Hello all,
I have decided to take the plunge into DIY audio. This is for a number of reasons. Primarily being price. But also that It seems like a hella lot of fun! Now I must admit that I have little electrical experience. However, after watching a number of instructional videos and research I have decided that I want to take the plunge and build a DIY phono stage. Why? because I ultimately would like a tube stereo amp, but as my speakers are too insensitive this would not be best at my stage and so I would like to first build a tube phono. Before eventually building a SE stereo amp which will drive high efficiency single extended range drivers.
I have chosen this schematic as it does not seem too complicated
RJM Audio - Tube passive phono preamplifier
However, If you have a better recommendation please let me know
I intend to build it using turret boards as well as basic prototype boards.
I believe I can follow the phono stage itself. So it is really the power supply stage which I would like help on.
I don't fully understand the transformer part. T1 gives out a 240v output. Do i need a transformer as I live in the UK where wall voltage 230v?
With the second transformer, will any transformer giving out 6.3 volts at 600ma plus do?
Forgive me if this is super basic stuff.
Any help is appreciated. Or links to information pages where I can learn more about this is appreciated.
I have decided to take the plunge into DIY audio. This is for a number of reasons. Primarily being price. But also that It seems like a hella lot of fun! Now I must admit that I have little electrical experience. However, after watching a number of instructional videos and research I have decided that I want to take the plunge and build a DIY phono stage. Why? because I ultimately would like a tube stereo amp, but as my speakers are too insensitive this would not be best at my stage and so I would like to first build a tube phono. Before eventually building a SE stereo amp which will drive high efficiency single extended range drivers.
I have chosen this schematic as it does not seem too complicated
RJM Audio - Tube passive phono preamplifier
However, If you have a better recommendation please let me know
I intend to build it using turret boards as well as basic prototype boards.
I believe I can follow the phono stage itself. So it is really the power supply stage which I would like help on.
I don't fully understand the transformer part. T1 gives out a 240v output. Do i need a transformer as I live in the UK where wall voltage 230v?
With the second transformer, will any transformer giving out 6.3 volts at 600ma plus do?
Forgive me if this is super basic stuff.
Any help is appreciated. Or links to information pages where I can learn more about this is appreciated.
A phono preamp is a very poor choice for a 1st project. Get some experience under your belt, before you try a phono preamp.
What sort of SS power amp are you currently using? Some sort of tubed line stage feeding it would be an excellent 1st project.
Isolation from the AC mains is ABSOLUTELY essential, for safety.
Forum rules prohibit circuitry that lacks a power transformer!
What sort of SS power amp are you currently using? Some sort of tubed line stage feeding it would be an excellent 1st project.
Isolation from the AC mains is ABSOLUTELY essential, for safety.
Forum rules prohibit circuitry that lacks a power transformer!Hi, Eli!
Thanks for the response.
I see I think you're probably right then! Well I'm using a yamaha solid state integrated amplifier.
What kind of Tube line stage feeding would you recommend?
Sorry If I seem like a novice. Its all a learning curve I suppose, but i'm determined to get good at this kind of thing so I'm happy to start with simpler circuits
Thanks for the response.
I see I think you're probably right then! Well I'm using a yamaha solid state integrated amplifier.
What kind of Tube line stage feeding would you recommend?
Sorry If I seem like a novice. Its all a learning curve I suppose, but i'm determined to get good at this kind of thing so I'm happy to start with simpler circuits
you can easily be killed not using a power transformer especially with 230v mains
get 2 of the 220 to 6.3v transformers and run the second one back to back off the first
6.3 v used for heaters 2nd transformer has 210 ish volts on it's secondary which powers the B+.
1.2A secondary on 1st transformer leaves enough for B+
I used the similar 6922 tube in an SX 780 using the dial light winding for the heater and a voltage tripler diode setup running off the main amp secondary ( 30 vac ) thats good for 140v B+
*tripler voltage starts off of the +40v output rail
twice the caps and diodes should yield 250v B+ as the currents are low
get 2 of the 220 to 6.3v transformers and run the second one back to back off the first
6.3 v used for heaters 2nd transformer has 210 ish volts on it's secondary which powers the B+.
1.2A secondary on 1st transformer leaves enough for B+
I used the similar 6922 tube in an SX 780 using the dial light winding for the heater and a voltage tripler diode setup running off the main amp secondary ( 30 vac ) thats good for 140v B+
*tripler voltage starts off of the +40v output rail
twice the caps and diodes should yield 250v B+ as the currents are low
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What kind of Tube line stage feeding would you recommend?
Sorry If I seem like a novice. Its all a learning curve I suppose, but i'm determined to get good at this kind of thing so I'm happy to start with simpler circuits
As a learning excercise try to figure out the gain structure of your system. How much gain or attenuation do you need a linestage to provide?
That's a pretty important part of trying to figure out what makes sense to build.
OK that sounds like a good idea. As i'm feeding my integrated amp with my computer through line stage I'm not sure I would really need any gain, so would there be any point in building such a line stage, as It would just act as a buffer not increasing gain. Or am I misunderstanding?
The R-S202D manual is not encouraging. The unit has a recording O/P, but lacks both a recording device monitor loop and the preamp out/amp in feature.
Still, things can be managed. You will use the tubed line stage you build to drive the CD I/P of the receiver. You will set the receiver's volume control to max. loudness. Source selection (no tuners sorry) and listening level will be controlled in the tubed device.
A buffered volume control is probably best, but 1 of the several 12B4 based designs in the archives could work out reasonably well.
Still, things can be managed. You will use the tubed line stage you build to drive the CD I/P of the receiver. You will set the receiver's volume control to max. loudness. Source selection (no tuners sorry) and listening level will be controlled in the tubed device.
A buffered volume control is probably best, but 1 of the several 12B4 based designs in the archives could work out reasonably well.
FYI my phono PCB is similar in topology to the circuit you have chosen, but with an extra cathode follower:
The Valve Wizard
The Valve Wizard
Hey, if you need a first tube diy project but you don't want to tackle a high gain/low noise project like a phono preamp, why not try a cathode follower buffer? Put a tube in between your CD player or DAC and the inputs to your Yamaha integrated amp. Selling points:
- A cathode follower has pretty decent power supply noise rejection, so the design of the power supply isn't super-critical.
- It's pretty easy to get low distortion performance out of a cathode follower. Any reasonably well designed and built CF will perform OK.
- A cathode follower doesn't add any gain, so it won't overload the inputs to your integrated amp.
- You can read all about how to design one in a great book entitled "Designing High Fidelity Valve Preamps"
or here: The Valve Wizard -Cathode Follower
Another project I built that was super easy was a low gain, low(ish) voltage 6DJ8 line stage with a volume control (at its input). I use it as a 'tube warmer-upper' in between the output from my Chromecast Audio and the input of my input switchbox/volume control ("passive preamp"). It runs on a +150V B+, draws only about 6mA total for the two triodes, and 6VAC 300mA for the heater. It probably makes a lot of harmonic distortion, but it makes the MP3-quality audio from internet radio sound less nasty. I like it well enough. That might be useful for you if you listen to internet radio or similar through your stereo system.
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- A cathode follower has pretty decent power supply noise rejection, so the design of the power supply isn't super-critical.
- It's pretty easy to get low distortion performance out of a cathode follower. Any reasonably well designed and built CF will perform OK.
- A cathode follower doesn't add any gain, so it won't overload the inputs to your integrated amp.
- You can read all about how to design one in a great book entitled "Designing High Fidelity Valve Preamps"
or here: The Valve Wizard -Cathode Follower
Another project I built that was super easy was a low gain, low(ish) voltage 6DJ8 line stage with a volume control (at its input). I use it as a 'tube warmer-upper' in between the output from my Chromecast Audio and the input of my input switchbox/volume control ("passive preamp"). It runs on a +150V B+, draws only about 6mA total for the two triodes, and 6VAC 300mA for the heater. It probably makes a lot of harmonic distortion, but it makes the MP3-quality audio from internet radio sound less nasty. I like it well enough. That might be useful for you if you listen to internet radio or similar through your stereo system.
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I agree that, as a learning experience, a cathode follower is a suitable 1st project.
An inexpensive, high performance, B+ supply can be obtained by using a "full wave" voltage doubler setup. A Triad N-68X isolation transformer, which should be obtainable in the UK, connects the doubler to the AC mains. Inexpensive UF4007 diodes are quite suitable, for this project.
An inexpensive, high performance, B+ supply can be obtained by using a "full wave" voltage doubler setup. A Triad N-68X isolation transformer, which should be obtainable in the UK, connects the doubler to the AC mains. Inexpensive UF4007 diodes are quite suitable, for this project.
Another idea is this phonoamp, Revenge by Mauri Pännäri from Finland. BF245B can also be used for the fets.
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Here's a simple cathode follower using a 12AU7 and EZ81 in the power supply:
I think this is a suitable first high voltage project for tube DIY beginners. More info, BoM, etc here: Muchedumbre Buffer Preamp – wauwatosa tube factory
Hammond 269Gx or 269Jx would work as power transformers if you can find them over in the UK. Could also use a 230V isolation transformer with a SS bridge or hybrid rectifier and a 6V filament transformer.
edit: oops, you can't use the 200 series from Hammond. Looks like the 370AX, 369GX, 369JX would be the universal primary options for you.
I think this is a suitable first high voltage project for tube DIY beginners. More info, BoM, etc here: Muchedumbre Buffer Preamp – wauwatosa tube factory
Hammond 269Gx or 269Jx would work as power transformers if you can find them over in the UK. Could also use a 230V isolation transformer with a SS bridge or hybrid rectifier and a 6V filament transformer.
edit: oops, you can't use the 200 series from Hammond. Looks like the 370AX, 369GX, 369JX would be the universal primary options for you.
+1
The only suggestion I have to add is that since you'll be using this project to drive the inputs of a solid-state integrated amp which might have an input impedance as low as 10k ohms, I think the 1.0uF 400V output capacitor will be too low a value. The reason is that a 1uF cap into a 10k load will roll off too much low bass response. Increasing the value of those caps to 4.7uF or 10uF will allow the low bass to pass through.
Therefore the output capacitor should be changed to 4.7uF 400V (or 10uF 400V would be better, if you can find a pair within your budget). The rest looks OK for your use.
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Edit to add: 10uF 400V will be hard to find in a high quality polypropylene film version. Audiophiles will tell you that an electrolytic cap won't sound good on the output. You can find metallized polypropylene or mylar (polyethylene) film 10uF 400V motor run capacitors pretty easily, and often for little money. Solen (SCR) also makes a suitable capacitor.
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The only suggestion I have to add is that since you'll be using this project to drive the inputs of a solid-state integrated amp which might have an input impedance as low as 10k ohms, I think the 1.0uF 400V output capacitor will be too low a value. The reason is that a 1uF cap into a 10k load will roll off too much low bass response. Increasing the value of those caps to 4.7uF or 10uF will allow the low bass to pass through.
Therefore the output capacitor should be changed to 4.7uF 400V (or 10uF 400V would be better, if you can find a pair within your budget). The rest looks OK for your use.
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Edit to add: 10uF 400V will be hard to find in a high quality polypropylene film version. Audiophiles will tell you that an electrolytic cap won't sound good on the output. You can find metallized polypropylene or mylar (polyethylene) film 10uF 400V motor run capacitors pretty easily, and often for little money. Solen (SCR) also makes a suitable capacitor.
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+1 back at you
I originally built this as a simple volume control to go with a tube power amp with a high impedance input. For a SS 10k input impedance amp, I'd go at least 2.2uf (-3db about 7hz, -0.5db @ 20hz). This should be mentioned in the write up somewhere.
4.7uF or 10uF definitely do the job too as long as you can find them in a size/price that works for you. I like the CD 940C series for input/output caps because they're easy to find at Mouser/Digikey/etc but they're 600Vdc rated so they get pretty big above 2uF.
I like the motor run output cap suggestion, too. I've only used them in crossovers and power supplies. Good budget cap idea for headphone OTL amp caps. I get mine at a farm equipment surplus store
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