SLO Preamp layout

T Wilcox said:
Since he's only doing the preamp I think the target voltage would be 375ish volts since thats what is at V3 on the SLO
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Yeah, after the first 10k dropping resistor though. But since he has no power tubes, no loop, and no clean. Maybe he should go 300vac transformer.

This will get 420vdc after full bridge rectification. Then if it's a bit high, it'll be super easy to knock that down a little.
 
PLX said:
Can't I use a voltage multiplier circuit with the Antek 200V ?
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Yes. Provided it can provide enough current. The current demand will go up.

Also keep in mind when I say 350v * 1.4 = 490vdc that's unloaded. Apply a load and that will drop. So you need to look at the specs of your Transformer, some will show 350v unloaded, 300v loaded to 0.25a etc..

Also you cant just go eliminating those "dropping" resistors because despite the nickname, that's not really what they are. They are actually part of the R/C filtering. They work with the filter caps to remove DC ripple. If you remove them, or lower them too low, then you get a nasty dirty DC line.
you can adjust them within reason to adjust your voltages.
 
CrazyNutz said:
Yeah, I've built them with, and without the FX Loop. It does sound slightly different. I'd say more classic/open without the FX loop, and more modern with.

I will say this, use the orange drop polypropylene caps (the 400v are fine), and the vishay metal film resistors. I've used others, and they don't sound right.

BTW I have a new O'netics power transformer for 100w collecting dust if you're interested.
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I would use metalised polyester caps (MKT), not polypropylene. I've done it with both and the original MKTs Soldano uses sound better IMO
 
PLX said:
Are D.C. heaters the key to getting the noise floor down in this circuit ?

Or are there other tricks.. using NOS 12AX7's etc
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I used regular ol' AC heaters in my builds and there was no noise. I did elevate the heaters in one build to reduce stress on the preamp tubes. But I didn't notice any benefit to noise (but there wasn't any to begin with). The key to low noise is using higher wattage, metal-film resistors and good lead dress. DC heaters certainly do lower the noise floor but it's not always needed.

Noise can come from external sources too. A lot of people spend time chasing gremlins when they're actually coming from dirty power or EMI.
 
FourT6and2 said:
I used regular ol' AC heaters in my builds and there was no noise. I did elevate the heaters in one build to reduce stress on the preamp tubes. But I didn't notice any benefit to noise (but there wasn't any to begin with). The key to low noise is using higher wattage, metal-film resistors and good lead dress. DC heaters certainly do lower the noise floor but it's not always needed.

Noise can come from external sources too. A lot of people spend time chasing gremlins when they're actually coming from dirty power or EMI.
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When you say "higher-wattage" resistors, you mean higher than called for in the schematic ?

:unsure:
 
PLX said:
When you say "higher-wattage" resistors, you mean higher than called for in the schematic ?

:unsure:
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1 watt is good. The specific ones Soldano normally uses are good. I've also had good luck with PRP and Beyschlag. But I don't think either of those will fit on a typical SLO PCB.
 
FourT6and2 said:
1 watt is good. The specific ones Soldano normally uses are good. I've also had good luck with PRP and Beyschlag. But I don't think either of those will fit on a typical SLO PCB.
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Do you sub the ones from the C3amps kit and use higher quality (or different) components ?
 
FourT6and2 said:
I would use metalised polyester caps (MKT), not polypropylene. I've done it with both and the original MKTs Soldano uses sound better IMO
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I've use metalized polyester film caps in this (mallory 150's) and absolutely hated it.

Which ones did you use, seems like maybe the orange drop polyesters could have been the original old schools. But those are film/foil, not metalized film.
 
CrazyNutz said:
I've use metalized polyester film caps in this (mallory 150's) and absolutely hated it.

Which ones did you use, seems like maybe the orange drop polyesters could have been the original old schools. But those are film/foil, not metalized film.
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Mallory 150s aren't amazing. The ones Soldano uses (or used) were Philips MKT 368 (if my memory is correct). And Mallory PVC/polyester in some places and Epcos T592.

When building other amps these days, I like ERO MKT 1813
 
PLX said:
Are D.C. heaters the key to getting the noise floor down in this circuit ?

Or are there other tricks.. using NOS 12AX7's etc
Click to expand...
NO. If you find the regular old AC heaters induce too much noise then just elevate the heaters with DC as with the methods already discussed. With four gain stages you can still have some hiss regardless.

I did find the the elevated heaters did quiet my 4 gain stage build more as well as lower the overall noise floor than without the Elevated heaters. I think Friedman uses DC heaters and his amps still have that high gain hiss which is inherent to most high gainer amps IMHO.
 
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