John Curl's Blowtorch preamplifier part II

Status
Not open for further replies.
Would a step attentuator with lots of wiping action and silver (?) contacts have worked better?
For sure.
Yet, in the 70th, we were aware of the 'grainy' sound that issued from a carbon pot (and carbon agglomerated resistances), and replaced them by a gold plated 24 pos switch and resistances bridge. An other advantage is that you can make-it constant impedance.
45 years later, i can testify that it still work like the first day.

This said, this is true for signal only. It would be stupid to change adjustable resistances where they just set a DC that can be shunted by a cap.
 

Attachments

  • mach50-volume.JPG
    mach50-volume.JPG
    258.6 KB · Views: 186
Last edited:
In case of potentiometers, I now feel that Frank is right all the way, and then some. I used to think most were about the same, until I changed one cheap pot (volume) on my H7K 6550 integrated amp, and stuck in an Alps blue pot. For months afterwards, I had trouble believeing what I was hearing, it went from a 2D perspective to a full 3D perspective. Lots of space, "air" the design obviously had in it, but was subsequently killed off by a cheap and nasty volum pot. In general, much as I like H/K roducts, my standard issue with them are poor quality pots and trim pots.

In fact, H/K will also use Alps Blue pots for volume control on their top of their line model of the day (1990-1999), the HK 680 integrated amp. To me, Alps Blue is the default pot, it's either that or something better. Pots can kill a lot of possible good sound.
 
For a trial period about 6 months during a particularly minimalist fad I tried without an attenuator at all, simply arranging the gain structure to suit a carefully chosen level which conveyed realism for most recordings. It's an interesting experiment, easy to simulate just leave the attenuator alone having found an optimal position that floats the boat. For critical listening it's fine I found. I still try to listen at a consistent level, the effect level has on psychoacoustics is profound.
 
Disabled Account
Joined 2012
Would a step attentuator with lots of wiping action and silver (?) contacts have worked better? Perhaps, but (if I understand correctly) as he has stated future things will use fixed resistors whose values have been determined before final installation---he is not advocating the use of potentiometers in general, or if used is fully aware of their potential drawbacks.

I would only use silver contacts if the switch was hermetically sealed. Even then, I would move/wipe the contacts now and then to break any possible oxide build-up. Gold over silver works better.

Many of the highest performance products -- test equipment - use small signal sealed relays..... small hermetically sealed --- used in Audio Precision, ShibaSoku and Several other High-End distortion analyzers and ultra low distortion generators. Might be used in audio. Never tried them though. Hard to source.


THx-RNMarsh
 
Last edited:
For a trial period about 6 months during a particularly minimalist fad I tried without an attenuator at all, simply arranging the gain structure to suit a carefully chosen level which conveyed realism for most recordings.

Sounds good ... I'm doing some experiments on a plain laptop's internal sound, and I'm always running at 100% volume - so even digital attenuation is taken out of the mix. Subjective results are surprisingly good - and one can see why at least in the processor behaviour; the player software is running almost constantly at 0% CPU time, it's doing no extra fiddling, just dumping the data into the DAC area.
 
Many of the highest performance products -- test equipment - use small signal sealed relays..... small hermetically sealed --- used in Audio Precision, ShibaSoku and Several other High-End distortion analyzers and ultra low distortion generators. Might be used in audio. Never tried them though. Hard to source.
THx-RNMarsh

Non-Latching Relays - online | RS Components
 
AX tech editor
Joined 2002
Paid Member
It is only opinion without data. No matter how clear you perceive it to be. Actually it is these kinds of tests that either confirm expectations or show something else ugly is really there. You'll never know for sure unless you actually try it.

For my next trick I may just show why high PSRR is nonsense!

Serious reply # 1:

Ed, I see where you come from, but please consider. The reasoning that jitter performance is determined by the final DAC fits perfectly with all what we know about these things and processes, and also fits perfectly with what we can measure on this.

The only opposition comes from casual, uncontrolled, unspecified and undocumented 'listening tests'.
Now you propose that I do one more listening test. If that is also casual, uncontrolled, unspecified and undocumented, it has no value whatsoever and I am wasting my time.
If however you suggest I do a fully documented, controlled and double blind listening test, I will be willing to send you my rate sheet with pleasure. But to be honest, I'd rather you hired someone else for this.

So, again Ed, no offense meant, but one should really think these things through before throwing out casual suggestions that potentially have big implications.

Jan
 
AX tech editor
Joined 2002
Paid Member
It is only opinion without data. No matter how clear you perceive it to be. Actually it is these kinds of tests that either confirm expectations or show something else ugly is really there. You'll never know for sure unless you actually try it.

For my next trick I may just show why high PSRR is nonsense!

Less serious reply # 2 (the kind most often given):

Ed, I can see where you come from. You should be pleased that I did the listening test you suggested and I can confirm that the final DAC does indeed determine the audible performance.

Jan
 
I suspect the plating is not as good an ohmic conductor as is the foil ES
The plating on the copper traces or in the via barrel is porous.
So an 18um thick copper trace on the outer layer of a multi-layer PCB that is plated up to 35um has a higher resistance than a 35um copper foil that might be used for the internal layers.
This is particularly important in high speed digital designs where striplines (which are based on copper foils in the internal layers of a PCB stackup) are preferred to microstrips (which use the outer layers in a PCB stackup). The stripline has more predictable and consistent performance compared to the microstrip.
 
Dan, my experiences are different from yours. I've never done anything specifically to address jitter, even though high levels of it presented to the circuitry near the DAC could cause audible problems or differences, because of inadequate engineering. To date, I've got SQ that's "good enough" for me by looking in other areas; reduction of possibly jitter related artifacts would just be icing on the cake ...
Fix the jitter and you fix a lot of sonic problems.
Sort of a two street....jitter will excite wrong downstream behaviours.... and fixing wrong downstream behaviours makes jitter less objectionable.
Jitter still needs to be fixed though.

Dan.
 
Originally Posted by Kindhornman
It is nice to see everyone getting along and actually working together, Nice to see Sy and John getting along for a change! Happy Mother's Day to all you mothers.

it is truly one of those Miracles I hear so much about. :)
-Richard
Wanna lay bets on how long it lasts ?.
I expect from past behaviours, that after the Vendetta is working and Bybee is mentioned it will all change from one minute to the next.
So it goes when sycophant/psychopaths go to work.

Dan.
 
and B..... is mentioned
Oh, NOOOOOOOO ! Not that name ! Don't open the Pandora's box !!!!
The forces of evil will spread on earth at a speed superior to that of light while the laws of physics will suffer the ultimate outrages !
An army of bloodthirsty objectivists will rush on the poor ordinary people we are ...
I doubt we could survive to such a crisis !
 
Last edited:
AX tech editor
Joined 2002
Paid Member
I use these 40 step resistive attenuators. They're quite nice and have a feel as good or better than the Seiden switches. They've eliminated the wiper contact by using a highly flexible wire.

An externally hosted image should be here but it was not working when we last tested it.


se

Steve what brand is that?

Jan
 
Status
Not open for further replies.