Try to search metal pen holder or cutlery holder with appropriate size.
It's a little ugly, but effective if you can ground it aesthetically.
It's a little ugly, but effective if you can ground it aesthetically.
I am starting to build 01a preamp and I can not find any information if filament pin1 is positive or negative or it does not matter? Other thing is that if I use Rod Coleman V9 regulator with 6 sic diodes connected to the positive side and sic diode cathode to the overall amp ground (not regulator - negative?)?
Like in this picture?
Like in this picture?
Connect the diodes to the negative side, with the V9.
I think it's worth comparing the sound of a good resistor - like the excellent non-inductive (Ayrton Perry wound ) Ohmite WNE, with a DC link bypass capacitor, against the diodes.
What value resistor and bypass capacitor to use with CX-301a? So the connection would be as shown in the picture?
SIC diodes sound edgy and unpleasant on music like classical and opera. I tore them all out and used good resistors and DC Link caps. Filament bias is even better.
I'm not surprised you preferred the resistor, Andy! I don't like diodes of any kind in the cathode.
Filament bias is perfect for 01A stages (only burns ca. 1.2W in the resistor), but you need to change the DC input voltage to 14 - 17V, to get the same 5V bias.
If you can make up 20 to 22 ohm with available Ohmite WNE resistors (parallel preferred) that will be well worth listening to.
The Ohmites are industrial resistors, made with high quality materials and construction, including copper leads, & Ayrton Perry winding .
They should be able to challenge most audio types IMHO
Filament bias is perfect for 01A stages (only burns ca. 1.2W in the resistor), but you need to change the DC input voltage to 14 - 17V, to get the same 5V bias.
If you can make up 20 to 22 ohm with available Ohmite WNE resistors (parallel preferred) that will be well worth listening to.
The Ohmites are industrial resistors, made with high quality materials and construction, including copper leads, & Ayrton Perry winding .
They should be able to challenge most audio types IMHO
If I use 20 ohm resistor then I connect it like in this schematic? What would then be a good bypass capacitor for that?
@euro21 Why are you using in the #712 post in filament 1k resistor R2 with 1000uF if others use only 20-25 ohm resistor? What is the difference? In this schematic pin 4 is used as positive voltage from regulator and pin 1 is flowing to ground through resistor and cap?
@euro21 Why are you using in the #712 post in filament 1k resistor R2 with 1000uF if others use only 20-25 ohm resistor? What is the difference? In this schematic pin 4 is used as positive voltage from regulator and pin 1 is flowing to ground through resistor and cap?
Yes, for filament bias, connect it like that. No need for a bypass capacitor: with filament bias, the Rk of 20 .. 22 ohm is low enough already.
BTW, low filament current is not recommended for long term use. At 200mA, the 01A might only live for ca. 100 hours. You can adjust the filament current to get 4.75V on the socket, but lower than that is not good.
Hi Rod,
The WNE range seems quite limited. To get 20R for filament bias I would have to connected two
WNE10RFET in series. Or two 50R an and one 100R in parallel. They seem reasonably priced at Digikey. Go parallel? Do you personally prefer these to the Mills MRA12?
4.75V at the socket is approx 235ma. Do I understand you correctly that it is best to keep the current at least that much?
Thanks. Nash
The WNE range seems quite limited. To get 20R for filament bias I would have to connected two
WNE10RFET in series. Or two 50R an and one 100R in parallel. They seem reasonably priced at Digikey. Go parallel? Do you personally prefer these to the Mills MRA12?
4.75V at the socket is approx 235ma. Do I understand you correctly that it is best to keep the current at least that much?
Thanks. Nash
Two 10R in series looks fine; there's a tiny noise improvement with parallel, but that applies to cheaply constructed parts more (current noise in the end cap and leadout attachment points).
I am not suggesting to throw out MRAs to fit the ohmites, but they are worth comparing, on account of excellent materials and low parasitics at a attractive price.
The specification for filament heating temperature is calibrated against the voltage, so the -5% must be applied to the 5V. Current between samples is not controlled nor specified, beyond the guide value.
I am not suggesting to throw out MRAs to fit the ohmites, but they are worth comparing, on account of excellent materials and low parasitics at a attractive price.
The specification for filament heating temperature is calibrated against the voltage, so the -5% must be applied to the 5V. Current between samples is not controlled nor specified, beyond the guide value.