Revisit High-Plate Classic with a 5-piece chassis

[ijedouglas]

Hi Ian, fantastic build again.
Do you think grounding points in this chassis have something to do with the sound of the amp?
Current flows can be a strange thing.
Maybe I do a PM on this.

Erwin

Thanks Erwin,

I'm convinced of it. If you look at the attention HAD paid in his amps to the grounds as well as the video of Ben Harper talking about HAD and his "electrical probes" with "zero charge", I think it's safe to say it plays a large role. These amps that I rebuilt are pretty much the same in components and layouts but differ in the chassis construction and materials.

[ElectronAvalanche]

Hi Ian, fantastic build again.
Do you think grounding points in this chassis have something to do with the sound of the amp?
Current flows can be a strange thing.
Maybe I do a PM on this.

Erwin

Thanks Erwin,

I'm convinced of it. If you look at the attention HAD paid in his amps to the grounds as well as the video of Ben Harper talking about HAD and his "electrical probes" with "zero charge", I think it's safe to say it plays a large role. These amps that I rebuilt are pretty much the same in components and layouts but differ in the chassis construction and materials.

Hi Ian,

fantastic job! Really looks like the original!

Can you elaborate a bit more on the grounds? Did you use different locations for the grounds in your previous builds or do you think it is the thickness of the materials? Or did you somehow measure the ground connections? I assume your previous chassis were also aluminium, so I can see that maybe the oxidation of the aluminium can differ from ground point to ground point or that the material is not 100% homogeneous and thus that some ground points might have some more resistance to others. I can still not wrap my head around how Dumble would have measured with "electrical probes" and what "zero charge" might translate into real technical features. If one would use specific ground washers (like these: https://www.tube-town.net/ttstore/en/co ... ns-m3.html) that have very sharp tooths on the bottom and thus really bite into the material (aluminium) thus getting to a layer of aluminium with zero oxidation than the point of contact for ground should be nearly perfect. Then only the potential imhomogenicity of the aluminium should make a difference.

Sorry for the rambling, but this is on the one hand extremely intriguing on the other hand I have a hard time to understand the concept from a scientific point of view. A monocrystalin block of aluminium should of course have the best conductivity but can you imagine Dumble measuring the stock aluminium blanks and then he either had to discard a "bad" batch. Or did he have some way to "fix" such batch? Could there be other factors at play here (psychoacustics? bias?)

Best Regards,

Electron

[martin manning]

If you look at the attention HAD paid in his amps to the grounds as well as the video of Ben Harper talking about HAD and his "electrical probes" with "zero charge"...

A description by someone without much knowledge of electronics, I'd guess. HAD may have been measuring the electrical resistance of his ground connections, perhaps with a 4-wire (Kelvin) probe?

[dbharris]

If I measure resistance between ground points with my DMM (not a top of the line model either), I will get readings in the range of 0.1 - 0.3 Ohms. This is after a light sanding of the aluminum ground points and then tightly attaching a toothed ground point to the chassis with a keps nut. I've always wondered what is acceptable or not, or even if that is the right approach for measuring...

-Dan

[GAStan]

A standard multimeter won't give very useful measurements in this case. I've used many multimeters throughout my career and very few will measure less than 0.1 ohm even shorting the leads together.

What's needed is a micro-ohmmeter. These are pricey in the 4 digit range. https://www.transcat.com/catalogsearch/ ... o-ohmmeter

Amazon has a couple in the $200 range but they actually, according to their specs, only go to .001 ohm, or 1 milli-ohm. Better than a multimeter but not a true micro-ohmmeter.

[ijedouglas]

If you look at the attention HAD paid in his amps to the grounds as well as the video of Ben Harper talking about HAD and his "electrical probes" with "zero charge"...

A description by someone without much knowledge of electronics, I'd guess. HAD may have been measuring the electrical resistance of his ground connections, perhaps with a 4-wire (Kelvin) probe?

Exactly

[ijedouglas]

If I measure resistance between ground points with my DMM (not a top of the line model either), I will get readings in the range of 0.1 - 0.3 Ohms. This is after a light sanding of the aluminum ground points and then tightly attaching a toothed ground point to the chassis with a keps nut. I've always wondered what is acceptable or not, or even if that is the right approach for measuring...

-Dan

I think that is part of the equation. The other part is similar to component construction. If a 100K Q-Line resistor sounds different to a 100K Xicon resistor, why wouldn't chassis A made from 1/16 inch aluminium composition X sound different to Chassis B made from 1/8 inch aluminium composition Y?

[ijedouglas]

Hi Ian,

fantastic job! Really looks like the original!

Can you elaborate a bit more on the grounds? Did you use different locations for the grounds in your previous builds or do you think it is the thickness of the materials? Or did you somehow measure the ground connections? I assume your previous chassis were also aluminium, so I can see that maybe the oxidation of the aluminium can differ from ground point to ground point or that the material is not 100% homogeneous and thus that some ground points might have some more resistance to others. I can still not wrap my head around how Dumble would have measured with "electrical probes" and what "zero charge" might translate into real technical features. If one would use specific ground washers (like these: https://www.tube-town.net/ttstore/en/co ... ns-m3.html) that have very sharp tooths on the bottom and thus really bite into the material (aluminium) thus getting to a layer of aluminium with zero oxidation than the point of contact for ground should be nearly perfect. Then only the potential imhomogenicity of the aluminium should make a difference.

Sorry for the rambling, but this is on the one hand extremely intriguing on the other hand I have a hard time to understand the concept from a scientific point of view. A monocrystalin block of aluminium should of course have the best conductivity but can you imagine Dumble measuring the stock aluminium blanks and then he either had to discard a "bad" batch. Or did he have some way to "fix" such batch? Could there be other factors at play here (psychoacustics? bias?)

Best Regards,

Electron

Hey Electron,

I missed your post but I think I (kinda) answered some of it in other responses.

Same grounds..

Regarding the old vs new chassis... I paid extremely careful attention to grounds on both old vs new chassis. I even went as far on the old chassis of sanding the ground location and then further applying some dielectric grease before fastening on the ground lugs to prevent any future oxidation. Measuring ground points gave me similar results between the 2. I too am extremely intrigued by this whole thing

[dbharris]

A standard multimeter won't give very useful measurements in this case. I've used many multimeters throughout my career and very few will measure less than 0.1 ohm even shorting the leads together.

What's needed is a micro-ohmmeter. These are pricey in the 4 digit range. https://www.transcat.com/catalogsearch/ ... o-ohmmeter

Amazon has a couple in the $200 range but they actually, according to their specs, only go to .001 ohm, or 1 milli-ohm. Better than a multimeter but not a true micro-ohmmeter.

Thanks, that is helpful to know. Not sure my needs require the fancy lab equipment

-Dan

[dbharris]

If I measure resistance between ground points with my DMM (not a top of the line model either), I will get readings in the range of 0.1 - 0.3 Ohms. This is after a light sanding of the aluminum ground points and then tightly attaching a toothed ground point to the chassis with a keps nut. I've always wondered what is acceptable or not, or even if that is the right approach for measuring...

-Dan

I think that is part of the equation. The other part is similar to component construction. If a 100K Q-Line resistor sounds different to a 100K Xicon resistor, why wouldn't chassis A made from 1/16 inch aluminium composition X sound different to Chassis B made from 1/8 inch aluminium composition Y?

It really is all of the little details combined....

[GAStan]

A standard multimeter won't give very useful measurements in this case. I've used many multimeters throughout my career and very few will measure less than 0.1 ohm even shorting the leads together.

What's needed is a micro-ohmmeter. These are pricey in the 4 digit range. https://www.transcat.com/catalogsearch/ ... o-ohmmeter

Amazon has a couple in the $200 range but they actually, according to their specs, only go to .001 ohm, or 1 milli-ohm. Better than a multimeter but not a true micro-ohmmeter.

Thanks, that is helpful to know. Not sure my needs require the fancy lab equipment

-Dan

I didn't mean to infer that we all need one of these on our benches, I apologize if it came across that way.

It would be nice to have access to one of these to check out a chassis just for the sake of knowledge. I guess it's a matter of "how important is it?" My personal answer is its not that important considering the cost, as a hobbyist level builder. OTOH if i were in the business of building and selling many boutique amps a year I could justify the expense to have one for R&D.

For the record I do not have one, nor do I have access to one. After reading this thread I'm considering getting one of the Amazon or Ebay versions that read milli-ohms just to see if any beneficial measurements can be taken with them. If I do I'll be sure to post results here.

[dbharris]

A standard multimeter won't give very useful measurements in this case. I've used many multimeters throughout my career and very few will measure less than 0.1 ohm even shorting the leads together.

What's needed is a micro-ohmmeter. These are pricey in the 4 digit range. https://www.transcat.com/catalogsearch/ ... o-ohmmeter

Amazon has a couple in the $200 range but they actually, according to their specs, only go to .001 ohm, or 1 milli-ohm. Better than a multimeter but not a true micro-ohmmeter.

Thanks, that is helpful to know. Not sure my needs require the fancy lab equipment

-Dan

I didn't mean to infer that we all need one of these on our benches, I apologize if it came across that way.

It would be nice to have access to one of these to check out a chassis just for the sake of knowledge. I guess it's a matter of "how important is it?" My personal answer is its not that important considering the cost, as a hobbyist level builder. OTOH if i were in the business of building and selling many boutique amps a year I could justify the expense to have one for R&D.

For the record I do not have one, nor do I have access to one. After reading this thread I'm considering getting one of the Amazon or Ebay versions that read milli-ohms just to see if any beneficial measurements can be taken with them. If I do I'll be sure to post results here.

I didn't take it that way at all, all good!