VSSA Through-Hole-PCB build thread - Page 2 - diyAudio
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Old 28th October 2013, 03:03 PM   #11
PMI is offline PMI  United States
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Originally Posted by jkuetemann View Post
@ PMI - I suppose the inclusion of these options was the reason for the 'encouragement' to take this off the PeeCeeBee thread?
Yes, that, and the fact that even though there is just one circuit layer, the board is not strictly speaking a single-layer design, with plated holes, and solder mask top and bottom. However, it can still be built with close to the original PeeCeeBee schematic, at the lower supply voltages.
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Originally Posted by jarkaa View Post
I´ve had my peeceebee running for few months now and I have new pcb with css option on a drawing board also...
Looking forward to seeing it!
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Originally Posted by JOHN BALI View Post
...
Pete maybe will buy some Alfets & I might join with him
Trying to get to it. I have almost finished testing the version with the top-side VAS transistors. I think I would like to use the ALF08N/P pair for the version with VAS on the main heatsink.
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Originally Posted by Bonsai View Post
Very nice looking layout PMI!
Thank you, I am gradually working my way up to your standards...
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Old 28th October 2013, 04:23 PM   #12
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Originally Posted by PMI View Post
I should take this one first...
....
You also need a reasonably clean supply, 45V with lots of ripple on top will be a no-go.

I actually look forward to some discussion about components, power dissipation, etc. in this thread. I tried to start some in the PeeCeeBee thread and did not get far.
Yes the component selection is good start...
1. I see some other CFA-amp use 2-3watt feedback resistor
see NX-amp by Bonsai
now where I can find these dale resistor
so 0.5watt is minimum if we go for higher supply (this what I thought).

2. Input cap must be there, I've omit it & blew some 10 ohm resistor because I play to much bass .
But I don't think that electrolyte the one you used is good enough, we need more option here. Big film caps also may act like an antenna...

3. 10ohm resistor dissipation (also on the zobel)

4. I'm curious what the sound with & without 10uF decoupling caps

5. Try to change VAS to another type to see how much the difference, like Jason used...
or may I change to to-220 device (driver transistor actually but easier to find) & what will happen...

Pete, sorry cos so many thoughts
more to come...

Regards
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Old 28th October 2013, 05:24 PM   #13
PMI is offline PMI  United States
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Originally Posted by JOHN BALI View Post
Yes the component selection is good start...
1. I see some other CFA-amp use 2-3watt feedback resistor
see NX-amp by Bonsai
now where I can find these dale resistor
so 0.5watt is minimum if we go for higher supply (this what I thought).

2. Input cap must be there, I've omit it & blew some 10 ohm resistor because I play to much bass .
But I don't think that electrolyte the one you used is good enough, we need more option here. Big film caps also may act like an antenna...

3. 10ohm resistor dissipation (also on the zobel)

4. I'm curious what the sound with & without 10uF decoupling caps

5. Try to change VAS to another type to see how much the difference, like Jason used...
or may I change to to-220 device (driver transistor actually but easier to find) & what will happen...

Pete, sorry cos so many thoughts
more to come...

Regards
The 2.2K feedback resistor was fine at 1/4 watt, up to 35V supply voltage. Probably up to 45V, because it does not see a continuous signal at high power, just during peaks. There are some better resistors one can use, low noise, higher power, same lead spacing. I am not planning on anything bigger than 1W here.

There are extra pads for bigger input caps, up to 15-mm. The Nichicon bi-polar electrolytic works well, and for testing, good enough.

The Zobel is split, so you can use two resistors. Pad spacing is also wider.
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Old 28th October 2013, 05:40 PM   #14
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Hi Pete,

Is there a schematic that matches your layout that you could post or link to? As you know I am very much in the learning stage and I would like to try to understand how the ccs works in the circuit.

Thanks, Terry
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Old 28th October 2013, 06:10 PM   #15
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Originally Posted by still4given View Post
Hi Pete,

Is there a schematic that matches your layout that you could post or link to? As you know I am very much in the learning stage and I would like to try to understand how the ccs works in the circuit.

Thanks, Terry
The schematic needs some cleanup, and some component values have to be updated. It will be posted here when I am done testing. The CCS works the same as the one shown in V1.4 of Lazy Cat's schematic. It takes the place of the resistor which has been variously posted as 15K, 18K, etc. in the other thread. It keeps the current close to constant ~2 mA over a wide range of supply voltage. You can just google "Jfet CCS" there are plenty of detailed examples and explanations, much better than anything I can post.

Since I know you have a Variac to test with, you can try changing your supply voltage up and down 10% or so, and measure the VAS current. You will probably observe that it varies with the supply voltage more than one might expect. With the CCS, mine stays pretty close to the 12-13 mA, where I set it.
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Old 28th October 2013, 07:18 PM   #16
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Sent ya PMs PMI. SOrry for the delay on the cap multis stuff. Want 6 of these as well if ya got 'em!!
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Old 28th October 2013, 08:13 PM   #17
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Originally Posted by PMI View Post
The latfets clip as close as 3V below the rail (tested). 100W is clearly specified in LC's documentation for VSSA, with one TO-264 package, and 45V rails. So, if you have a correctly rated heatsink, and manage to keep two devices cool, it should do just fine.

You also need a reasonably clean supply, 45V with lots of ripple on top will be a no-go.

I actually look forward to some discussion about components, power dissipation, etc. in this thread. I tried to start some in the PeeCeeBee thread and did not get far.
Thanks for that explanation. Looking at the SOA graph for the ALF08N, it seems that ~100W is around the limit for a single pair. Do you need some sort of current limiting to drive 4R loads to peak power with 45VDC rails?

Has there been any discussion about doubling the OPS to 2 pairs?

Last edited by Ranchu32; 28th October 2013 at 08:15 PM.
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Old 28th October 2013, 09:57 PM   #18
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Originally Posted by Ranchu32 View Post
Thanks for that explanation. Looking at the SOA graph for the ALF08N, it seems that ~100W is around the limit for a single pair. Do you need some sort of current limiting to drive 4R loads to peak power with 45VDC rails?

Has there been any discussion about doubling the OPS to 2 pairs?
Can't use a single pair at 45V into 4 ohms. Not as it stands. You have to lower the voltage. You might be able to use the double-die TO-264 ALF16. The dies are matched at the factory when they put them in the package. Have not tried that yet, it will most likely need some other component value changes. It will be more difficult to mount on the heatsink, because the mounting hole will be just outside the board outline.

Yes, two pair has been talked about, in the PeeCeeBee thread, and a layout has ben posted by Shaan. John Bali is working on one.
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Old 28th October 2013, 10:01 PM   #19
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What would you recommend as a suitable max into 4R? About 35VDC?
Would be interested in some boards if you end up doing a run. Interesting to compare with LC's VSSA amp, which I have almost completed and will post details in his thread soon.
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Old 28th October 2013, 10:48 PM   #20
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Originally Posted by Ranchu32 View Post
What would you recommend as a suitable max into 4R? About 35VDC?
Would be interested in some boards if you end up doing a run. Interesting to compare with LC's VSSA amp, which I have almost completed and will post details in his thread soon.
30~35V into 4 ohms, if you want to stay safe, but you could push it quite a bit, if you wanted to. With care, you can make some assumptions about the average current, and calculate back from that. most people want the extra power for dynamic range, not to blast out a continuous 1KHz sine wave at maximum power (chuckle).

edit:

I am planning on making a couple small board orders, and for now I am just keeping a list of interested people.

Last edited by PMI; 28th October 2013 at 10:51 PM.
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