So...
Kofi is putting together an analogue package for a friend and is considering building a tube phono preamp. I use Thorsten's El Cheapo right now and I think it sounds great, but I'm looking to make a different one for comparison's sake and I've read some good things about Steve Bench's RIAA.
Anyone else have an opinion on this RIAA stage they'd care to share? Any power supplies (regulated or just well filtered) that I should consider? Any other phono stages worth considering?
Kofi?
Kofi is putting together an analogue package for a friend and is considering building a tube phono preamp. I use Thorsten's El Cheapo right now and I think it sounds great, but I'm looking to make a different one for comparison's sake and I've read some good things about Steve Bench's RIAA.
Anyone else have an opinion on this RIAA stage they'd care to share? Any power supplies (regulated or just well filtered) that I should consider? Any other phono stages worth considering?
Kofi?
Hi Kofi Anan, ....
.....if I had the time I'd built that one by Allen Wright:
http://www.vacuumstate.com/index.tpl?rubrik=8&lang=2&a=%93C%29%C9%26j%26_&b=733755.5849974914
IIRC Allen Wright refers to the Loesch Pre somewhere in his PreAmp Cookbook.
(Uppermost schem, left part ;-) )
Hope this helped
Greez
SigFire
.....if I had the time I'd built that one by Allen Wright:
http://www.vacuumstate.com/index.tpl?rubrik=8&lang=2&a=%93C%29%C9%26j%26_&b=733755.5849974914
IIRC Allen Wright refers to the Loesch Pre somewhere in his PreAmp Cookbook.
(Uppermost schem, left part ;-) )
Hope this helped
Greez
SigFire
.......ooops, sorry indeed for not takin' this into account while postin' "quick'n dirty". I knew that there where 2 Loeschs.
Referin' to A.W.'s book I seemed to have overlooked the expression "legendary" before the name Loesch. ;-)
(It's been quite a long time since I had time to look through it.)
Greez
SigFire
Referin' to A.W.'s book I seemed to have overlooked the expression "legendary" before the name Loesch. ;-)
(It's been quite a long time since I had time to look through it.)
Greez
SigFire
Here's my take on Steve's phono amp. In the final version, I removed the bypass resistors for the LED. http://www.diyaudio.com/forums/showthread.php?postid=1083419#post1083419
The supply, as shown in the next post works well, but more complicated than necessary. The Miada regulator part is mostly there to protect the current regulator from over voltage if there is no current draw in event of a fault down the line. Also, I wanted to make one for the experience. If you design the supply front end so that the voltage with no load other than the bleeder resistor, doesn't exceed the rating of the current regulator, you can omit it. You can also probably omit the Morgan Jones filament lift with DC filaments, or sub in a simpler one. But the MJ version is pretty straightforward and uses cheap parts.
John Broskie also has some nice shunt regulators, based on Mosfets; http://www.tubecad.com/2007/07/blog0115.htm, and even some kits.
If you look carefully, you will see that Allen Wright's phono amp is actually pretty similar to Steve's amp. He puts his super linear cathode follower on the back end, I used the follower from Broskie's Aikido, and used his noise canceling scheme. If your next stage has an input impedance of 100k or more, you can omit the follower (may have to tweak the final RIAA cap some). In the Wright amp, use a 50K load, and you can omit the follower. If no follower is used, you either have to use short interconnects (their capacitance is in parallel with the final RIAA cap), or tweak the final cap with your interconnects in place.
Sheldon
edit: I see that Salas just posted a shunt reg., and for Steve's amp, of all things: http://www.diyaudio.com/forums/showthread.php?s=&postid=1685067#post1685067
The supply, as shown in the next post works well, but more complicated than necessary. The Miada regulator part is mostly there to protect the current regulator from over voltage if there is no current draw in event of a fault down the line. Also, I wanted to make one for the experience. If you design the supply front end so that the voltage with no load other than the bleeder resistor, doesn't exceed the rating of the current regulator, you can omit it. You can also probably omit the Morgan Jones filament lift with DC filaments, or sub in a simpler one. But the MJ version is pretty straightforward and uses cheap parts.
John Broskie also has some nice shunt regulators, based on Mosfets; http://www.tubecad.com/2007/07/blog0115.htm, and even some kits.
If you look carefully, you will see that Allen Wright's phono amp is actually pretty similar to Steve's amp. He puts his super linear cathode follower on the back end, I used the follower from Broskie's Aikido, and used his noise canceling scheme. If your next stage has an input impedance of 100k or more, you can omit the follower (may have to tweak the final RIAA cap some). In the Wright amp, use a 50K load, and you can omit the follower. If no follower is used, you either have to use short interconnects (their capacitance is in parallel with the final RIAA cap), or tweak the final cap with your interconnects in place.
Sheldon
edit: I see that Salas just posted a shunt reg., and for Steve's amp, of all things: http://www.diyaudio.com/forums/showthread.php?s=&postid=1685067#post1685067
Kofi Annan said:
Steve Bench's is the best you can make. Have made Loesch's grid leak cascade one you linked as well. Comes second. You may need to change C1 from 5n7 to 6n8 for the Bench if you make it. It measured and sounded tiped up in my case with the original value.
It will only sound good with an active regulator. Mosfet Maida does a good job. But my recent developement for the Steve Bench PSU may interest you. Upgrades it strongly.
See link.
Alright! Thanks for all the responses!
I think this is a winner. I'm thinking I'll CLC before the regulated schema and I'm guessing I won't have to twiddle much.
Salas-- it looks like you've got one supply per channel if I read your wiring correctly. The Bench RIAA only draws aobut 10mA for both channels. Did you experience any issues with this?
I understand that some regulators require a minimum current to function properly. I don't think this one is subject to that, but I just wanted to check.
Thanks.
Kofi
I think this is a winner. I'm thinking I'll CLC before the regulated schema and I'm guessing I won't have to twiddle much.
Salas-- it looks like you've got one supply per channel if I read your wiring correctly. The Bench RIAA only draws aobut 10mA for both channels. Did you experience any issues with this?
I understand that some regulators require a minimum current to function properly. I don't think this one is subject to that, but I just wanted to check.
Thanks.
Kofi
No issues Kofi. Common high voltage shunt supply actually. That supply has constant current, no dependence on load. There is a separate heater transformer (toroid) on that photo, and gives juice to 2 heater regulators. One 12.6 one 6.3. The cascode sounded better when the heater supplies of lower and top tubes got totally separate and different for voltage. Of course that is something not easily guessed. You were right to assume that maybe I used more HV circuitry.
Thanks! I should have noticed that it was single channel...
One more-- in your post, you mentioned:
I'm guessing this means that the PSU will have to supply about 80mA of current for both channels including the rectifier. I just wanted to confirm as I was going to run a CLC in the front end and needed to know approximate current draw.
Since we're dealing with CLC and no resistors in the supply before the regulator, I'm thinking the current draw estimation need not be exact. I'm just looking to supply about 230V in, per your post, and I should be fine.
I think this means that I could get away with about a 180V mains transformer with solid state rectification (180 x 1.414 = 254V less approx. 10 - 20V for L resistance) and get the recommended 230V.
Sound right?
One more-- in your post, you mentioned:
I'm guessing this means that the PSU will have to supply about 80mA of current for both channels including the rectifier. I just wanted to confirm as I was going to run a CLC in the front end and needed to know approximate current draw.
Since we're dealing with CLC and no resistors in the supply before the regulator, I'm thinking the current draw estimation need not be exact. I'm just looking to supply about 230V in, per your post, and I should be fine.
I think this means that I could get away with about a 180V mains transformer with solid state rectification (180 x 1.414 = 254V less approx. 10 - 20V for L resistance) and get the recommended 230V.
Sound right?
Hi,
The shunt draws 60mA all the time because there is a constant current source in it. 20mA of that current will go to the Bench 2 channels, and 40mA will be burning on the IRF840 and used as dynamic headroom on signal demand.
Give some trafo headroom, in constant current conditions the transformers heat up if near in mA and they shag below their spec AC voltage. They normally go DC=1.35X anyway with losses. I would use a 200V 250mA (50VA) one.
The shunt draws 60mA all the time because there is a constant current source in it. 20mA of that current will go to the Bench 2 channels, and 40mA will be burning on the IRF840 and used as dynamic headroom on signal demand.
Give some trafo headroom, in constant current conditions the transformers heat up if near in mA and they shag below their spec AC voltage. They normally go DC=1.35X anyway with losses. I would use a 200V 250mA (50VA) one.
Use the 317 as a current source. It will not shock the heaters, and the tubes will sound appreciably better. I(A) is the nominal heater current. When you need 0.3A the resistor must be 4R2. Then the tube will develop 6.3V in about 2 minutes. Because the resistor will heat up to about 0.4W constantly, use a 2W one so to survive in the long run. You may need to trim the value in practice by paralleling resistors, because of tolerances in 317 Vref, tube, and resistor. Heat tubes up at 6.1V or 12.3V. Maybe a 4R3 will get you directly there at less than 6.3V. Or a 15R//20R for less than 12.6V if heaters in series. It is a benefit for reliability and life and the tube current gain remains virtually the same. Use 4X 317 each for one tube. At such power delivery you may need no heat sinks, but put very little ones for long term reliabilty. Sounds better with dedicated I sources. The 317s cost peanuts. A 0.1uF cap across the front of each 317 is good to have if it is fed with longish wires, and a 2200uF/25V capacitor after the resistor, shunting the heaters to ground is enough.
Use a 12.6V 2A secondary, rectify, and filter with 10000uF 25V. Then feed the 317s from there.
Use a 12.6V 2A secondary, rectify, and filter with 10000uF 25V. Then feed the 317s from there.
Attachments
This is perfect-- thanks.
I just ordered a 200V / 200mA power transformer with a 16V winding from Jack Eliano at electra-print. Jack has wound me some great stuff in the past and I just like dealing with him, although you have to budget lots of time for the curmudgeonly banter...
Anyway, in typical Jack fashion, he told me I didn't need another winding for the 6.3V filament for the 6DJ8. Instead, he insisted that I wire the 6DJ8 filaments with the rectified and regulated DC 12.6V. He said I could just wire the 6DJ8s "in series like Christmas lights" and they would get the 6.3V they needed.
I have no idea what the hell he's talking about.
Can anyone translate in Kofi-speak?
Kofi
PS-- I also ordered a 5H / 250mA choke from him for the CLC front end. Got lots of iron on the way.
I just ordered a 200V / 200mA power transformer with a 16V winding from Jack Eliano at electra-print. Jack has wound me some great stuff in the past and I just like dealing with him, although you have to budget lots of time for the curmudgeonly banter...
Anyway, in typical Jack fashion, he told me I didn't need another winding for the 6.3V filament for the 6DJ8. Instead, he insisted that I wire the 6DJ8 filaments with the rectified and regulated DC 12.6V. He said I could just wire the 6DJ8s "in series like Christmas lights" and they would get the 6.3V they needed.
I have no idea what the hell he's talking about.
Can anyone translate in Kofi-speak?
Kofi
PS-- I also ordered a 5H / 250mA choke from him for the CLC front end. Got lots of iron on the way.
I'm sorry to seem dumb, but I can't reconcile how the heaters will see 6.3V when wired in series with a 12.6V supply without a center tap. I know this is basic stuff, but I always get tripped up on the heater wiring.
So, let's say pins 4 and 5 are the filament pins for the 6DJ8. If I need the potential between the pins to be 6.3V, how can I use the 12.6V supply to achieve this?
Whoever answers this, I owe you one...
Kofi
So, let's say pins 4 and 5 are the filament pins for the 6DJ8. If I need the potential between the pins to be 6.3V, how can I use the 12.6V supply to achieve this?
Whoever answers this, I owe you one...
Kofi
Kofi Annan said:
If you put two 6DJ8 tube filaments in series, the voltage is divided by half for each filament. Think if the filament as a resistor (which it is - just run hot). If you have two equal resistors in series, the potential across each resistor is half of the total. You are making a voltage divider.
For the 12AY7 in the same amp, you connect the supply across the AY7 filament, both AY's in parallel, so those filaments see 12.6V end to end. There is an alternative connection for the AY7 if you want that too. Need a diagram?
Sheldon
The resistor metaphor helps...
So, I'll have two 6DJ8s (one for each channel), which means that if I connect the 12.6V supply to pin 4 of tube 1, then connect pin 5 of tube 1 to pin 4 of tube 2 and pin 5 of two to ground, I've effectively made a voltage divider that causes tube 1 to see 6.3V (12.6V on pin 4 - 6.3V on pin 5) and tube 2 to also see 6.3V (6.3V on pin 4 and 0V on pin 5).
How'd I do?
Ughhh.
Kofi
So, I'll have two 6DJ8s (one for each channel), which means that if I connect the 12.6V supply to pin 4 of tube 1, then connect pin 5 of tube 1 to pin 4 of tube 2 and pin 5 of two to ground, I've effectively made a voltage divider that causes tube 1 to see 6.3V (12.6V on pin 4 - 6.3V on pin 5) and tube 2 to also see 6.3V (6.3V on pin 4 and 0V on pin 5).
How'd I do?
Ughhh.
Kofi
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