Resistor Types vs Placement in Circuit

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FourT6and2
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Re: Resistor Types vs Placement in Circuit

Post by FourT6and2 » Mon Jul 10, 2017 2:42 pm

pdf64 wrote:
Mon Jul 10, 2017 1:09 pm
FourT6and2 wrote:
Sat Jul 08, 2017 10:25 pm
...I wouldn't use CCs on the input plate stage (V1a) or the second stage in a high-gain amp (V2a) for noise reasons. The stage just before the PI in the amp I'm building is a cathode follower and just has the single 100K resistor on the tube socket as seen in typical Marshalls. The article says the PI Plates would be a fine place to use CCs. While a global NFB affects how much a CC will distort there, it still does distort a little, no?..
As your 2nd stage plate only seems to have the gain of the power amp after it, I think that the ratio of likely signal level to potential CC noise is high, and so a CC would be fine there, as per RGs guidance.
As the gain of a CF stage is close on unity and pretty much independent of the cathode resistor value, the voltage coefficient of characteristic of a CC cathode resistor won't be able to have any effect on the stage output, ie there's no potential a CC cathode resistor on a CF stage to add harmonics.

The degree to which a global NFB loop is able to reduce distortion is dependant on the open loop gain and the negative feedback ratio.
Generally, the loop reduces gain by about 6dB, so (within the linear range) I think that the distortion generated within the loop will be reduced by a similar amount.
Be aware that although NFB reduces distortion overall, whilst reducing low order harmonics, new higher order harmonics are introduced, so the tonality may be less pleasant.
Also, with NFB, because the large signal performance within the linear range is more accurate, with slighter higher signal levels the onset of clipping will be more pronounced / extreme, with a potentially harsher tonality.
With amps that have a presence control in the NFB loop, at higher frequencies the degree of NFB will be dependant on the presence control setting.

I think that even order harmonics that are introduced equally in both sides of a balanced system (eg CC LTP plate resistors) will result in odd order harmonics when the balanced signals are combined back to single ended
Good info, thanks!

I'll probably just stick with MF everywhere, then. Seems that will be more beneficial in the grand scheme of things than trying to futz about with CC mojo :)

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Ken Moon
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Re: Resistor Types vs Placement in Circuit

Post by Ken Moon » Wed Jul 12, 2017 4:34 pm

I've done a lot of experimenting with different resistors in a mid-gain rock amp (the AX84/Gothik Amps Talon), where I had three working prototypes and could do proper A/B comparisons.

The only place I ended up using CC was for the unbypassed cathode resistor on the 3rd gain stage (just before the PI), and on the grid stoppers for the 6V6 power tubes. The unbypassed cathode resistor on the second stage seemed to sound a teeny bit warmer with the CC, but not enough to worry about. The other spots did make a difference in tone, which I would describe as warmer and musically pleasing.

I wouldn't bother getting NOS CC's, because they dry out (or something) and drift over time. Just go with new manufacture from IRC or Ohmite, which you can get at Mouser/Newark/etc. And go with the highest wattage you can fit in your layout - 2 watt for the cathodes and 3 watters for the power tube grid stoppers is what I use.

I do like the sound of the KOA/Kiwame SPR2 series carbon films for preamp grid stoppers and for voltage dividers etc in the signal path. They are neutral sounding, and are small and pretty 8)

For plates, I go only with IRC GS3 series, nice little 3-watt metal films that are bulletproof, and for power, I only use the Vishay Mills non-inductive wirewounds, which come in 5,7,10 and 12 watts.

But remember, nobody but you will ever notice :(

And the ultimate judge of what's better is you - if you love your amp, you'll make better music with it :D

FourT6and2
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Re: Resistor Types vs Placement in Circuit

Post by FourT6and2 » Wed Jul 12, 2017 5:18 pm

Ken Moon wrote:
Wed Jul 12, 2017 4:34 pm
I've done a lot of experimenting with different resistors in a mid-gain rock amp (the AX84/Gothik Amps Talon), where I had three working prototypes and could do proper A/B comparisons.

The only place I ended up using CC was for the unbypassed cathode resistor on the 3rd gain stage (just before the PI), and on the grid stoppers for the 6V6 power tubes. The unbypassed cathode resistor on the second stage seemed to sound a teeny bit warmer with the CC, but not enough to worry about. The other spots did make a difference in tone, which I would describe as warmer and musically pleasing.

I wouldn't bother getting NOS CC's, because they dry out (or something) and drift over time. Just go with new manufacture from IRC or Ohmite, which you can get at Mouser/Newark/etc. And go with the highest wattage you can fit in your layout - 2 watt for the cathodes and 3 watters for the power tube grid stoppers is what I use.

I do like the sound of the KOA/Kiwame SPR2 series carbon films for preamp grid stoppers and for voltage dividers etc in the signal path. They are neutral sounding, and are small and pretty 8)

For plates, I go only with IRC GS3 series, nice little 3-watt metal films that are bulletproof, and for power, I only use the Vishay Mills non-inductive wirewounds, which come in 5,7,10 and 12 watts.

But remember, nobody but you will ever notice :(

And the ultimate judge of what's better is you - if you love your amp, you'll make better music with it :D
Thanks for the info!

I think the plan is to stick with metal film pretty much everywhere. I have PRP 1-watt, Vishay/Beyschlag MBE0414 1-watt, Vishay CCF60, and Takman REY. Of those, I'm building one amp with PRP and one with Beyschlag to compare. The CCF60s are good for the bias supply because they're a bit smaller and will fit in the tight space on my board.

I have a bunch of those Kiwame 2-watter CFs as well. They are nice and small. Same size as 1-watt from other companies. Only place I could see using them as a grid stopper in the preamp would be on V1b (pin 7) I guess. Maybe I'll try it and see if there's a difference. Or maybe I'll try build another amp with just those. If the MF amps sound good, I'll probably just stick with those for the time being though.

Carbon Comp for power tube grid stoppers? Interesting. Maybe not in a high-gain amp, though. I'd want the power section to remain tight and clinical, so to speak. But maybe worth a try.

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Ken Moon
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Re: Resistor Types vs Placement in Circuit

Post by Ken Moon » Wed Jul 12, 2017 5:30 pm

I know it sounds weird to use CC's for power tube grid stoppers, but I first tried this on a silverface Champ, Where I soldered a 2-watt 6k8 CC right to the grid pin on the 6V6.

I'm not a hi-gain amp lover myself, so this might make it sound worse to you, but I liked it, and continued to do it on 5E3s and other amps to good effect.

FourT6and2
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Re: Resistor Types vs Placement in Circuit

Post by FourT6and2 » Wed Jul 12, 2017 5:35 pm

Ken Moon wrote:
Wed Jul 12, 2017 5:30 pm
I know it sounds weird to use CC's for power tube grid stoppers, but I first tried this on a silverface Champ, Where I soldered a 2-watt 6k8 CC right to the grid pin on the 6V6.

I'm not a hi-gain amp lover myself, so this might make it sound worse to you, but I liked it, and continued to do it on 5E3s and other amps to good effect.
This is the type/style of amp I'm building at the moment: https://youtu.be/rKW5f5THPQY?t=30s

FourT6and2
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Re: Resistor Types vs Placement in Circuit

Post by FourT6and2 » Wed Jul 12, 2017 5:44 pm

Wow, looked at those Mills wirewounds. lol I don't think I can bring myself to spend $5 on a dropping resistor that's just gonna go on a filter cap when a metal oxide will do just fine.

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Ken Moon
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Re: Resistor Types vs Placement in Circuit

Post by Ken Moon » Wed Jul 12, 2017 5:45 pm

Oh yeah!

That's an awesome amp, but looks like quite a build :shock:

It sounds great in the video - hope you get the same results :)

My problem with hi-gain amp design is controlling hiss - I've tried and tried, and my success has been limited at best :cry:

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Ken Moon
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Re: Resistor Types vs Placement in Circuit

Post by Ken Moon » Wed Jul 12, 2017 5:49 pm

Those Mills are expensive, but I tend to go overboard sometimes.

On this amp, I used just about every booteek component I could find, all in the "perfect" place, of course :roll:

Image

SoulFetish
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Re: Resistor Types vs Placement in Circuit

Post by SoulFetish » Sat Jul 15, 2017 5:54 am

FourT6and2 wrote:
Sun Jul 09, 2017 3:31 pm
And to be fair, none of those guys are making high-gain amps. And by high-gain, I mean at the very LEAST, something like this: https://youtu.be/1WY2lICcJvo?t=49s I think noise—whether pink or white or purple or blue—is probably a bad thing in this case.
Aiken makes definitely high gain amps.

SoulFetish
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Re: Resistor Types vs Placement in Circuit

Post by SoulFetish » Sat Jul 15, 2017 6:04 am

Ken Moon wrote:
Wed Jul 12, 2017 5:49 pm
Those Mills are expensive, but I tend to go overboard sometimes.

On this amp, I used just about every booteek component I could find, all in the "perfect" place, of course :roll:

Image
Look at all those film caps. A man after my own heart.
Not all film caps... but, hey, nobody's perfect

FourT6and2
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Re: Resistor Types vs Placement in Circuit

Post by FourT6and2 » Sat Jul 15, 2017 1:36 pm

SoulFetish wrote:
Sat Jul 15, 2017 5:54 am
FourT6and2 wrote:
Sun Jul 09, 2017 3:31 pm
And to be fair, none of those guys are making high-gain amps. And by high-gain, I mean at the very LEAST, something like this: https://youtu.be/1WY2lICcJvo?t=49s I think noise—whether pink or white or purple or blue—is probably a bad thing in this case.
Aiken makes definitely high gain amps.
Never seen or heard of an actual Aiken amp anywhere. The guy has great content on his website, though.

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