The Russian Telflons (фтоуропласт) are certainly worth trying, I use the К72П-6 56nF/500V which are easy to find. The 1.25 inch pipe cutter from Rapid Electronics can fetch the steel case off them, when you get the hang of it (buy an extra cap to practice)
Rapid Electronics - Pipe Cutter 3-32mm
My other favourite is a sleeper - the LCR components PC/HV/S high quality industrial polypropylene. For coupling, there may be a better cap, but I have not found one. 1kV or 1.5kV rating, too. These can be used from preamps all the way up to Tesla coils - they are so well built.
LCR COMPONENTS|PC/HV/S/WF 100NF 1KV|CAPACITOR, 100NF, 1000V | Farnell United Kingdom
I don´t know Rod´s circuit, but perhaps it´s a good idea to use an Ultra Low ESR PSU like i use it for the Salas shunt´s in my DAC...
Hi Andy,
Before drawing conclusions, it is best to get an understanding what your implementations of the PSUs actually do. Choke input is not just equal to any choke input. Hook up a scope and check AC voltages across the secondary of the transformer and right after the rectifier bridge. Especially with choke input you can have some nasty spikes there which can creep into the circuit. Sometimes it is a good idea to tame these with a small cap in front of the choke. Try something like 47uF and move upwards until the spikes with rough edges dissappear.
Best regards ... Thomas
Before drawing conclusions, it is best to get an understanding what your implementations of the PSUs actually do. Choke input is not just equal to any choke input. Hook up a scope and check AC voltages across the secondary of the transformer and right after the rectifier bridge. Especially with choke input you can have some nasty spikes there which can creep into the circuit. Sometimes it is a good idea to tame these with a small cap in front of the choke. Try something like 47uF and move upwards until the spikes with rough edges dissappear.
Best regards ... Thomas
Andy, this is good advice from Thomas.
Choke input means a big reduction in the peak current into the reservoir caps. Reducing this current can improve the sound of other parts of the audio system connected to the same mains supply.
The type of mains trafo is also important. split bobbin type reduces noise transfer from the mains (compared to toroidal or overwound types), and high quality trafos with an Electrostatic screen can be even better still. My preference is to use an isolating transformer, and an HF barrier in the safety earth (Sadly, safety earth can transmit some troublesome noise): the drawing shows a suggestion for connecting it.
Attachments
Hi Andy,
I never liked battery bias. And I also never 'settled' on filament bias
In most of my designs I use regular cathode bias with the ultrapath topology. I only use filament bias if all other aspects in the design are already on the best possible level and when the heat generated in the filament bias resistor is of no concern. While the latter is not much of an issue in a 26 stage, the heat dissipation can be excessive with 801As.
Best regards ... Thomas
I never liked battery bias. And I also never 'settled' on filament bias
In most of my designs I use regular cathode bias with the ultrapath topology. I only use filament bias if all other aspects in the design are already on the best possible level and when the heat generated in the filament bias resistor is of no concern. While the latter is not much of an issue in a 26 stage, the heat dissipation can be excessive with 801As.
Best regards ... Thomas
Hi!
I fully agree with Rod on this. Using cheap power transformers is cost saving in the wrong place. Especially if the power supply changes seem to have a big impact on the sound, this could be due to a poor power trannie. I settled on power transformers with two independent screen windings. In fact the screens are not windings, but electrostatic screens made with foils. Also the core material of the power transformer has an impact.
Best regards ... Thomas
I fully agree with Rod on this. Using cheap power transformers is cost saving in the wrong place. Especially if the power supply changes seem to have a big impact on the sound, this could be due to a poor power trannie. I settled on power transformers with two independent screen windings. In fact the screens are not windings, but electrostatic screens made with foils. Also the core material of the power transformer has an impact.
Best regards ... Thomas
DIYers that are enthusiastic about battery bias usually have favourite brands of alkaline batteries, and perform noise measurements to compare them. Using large value caps across a 9V alkaline suggests they are not quiet enough.
Other battery chemistry, especially lead-acid gel cell, and NiMH are known to be too noisy. There's measurements available on this site, to be searched out.
Other battery chemistry, especially lead-acid gel cell, and NiMH are known to be too noisy. There's measurements available on this site, to be searched out.
IC Manufacturer's application note. http://ww1.microchip.com/downloads/en/AppNotes/01276a.pdf
Two caps, two resistors, one led + one cheap wall mart p.s. (you might already have a suitable one around)
Two caps, two resistors, one led + one cheap wall mart p.s. (you might already have a suitable one around)
For the application discussed here, you have probaly trashed the preamp and built a new one before you will have to recharge the batteries.
I suppose that the shelf life of this type of batteries are even better than with lithium batteries. Since the grid draws extremely little current, I would expect a LiFePO4 to last many years in a linestage.
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