Well, it was with my bench HT supply and breadboarded with clips and long cables. Low frequency ripple though. I'd do a proper test with an accurate multimeter and the proper power supply over the weekend and report back...
Measured properly today and got just 4 mVrms of output ripple. Similar noise I get when HT supply is turned off, so it's my workbench noise what I get at the output. Still need to test stability with the 26 preamp as just loaded the Salas regulator with a resistor.
Btw: after a long search on eBay finally managed to get hold of a pair of mesh AZ1!
Cheers,
Ale
Btw: after a long search on eBay finally managed to get hold of a pair of mesh AZ1!
Cheers,
Ale
From my experience of building a few shunt regulators, 4mV ripple is way too large. You're either not measuring it properly or the regulator isn't working well enough. My shunt regulator, when measured properly, shows ripple below 200uV p-p.
I've an update on my 26 preamp. I mentioned before that using the Hammond 156C plate chokes gave me some nasty hum/ripple on B+. Replacing the plate chokes with either 4k resistors or IXCP10M90S ccs got rid of the hum, so I thought it was some weird interaction between my shunt regulator and the chokes. But no, it wasn't.
I replaced the discrete shunt regulator with a VR-150 tube regulator, and the ripple was still there. Tried to cover the chokes with some metal cans but this shielding had no effect.
Next I separated the power supply from the rest of the amp; indeed, those of you who said that the plate chokes pick hum from the rest of the power supply were right. Even at a distance of 3 feet there was some hum picked from the psu transformer. Moving the psu about 5 feet away from the tubes+chokes shows no ripple at the plates! To me this was quite surprising.
I've an update on my 26 preamp. I mentioned before that using the Hammond 156C plate chokes gave me some nasty hum/ripple on B+. Replacing the plate chokes with either 4k resistors or IXCP10M90S ccs got rid of the hum, so I thought it was some weird interaction between my shunt regulator and the chokes. But no, it wasn't.
I replaced the discrete shunt regulator with a VR-150 tube regulator, and the ripple was still there. Tried to cover the chokes with some metal cans but this shielding had no effect.
Next I separated the power supply from the rest of the amp; indeed, those of you who said that the plate chokes pick hum from the rest of the power supply were right. Even at a distance of 3 feet there was some hum picked from the psu transformer. Moving the psu about 5 feet away from the tubes+chokes shows no ripple at the plates! To me this was quite surprising.
In my noise workbench can't measure anything below 4mv. Surprised you can measure 200uV!
Interesting comments around noise pick up, had a similar experience with a PP amplifier and since then all my designs have separate chassis. My 45 SET works like a charm with separate chassis and DC filaments and cant hear any audible hum even with my Grado headphones!
Same issue with my SSHV OPT headamp, even 3 feet away from the power transformers the OPT's pick up 60hz hum.
Since this discovery I am not a fan of choke loading.
I really think that folks prefer the sound of an expensive choke over a CCS because of this soothing 60hz "dither."
Hammond 156C choke: what you pay is what you get....
This is an open frame EI choke, and therefore very sensitive to stray fields.
This build is the worst you can possibly pick to load your beloved 26...
Much better will be a single c-core with two bobbins, so that much of the iron is screened by the coils.
When necessary some mumetal shielding and there you go, a quiet choke....
This is an open frame EI choke, and therefore very sensitive to stray fields.
This build is the worst you can possibly pick to load your beloved 26...
Much better will be a single c-core with two bobbins, so that much of the iron is screened by the coils.
When necessary some mumetal shielding and there you go, a quiet choke....
How many people can afford a mu-metal shield for a big choke? Foil ain't going to cut it. Where do you find a c-core choke for this tube? Have you taken any measurements on this?
Considering this is a preamp and the slightest bump at 60hz is going to be multiplied by the main amp, a quality CCS just seems the way to go.
I finally found a few decent #26 tubes, so am experiementing but on a theoretical level, a #26 preamp just looks wrong for a choke load, would hate to spend major dollars to prove myself right.
Hi!
You should not be dismissing choke loading all together just because you had a bad experience with a cheap choke.
I used choke loading even in the first stage of my Octal Phonopreamp.
A 6SC7 loaded with a Lundahl 1667 choke. There is zero hum pick up.
And that stage has to amplify signals which are much lower than average line level. We are talking signals 40dB below!
Best regards
Thomas
You should not be dismissing choke loading all together just because you had a bad experience with a cheap choke.
I used choke loading even in the first stage of my Octal Phonopreamp.
A 6SC7 loaded with a Lundahl 1667 choke. There is zero hum pick up.
And that stage has to amplify signals which are much lower than average line level. We are talking signals 40dB below!
Best regards
Thomas
No - I don't agree. I tried active loads and I found that chokes sounded smoother and just better overall. 26 isn't "wrong" for a choke at all, it just needs one with high inductance. From 200H up you shouldn't really have a problem. There are excellent models like the Lundahls and also really good hand made chokes. I wouldn't hesitate to use high quality chokes, but I still maintain that if you can deal with the hum, the 156C x 2 is a pretty good sounding cheap option. Depends on your speaker sensitivity etc. I don't have problems with 89db speakers. Others use these chokes and like them too.
Andy
Hi!
I fully agree with Andy. The 26 is not 'wrong' for a choke load. In the right application and if the output impedance of 7k is sufficient, the 26 works nicely with a choke load. As Andy wrote: you need to pick the right choke or take the right measures that your choke does not pick up noise. I'm currently offering some of those Hammond 150Hy chokes on ebay. Have a look if you are interested (sorry for the advertisement)
Thoma
I fully agree with Andy. The 26 is not 'wrong' for a choke load. In the right application and if the output impedance of 7k is sufficient, the 26 works nicely with a choke load. As Andy wrote: you need to pick the right choke or take the right measures that your choke does not pick up noise. I'm currently offering some of those Hammond 150Hy chokes on ebay. Have a look if you are interested (sorry for the advertisement)
Thoma
IKO, I faced the same issue. Even if change the angle of the plate chokes will have impact on hum level. Really irritating. Finally I was able to control the hum with some isolation but lately moved to CCS as you did, which infact removed the hum completly.
Agree. Could hear a clear difference in sound with chokes. Much superior. I was reluctant to remove chokes and moved towards CCS, but it seems more cost effective solution until I am ready spend some on good quality chokes. EP 200H chokes of mine worked nicely but still I had to struggle with them to keep the hum minimum.
I'm back to chokes now, and I like the sound. Yes, my power supply is now in a separate box and it's about one meter away from the proper preamp. But hey, it's a small price to pay.
When no music is playing and I put the volume way up there's a slight valve hiss, probably from the 0D3 regulator. Although it's inaudible to me at normal listening volume, I might take the 0D3 out.
When no music is playing and I put the volume way up there's a slight valve hiss, probably from the 0D3 regulator. Although it's inaudible to me at normal listening volume, I might take the 0D3 out.
I placed the two LL1660 transformers inside the chassis (i.e. hanging from the top plate) and am still in the process of building the power supply chassis. No hum or noise at all introduced by the 26 unless you put your hands close to the tubes
One question regarding the power supply choke orientation. I have two 20H chokes part of an CLCLC stage for the raw HT supply and I'm planning to mount them on the top plate. Can I put them in parallel or do I need to orientate them in 90 degrees between each other?
Thanks
Ale