Krill - The little amp that might...

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#521
The servo should be implemented as an inverting stage for best performance.
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I don't agree.
I think that the non-inverting offers better performance.
It allows both pre and post filtering as well as the integrating function.

The Thread started by DX and mostly contributed by Gootee:
http://www.diyaudio.com/forums/showthread.php?postid=1283350#post1283350
has a lot of useful info and a sim of various inverting and non-inverting servos.
 
#524
Steve Dunlap said:
I did not claim that distortion was canceled, only reduced. I felt this was caused by the balance achieved just as with the trim pots.

Either version passes a square wave. I changed the time constant and added the input filter because of your comments.

I spent a fair amount of time thinking about what you said earlier, and you are correct on all points. The servo should be implemented as an inverting stage for best performance. The DC operating points were stabilized with the earlier version. The LDR may have been modulated at very low frequencies, but the resistor parallel with it insures that it will pass a square wave even if the LDR turns off.

The LDR does act like a LP filter and that explains why I didn't catch the modulation you pointed out in my measurements. The high frequency distortion measurements showed improvement. I never tested the low frequency distortion because it had always been very good. At high frequencies, the LDR was not responding and not modulating the signal.

No production units were ever built with the servo. I was still testing the original amp when my health went really fast. When I could no longer work, I withdrew into myself and gave up audio design - and pretty much everything else. It is nice to be back after 13 years. I have no doubt that AndrewT and others here will point out any other blunders I make.

I will rework the servo and post the changes.
Click to expand...
Thanks guys 🙂

Steve, would you be able to post a version of the 100 watt Krill with the DC Servo you recommend ...
🙂
 
#525
Hello,
went ahead with the assembly of the boards and have some questions:

-is it normal that both the 50W amp and the 100W amp have the same voltage gain?

-the space reserved on the board for many electrolytic caps (namely C3, C4, C15..C18) looks pretty small for the capacitance/voltage combinations required (5mm pitch, 13mm diameter for 470uF/100V or 330uF/160V).
The space for C19 and C20 is waay too small (how can I fit a 100uF-100V in a 5mm diameter space?).
Does this mean that the "old" monoblocks used different values?

Ciao

Andrea
 
#526
Hi,
many manufacturers who make a range of amplifiers often have the same gain for all of them. This allows a mixture or swap without changing anything else in the system and is particularly valuable if you were to use them for bi-amping (not active speakers).
eg.
you may have a 4 to 8ohm speaker that can be bi-wired.
Using the top quality 40W amplifier on the treble and the 120W (65W into 8ohm) for the bass/mid driver would work out the box.
 
#527
KLe said:

Thanks guys 🙂

Steve, would you be able to post a version of the 100 watt Krill with the DC Servo you recommend ...
🙂
Click to expand...


When I finish the new design for the servo (later today), I will post the 200W amp schematic again. The servo can be added to any of my amps exactly as it is in the 200W amp. Some resistor values will change. I will list the changes. I will eventually redraw the 50W and 100W amp schematics to include the servos.
 
#529
Andypairo said:
Hello,
went ahead with the assembly of the boards and have some questions:

-is it normal that both the 50W amp and the 100W amp have the same voltage gain?

-the space reserved on the board for many electrolytic caps (namely C3, C4, C15..C18) looks pretty small for the capacitance/voltage combinations required (5mm pitch, 13mm diameter for 470uF/100V or 330uF/160V).
The space for C19 and C20 is waay too small (how can I fit a 100uF-100V in a 5mm diameter space?).
Does this mean that the "old" monoblocks used different values?

Ciao

Andrea
Click to expand...

The Digi-Key part numbers for the 470uF and 330uF caps are in the spread sheet I made for the BOM. I will post that later.

The 470uF caps are 63V not 100V as shown in the schematic.

C19 and C20 are 10uF, not 100uf. Another correction to be made on the schematic. These caps can be either 63V or 100V. I have the 100V listed in the BOM. The Digi-Key part number is giver for these also.

If you can open an Excel spread sheet I will send you the BOM that way. All part numbers are links to the part from their supplier. E-mail me if you want the spread sheet.
 
#532
Here is the BOM for the 100W amp. The part numbers shown correspond to case sizes and lead spacings that fit the boards I am selling. Once I finish making the schematic match the board, I will post that again. I will also add the schematic designations to the BOM and re post it.
 

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#535
Here is the 200W amp with the new servo. I will add the servo to the 50W and 100W amp schematic at a later time.

I must say that I have not built this version of the servo and probably never will. I will be as much help as possible to anyone that does build it.

This servo simulates very well and gives results that are a little hard to believe. With real world parts the performance will be less, but still pretty good. I used TL072 op amps for the simulation and in the schematic.

If you plan to build this, I would recommend using the That 1200 line receiver for the differential amp. I will leave the choice for the integrator up tp you. Using the That 1200, you should be able to reduce the audio portion of the signal by 90dB before the integrator. I included the cap filter suggested by AndrewT. The output of the integrator shows an additional 55dB attenuation at 1Hz and with a slope of 6dB per octave (just as expected). Hopefully this will minimize modulation of the LDR.

You will want to use 1% or better resistors. The values shown are to set the input to the diff amp the same and selected for impedance match as seen by the inputs.

The file is still a pdf but I had to Zip it to get it to a postable size.
 

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#537
I have made, once again, the amplifier into the simulator

Have not build this last simulator product.... small adjustments into some resistances, very small adjustments, then i had much better results into analises and tone simulations.

So, despite i have failed into some earlier constructions (sounded excelent despite some off set) i see errors happened into my board.

My boards will arrive in a couple of days... already travelling internally in brazil and a friend will assemble the one to me, as i cannot be sitted for too long... if some problem happens i will make the debugging by myself.

Repeating... schematic is from Steve Dunlap.... small adjustment in resistances were made only!

Be happy... excelent amplifier folks!

regards,

Carlos
 
#539
post 535.
Is an opamp with a cap on the inverting input stable?
I think you can only do the input filter as shown when on the non-inverting input.

If you split the 1M0 and filter the junction of the two 510k, then I think it will work. But, the non-inverting still seems intuitively better.
 
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