upgrades
- Thread starter mete
- Start date
We are kicking around future upgrade kits, but we outlined a couple in the intro in the manual (bottom of page 7), including changing some capacitor and resistor values. Obviously that’s not a comprehensive list but it’s a starting place. I’d love for folks to try things out so we can document some experiments on the forum.
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Build it bone stock first so you can understand what the upgrades that you make do for the sound. It also makes it much easier to troubleshoot any build issues. It may seem more efficient to incorporate the mods at the initial build, but in the long run it doesn't really offer as much reliability or educational gain.
I have phrased the question too broad. I didnt mean any change modifying the circuit topology, not even changing the values of any components. I just meant using a better component in some respect in the same location having the same value. For example, Crack is not supplied with film caps (but S4X is), things like that.
I understood what you meant. I still think you should build the kit first with the parts provided. “Better component” is a worthwhile goal, but only if the amp works the way it was intended as a starting point for any comparison. Otherwise how can you tell if the replacement component sounds better?
The problem is it is slightly impractical for me to modify the amp later and I am not sure if I will remember the sound of previous state to make a comparison 
Some of what I am asking is actually about the tolerances in the circuit, if the supplied Rbias is 5% but if it makes sense to match this to 1% or even better then I can do that from the start (or use a lower tco resistor etc.), I dont think I need to hear the sound for that and it doesnt affect troubleshooting in case of a problem. Capacitors are more tricky I guess, since the obvious ones are already film capacitors.
Some of what I am asking is actually about the tolerances in the circuit, if the supplied Rbias is 5% but if it makes sense to match this to 1% or even better then I can do that from the start (or use a lower tco resistor etc.), I dont think I need to hear the sound for that and it doesnt affect troubleshooting in case of a problem. Capacitors are more tricky I guess, since the obvious ones are already film capacitors.
I'm sorry that I'm having a little difficulty understanding your end goal. Most often modifications are done to change the sound, with the hope that it improves it. It doesn't seem that this is necessarily your focus.
In some cases a change might be considered for improved reliability. This might include putting in electrolytic caps with a higher voltage rating, longer lifetime rating and/or higher temperature rating. As a sweeping generality you could replace electrolytic caps with film caps of equal or higher capacitance and voltage rating for higher reliability. However the equivalent film cap is usually far too big to fit where the 'lytic does and one needs to check dimensions before ordering parts.
As far as tolerance of resistors goes the tolerance rating of the stock components is well within that needed in the circuit. Typically resistors are changed for sonic benefits, most often for different tone or improved resolution, occasionally for lower noise or better RFI rejection. This is usually done by changing the actual composition type of the resistor used, for example metal film rather than carbon film or tantalum rather than metal film. The only cases I can think of where really tight tolerance might have an impact is in stereo stepped attenuators where it may optimize channel balance and R2R ladder DACs with discrete resistor ladders where you need like 0.0001% tolerance over a wide temperature range for high resolution.
I do think you would remember the sound of the previous version if you made a change that had an impact on the sonic quality of the amp. At least my experience with these kits over the years seems to support that.
In some cases a change might be considered for improved reliability. This might include putting in electrolytic caps with a higher voltage rating, longer lifetime rating and/or higher temperature rating. As a sweeping generality you could replace electrolytic caps with film caps of equal or higher capacitance and voltage rating for higher reliability. However the equivalent film cap is usually far too big to fit where the 'lytic does and one needs to check dimensions before ordering parts.
As far as tolerance of resistors goes the tolerance rating of the stock components is well within that needed in the circuit. Typically resistors are changed for sonic benefits, most often for different tone or improved resolution, occasionally for lower noise or better RFI rejection. This is usually done by changing the actual composition type of the resistor used, for example metal film rather than carbon film or tantalum rather than metal film. The only cases I can think of where really tight tolerance might have an impact is in stereo stepped attenuators where it may optimize channel balance and R2R ladder DACs with discrete resistor ladders where you need like 0.0001% tolerance over a wide temperature range for high resolution.
I do think you would remember the sound of the previous version if you made a change that had an impact on the sonic quality of the amp. At least my experience with these kits over the years seems to support that.
Natural Sound
Active member
How about a C4S upgrade like offered in the pre S4 offerings? Is that in the works or not necessary with the new circuit topography?
We had a manual shot for the C4S upgrade we had designed but there wasn't as much benefit as we'd like so we are taking it back to the drawing board. We've left the holes for the C4S in the final chassis plate in the event we can come up with something we feel like is worth the time and money for you all to install.
Paul Joppa
Moderator
It's in the works. The first prototype is not behaving as expected, and we won't offer it until we understand what's going on.
Maybe to rephrase it, if you aimed 80/20 in some of the parts supplied, and stopped at a point where the cost/benefit started to diminish to an acceptable point, I am asking what would be the parts that would push this to 90/10 for example. If the stock parts are already at objectively best state (naturally I mean best considering all other components and variability etc. not like absolute best), and any further change requires a subjective judgement (of the sound), then I already have my answer. I see the parts in the schematic and the checklist but I dont see the details as I dont have my kit yet, so I might be asking or saying things too early, I am aware of that.
A stepped attenuator or something like an R2R DAC is a clear example, but anything affecting the gain or freq. response would be a candidate I guess.
Maybe. I had a separate Crack for experimentation, might need something similar here, maybe later.
That is very good.
Paul Joppa
Moderator
Over the years, the S.E.X. amps have been continuously refined, and many weak points have been brought into balance. There have been three generations of transformers and chokes, for example. And we now use long-life, high temperature electrolytics wherever possible. I am grateful to Doc B for supporting a continuing push for better quality and reliability, in spite of the increased cost.
In my mind, there is more opportunity now in using better tubes (like DHTs) and/or better circuits (like feedback? - the jury is still out on that one). That's why we offer a 2A3 amp and a 300B amp with shunt-regulated driver power supplies.
All that said, there is still some possibility in signal-path capacitors (interstage and parafeed output) The Solens that we often use are pretty good, though they do seem to take a long time to fully break in. But there are audible differences among caps, though IMHO it's more a matter of taste than anything measurable.
In general, there are still some opportunities in longevity/reliability of mechanical parts, such as potentiometers, rotary switches, and interconnects. Another reason to leave out the volume control ... :^)
In my mind, there is more opportunity now in using better tubes (like DHTs) and/or better circuits (like feedback? - the jury is still out on that one). That's why we offer a 2A3 amp and a 300B amp with shunt-regulated driver power supplies.
All that said, there is still some possibility in signal-path capacitors (interstage and parafeed output) The Solens that we often use are pretty good, though they do seem to take a long time to fully break in. But there are audible differences among caps, though IMHO it's more a matter of taste than anything measurable.
In general, there are still some opportunities in longevity/reliability of mechanical parts, such as potentiometers, rotary switches, and interconnects. Another reason to leave out the volume control ... :^)
