2SC2240 versus 2SC1815??

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi Kim,
You'd want to use 2SC1815L rather than 2SC1815. the noise figure for the 1815 is 10dB and the 1815L is 3dB. This is slightly worse than the 2SC2240 at 2dB.
These are both very similar and cheap to buy. I've used both depending on the voltage applied. I really think the circuit will have more effect on the sound than either of these parts could.

I guess my answer to you is: what have you got on hand or, do you have a coin?

-Chris
 
Hey

Thanks both off you

I can see in the datasheet for 2SC1815L that it says 0.2dB noise figure its´s bit lower than 3dB, I dont´t know how big difference that will make in my circuit though.

Look at my messe:
Critics needed under solidstate.

There you can see my circuit with symmetrical folded back casode coupling.
Supply will be +-22V
Current in inputstage 3.5mA in each transistor, and 10mA in votage amplifier stage.
so 22V - Ure = 22V - 2.4V = 19.6V * 10mA = 196mW. I think thats to high for 2SC2240 in a cabinet
(50degrees celcius air inbox)
Thanks
 

janusz

Member
2004-10-05 9:45 am
Perth
2sc1815L vs 2sc2240

Hi Kimschips,

Specs for 2sc1815L are somewhat better than those for 2sc2240 so you can use the former in the input stage. I use 2sc2240 in my version of the Stochino amp as the input stage requires high voltage transistors.

In the VA stage, however, you need somewhat more powerful ones. You could use 2sc2235Y, if low output capacitance and Hfe are not crucial, or KSC1009G (very cheap but low capacitance and Hfe) or 2N5551 (low ouput capacitance but not so high Hfe).

The latter are used in the Stochino amp which is very fast (slew rate over 300V/us). When it comes to VA stages you have quite a choice of transistors including more powerful ones.

Cheers,
 
Thanks

But why do I need a more powerfull device than 2SC1815 in my voltage amplifier stage?

it´s only a preamplifier and with +-22V supply-> 200mW dissipation.

It´s very important with low capacitance and very linear Hfe transistors
transisors like 2sc4793 2sd1763 and 2Sa1606 sound awfull in voltage amplifier stage, the sound is "heavy" slow and cold but they are linear


Best regards
 
Hi Kimschips,
YOU told us in post 4 why you need to dissipate more power in the VAS. 196mw from a 300mw transistor in a high ambient temp is asking for trouble.
Even 1w would be better and Eline better still. All of these can have a small flag heatsink added for a slightly lower case temp.
There are 5w hivolt, hispeed & higain transistors available but the prices are much higher.
 
Hello helloo

You are right about bigger transistors can handle more dissipation. But I calculated 2SC1815 to be right in my voltageamplifier stage. look:
Inbox air temp 50degrees celcius (worst case)

Crystal temp (tj) is calculated like this for 2sc1815:

(tJ / Ptransistor) * watt dissipated in transistor)) + Ta surrounded temperatur celcius->
(125 / 400mW) * 196mW)) + 25gr celcius = 86.25degrees celcius which is fine because 2SC1815 can handle 125degree celcius (tj)
with Ta = 25degrees celcius

Calculated 2SC2240 will optain tj with 105degrees celcius-> to close to the transistors 125degrees tj.

AndrewT
There are 5w hivolt, hispeed & higain transistors available but the prices are much higher.

What kind off transistors are you thinking off here?
(I don´t care with price I only wnat the best components)
Best regards

Kim
 
Hey

I wrote something wrong in my last post.

My calculation are for crystal temperatur in a transistor "placed" in a box which have an air temperatur at 50degrees celcius.
And because datasheet says maximum ratings with 25degrees that´s is why i add 25degree temp.

If air temp is 75degree add 50degree instead off 25 and so on

Best regards
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi Kim,
You are running them too darned hot. Over time the solder will recrystallise and the transistors will become noisy. Try to run these as cool as you reasonably can. If you don't believe me, open an older Harmon Kardon and tell me what you find.
You will find in any low noise / high reliability application, the parts are run cool. Sometimes with a fluid bath heatsink system for the inputs.
-Chris
 
Hi Kimschips,
sorry it took so long to get back, now got data to hand.
look up these 2sa types, I'm sure you'll find something that suits. Many are video drivers, & I suspect best gain will be by selecting lowest voltage and lowest power rather than choosing the highest specs.
1110, 1142, 1209, 1360, 1405, 1406, 1407, 1380, 1538, 1539, 1775, 2sc2590. haven't found a complement to that one.

I second the running cool, try to keep case temp below 50degC and junction temp below 70degC. and the cooler the better.
 
Hey

Thank you both.

Anatech you are right about to driving transistors to hot breaks them down fast.
I just calculated a worst case temp if the preamplifer is placed in a closed shelf you know.

AndrewT thats are very fine transistors, I use 2SA1407 (voltage amplifier) and 2SA1360 (predriver) in my power ampliefier

I am now using 2SA1360 and 2SC3423 in my voltage amplifier they are ok, I think there a better with IC = 10mA) and more linear.

Anyone tried BFN18 (smd)

Best regards