mean like this?
Attachment:
Schematic (CF Input - 4S output) small.jpg

Just remember that with this configuration, you get a 21dBv boost when you remove the tone stack. If you don't want this to happen, then place a 10MΩ resistor in the defeat line between the poles of the switch.
20*log[1/(10+1)] = -20.8dBv
Simple. :up:


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 Post subject: Re: Baxandall circuit
PostPosted: 28 May 2015, 22:35 
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Matt, looks even better now. I fellow Melbourne Audio Club member, when reveiwing new gear, brings out a preamp with a bass and treble control. He tweaks until he feels the bass\trebel levels are right. When he looks back at the settings he can tell how good the gear will be without the "tone" controls in place. If he needs to boost or reduce bass or treble too much me deems the gear not satisfactory because he never uses this preamp when listening seriously. He has bought a few of my tube preamps and power amps and he always puts them through this test.

I'd just like to bring back the bass and treble controls in a tube pre, with defeat of course. Thanks Matt. Best add this one to the bucket list.

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