Hi Mike,
You have no problems with me. I'm just trying to answer questions.
I will try to do two things. I am in audio service, so I try to keep people from damaging their equipment unnecessarily. I've seen that too many times. I've also seen many upgrades go horribly wrong. The other thing I do is try to keep people on track with their realistic goals. Hence my comment on "feature creep". You had a successful plan in mind, and that's fine. My wish is for your success, resulting in a usable amp for years to come. But, you are correct in that it is your amp and yours to do with as you please.
Finally, many people in all professions may become focused on so many small details of a project that they loose sight of the end goal. My advice is simple. Try to look at the entire project as a complete system. Evaluate problems in relation to the system to avoid chasing issues that don't matter. Finally, complete a project in discrete steps so that if something doesn't work, it's easier to troubleshoot and fix. I was also a project manager and have seen this problem more than once.
As far as new members are concerned, I think they will see that it's always fine to post as long as that post is not an attack on another member. I find it unfortunate that the "Mr. Ball" issue came up. There is history there.
Best, Chris
You have no problems with me. I'm just trying to answer questions.
I will try to do two things. I am in audio service, so I try to keep people from damaging their equipment unnecessarily. I've seen that too many times. I've also seen many upgrades go horribly wrong. The other thing I do is try to keep people on track with their realistic goals. Hence my comment on "feature creep". You had a successful plan in mind, and that's fine. My wish is for your success, resulting in a usable amp for years to come. But, you are correct in that it is your amp and yours to do with as you please.
Finally, many people in all professions may become focused on so many small details of a project that they loose sight of the end goal. My advice is simple. Try to look at the entire project as a complete system. Evaluate problems in relation to the system to avoid chasing issues that don't matter. Finally, complete a project in discrete steps so that if something doesn't work, it's easier to troubleshoot and fix. I was also a project manager and have seen this problem more than once.
As far as new members are concerned, I think they will see that it's always fine to post as long as that post is not an attack on another member. I find it unfortunate that the "Mr. Ball" issue came up. There is history there.
Best, Chris
Hi Mike,
To effectively shield a mains transformer, distance is the most effective method. You can try rotating the power transformer to see if your AC hum level changes. Remount in the best location. Also, mounting the power transformer on it's own thick steel plate or basket will help keep leakage flux out of your chassis. You must allow the metal basket and transformer core to remain grounded to your mains ground. This is a must. Air flow slots will help cool the transformer. Rotating your transformer may give you the biggest bang for the buck - or not. It all depends on what the manufacturer did. Those areas may possibly be optimized already.
Sensitive areas to consider shielding with any audio project: Any high gain section (like phono, tone amp or input stage) and especially circuits that operate at a high impedance and high gain.
-Chris
There is no concern given the AC mains frequency and harmonics involved here. Another non-issue, but you are thinking the right way to explore the possibilities.
To effectively shield a mains transformer, distance is the most effective method. You can try rotating the power transformer to see if your AC hum level changes. Remount in the best location. Also, mounting the power transformer on it's own thick steel plate or basket will help keep leakage flux out of your chassis. You must allow the metal basket and transformer core to remain grounded to your mains ground. This is a must. Air flow slots will help cool the transformer. Rotating your transformer may give you the biggest bang for the buck - or not. It all depends on what the manufacturer did. Those areas may possibly be optimized already.
Sensitive areas to consider shielding with any audio project: Any high gain section (like phono, tone amp or input stage) and especially circuits that operate at a high impedance and high gain.
-Chris
mikesnowdon said:
Hi Mike,
A uprocessor can be shielded easily with copper-clad PCB etch sheet. You can get this from Fleebay or Maplin. Cut to size and glue in place - neat. I did this in my CD63. I'd expect no to low gains in an amp.
I don't think thin steel will shield a tx amazingly well - I think you need a special material like mu-metal - http://en.wikipedia.org/wiki/Mu-metal
Simon
A sheet of steel is better than nothing. The best thing is the mu-metal that SimontY proposed, but it is incredibly expensive and not easy to get by.
A less expensive and still very good shielding material is tin plate or tin foil. Electronics suppliers sell small tin plate cases especially for shielding, open at the bottom to put over components on a PCB, with solderable pins for grounding. One manufacturer is Teko.
A less expensive and still very good shielding material is tin plate or tin foil. Electronics suppliers sell small tin plate cases especially for shielding, open at the bottom to put over components on a PCB, with solderable pins for grounding. One manufacturer is Teko.
Hi Mike,
Shielding the uP is normally done. I wasn't aware yours wasn't. If there is a metal chassis between the micro and the rest of the world, you only need to consider any wires that carry data and / or clock to the micro. Be very careful if you plan to use a shielded data cable though. The pulse shape is important. You need to preserve the rise and fall times as well as the timing between clock and data.
The previous suggestions for shielding are bang on. The fast edges on digital signals are what may cause a buzz in your audio. A nice copper shield would work well on the radiated noise. Ground the cover to your digital ground.
Try moving the wires from the micro around to see if that is causing your noise. You may be able to dress the leads where they don't interfere that much if this is the cause.
-Chris
Shielding the uP is normally done. I wasn't aware yours wasn't. If there is a metal chassis between the micro and the rest of the world, you only need to consider any wires that carry data and / or clock to the micro. Be very careful if you plan to use a shielded data cable though. The pulse shape is important. You need to preserve the rise and fall times as well as the timing between clock and data.
The previous suggestions for shielding are bang on. The fast edges on digital signals are what may cause a buzz in your audio. A nice copper shield would work well on the radiated noise. Ground the cover to your digital ground.
Try moving the wires from the micro around to see if that is causing your noise. You may be able to dress the leads where they don't interfere that much if this is the cause.
-Chris
Good.
Ragarding the cable from 'mprocessor to main PCB. Rather than change it would it be ok to just sheild it with some copper braid then cover with heatshrink?
Also, Im still considering the use of a dedicated trafo for the front panel PCB. I know there should be sufficient isolation by the regulator but the power rails (and ground) to the front PCB run from the rear of the main PCB (where the v regs are) and go past the preamp section. Infact Im not sure if the digital and anaaloge grounds are even seperate.
If I did this I would use some kind of grounded 'copper can' on the new PSU and Trafo. Im also still considering the use of a Shaffener filter on the mprocessor section to add further isolation and to filter any crap from getting onto the pre/power stage's supplies via the AC line.
Im looking at a simple soloution:
- Use the existing 7805 reg and associated caps. I will need to add a bigger cap at the input (is 470uF ok?).
- Mount reg caps and diodes on a small pcb (there are some nice ones available for a neat job which are small enough).
- Add a small 1A 7v Trafo, maybe one of those small torroids which have the blue plastic cover. This can then be covered with copper foil.
- Run a AC line from the IEC using shielded mains cable around the underside of the PCB. (Is there really such an issue with noise here if I use a good filter?)
Any ideas on the best way to achieve this?
ML,
Mike.
Ragarding the cable from 'mprocessor to main PCB. Rather than change it would it be ok to just sheild it with some copper braid then cover with heatshrink?
Also, Im still considering the use of a dedicated trafo for the front panel PCB. I know there should be sufficient isolation by the regulator but the power rails (and ground) to the front PCB run from the rear of the main PCB (where the v regs are) and go past the preamp section. Infact Im not sure if the digital and anaaloge grounds are even seperate.
If I did this I would use some kind of grounded 'copper can' on the new PSU and Trafo. Im also still considering the use of a Shaffener filter on the mprocessor section to add further isolation and to filter any crap from getting onto the pre/power stage's supplies via the AC line.
Im looking at a simple soloution:
- Use the existing 7805 reg and associated caps. I will need to add a bigger cap at the input (is 470uF ok?).
- Mount reg caps and diodes on a small pcb (there are some nice ones available for a neat job which are small enough).
- Add a small 1A 7v Trafo, maybe one of those small torroids which have the blue plastic cover. This can then be covered with copper foil.
- Run a AC line from the IEC using shielded mains cable around the underside of the PCB. (Is there really such an issue with noise here if I use a good filter?)
Any ideas on the best way to achieve this?
ML,
Mike.
Hi Mike,
To be honest with you, many of these later considerations might well be better on your kit super build. Work to solve the worst issues with your existing amp. Some mild upgrades and leave it for now. Build your really good amp and you can always return to this amplifier and apply what truly works well. Leave this one as stock as you reasonably can for now. Even if you completely do this one over, solve your issues first. Once it's stable you can add to it and actually be able to evaluate the changes as you go. You will learn more too.
-Chris
I would redress these wires rather than attempt to shield them in any way. First though, confirm if they are even a problem by moving the wires around a little.
The grounds must be connected not matter what you do. Otherwise the digital commands will have no reference (it will not work).
To be honest with you, there is probably more noise on the line than what your digital stage is creating. My personal opinion is that adding a transformer may cause far more trouble than it solves.
Sure, but the smaller cap might be better. You might even use R-C sections to reduce the inrush charge current per cycle and allow your regulator to run cooler. Just make sure your regulator sees 3 V above your regulated output minimum. You need to use a 'scope as we are talking about the trough on the AC ripple. Add some 0.1uF film caps at the input and output to eliminate any low amplitude oscillations. Check with a ..... 'scope.
Why not save this for a later date - if you find that you need to do this. I would not cover with foil, just use it as it is. Mount away from everything else.
Can you route around the PCB? Under might be okay if you stay near the output or existing power supply.
To be honest with you, many of these later considerations might well be better on your kit super build. Work to solve the worst issues with your existing amp. Some mild upgrades and leave it for now. Build your really good amp and you can always return to this amplifier and apply what truly works well. Leave this one as stock as you reasonably can for now. Even if you completely do this one over, solve your issues first. Once it's stable you can add to it and actually be able to evaluate the changes as you go. You will learn more too.
-Chris
Using LM317 regs.
Apparently these have much lower noise than the standars 78** variety so I'd like to look at using them for the preamp section.
Ive had a look at the datasheets and the only barrier isd that they have a different pinout. Can I simply bend the legs so they 'drop in' inplace of the 7815/7915 regs? Woul I need to change any cap values? I dont have a working scope or even know how to use it yet so Im hoping for a simple soloution.
Any advice here would be greatly appreciated as I'd like to do the same on the DAC's in my CDP.
Rgds,
Mike.
Apparently these have much lower noise than the standars 78** variety so I'd like to look at using them for the preamp section.
Ive had a look at the datasheets and the only barrier isd that they have a different pinout. Can I simply bend the legs so they 'drop in' inplace of the 7815/7915 regs? Woul I need to change any cap values? I dont have a working scope or even know how to use it yet so Im hoping for a simple soloution.
Any advice here would be greatly appreciated as I'd like to do the same on the DAC's in my CDP.
Rgds,
Mike.
Thanks.
I also found a calculator for the LM337 neg reg.
(Also does the positive) Link:
I noticed the national semi datasheet reccomends 100uF Tants for the output and 10uF Tant for input. Does that make my 1000Uf Pana FC and 220uF Balckgates obsolete if I use these regs? Surely even with this type of reg the smoothing caps are determined by the load?
PS: I figured out a way to hardwire in a resistor and pot to acheive the same 'pinout' as the 78** type. Maybe later I'll draw it up and post an image.
PPS: This all based on the asumption that these regs are quieter than 78** types. Are they?
Mike
I also found a calculator for the LM337 neg reg.
(Also does the positive) Link:
I noticed the national semi datasheet reccomends 100uF Tants for the output and 10uF Tant for input. Does that make my 1000Uf Pana FC and 220uF Balckgates obsolete if I use these regs? Surely even with this type of reg the smoothing caps are determined by the load?
PS: I figured out a way to hardwire in a resistor and pot to acheive the same 'pinout' as the 78** type. Maybe later I'll draw it up and post an image.
PPS: This all based on the asumption that these regs are quieter than 78** types. Are they?
Mike
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