Film Resistor Question

[rawnster]

In trying to lower the hiss in my express build, I've been thinking/reading/gathering all the info I can on different resistor types. Obviously, most think film resistors are the quietest and the most anemic sounding. Even so, I ran across a "new" film resistor that is supposed to be designed for audio. What do you guys think about this? Is this just a rabbit trail, or something worth pursuing?

Precision Resistive Products:
PR9372 Audio Resistor:
http://www.prpinc.com/new_products.htm#PR9372

Quote from the website:
PR9372 Audio Resistor
The PR9372 Audio Application leaded Nichrome thin film resistor is now available in volume production and has been specifically designed to support audio circuit applications. The PR9372 has special construction features that promote the desired no/low noise (thermal EMF) characteristics required in high-end audio application circuitry. The PR9372 is available in both a ¼ watt and ½ watt power ratings and in a variety of standard resistance tolerances and temperature coefficients. Tape and reel or bulk packaging is available. Samples are available and production delivery is from stock to 6 weeks. Pricing is dependent on the combination of power rating, temperature coefficient and resistance tolerance selected.

product specs:
http://www.prpinc.com/pdf/Audio_PR9372_Series.pdf

[rawnster]

Here's another VERY interesting company that sells the resistors mentioned above.

Sonic Craft:
http://www.soniccraft.com/prp_resistors.htm

[fishy]

Ron,

You can get them from here. Haven't tried them though. Maybe someone else can comment.

http://www.partsconnexion.com/catalog/resistors.html
Check the PRP tab.

Partsconnexion has some cool stuff.....
Dave at Westlabs sells some similar resistors also. Not sure if they are the same.

Pete

[jjman]

I spent much time testing different plate resistors for the 1st stage on mine. One of the 3watt metal films from mouser came out the quietest. I think it was a Dale?

I'd also be very interested in how these compare. Presumably the 1watt would be the quietest?

[rawnster]

I spent much time testing different plate resistors for the 1st stage on mine. One of the 3watt metal films from mouser came out the quietest. I think it was a Dale?

I'd also be very interested in how these compare. Presumably the 1watt would be the quietest?

Cool. I'll buy some PRP resistors and see what happens.

[rawnster]

Well, so far I tried some metal film resistors from Westlabs. No luck. Did not lower the noise floor. On a good note, they didn't alter the tone.

This hissing is getting frustrating.

[dBe]

Here's another VERY interesting company that sells the resistors mentioned above.

Sonic Craft:
http://www.soniccraft.com/prp_resistors.htm

+1 on Sonic Craft

Jeff Glowacki knows his stuff.

Dave

[jjman]

The 1st tube also contributes significantly to the hiss level in this setup. I taped the hiss level from about 10 different 12ax7s during my crusade. Then eyeballed the volume levels of each and listened to each on it's own track on Sonar (Cakewalk.) Unfortunately the quietest 2 were a little microphonic. They were Chinese Ruby 7025STRs.

Ended up with a Mullard for the lowest hiss with no microphonics. Still plenty o'hiss though.

Have you tried the 3watt "flameproof" MF's from Mouser yet? (They have no stripe/bands on them.) The striped brand of 3watt MFs may also say "flameproof" but are noisier. I used my scope to see the noise level.

"Wishful thinking" can enter the picture on comparison tests so I always try to document with a measuring device so my hopes are out of the equation.

[rawnster]

The 1st tube also contributes significantly to the hiss level in this setup. I taped the hiss level from about 10 different 12ax7s during my crusade. Then eyeballed the volume levels of each and listened to each on it's own track on Sonar (Cakewalk.) Unfortunately the quietest 2 were a little microphonic. They were Chinese Ruby 7025STRs.

Ended up with a Mullard for the lowest hiss with no microphonics. Still plenty o'hiss though.

Have you tried the 3watt "flameproof" MF's from Mouser yet? (They have no stripe/bands on them.) The striped brand of 3watt MFs may also say "flameproof" but are noisier. I used my scope to see the noise level.

"Wishful thinking" can enter the picture on comparison tests so I always try to document with a measuring device so my hopes are out of the equation.

I have not tried the 3watters from mouser. But I'm feeling that this journey will be somewhat of a lost cause. The hiss is significant enough that even cutting it in half will still be too much. The quietest the amp will get is when I turn the volume knob up enough just so that the guitar begins to come through. I stop right there. That's about 8 oclock on the dial. Any higher, then it's hiss city. Perhaps going back to a 12AU7 is my best bet in using this amp in a gig setting.

My gigging situation is where I'm miced so that there's enough coverage in the room. I'm not miced to increase volume perse. Anyway, there are lots of quiet times in the set. In these quiet times, the amp is hissing away through the PA. And I can't mute my channel, for I'm playing. Thus lots of dynamics in the music. I hope some of this makes sense and you all don't think I'm too much of an idiot.

[Zippy]

Have you considered de-tuning your Express for slightly less gain? Given where you are operating the amp, it sounds like you have a lot more gain on tap than you are needing/using. It's the gain that is contributing to the high noise floor.

[rawnster]

Have you considered de-tuning your Express for slightly less gain? Given where you are operating the amp, it sounds like you have a lot more gain on tap than you are needing/using. It's the gain that is contributing to the high noise floor.

Hey Zippy, I hadn't really thought of that, for I figure a lower output preamp tube would do about the same thing. With a gain factor of about 44 for a 12AY7 and a gain factor being around 20 for a 12AU7, I was thinking that this would be an easier route to go. Am I mistaken?

[fishy]

Ron,
I think Zippy has a good point. The Express has plenty of gain to spare and although it moves away from a traditional TW, it does need to fit your needs and I think your saying that is not the case here.

The files section has several versions based on an Express which might be worth reviewing.

I have my ideas about doing it but I still have my Express on the bench myself so I am sure there are others better suited to advise.

Pete

[tubelovin]

I've suffered the same problems with other builds, even lower gain amps, so I know how you feel. I tied lots of resistors without an ounce of improvement. Trying lots of tubes was my only help.

Is there anything layout wise that can be done?
Goodluck and keep us posted on anything that does or does work.

[Ron Worley]

You could try a noise gate, that might make it a go, along with turning down and / or a 12AT7.....

Ron

[rawnster]

I've suffered the same problems with other builds, even lower gain amps, so I know how you feel. I tied lots of resistors without an ounce of improvement. Trying lots of tubes was my only help.

Is there anything layout wise that can be done?
Goodluck and keep us posted on anything that does or does work.

So you really found some good results from tube swapping? I've swapped quite a few current production 12AX7s and a few NOS. But no combo I tried really brought the hiss down to any noticeably lower level. I was going to try a Tungsram, but am afraid to drop a ton of money to chase what could be a rabbit hole. Did you try one of these? Some guys in for sale section seem to really believe they are "the tube" for trainwreck amps. hmmm....