First a nice build you've done.
Regards your strange pulse (140 times per minute) noise I'll tell your my story here.
I have build a couple of 4P1L for some of my good friends. They're 100% the same. 2 of these amps are playing, and on there location they have never had this strange pulses.
I have it periodic when I play in my apartment, and If I switch amp, then their 4P1L will also generate this electric pulse on my location.
Another friend lives just over me in the same house (own apartment), and when I have these pulses he have them too.
In the holidays (3 weeks) here in Denmark, there wasn't a single of these strange pulses. Monday morning after the holiday at 9am, these pulses started again, quite weird.
In the area I live we have some entrepreneurs who are renovating a larger building for a school, when they aren't working the changes for these pulses are lowered with at least 80 percent.
Right now Sunday 9am 13 september 2015 in Denmark, I'm playing on my 4P1L, and I'm not disturbed by these pulses.
I've tried everything on my own location. Vario-isolation trafo in Front. Network filter in front. Switch outlet. Switch phases. Snopper. Nothing can stop it.
When I first wrote about it, I don't think anyone on this thread have had these strange pulses, but now I can see I'm not the only one.
PS! In the first 6 month I haven't got any of these pulses on my own 4P1L. I've build an extra and again if the pulses are "online", I can switch to the other amp and It's 100% certain these pulses will be present.
My question to you is, do you have these pulses all the time. Or do you have periods where the're gone ???
Michael
Hi Michael,
First I added another choke to HT, then another RC section to Heaters supply - nothing changed regarding noise. So I moved away HT supply from the rest of the circuit and that pulse noise was gone.
I reworked HT supply: made it LCRC filtered, removed tube diodes, set up a standard shottky bridge with old soviet caps and Kevin's softstart board. And moved it away a bit.
So now hi frequency noise and that strange pulse is gone. There is a slight hum which I hear when I put my ear close to the speaker. Maybe there is a ground loop somewhere.
Next thing to do will be changing to LC filtering in the heater supply.
Br
zz
P.S. Forgot to add 🙂
The sound regarding image and stage is great! As my wife said listening to Al di Meola guitar "like riding the Milky Way".
I
First I added another choke to HT, then another RC section to Heaters supply - nothing changed regarding noise. So I moved away HT supply from the rest of the circuit and that pulse noise was gone.
I reworked HT supply: made it LCRC filtered, removed tube diodes, set up a standard shottky bridge with old soviet caps and Kevin's softstart board. And moved it away a bit.
So now hi frequency noise and that strange pulse is gone. There is a slight hum which I hear when I put my ear close to the speaker. Maybe there is a ground loop somewhere.
Next thing to do will be changing to LC filtering in the heater supply.
Br
zz
P.S. Forgot to add 🙂
The sound regarding image and stage is great! As my wife said listening to Al di Meola guitar "like riding the Milky Way".
I
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Dear Michael,
please find attached the complete "documentation" I have. And, btw., I'm a newby myself.
Well, as I previously stated: this findings conclusion holds for me.
But as human beings don't have an acoustic imagination, give it a try.
After that you will not know weather there might have been some lower end extension missing, or eventually (I'm guessing) be compensated through your loudspeaker positioning.
I'm only encouraging to try what I found worked good for me. Nothing more.
All the best,
Ulrich
Attachments
Hi,
I am a bit confused now. I have some grounding issues: hum and buzz. Can anyone post a drawing of all ground point connections, please? I mean input and output, bias resistor, transformer secondary, and SSHV input and output ground points.
Br, zz.
I am a bit confused now. I have some grounding issues: hum and buzz. Can anyone post a drawing of all ground point connections, please? I mean input and output, bias resistor, transformer secondary, and SSHV input and output ground points.
Br, zz.
Hi zz, This is how I recommend the general wiring scheme for filament bias. Much the same for other bias methods.
Trafo CT wires to C4.
It does not have to be a "single-point" ground - just think about the current flowing in each wire, and consider if it's OK to mix together currents by sharing wiring run. If in doubt, use a separate wire.
Trafo CT wires to C4.
It does not have to be a "single-point" ground - just think about the current flowing in each wire, and consider if it's OK to mix together currents by sharing wiring run. If in doubt, use a separate wire.
Attachments
Thanks, Rod. Of course, I saw this drawing. It is unclear how to wire SSHV two ground points. Also not sure about output transformer (negative point), at the drawing it is not grounded.
SSHV FORCE and SENSE connexions can both be made to the same point - eg the filament bias resistor's ground node.
Output trafo secondary grounding can be made at the power amplifier's input stage. In this case, please check that the power amp's input[-] is connected to safety ground (Earth). Connecting the secondary to line-amp ground may give a current-loop, and humm!
Output trafo secondary grounding can be made at the power amplifier's input stage. In this case, please check that the power amp's input[-] is connected to safety ground (Earth). Connecting the secondary to line-amp ground may give a current-loop, and humm!
FORCE and SENSE wires of a Regulator are there to prevent errors (dc and dynamic errors) caused by the [complex] impedance of the output wiring. So they go to the same point, but carry very different currents.
Got it! My test amp has no safety earth and the main amp has it 🙂 So I see 2 grounding schemes in this case.
In my case F and S points are connected at the Regulator and a single wire is to be connected to a bias resistor ground point. Input ground point of the reg is connected to C2 ground and C2 ground is connected to a bias resistor ground point. Sounds like a loop but I guess it is not.
Can anyone recommend Input Transformer (Lundahl, Jensen) for Ballanced to Unballanced conversion in this Line Stage, please?
There are a bunch of choices for input transformers in the Lundahl catalog. There are two choices that sound great, are not terribly expensive, and are interesting, because they use the same coils, but different core material. The LL1544A uses amorphous cobalt and has the most transparent sound, while the LL1545A uses mu-metal (like the Jensen and Cinemag products do), which gives the sound a slightly warmer tone, but slightly less open sound. Once users have tried the cobalt amorphous transformers, they are surprised at how little transformer sonic signature there is with this core material. That's not always the right solution, sonically speaking, but it's worth knowing about.
Kevin - good to see you on the line here. Can I ask you a similar question? I have just enough volume at present from my ES9023 DAC but nothing to spare, so may be wanting a 1:2 input transformer, particularly if I succumb to building a Soekris or DDDac and taking the signal straight from the output. The ES9023 gives me around 2v, but the Soekris would be more like 1.5v. My 4P1L stage is single ended, as is the amp.
Choices: LL7903 is being used, or what?
Choices: LL7903 is being used, or what?
Thank you, Kevin. I saw those LL1544A this morning when I was reading about PP amps at your site. 🙂
By the way, what is the expected time for new products you mentioned there for 4P1L pre-amp?
By the way, what is the expected time for new products you mentioned there for 4P1L pre-amp?
The LL7903 is a great choice if the output impedance of your current DAC is respectably low, like less than 1K. I've used other Lundahl transformers over the years for this sort of thing, such as the LL1676, LL1545A, and the LL1544A. All gave really good results with just the "shading" differences noted in the post above.
Every week I think that this will be the one when I can assemble all of the "modules" to a chassis and have something to demonstrate the parts that I will have for sale. Last night I got irritated with myself for being too anal about it and decided to put the preamp parts together on a piece of plywood and get on with it. So, I'm not there yet, but will be very soon. Plywood is a great medium for advancing designs. Metal is somehow inhibitory...
Good news. Nothing wrong with wood for a chassis. I think it is superior except for those living in cities and in need of isolation. One can see from the picture GOOGLE displays when you look for K&K that you are NOT in the city and neither am I.
I would like to have two per channel - one with minimal gain and the other with an additional 6 dB - should this be possible with your available transformers? Or will it require an input transformer, also?
I would rather they be paralleled instead of in series but if that is the only way ...
Take care,