john65b,
A cursory glance at balanced signals and a quick view of the Aleph schematic shows me that there is a SS front end at the input of the amp no transformer.
As I understand the balanced cable design the two conductors carry an out of phase signal and have equal impedance to ground. Thus when summed any noise introduced into the conductors would be out of phase and cancel out? To me this looks just like a "split load" phase inverter from a PP amp? Google the "split load phase inverter" There is a typical circuit found in williamson amps using 6SN7 that is Direct Coupled just like what we are playing with here.
I think the only concerns with this is the diffing output impedance from the plate and cathode. The coupling cap value is important to avoid loss of bandwidth but other than that you are pretty well on the way.
A cursory glance at balanced signals and a quick view of the Aleph schematic shows me that there is a SS front end at the input of the amp no transformer.
As I understand the balanced cable design the two conductors carry an out of phase signal and have equal impedance to ground. Thus when summed any noise introduced into the conductors would be out of phase and cancel out? To me this looks just like a "split load" phase inverter from a PP amp? Google the "split load phase inverter" There is a typical circuit found in williamson amps using 6SN7 that is Direct Coupled just like what we are playing with here.
I think the only concerns with this is the diffing output impedance from the plate and cathode. The coupling cap value is important to avoid loss of bandwidth but other than that you are pretty well on the way.
look here at williamson circuit
use the first two halves of the 6sn7 the amp and phase inverter?
Practical Phase Inverters.
use the first two halves of the 6sn7 the amp and phase inverter?
Practical Phase Inverters.
Cold,
The 6SN7 circuit I posted is more like the 12DW7 on your link....with a 6SN7. I don't care about the low -ish gain of teh 6SN7, as I will make it up (and then some) with a 6db increase from a balanced input ayway. Just looking for a clean, attenu-able balanced signal to a balanced input amp...I feel I am getting close...just need to kill the annoying hum.
I gave the pre to a friend and he liked it quite a bit, although I really need to get that hum down. I ordered new 6SN7, and will try DC on heaters.
I actually was thinking of trying a Hum Pot on 6SN7 heaters like my Magnevox 6V6 amp has - float the 6.3VAC CT leads and put a 100 ohm pot to ground - between the 3.15VAC - 0 - 3.15VAC... heaters still see the 6.3VAC, but the ground point moves to reduce hum (I may not be describing this correctly)
The 6SN7 circuit I posted is more like the 12DW7 on your link....with a 6SN7. I don't care about the low -ish gain of teh 6SN7, as I will make it up (and then some) with a 6db increase from a balanced input ayway. Just looking for a clean, attenu-able balanced signal to a balanced input amp...I feel I am getting close...just need to kill the annoying hum.
I gave the pre to a friend and he liked it quite a bit, although I really need to get that hum down. I ordered new 6SN7, and will try DC on heaters.
I actually was thinking of trying a Hum Pot on 6SN7 heaters like my Magnevox 6V6 amp has - float the 6.3VAC CT leads and put a 100 ohm pot to ground - between the 3.15VAC - 0 - 3.15VAC... heaters still see the 6.3VAC, but the ground point moves to reduce hum (I may not be describing this correctly)
Well the hum pot did nothing. I will have to play with the DC on heaters. Problem is all heaters - 6SN7 and 6X5 - are all connected, and I will have all three on DC. I have never put DC on Rectifier tube filaments, but on Rectifier datasheets show AC or DC (I checked), so it should work.
More later...
More later...
I struggled with tube and ss rectifier. I saw a few amps that had the same 6.3V heater winding on all tubes including the rectifier, so I went with the 6X5. I do not have a 5V or a second 6.3V winding on my transformer (Hammond 369EX). I usually put a SS rectifier on these test preamps, but chose the 6X5 to try something different...
What I could do is put two 1N4007 diodes upside the heater plates like attached. This is essentially a SS rectifier with the 6X5 tube rectifier acting as a soft start...could this get rid of the hum? I could just detach from the plates all together...I now have the hole in my chassis...
I was contemplating this on another amp, but did not put in the diodes
What I could do is put two 1N4007 diodes upside the heater plates like attached. This is essentially a SS rectifier with the 6X5 tube rectifier acting as a soft start...could this get rid of the hum? I could just detach from the plates all together...I now have the hole in my chassis...
I was contemplating this on another amp, but did not put in the diodes
Attachments
Last edited:
I said the rectifier "may" be part of the problem. I just don't know, as I haven't used the same winding for both. But thinking about it, I see no reason it "should" be a problem. Is it really certain that the heater supply is the problem? Is the hum 60Hz? Checked with a scope? Tried lifting the heater supply? Maybe strap up 4 D cells for a quick check, before you do too much work.
Sheldon
Sheldon
Hey, I like the strapping four D batteries idea...cool.
I have ungrounded the Heater supply, put in a .1uf cap to ground, directly to ground, and a pot to ground. When the filament Centertap is just connected to the IEC Ground it sounds the quietest, but still noticeable hum...
I have ungrounded the Heater supply, put in a .1uf cap to ground, directly to ground, and a pot to ground. When the filament Centertap is just connected to the IEC Ground it sounds the quietest, but still noticeable hum...
Last edited:
OK, tried the 4 D batteries...ad very little hum. SO I slapped together a standard rectifier circuit and it is now supplying 6VDC (a little starved) to all heaters. Very little and acceptable hum.
Some pics are below. Now don't laugh, yes, its an IKEA wooden salad bowl. I can't go through that store without finding things to make amps out of. The wife says I need an intervention on this hobby.
Anyway,
B+= 235V
Amplifier Triode 1
Plate Resistor 20K
Plate Voltage 135V
two red LEDs at cathode and 3.2V
Around 5ma through first triode
Splitter Triode 2
Plate and Cathode resistor 47K
Plate Voltage 135V
Cathode Voltage125V
Output caps are Sprague Vitamin Q 1uf
Currently driving my Icepower ASC200 monoblocks and sounds pretty sweet. More critical listening tomorrow on the Aleph.
Some pics are below. Now don't laugh, yes, its an IKEA wooden salad bowl. I can't go through that store without finding things to make amps out of. The wife says I need an intervention on this hobby.
Anyway,
B+= 235V
Amplifier Triode 1
Plate Resistor 20K
Plate Voltage 135V
two red LEDs at cathode and 3.2V
Around 5ma through first triode
Splitter Triode 2
Plate and Cathode resistor 47K
Plate Voltage 135V
Cathode Voltage125V
Output caps are Sprague Vitamin Q 1uf
Currently driving my Icepower ASC200 monoblocks and sounds pretty sweet. More critical listening tomorrow on the Aleph.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
- Status
- Not open for further replies.