If you're talking about the turntable ground wire, try it connected to preamp earth ground (safety ground) and then try it floating; one or the other will be lower in hum.
As far as the cables from the cartridge, if you're using a single-ended phono input, then do what Chris says. Optimum way to run a phono stage is balanced input with a shielded twisted pair from each cartridge channel.
As far as the cables from the cartridge, if you're using a single-ended phono input, then do what Chris says. Optimum way to run a phono stage is balanced input with a shielded twisted pair from each cartridge channel.
In fact, SY, I'm using a shielded twisted pair from the input jacks: and the jacks aren't grounded togheter, but they're grounded at the tube's cathode ground. But if I shield them as you say, where do I have to ground the shield? I guess at the rca jack, to avoid noises entering the cathode's ground...
Well, you want the safety ground as close to the input grounds as possible. If you've shielded the twisted pair, just connect the shield on one end, conventionally the turntable end.
Hi Giaime,
This is a single ended system you have built. Since it's yours, why not wire a custom plug in parallel. That way you can ground the shield at the chassis and still bring the other lead from the cartridge to a point close to the cathode. You normally need to add some capacitance anyway to resonate the cartridge at the proper frequency.
-Chris
This is a single ended system you have built. Since it's yours, why not wire a custom plug in parallel. That way you can ground the shield at the chassis and still bring the other lead from the cartridge to a point close to the cathode. You normally need to add some capacitance anyway to resonate the cartridge at the proper frequency.
-Chris
SY said:
Yeah? I didn't know this. Actually, the safety ground is connected to the main filter cap before the B+ regulator. I'll have to try how does it sound with the safety ground (that means also the transformer chassis) tied to the input jacks.
Thanks a lot!
But it's not totally clear to me the "single ended" thing vs "balanced"... and the post by Chris is totally dark for me
Could you explain a little more?
Hi Giaime,
Okay, this is "Chris light". Sorry, was just looking at the plane thread again.
Single ended: Your audio signal is treated as a hot and common. The input stage is not balanced.
Balanced : The audio signal has a + phase and a - phase. It is not referenced to ground necessarily. The signal is handled by a differential pair or an "instrumentation amplifier" type circuit. The differential amp would be a "long tailed pair", made using both sections of a dual triode for instance. The cathodes would be connected to a common current sink in the standard case.
-Chris
Okay, this is "Chris light". Sorry, was just looking at the plane thread again.
Single ended: Your audio signal is treated as a hot and common. The input stage is not balanced.
Balanced : The audio signal has a + phase and a - phase. It is not referenced to ground necessarily. The signal is handled by a differential pair or an "instrumentation amplifier" type circuit. The differential amp would be a "long tailed pair", made using both sections of a dual triode for instance. The cathodes would be connected to a common current sink in the standard case.
-Chris
Hey Chris,
Saw some thing on another thread that throws me... shouldn't heater circuits be reference to some AC ground (ground or DC divider)? Especially if the same cathodes are unbypassed?
Saw some thing on another thread that throws me... shouldn't heater circuits be reference to some AC ground (ground or DC divider)? Especially if the same cathodes are unbypassed?
Heaters absolutely need a DC reference!
Besides using a diff amp as Chris mentioned, you can also use an input transformer. There's a nice diagram of exactly how to implement this in Morgan Jones's "Valve Amplifiers". You DO have Morgan Jones's book, don't you?
Besides using a diff amp as Chris mentioned, you can also use an input transformer. There's a nice diagram of exactly how to implement this in Morgan Jones's "Valve Amplifiers". You DO have Morgan Jones's book, don't you?
YEAH... just losing my mind is all.
Some schem on another thread has the heaters described as "floating". Would seem to nuts me... 330 ac pk-pk common-mode coupled to the cathode via 50 pF(???).
Some schem on another thread has the heaters described as "floating". Would seem to nuts me... 330 ac pk-pk common-mode coupled to the cathode via 50 pF(???).
Hi poobah,
You really can't allow heaters to float. DC reference them to some positive voltage referenced to ground. Bypassed to the "dirty" ground. It's amazing how quiet AC heaters are when brought positive.
Transformers for the phono ... Not convinced yet. I used to sell nice Ortofon step up transformers. Then you got a real preamp. Mind you, that was the Seventies.
Betcha those Ortofons would stack up well today too. I still use a VMS-30E cartridge.
-Chris
You really can't allow heaters to float. DC reference them to some positive voltage referenced to ground. Bypassed to the "dirty" ground. It's amazing how quiet AC heaters are when brought positive.
Transformers for the phono ... Not convinced yet. I used to sell nice Ortofon step up transformers. Then you got a real preamp. Mind you, that was the Seventies.
Betcha those Ortofons would stack up well today too. I still use a VMS-30E cartridge.
-Chris
That's what I thought... freaked 'cause I was telling Giaime the very same thing a couple of days ago... never actually wired a heater, but it all seems pretty obvious. Just losing my marbles. Somebodies pushing a schematic I saw with "floating heaters"... yes AC... nutcase probably, Oops!, sorry, I meant sanity challenged.
Maybe a directly heated cathode follower... yeah... yeah
😀 😀
Maybe a directly heated cathode follower... yeah... yeah
😀 😀
While on the subject of heaters....I figured i would throw in my 2 cents...
There seems to be lots of concern over "regulating" the heaters to EXACTLY 6.3V ...... I don't see the need...
If you instead regulated the heaters with a constant current source you would notice different voltage drops for various heaters of the same valve type....
Instead I propose you regulate the Wattage of the heater instead....
Chris
There seems to be lots of concern over "regulating" the heaters to EXACTLY 6.3V ...... I don't see the need...
If you instead regulated the heaters with a constant current source you would notice different voltage drops for various heaters of the same valve type....
Instead I propose you regulate the Wattage of the heater instead....
Chris
cerrem said:
Interesting point Chris, in fact I've set my heater regulator not on 12.6V, but on total current consumption of 450mA 😉
I should however add that my Sylvania 12AX7A need fair less voltage to heat up properly than those (already mentioned to be) strange Siemens ECC81...
Anyway, expect a loooong post from myself about my preamp grounding. Today's afternoon I will go to give an exam and after... ground ground ground!
I anticipate a few questions:
- in what point of the signal chain should the safety ground be tied to (aside from the chassis, which is a thing that for now I don't have, since it's build on a wooden board)?
- where do I have to reference my heater regulator to the B+ regulator ground? Now I'm referencing it at the audio ground of one of the ECC81 cathodes.
More later...
I've tried the phono stage... man what a sound. The only problem is a little too much background noise, but I guess that with proper shielding it will be quiet.
Amazing sound, it really make my turntable (oh, in fact the whole system) sound extremely good. Surprizing amounts of bass too!
My NAD3020 was very ashamed.
Amazing sound, it really make my turntable (oh, in fact the whole system) sound extremely good. Surprizing amounts of bass too!
My NAD3020 was very ashamed.
Hello!
The preamplifier has been running all day, to test which components do get hot. The LM317 for the B+ is cold, the IRF840 is warm, and the LM317 for the filaments is hot but touchable. Also the two power transformers are warm, not hot.
I'm looking for suggestions to build a case for it: I'll post some photos of realizations that I found on the net (thanks to the diyers which contributed them) to show what I have in mind.
This one looks good, but I find a little difficult to make that wooden chassis, I'm not pratical with wood working.
I like this one for the construction. He took a C shaped metal sheet and attached the wooden sides to it. Very simple and clever. I'd like something like this, but with the 3 tubes and the transformers on the top. Something like this:
But I've got a problem: my two power transformers look so bad, the hi-volt one has bell endings but has those nasty screw terminals to connect wires (also mains is exposed this way - no good
), the filament one has solder terminals, that means that the upper 2 ones carry full mains voltage. Also bad thing. Do you know a soultion for this? Or should I go out and spend the big bucks to get a complete hi-volt + filament transformer?
Also I planned to make a PCB for the filament and b+ regulator, keeping the audio circuitry on p2p turrets. First of all, is there any problem in re-using p2p turrets from old amps? I can't find them new, but I've got may from an old amp.
Also some problem to mount both the filament's LM317 and the B+ IRF840 on the same heatsink to reduce space? Of course they will have 320V and 12V on them, so I'll insulate them.
Some thoughts? I will post the pcb design soon (I plan on using Eagle, but Sprint Layout looks so easy...)
The preamplifier has been running all day, to test which components do get hot. The LM317 for the B+ is cold, the IRF840 is warm, and the LM317 for the filaments is hot but touchable. Also the two power transformers are warm, not hot.
I'm looking for suggestions to build a case for it: I'll post some photos of realizations that I found on the net (thanks to the diyers which contributed them) to show what I have in mind.
This one looks good, but I find a little difficult to make that wooden chassis, I'm not pratical with wood working.
I like this one for the construction. He took a C shaped metal sheet and attached the wooden sides to it. Very simple and clever. I'd like something like this, but with the 3 tubes and the transformers on the top. Something like this:
But I've got a problem: my two power transformers look so bad, the hi-volt one has bell endings but has those nasty screw terminals to connect wires (also mains is exposed this way - no good
), the filament one has solder terminals, that means that the upper 2 ones carry full mains voltage. Also bad thing. Do you know a soultion for this? Or should I go out and spend the big bucks to get a complete hi-volt + filament transformer?Also I planned to make a PCB for the filament and b+ regulator, keeping the audio circuitry on p2p turrets. First of all, is there any problem in re-using p2p turrets from old amps? I can't find them new, but I've got may from an old amp.
Also some problem to mount both the filament's LM317 and the B+ IRF840 on the same heatsink to reduce space? Of course they will have 320V and 12V on them, so I'll insulate them.
Some thoughts? I will post the pcb design soon (I plan on using Eagle, but Sprint Layout looks so easy...)
I've discarded Eagle, it has so many bugs. I connect things in the schematics but on the board he shows components with no connections.
I'm trying with Sprint Layout...
I'm trying with Sprint Layout...
Hi Giaime,
I still lay out by hand. I get frustrated with cad software.
Guess I have to start sometime. I might have to start yoga first! 😀
-Chris
I still lay out by hand. I get frustrated with cad software.
Guess I have to start sometime. I might have to start yoga first! 😀
-Chris
cerrem said:
Hi Chris,
Interesting idea! I have used voltage regulators and current regulators but hadn't thought about regulating the power. Do you have a particular circuit in mind?
Dave
anatech said:
Dear Chris,
I got frustrated too with SprintLayout, so I decided that the ones that I made on perfboard are good even for the finished one 😀
Now I'm thinking about a chassis. I will made a C shaped metallic sheet, but I have to make a detailed drawing on where to put the holes... Maybe, at this time, I will post the finished results if I can 🙄
Because of very little money, I know it's bad but I'm restricted to use old turret boards and old tube sockets. I would have to make a mail order, and buy some capacitors, the resistors, the sockets, a proper potentiometer etc etc... maybe when I'll get some money.
This Christmas is soooo poor with money for me
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