Tad,
Yes, I will make new universal power board for at least four pairs output devices.
I did test for a separate rails for LME. Let me dig them out.
Panson
Dual Drivers for Four-Pair ThermalTrak
I slightly modified the existing four-pair TT power board to have dual drivers (MJE15030/15031 x 2). Each driver pair drives two TT. Here is THD vs freq for 2.7 R, 4 R and 8 R loads. At 121 W into 2.7 R, THD is only 0.003 %.
I slightly modified the existing four-pair TT power board to have dual drivers (MJE15030/15031 x 2). Each driver pair drives two TT. Here is THD vs freq for 2.7 R, 4 R and 8 R loads. At 121 W into 2.7 R, THD is only 0.003 %.
Attachments
Perhaps I don't have a good understanding of this circuit but to me using multiple drivers in // or one driver for the output transistors in // gives the same current requirement for the VAS ( distributivity of multiplication with respect to sum).
It seems to me that the main advantage of multiple drivers is less current in each driver and so less distortion.
JPV
the drivers as well as the outputs suffer gain droop at higher currents.
If the drivers only have to drive 2pair instead of 4pair of outputs then the driver gain will be higher and thus the VAS current into the bases of the drivers will be less.
That is equivalent to saying the VAS sees a higher load impedance.
If the drivers only have to drive 2pair instead of 4pair of outputs then the driver gain will be higher and thus the VAS current into the bases of the drivers will be less.
That is equivalent to saying the VAS sees a higher load impedance.
wiring plays a vital role in performance
Here is a plot for the low-level grounding wire placement. This wire connects power supply 0V and small-level signal section ground. The highest THD curve is obtained by placing that wire ~1 cm from output devices.
The other curves are associated with other wire placements with slight displacement with each other. With the best placement in the test, the THD at 20 kHz for 2.7 Ohm is 0.002 %!
Here is a plot for the low-level grounding wire placement. This wire connects power supply 0V and small-level signal section ground. The highest THD curve is obtained by placing that wire ~1 cm from output devices.
The other curves are associated with other wire placements with slight displacement with each other. With the best placement in the test, the THD at 20 kHz for 2.7 Ohm is 0.002 %!
Attachments
You actually can use a ground-plane with excellent results. I finally bite the bullet and went for ground-plane topology, after being told many times ground-planes are no good for amplifiersBruno Putzeys from Hypex finally convinced me, and thought us how to do it.
If you take very good care about placement of components, (start with a empty piece of paper and draw out the ground loops out). Another point, my amplifiers are all feed balanced, so the negative input reference to the output of the driver opamp instead of the ground-plane. That can be the biggest reason why I don't have any ground-loop related hum.
I used the LM4702 in a multichannel amplifier application, with one unbroken total ground-plane, and the THD measurements are below the limits of what I am able to measure (0.0005%). I never achieved this results with star grounding. Noise floor is inaudible low.
Second benefit, I can put my cellphone in front of the circuit and no "buzz" anymore over the speakers.
A ground-plane design does sound different then a star-ground design. The same circuit with ground-plane sound more analytical, and a more airy in the high-end. and it seems subjectively speaking, more resolving details. Most strange was that the bass seemed a factor 10 tighter with the ground-plane. Can't really explain why in technical terms, but it was very noticeable in a listening panel of people.
One other note though, my design is a 4 layer board, and all high current supply lines and loudspeaker lines are all stacked on top of each other and are kept away from the LM4702 and other low current stages. Magnetic influences are minimized.
My opinion is, with careful design and routing, one can make superior results with ground-plane topology, and the LM/LME driver chips can work perfectly with ground-planes.
There is a understandable "fear" fro ground-planes, but we should overwin those, learn from RF experts and papers and give it a try.
With kind regards,
Bas
Sebastiaan,
you have been recently at a EMI Signal Integrity class haven't you ?
I was, and boy what an eye opener it was. I am looking at a circuit board with a different set of eye' s now. Thanks for highlighting this very important yet often overlooked or better said neglected approach.
Keep the loop area as small as possible and things magically fall into the right place
panson_hk,
great job, I am looking forward to the final version.
Thanks for your awesome contribution
DIYAUDIO forever
Cheers
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Sebastiaan,
you have been recently at a EMI Signal Integrity class haven't you ?
I was, and boy what an eye opener it was. I am looking at a circuit board with a different set of eye' s now. Thanks for highlighting this very important yet often overlooked or better said neglected approach.
Keep the loop area as small as possible and things magically fall into the right place
Cheers
Dear KCT,
Indeed an eye opener. And yes the way you look at circuit boards, traces and inductance change forever! Also it becomes obvious how many commercial designs are just plane wrong, with 100nF caps on the weirdest places with high inductance "ground" traces all over the board.
And you are right also, that like you, I started to look at circuit boards as river and a drain. Once you can visualize where the water flows, what is in the path, and where the high and low currents are located things fall into place. A given with higher frequencies RF returns is that they stay "glued" to the the source traces. And this point also makes you realize that many commercial ground planes are also wrong designed.
For general readers,
Keep dirty current and/or high current circuits as close to the return point as possible, and place sensitive and low current circuits around it. The dirty and high currents will find their way to the drain without affecting the surrounded circuits.
People (and me as well in the past) who get hum, RF or other noise with ground-planses didn't maintained a good component placing and routing discipline. Once again think about your shower sink and imagine how water flows to the drain
If you design as above thump of the rule, you can get away with an unbroken (and it must be unbroken!) one layer ground plane, with high and low current mixed signal, and get an extraordinary good result. A result in my opinion you can't beat with star grounding. The Focal SM9 commercial active loudspeaker is the living proof of it. All boards have unbroken ground-planes.
Everyone who want to get closer to ground-plane designs, should read everything Herry Ott has ever written. Best stuff ever.
Once you start to understand PCB design one can focus less on expensive exotic "audiophile" components. A good PCB design with cheap TIP35 transistors will outperform a bad design with state of the art components.
It turns out for me that a good PCB design gave the most significant improvement in sound. Assumed the design and topology are top-class of course
As addition on above (still reasonable on topic I think). Like others indicated as well. Don't burry low current circuits in a loop of high current traces. What you often see is the VCC and VEE traces all on the outsides of the boards, and the VAS and low current circuits in the middle. Don't ever do that! In class A/B amplifiers the inductance between the VEE and VCC rise with current draw and many odd harmonic spikes occur. Those AC magnetic radiations in between the outer VEE and VCC traces go all over the board and affect everything on it's way in between. If you want low THD. this can't be good... Keep VEE and VCC traces close together as a pair or stacked in multilayer boards. Let them enter the amplifiers from one side, and keep the low current circuits at the other side.
In all matters keep differential lines always together as close pair or stacked layers, and keep the distance as small as possible between the opponent traces. How often we see op-amps based circuits where the VCC and VEE lines are distributed independently. Keep them always close together as pair.
Keep the speaker output traces close to the power amplifiers VEE and VCC traces. Again the Focal SM9 speaker has this all incorporated. VEE, VCC en Output are all stacked in a 4 layer multilayer PCB with layer 2 as unbroken ground-plane. The results are stunning.
Last but not least, If you use an unbroken ground-plane, you can make better advantage of local de-coupling with 100nF caps. Place them direct to the VEE or VCC pins of each transistor. The inductance to ground return is way less then any star-ground topology. Don't put any 100nF caps in the PSU it-selves, only direct at the pins of the last device.
Please don't take my post as a "smart ***" response. I still learn every day and that is the fun part of life and designing. My contribution is meant to share my enthusiasm for the discoveries I did, and I hope to trigger those who didn't saw the light yet, or who are afraid for ground-planes to give it a second thought and learn a bit about it. I really think that PCB design to often is underestimated, and that is kind off odd since we all looking for the highest performance here.
No doubt people will comment my approach is over the top, but the scoreboard (measurements) doesn't lie. I swear by 4 layer board designs for amplifiers. Where layer 1 is all the low current and low signal level traces. Layer 2 an unbroken all cupper ground plane. Layer3 and layer 4 contains the high current traces. Preferably VCC on payer 3 and VEE on layer 4 stacked as semi power-planes.
The layer 2 ground-plane gives a good isolation between low and high current traces since it acts as shield in between. Despite the fact that the overall capacitance will increase, my amplifier designs are more stable with higher bandwidth en less compensation due the excellent inductive and RF qualities of the board.
With kind regards,
Bas
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Yes.
each "input" and each "output" are circuits. Always run them as Flow and Return pairs. Keep the loop area as small as possible.
Think in "currents" rather than of signals or voltages.
Don't let "currents" share the same length of circuit trace or wire. Different circuits can meet at a point, when necessary.
Do you know if they plan to post an internet video (you tube) of that lecture?
each "input" and each "output" are circuits. Always run them as Flow and Return pairs. Keep the loop area as small as possible.
Think in "currents" rather than of signals or voltages.
Don't let "currents" share the same length of circuit trace or wire. Different circuits can meet at a point, when necessary.
Do you know if they plan to post an internet video (you tube) of that lecture?
Dear Andrew,
I still have the power-point sheets in hard paper from one of the AES evening given by Bruno Putzeys. I will ask him permission if I may scan it and post it on DIY audio.
With kind regards,
Bas
Search on JCX's posts here. He's done a few "multi loop" designs using localized feedback. He's also someone who seems to actually understand all the complex math behind making such designs stable which is often the biggest issue. I believe he does really high-end op amp work (sensors?) for his day job.
For general readers,
Keep dirty current and/or high current circuits as close to the return point as possible, and place sensitive and low current circuits around it. The dirty and high currents will find their way to the drain without affecting the surrounded circuits.
People (and me as well in the past) who get hum, RF or other noise with ground-planses didn't maintained a good component placing and routing discipline. Once again think about your shower sink and imagine how water flows to the drain
If you design as above thump of the rule, you can get away with an unbroken (and it must be unbroken!) one layer ground plane, with high and low current mixed signal, and get an extraordinary good result. A result in my opinion you can't beat with star grounding. The Focal SM9 commercial active loudspeaker is the living proof of it. All boards have unbroken ground-planes.
Everyone who want to get closer to ground-plane designs, should read everything Herry Ott has ever written. Best stuff ever.
Once you start to understand PCB design one can focus less on expensive exotic "audiophile" components. A good PCB design with cheap TIP35 transistors will outperform a bad design with state of the art components.
It turns out for me that a good PCB design gave the most significant improvement in sound. Assumed the design and topology are top-class of course
Multi-layer pcbs and SMD parts will end up extinguishing DIY audio, that's what I feel.
The problem with designing more than two-layer pcbs is that you can't make the actual boards yourself, and need to be done with equipment DIY aficionados can't get to.
What I wonder is how you can adapt ground plane techniques to a DIY design, one you can actually develop yourself. As I have been working on how to design a single-plane pcb for Sulzer/Jung/Didden supplies, one compromise I thought might work is adapting what I call the "dead bug" principle, which is soldering all through-hole parts on one side, as if they were SMD parts, if you know what I mean.
Doing that you can use a dual-layer board and only use one layer as ground plane, punching holes only for ground links. Would that work and fulfill the principles you mentioned?
It would be very helpful if you designed a pcb to show exactly what you mean, if possible.
Carlos
The lme49830 works well under +-40V and 300ma per Mosfet.So far 2sk1058/J162 made by Hitachi is my favorite choice,someone says it's sounds like vacuum tubes in class A.I disagree with that point,my KT88 push pull is a wild,rude,rock n roll,mind missing machine and nothing can displace that iron block.
I don't understand why people still like discrete "front end" designs than this chip,what a nightmare when matching transistors.
I don't understand why people still like discrete "front end" designs than this chip,what a nightmare when matching transistors.
lme49830....
Myself and 2 of my friends have built each an amp using a board found on the internet (it was NOT Panson) and including the LM49830 and IRFP240/9240 as vertical mosfet outputs. For several recordings it sounded marvelous but for most others it sounded harsh
and worse at medium volume of listening...
In my amp I used about 300ma (b/c I know that mosfet need more current...) of bias per mosfet and 2 pairs for an 80W rms amp under 8 ohms .
I also used genuine parts and my LM49830 came directly from National as samples and mosfets were matched from a member of this forum who has a store. We also tried a few tweaks in there w/o significant improvement. I could not see anything wrong at the scope and the THD at 1KHz was under 0.01% from what I remember...
At this moment, the 3 of us have dismantled our respective amp to use it for other configurations.
Maybe I shold have tried the Lateral mosfet b/c I use them a lot in many amps already....
Maybe also the layout of the board we used had flaws... Maybe Panson boards would work better...
Fab
Myself and 2 of my friends have built each an amp using a board found on the internet (it was NOT Panson) and including the LM49830 and IRFP240/9240 as vertical mosfet outputs. For several recordings it sounded marvelous but for most others it sounded harsh
and worse at medium volume of listening... In my amp I used about 300ma (b/c I know that mosfet need more current...) of bias per mosfet and 2 pairs for an 80W rms amp under 8 ohms .
I also used genuine parts and my LM49830 came directly from National as samples and mosfets were matched from a member of this forum who has a store. We also tried a few tweaks in there w/o significant improvement. I could not see anything wrong at the scope and the THD at 1KHz was under 0.01% from what I remember...
At this moment, the 3 of us have dismantled our respective amp to use it for other configurations.
Maybe I shold have tried the Lateral mosfet b/c I use them a lot in many amps already....
Maybe also the layout of the board we used had flaws... Maybe Panson boards would work better...
Fab
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