DIY Audio Projects Forum

Baxandall circuit
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Author:  ILoveHiFi [ 26 May 2019, 20:35 ]
Post subject:  Re: Baxandall circuit

If any resistor blows thats likely the schematic or installation plorbem, resistor defects are extremly rare, let along say cheapo transitors from china cost you $1USD for 200-400pcs, never had any defects or plorbems from these cheap like for free transistors

Author:  whaam68 [ 05 Jun 2019, 07:53 ]
Post subject:  Re: Baxandall circuit

Just checking ....I have 4S I built some time back in storage which worked perfectly. I drifted to vintage Solid State over the years as I found I needed EQ but am now drifting back to valves/tubes. I don't need a defeat is the first circuit posted in this thread still valid to mod my 4S to add tone controls?

Author:  john55 [ 05 Jun 2019, 09:44 ]
Post subject:  Re: Baxandall circuit

I've been playing with variations of this circuit for nearly a year now. The best circuit is on page 3 of this thread. If you use one tube for the 2 buffers and one tube to gain back your missing 20 dB on each channel, you can still tube roll. I rewired my 4S rather than build from scratch,and it worked fine. I didn't wire in a defeat switch on my last build.

Author:  whaam68 [ 05 Jun 2019, 09:58 ]
Post subject:  Re: Baxandall circuit

Thanks John!

Author:  john55 [ 06 Sep 2019, 06:02 ]
Post subject:  Re: Baxandall circuit

A bit of help please. This is the third tone stack pre-amp I've built so I should know what I'm doing, but it appears I don't.
I have a 4S pre-amp and a 6V6 Lacewood V2 built in one chassis and I've rewired the 4S pre-amp as a tone stack pre-amp.
I've wired up the tone stack without a defeat switch as per the schematic below.
The outputs go directly into the grids of the 6SN7 in the 6V6 Lacewood, as I have two volume controls on the tone stack.
I did all the normal checks for voltages and fired it up. Nothing.....
I've fed in a 1000Hz signal at 2 volts and this what I can see on my 'scope. Why on earth would the output voltage be so low. I expected to see it drop in the tone stack and then return to 2 volts at the output.
The 6V6 Lacewood is working fine and I've checked the wiring numerous times. Changing valves doesn't make any difference and I've buzzed out the valve base to make sure all connections are good.
Anyone got any ideas?

Author:  john55 [ 06 Sep 2019, 09:52 ]
Post subject:  Re: Baxandall circuit

More info....
I used a valve base that sits inside a copper fitting. All leads are soldered on and then heat sleeved, then the whole thing is potted in araldite. Before I used it, I checked for continuity and shorts. All good. Could this problem be something to do with this? As I can see 125mV right up to the grid on the second valve in the circuit, does that guarantee the problem is after this voltage reading?
I also haven't included the 33uF bypass capacitors, but that should only drop the gain a little?

Author:  bone [ 06 Sep 2019, 15:36 ]
Post subject:  Re: Baxandall circuit

What input impedance is your 'scope? I would say it needs to be 10M at least

Author:  john55 [ 22 Mar 2020, 15:09 ]
Post subject:  Re: Baxandall circuit

What size load would I need to put on the output of this circuit to be able to fire it up, stand alone and trace the signal with a scope.

Author:  ILoveHiFi [ 23 Mar 2020, 05:42 ]
Post subject:  Re: Baxandall circuit

125mV of dc on the grid is absolutley normal because of the circuit design.

The circuit can be powerd up without load even if you input a test sine or square wave.

Cathode bypass capacitors only incraece the voltage gain at the same time distortion, makes zero diffrence to the DC biasing of the circuit with or without the one added.

Author:  john55 [ 23 Mar 2020, 06:24 ]
Post subject:  Re: Baxandall circuit

Thanks ILoveHiFi,
I did manage to sort out the problems with the last tone stack (6th September 2019 post).
This is a new one incorperated into another Lacewood 6V6. There is a fault I need to sort out, but it would be easier to trace it without it being connected to the 6V6. Thanks for the info about firing up without a load on the circuit. I can get on with it now.

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