Hi all,
I am about to order the parts for my first valve build which is a 4S Preamp which can use any 12*7 tube.
4S Universal Preamplifier for 12A*7 Tubes
I am going to order Hammond 369EX transformer as I am 8n the U.K. and so need 240v
https://www.mouser.co.uk/datasheet/2/177/300-951115.pdf
Further details of the design development and specs of the 4S are found here
The “Universal” Preamp | Cascade Tubes
Has any one built or used this preamp, or any views on the circuit design, or any advice?
Thanks
I am about to order the parts for my first valve build which is a 4S Preamp which can use any 12*7 tube.
4S Universal Preamplifier for 12A*7 Tubes
I am going to order Hammond 369EX transformer as I am 8n the U.K. and so need 240v
https://www.mouser.co.uk/datasheet/2/177/300-951115.pdf
Further details of the design development and specs of the 4S are found here
The “Universal” Preamp | Cascade Tubes
Has any one built or used this preamp, or any views on the circuit design, or any advice?
Thanks
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Yes, save your money! That is a poor design.
Truly universal is not possible. A volume control in the O/P circuitry is very bad. I could go on & on.What are your goals?
Perhaps, but it's a nice simple thing to start with tubes 🙂Yes, save your money! That is a poor design.
The only objection is the much to heavy rectifier tube.
You can use a EZ90/6X4 , much cheaper.But it has a 7pin miniature base, must replace the 9pin noval.
Mona
How is it that a circuit which has no purpose can be considered "nice"? That is, I cannot think of a purpose for this circuit in any modern audio system. It is not even a good learning exercise, except as an example of how not to design a circuit and how not to build it.
Well, by playing with it you find out how it works (or not 😀 )
It's by making mistakes that learn, no ? 😎
Mona
It's by making mistakes that learn, no ? 😎
Mona
Yes, save your money! That is a poor design.
What are your goals?
I had thought of simply purchasing a Marantz 7 clone preamp from eBay as a valve preamp
12AX7B Tube Pre-Amp Vacuum tube Bluetooth preamplifier Based on the Marantz M7 | eBay
But I thought the money I could spend on that and not know about the parts being genuine or not, reliability, import duty etc I could attempt a simple build. I have always understood that the less components the better for sound etc
It appealed to me being able to change the 12*7 tubes without hassle, although people on the forum think that the 12au7 is the way to go.
What would you say is inherently wrong with the circuit?
I would be interested in building a simple preamp with something like the
630p eh as the preamp tube.
So over to you to suggest something simple and superior
Thanks
I have built one of these, but with a few major differences.
First, the goal of the circuit was to be able to tube roll pretty much all the 12a_7 familly without any adjustments needed between tube changes. It helps to find wich tube sounds you like the most.
The volume Is on the output to avoid amplifying the noises the the pot creates. But yes, it changes the output impedence when you adjust the volume. if built this way, the 4s might not be able to drive all power amps, especially solid states ones.
My build is quite different than the original 4s preamp. A cathode follower buffer stage was added after the amplification stage in order to lower the output impedence. It allows the 4s to drive pretty much any amp out there. Mine also has a switch that allows me to choose between a low and a high output impedence depending on the amp that the 4s is driving. The low frequency roll off is than approximately correct for most solid states and valve power amp.
With the cathode follower added to the circuit, the volume pot was installed in the input, so the output impedence does not varry with each volume adjustments.
I don’t think that this preamp was ever meant to be part of a main stereo system. It’s a toy for the tube geek to play around with. It’s also quite easy and fun to build in a point to point layout.
First, the goal of the circuit was to be able to tube roll pretty much all the 12a_7 familly without any adjustments needed between tube changes. It helps to find wich tube sounds you like the most.
The volume Is on the output to avoid amplifying the noises the the pot creates. But yes, it changes the output impedence when you adjust the volume. if built this way, the 4s might not be able to drive all power amps, especially solid states ones.
My build is quite different than the original 4s preamp. A cathode follower buffer stage was added after the amplification stage in order to lower the output impedence. It allows the 4s to drive pretty much any amp out there. Mine also has a switch that allows me to choose between a low and a high output impedence depending on the amp that the 4s is driving. The low frequency roll off is than approximately correct for most solid states and valve power amp.
With the cathode follower added to the circuit, the volume pot was installed in the input, so the output impedence does not varry with each volume adjustments.
I don’t think that this preamp was ever meant to be part of a main stereo system. It’s a toy for the tube geek to play around with. It’s also quite easy and fun to build in a point to point layout.
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As previously stated, the claim of universality is false. The 12AU7/ECC82 is non-linear. The more linear 6FQ7/6CG7 and 12BH7 usually work in 'U7 circuits, providing the requisite doubled heater current is available.
Again, I ask what your goals are. What level of drive signal does your power amplifier require? Many amps need zero gain in the "line" stage. Either a passive or buffered control center is an appropriate mate for such an amp. Amplifying the signal and then attenuating it, to adjust overall gain structure, has an adverse impact on S/N performance.
Making mistakes while trying to do something sensible is one way of learning. There are others too.Ketje said:
Making mistakes by choosing to do something which is not sensible will merely teach someone not to choose daft things to do.
Almost any circuit which tries to accomodate 12AX7 and 12AU7 without other changes is making a big mistake. Their characteristics and biasing are so different that one circuit cannot cope with both. The circuit is only "universal" in the sense that it will probably behave somewhat badly with almost any valve and will be inappropriate for almost any audio system.
The circuit has too much gain.
The circuit has very high output impedance.
The circuit may have significant distortion.
The volume control is in the wrong place.
The rectifier is too big for the job.
^ replace that 12AU7 with a more linear tube like the 6CG7 and it may end up a pretty useful circuit.
I've never been a fan of the 4S builds at all, for all the above stated reasons. My main gripe with the idea is the often excessive gain, the high output impedance, and poor choice of tubes. I understand that the 12Ax series are popular, but they are a poor family of tubes for such an application without major design additions/changes.
If you want a simple preamp there are better designs.
I've never been a fan of the 4S builds at all, for all the above stated reasons. My main gripe with the idea is the often excessive gain, the high output impedance, and poor choice of tubes. I understand that the 12Ax series are popular, but they are a poor family of tubes for such an application without major design additions/changes.
If you want a simple preamp there are better designs.
Hi Eli,
I have a Quad 606 power amp upgraded by Quad to 909 status last year.
Quad 606 Power Amplifier Specification
Power Output: 140 watts per channel (8 ohms)
Distortion: < 0.01%
Input Sensitivity: 500mV
Input Impedence: 20Kohm
Crosstalk: -100db (100hz), -85db (1 khz) and -65db (10khz)
Hum and Noise: 105db
Voltage Rating : 220-200V AC (110-120V via simple power board modification)
Dimensions (WxHxD): 321 x 140 x238 (mm)
Weight: 12kg
I also have a Quad 303 which was refurbished and upgraded by Audiolabs.
Specifications
Power output: 45 watts per channel into 8Ω (stereo)
Frequency response: 30Hz to 35kHz
Total harmonic distortion: 0.1%
Input sensitivity: 0.5V
Signal to noise ratio: 100dB
Speaker load impedance: 4Ω to 16Ω
Dimensions: 120 x 159 x 324mm
Weight: 8.2kg
I would like to use a valve preamp with these with a EAR 834P Phono MM clone.
I listen to all sorts of music and can stream from my server into a DAC although I am looking to get more into vinyl. Ido have a symphonic 40w pp integrated as well. I think it would be helpful for me to build something that has online support and encouragement
Does that help?
Thanks
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As you appear to need no gain, what role exactly do you envisage for your 'preamp'? Of course it is possible to design a preamp to add a little distortion, noise and restricted frequency response if that is what you require - but you can buy a cheap Chinese 'tube buffer' to do that.
the original 4s preamp wont work with your quad 606. The output impedence of the 4s is too high for the 20k input impedence. Have a look at this thread:
DIY Audio Projects Forum • 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage
DIY Audio Projects Forum • 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage
Why do you need a preamp when the amplifier has 500mV input sensitivity? Especially if you plan to use it with an EAR834 type of phono pre, as they can ouput 30 volts easy. Are you looking for a buffer to drive the 20K input impedance of your Quad? It couldn't hurt if used with the EAR, as the 12AX7 used in them is a poor choice for a cathode follower, giving high output impedance into lower impedance loads.
I think you would want to stay away from any preamp with gain, unless it is very low (3 or 6X max maybe) otherwise you wll just be throwing it all away and increasing your distortion and noise floor.
I would stay away from the 4S design for such a build, and look to a basic cathode follower stage using a higher gm tube, or even something like the 6V6 line preamp from Salas- it can be built as a cathode follower (gain of ~1) or with gain (3~7 depending on choices) as needed for your application, with the cathode follower config being a good choice for you.
I think you would want to stay away from any preamp with gain, unless it is very low (3 or 6X max maybe) otherwise you wll just be throwing it all away and increasing your distortion and noise floor.
I would stay away from the 4S design for such a build, and look to a basic cathode follower stage using a higher gm tube, or even something like the 6V6 line preamp from Salas- it can be built as a cathode follower (gain of ~1) or with gain (3~7 depending on choices) as needed for your application, with the cathode follower config being a good choice for you.
Oh dear, this seems to be where I get my coat .....🙁
I have spent hours on mouser drawing up a project list and some other sites. My Kemet Rifa 33uf 400v caps arrived today.
Would I be better off with a passive pre amp on the 606 then? If so what would you recommend for a potentiometer?
Where would I seek to build a valve preamp? Is it really only for a valve power amp? If I were to try and build a Williamson or Mullard type power amp what would you recommend then for a simple valve preamp and type of circuit?
Thanks
Those numbers spell the requirements out. As a "standard" CDP exhibits a 2 VRMS O/P, "line" stage gain is both unnecessary and undesirable. The amp's 20 Kohm I/P impedance is fairly awkward. A 2 Kohm passive setup would be needed to satisfy the 1:10 driving/driven rule and 2 K is way too low a load for many (most?) signal sources. A buffered control center is (IMO) the proper choice. High transconductance (gm) triode cathode followers will exhibit a suitably low O/P impedance. JJ's ECC99 is a good candidate tube/valve.
All the online support needed can be obtained on this "board".
My suggestion-
https://www.diyaudio.com/forums/tubes-valves/102352-6v6-line-preamp-15.html#post1995090 cathode follower version
Quality stepped attenuator (or potentiometer) at the input, good quality capacitors, and a pair of big cathode resistors, very simple and reasonable design. Will work well with 15K and up loads, so should do well for you. A simple circuit that can be "hotrodded" as needed to your heart's content. Same thing with 6DJ8/ECC88, ECC99, 6N6P, etc types will also do very well. With the 6V6 the Zout is ~1.5K or so in cathode follower mode.
https://www.diyaudio.com/forums/tubes-valves/102352-6v6-line-preamp-15.html#post1995090 cathode follower version
Quality stepped attenuator (or potentiometer) at the input, good quality capacitors, and a pair of big cathode resistors, very simple and reasonable design. Will work well with 15K and up loads, so should do well for you. A simple circuit that can be "hotrodded" as needed to your heart's content. Same thing with 6DJ8/ECC88, ECC99, 6N6P, etc types will also do very well. With the 6V6 the Zout is ~1.5K or so in cathode follower mode.
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Those parts will be fine in your PSU filter. 😉 A WVDC rating larger than absolutely necessary is not a problem.
The 4S preamp is the first tube circuit I built and it was a great learning experience. I did make some modification to the original circuit, for example I used my own power supply (135Vdc, regulated), 100k audio pot, added a input decoupling capacitor and DC heaters at 12V.
The "high gain" (albeit mine was probably less due to the lower supply voltage) was not a problem for driving a class D audio development board (MAX98400AEVKIT+), a B&K ST260 power amp and the Pass F4 power amp. I usually kept the volume at preamp at max and varied my source's volume.
Why is the volume control in the wrong spot and where should it be? If the restive volume control is placed on the input one would still have deal with high pass RC filter issues. In a perfect world I would use a variable transformer for volume control, but I have to live within a budget...
I plan to build the ECC802S SRPP Tube Preamplifier (DIY ECC802S (12AU7 / ECC82) Vacuum Tube SRPP Preamplifier) next to drive the Pass F4 power amp. Has anyone built this preamp with success?
The "high gain" (albeit mine was probably less due to the lower supply voltage) was not a problem for driving a class D audio development board (MAX98400AEVKIT+), a B&K ST260 power amp and the Pass F4 power amp. I usually kept the volume at preamp at max and varied my source's volume.
Why is the volume control in the wrong spot and where should it be? If the restive volume control is placed on the input one would still have deal with high pass RC filter issues. In a perfect world I would use a variable transformer for volume control, but I have to live within a budget...
I plan to build the ECC802S SRPP Tube Preamplifier (DIY ECC802S (12AU7 / ECC82) Vacuum Tube SRPP Preamplifier) next to drive the Pass F4 power amp. Has anyone built this preamp with success?