#26 pre amp

[nicoch58]

diy resistor ?Lossless SD-card player
costantine wire......
duelund are 25w if I remember well
mundorf too

[nicoch58]

duelund 10w
mundorf 20w

arcol
HS - Wirewound from ARCOL UK, specilists in resistor technology

[andyjevans]

Thanks for the information on Dueland and Mundorf. Have you tried them or compared them at all?

The Arcol is aluminium clad - I'm not having much fun with those!

Andy

[Sheldon]

Originally Posted by Rod Coleman

Andy, I assume the Vitreous part was
perhaps a noninductive (wound in a Ayrton-Perry style)

I wonder how much an issue the winding type is in real life. The specifications of either standard or non-inductive are rarely given. I've measured a few by making a voltage divider with a wirewound and metal film in series. Then I connect the signal generator across the pair and the scope across the WW. Up to 1MHz, I can't see any difference measuring across the WW (regular white ceramic types) or MF. Above that I get some generator artifacts, independent of resistor type. I can't see them affecting frequency response. Maybe oscillation issues in some positions?

Sheldon

[nicoch58]

the duelund cost to much and I prefered in my previous speakers a simple kiwane on tw...

|| DHTRob - Projects: An audiophile DIY resistor.. ||


http://www.diyaudio.com/forums/attac...541a-wwres.jpg

[Rod Coleman]

Originally Posted by Sheldon

I wonder how much an issue the winding type is in real life. The specifications of either standard or non-inductive are rarely given. I've measured a few by making a voltage divider with a wirewound and metal film in series. Then I connect the signal generator across the pair and the scope across the WW. Up to 1MHz, I can't see any difference measuring across the WW (regular white ceramic types) or MF. Above that I get some generator artifacts, independent of resistor type. I can't see them affecting frequency response. Maybe oscillation issues in some positions?

Sheldon

The frequency response over audio is not likely to be a problem. But inductance is usually unwanted, especially at low-level audio. I'll have to degrade into hand-waving to say why; measuring the effects would be hard to do.

First, even a few uH will act like a search coil and increase the coupling effect for any nearby fields. Capacitor-input dc heater supplies might send peak currents of 5A into the first electrolytic in the supply. How long is the circumference of the loop of wiring between the trafo to rectifier to 1st Capacitor? The area of this loop is an electromagnetic moment (leverage), which expresses its ability to couple to other conductors. Power-tube ac heat, radio stations, B+ supply cap charging (E-field and B field) will all couple easier into big wirewounds.

The other effect, as you noted, is oscillation. ECC88/6DJ8 can amplify near to GHz! other valves have wide bandwidths too. If you've chosen a stopper (noninductive carbon composition, for sure!) correctly to limit bandwidth to 100kHz or less, and mounted it right on the pins, your circuit might be immune to VHF instability. But if instability happens, often only during a small part of the signal waveform, it could feed to the next stage and be detected like an AM receiver.

Whether the winding style of your wirewound makes a difference depends on design and layout of the rest of the circuit, I suspect. But I always look out for the old Ayrton-Perry wound resistors when I'm 'decommissioning' some old electronic junk!

[andyjevans]

How would you know an Ayrton-Perry winding if you met it on a dark night?

Andy

[Rod Coleman]

Originally Posted by andyjevans

How would you know an Ayrton-Perry winding if you met it on a dark night?

Andy

For new parts, only the data sheet knows - see pic!

for old style, there's no endcaps, just wire entry, with a stub poking out next to the entry-point. I'll get a pic when I'm out with the camera. Sad to say, nobody made these, since the 1980s, as far as I know.

See how they're wound:

Ayrton-Perry winding - Wikipedia, the free encyclopedia

[andyjevans]

I have one or two resistors that look like what you are describing. The wire comes straight out of the end, plus a short second piece of wire which is kind of doubled over to the case. Does that sound like it?

I found a few like this in my parts drawers - 10 ohms at 30W. I can touch it very quickly when it's conducting. Do you think 30W in free air is safe? I could parallel/series them for 60W but that means using 8 in total. Perfectly possible if 30W isn't enough, but maybe a bit over the top?

This resistor sounds great, incidentally. Best yet.

Andy

Andy

[Richard]

Hi Andy,

Did you ever get around to trying battery grid bias (with the cathode grounded)? I'm running my 26 pre in that configuration and it also sounded better than cathode bias.

I might give filament bias a shot, but wanted to clarify the calculation of the resistor.

On the AA thread Thomas indicated “The resistor is sized such that the voltage drop caused by the filament current provides the desired bias voltage.”
Resistance of filament = 1.5V/1.05A = 1.4 ohms
Bias voltage = -10V/1.05A = 9.5 ohms
How does the current regulated filament voltage come into this?

Rich