A Lateral MOSFET Power Amplifier Design (second try)

After my first experience with a design from one book, design that has been declared on this site to be very bad and buggy, I started to read a second book; "Designing Audio Power Amplifiers", from Bob Cordell, specially the whole chapter on MOSFET.

The preceding, (read the bad) design is completed and tested with good starting results, except for an oscillation that, in my opinion, come from one MOSFET that I had to twisted the Drain and Source pins with wires after an error on my PCB. I decided to relay this circuit board as a prototype. For it's history:

Now I am ready to start over from the beginning with a new design from Bob Cordell book. My choice would be, from his suggestion, the IPS and VAS design of figure 9.20 and the OPS design from figure 14.17, and build them so I could use all my actual parts, same cabinet and Heat-Sink, same PCB mechanical dimensions on the Heat-Sink, same transistors, high power resistors, etc...

For those of you who have already tried these designs, do you have any concern about their schematics that I should be aware of, before I am starting anything?

Hello Sevy

I worked with Bob Cordell to design the pcb set for the Hafler dh-220c upgrade. We discuss that design in the Hafler Dh-220 mod thread.
The book has a few errors as you have discovered, to bad not so easy to make corrections but there could be an errata page on Bob’s web site, so I’ll suggest it to him.
Also there is more info on Bob’s web site for the dh-220c
I’ll have to refer to the book what figures you are referring to if they are the ones for the Dh-220c design
As a suggestion it would be advantageous for anyone reading Bob’s book and building power amplifiers to learn and perform LTSpice simulations on your designs, helps in understanding how they work and compare to the actual circuits in operation

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@vilfort Thank you for these videos link. I watched the first one entirely. It was a very good revision of the MOSFET chapter of his book and I could understand every words Bob says. The audio and video quality is terrific. I started the second one but did finished yet.

This morning I was ready to start putting everything into the KiCad software. Unfortunately, I am already blocked at the LSK489 and LSJ689 schematic transistors. First, they don't exist in the library! I am comfortable to create my own library parts but these are two units in a single package. It is already risky to create a library part with it's footprint with three legs without making mistake, now this one has two parts in a single package, nothing to minimize risk or error on the final PCB!
Second, I could find the LSK489 on Mouser, but as usual, the brother LSJ689 is not available :-/

Are these already obsolete?

Does some one have a good source for these JFET?
Is is a good think to sacrifice the benefit of these JFET and replace them with 2N5401/2N5551 transistor? I bought 100 of each!
Lsj689 is not obsolete it’s just not stocked by mouser or digikey. Always refer to the mfr web site
For the Dh-220c kits I sell on eBay I buy mine directly from linear systems
I have bought them elsewhere too iirc it was a place in Florida but that was a few years ago
You are on your own if you want to modify the existing designs. I would not suggest it based on what I have determined as your experience level. First thing is to learn LTSpice :)
It’s pretty common to have to build your own library components for unique parts, all part of learning ecad, a lot easier than building a 3D model I would think
Dh-220c uses a lot of 2n5551/5401 except for the input diff pairs.
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From the datasheet, the LSK489 exist in three versions: LSK489, LSK489A and LSK489B. The difference seem to be the Idss value. Should I choose one specifically?

We specified lsk489 before they offered Idss grading. Does not matter because lsj689 is not graded anyways. I test, select/match them as pairs. That’s why I designed a sot-23 to dip6 adapter to make selection and service easier.
Bob has a write up on selecting the jfets in his web site, all a good read in understanding the mechanism
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It’s pretty common to have to build your own library components for unique parts, all part of learning ecad, a lot easier than building a 3D model I would think
Of course the easiest way to build a new part is to start with an existing closest one. The only one I can find in the library list, close to a JFET, is the BF545A part. Now I did that mistake with the inverted Drain and Source of the PNP ECX10P20 in my first design and I don't want to do a similar mistake here. Again the Gate of this library is placed in the center compared to the Gate of the Figure 9.20 Example IPS-VAS of the book. Both are labeled "Passive" in the library. Does the Drain and Source pins really are Passive pins or this particular library part is different?

You need to double check your work and the library. Need to check schematic symbol, pin numbering, assignments against pcb footprint and pin orientation against the device data sheet
I would not worry about the pin function assignment, passive that just for some electrical rules checking.
I do not use kicad so I can only speak in ecad general terms and usage.
One thing I have learnt over the years do not trust the generic libraries in the ecad toolset distribution, everything needs verification.

So I have finished to reproduce the schematic of both Figures 9.20 and 14.17 of Bob Cordell book "Designing Audio Power Amplifiers, Second Edition" into one page. But I have some questions...

My schematic is attached as a PDF file below. Please be aware that except when specifically noted in italic and underscore, I do refer to my own parts naming in all the questions below.

  1. I am not sure if R8 (220 Ohms) and C2 (100 pF) are part of the VAS or part of the OPS section? In the book, they are draw in Figure 9.20 with a box label BIAS, but the details of the BIAS box are on Figure 14.17 with two unconnected wires above R31 and below R33 of Figure 14.17 . Also, I am not sure I did the right connection of the R8 node. Is it attached to the lower part of the variable resistor? Cause this is not clear when you refer to Figure 14.17, the R8 resistor is not represented.
  2. In Figure 9.20, the +Vrail and -Vrail have a label +55V and -55V respectively. Although reading back the book while writing this I noticed that the -Vrail doesn't have this -55V label but I have put both +55 VDC and -55 VDC in my schematic.These voltages are also labelled on Figure 14.17 as +55V @ load and -55V @ load. The two arrow pointing back to the VAS and IPS section in Figure 14.17, after both C10 and C12 respectively, must be to another lower voltage after the 10 Ohms resistors. But back in the Figure 9.20, the voltage are still at +55V and -55V as listed in the beginning of this paragraph. Does that mean that the rail wires of the VAS and IPS are connected before the 10 Ohms resistors directly to the rails as represented in my schematic version, or they are connected to the end of the arrows of Figure 14.17, rejoining C10 and C12 respectively?
  3. While creating my parts list, I tried to use WIMA MKS 2 Polypropylene capacitors but I wasn't able to find all values in this series. Is it a good choice to use something else, like MKP_4 or FKP_2 ? Here are my actual parts list:
  4. As for the Power of resistors, I am not sure what power I should expect for R506 and R606? They should see all the currents of the IPS and the VAS, right?
And if you find anything else I should be aware before starting the PCB, please let me know, as weel as any mistake I could have made myself :)


  • Figure 14.17.Rev1.0.pdf
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Corrections to the schematic PDF. The -15 VDC Zener and capacitor were inverted! Transistors Q303 and Q403 had their collector and base pins wrong. Fixed.
Sometime you only see this when you place the parts one beside the others. The logic pop-up!


  • Figure 14.17.Rev1.0.pdf
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Hi, I am reading the chapter on LTSpice. Man! This tool is amazing. I have little experience with the simulator of my preceding software gEDA, but this one has much more features.
Now, I use Linux at 99% of the time but I have a Windows partition on my computer. LTSpice is only available for Windows and Mac. I installed it and started using it in Windows in parallel to reading the book chapter on the subject.
But yesterday I discovered that my KiCad software also has a simulator in witch I can choose the LTSpice compatibility. Unfortunately, it does understand some of my actual drawing parts.
So I am wandering if the original HAFLER 200 schematic is already available as a LTSpice schematic. It would be much easyer for me to start with it and make the change for my parts before simulate the circuit.
Any link for it?
Thanks in advance...
I have achieved a lot since my last post. First, I found a ton of LTSpice libraries compatibles with my KiCad software under Linux. Here is the link...

Second, and the most beautiful thing, I don't have to redraw the schematic to use the simulator. I only have to add three Simulator components; 2 DC voltage sources and one AC voltage source.

Third, I found one library that had the two LSK489 and LSJ689 JFET. Here is the link:

But now, when I try to run the DC simulation, I get this error message and I cannot figure why I got it (if we pass over all the warnings for now):

Note: Compatibility modes selected: lt​
warning, can't find model 'net-q206-pad5' from line​
jq206 net-r205-pad1 net-q204-pad1 net-q106-pad3 net-q206-pad5 net-q205-pad1 net-q106-pad7 lsj689a-ls​
warning, can't find model '<no_net>' from line​
jq? <no_net> <no_net> <no_net> <no_net> <no_net> <no_net> lsj689a-ls​
Circuit: KiCad schematic​
Warning: Model issue on line 10712 :​
.model d1n5240 d(is=1.953f rs=2.305 ikf=0 n=1 xti=3 eg=1.11 cjo=68p m=.3 ...​
unrecognized parameter (ibvl) - ignored​
unrecognized parameter (nbvl) - ignored​
unrecognized parameter (tbv1) - ignored​
Warning: Model issue on line 10737 :​
.model d1n5245 d(is=3.142f rs=3.536 ikf=0 n=1 xti=3 eg=1.11 cjo=80.5p m= ...​
unrecognized parameter (ibvl) - ignored​
unrecognized parameter (nbvl) - ignored​
unrecognized parameter (tbv1) - ignored​
Error on line 39 or its substitute:
jq206 net-r205-pad1 net-q204-pad1 net-q106-pad3 net-q206-pad5 net-q205-pad1 net-q106-pad7 lsj689a-ls
Unable to find definition of model net-q206-pad5
Background thread stopped with timeout = 0​
Error: no such device or model name​
Error: no such device or model name​
Error: circuit not parsed.​
My understanding is that the jq206 model has 6 nets listed above and that they correspond to each pin of the model, like this:

1(S) -> net-r205-pad1
2(D) -> net-q204-pad1
3(G) -> net-q106-pad3
5(S) -> net-q206-pad5
6(D) -> net-q205-pad1
7(G) -> net-q106-pad7

Is if it doesn't see the connection between Q206-pad5 and R206-pad2. When I play with them, trying to redo the connection, I got the same error excepted that it complain with:

Unable to find definition of model net-r206-pad2

What do I miss ??