Another thing to consider is driver junction temp. If I run a sim at 1/3 power (20W at 8R load), the drivers dissipate around 120mW.
I start the sim with the drivers and output devices at 25C and set the bias at 50mA.
If the drivers do not have heatsinks, their junction temp rises to around 50C and bias rises to 188mA
If I use a 7.5 °C/W heatsink (like Aavid 531202B02500G), their junction temp rises to only 30C and bias rises to 79mA.
Now, running a sine wave 1/3 power is pretty tough and likely harder than anyone would run it it real life (if you want to keep your hearing), but it does illustrate that keeping the drivers cool helps with bias stability
I start the sim with the drivers and output devices at 25C and set the bias at 50mA.
If the drivers do not have heatsinks, their junction temp rises to around 50C and bias rises to 188mA
If I use a 7.5 °C/W heatsink (like Aavid 531202B02500G), their junction temp rises to only 30C and bias rises to 79mA.
Now, running a sine wave 1/3 power is pretty tough and likely harder than anyone would run it it real life (if you want to keep your hearing), but it does illustrate that keeping the drivers cool helps with bias stability
ZTX also has some nice tiny through hole transistors for that place. Anyway i understand your point but because i have better option available i didn't think about 1W types. If you can remember, once very popular DIGI-125 also used BC556 for it's VAS. Btw what is the best approximate value of so called "speed up" capacitor across the bias tr Q9 ? I think it depends on used active components & layout.
I don't think the value of the cap is critical. Anything in the 100n to 220n is commonly used. However, some design will put this in the 10u to 47u range. From what I've read on this, there's doesn't seem to be a lot of consensus on how to size this.
Maybe some far more knowledgeable than me can chime in.
Maybe some far more knowledgeable than me can chime in.
I don't want to build (not even possible..) every amplifier in this galaxy, so i picked couple of design on various topology. P3A is one of them. I have read extensively about it. But as you know it's very hard for amature enthusiasts to possess Exotic components like low noise Ksa992, so for LTP I have no choice other than BC546 (which is fine I guess, although i've 2n5551 but pinout is different. I think BC546 has the edge here because of it's lower VCE). Fortunately I have some excellent transistors for VAS stage. Rest is as Rod recommends, BD for drivers & MJL or TIP for outputs. Because of the nature of CFP I bought medical grade multi-turn Bourns trimmer from RS otherwise normal single turn fat blue trimmers are my go to choice but I thank you for the suggestion on Driver temperature. I'll keep that in my mind.
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What do you mean by exotic KSA992? In the US, they are readily available from Mouser and DigiKey for $0.37 each. Buy 10 and they're $0.27 each. This is why I suggested them - easy to source and cheap. BC546 for example is $0.33 at DigiKey. The BD140 that is recommended for this position is $0.72 - nearly twice the price.
I'd also suggest building with the BD140 first. A part know to be stable with this design. Then try different components and see if you like the change. And if you encounter stability issues, then you know its likely due to the parts change.
By exotic i meant their characteristics & the only good source of ksa992 i have is RS COMP but minimum order quantity is high (& when i buy such transistor i buy in pair). I thought when i have hundreds of genuine Fairchild BC546/56 why buy another type? I also have Fairchild KSA1381 (only pnp part) which you mentioned earlier as well as Sanyo 2SA2911 for voltage amplifying stage. For drivers BD139/40 from ST. So i have everything required for a 1st class P3A except time & intention. But as of now I'm happy with my LM3886 set up 🙂
Best Regards
Does it matter who's BD139/140 I use?
Mouser has On Semi/Fairchild or STM
It would make sense to me to use the On Semi/Fairchild since I'm using On Semi/Fairchild Outputs.
Mouser has On Semi/Fairchild or STM
It would make sense to me to use the On Semi/Fairchild since I'm using On Semi/Fairchild Outputs.
I noticed that the On Semi, non-fairchild branded BD139/140 are available in a T0-220 package.
Would it be adventageous to use the higher power package?
Would it be adventageous to use the higher power package?
Finally, I found the board , please ignore the dust on the components....
I used mje15034/35 and bd140 for Q5. mjl21193/94 for q7 and q8.
This worked fine , no complains.
I used mje15034/35 and bd140 for Q5. mjl21193/94 for q7 and q8.
This worked fine , no complains.
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H
HAYK
I tried on simulation ksa1381 for VAS with very good result.
https://www.diyaudio.com/community/...rossover-p3a-of-rod-elliot-as-example.402148/
https://www.diyaudio.com/community/...rossover-p3a-of-rod-elliot-as-example.402148/
Input. Bc550c
Vas driver . 2sa1145 Y
Driver. Tta004b ttc004b
Bias. Tta004b
Output. Sanken 2sa1216 2sc2922 Y.
Works great too in real life,
Vas driver . 2sa1145 Y
Driver. Tta004b ttc004b
Bias. Tta004b
Output. Sanken 2sa1216 2sc2922 Y.
Works great too in real life,
Version 2.3
I reversed the wiring on the trim pot so that the turns go in the correct direction.
Tidied up the labeling to how I like it
Nobody seems to have any negative feedback on the layout so I think I will stare at it for another hour to make sure I'm happy and then place the order.
I reversed the wiring on the trim pot so that the turns go in the correct direction.
Tidied up the labeling to how I like it
Nobody seems to have any negative feedback on the layout so I think I will stare at it for another hour to make sure I'm happy and then place the order.
It doesn't matter, what is matter is the spec. ST is an European giant, has good reputation for their products.
MJE150XX series is like a tank! You don't need such transistors for P3A, also their collector to base capacitance probably higher than the to-126 BD139/40.
CDIL from India also make the BD139/140. and many other classic transistors. They are cheap, and as far as I have experienced they are good. I can buy them in Europe, don't know if they are distributed in the USA.
When you use progressive power supply caps, you usually use RC filters. Like 1R or 2R for the drivers and 10R or 20R for the Ips/Vas. You have the caps but no resistors