Hi potstip
I could not locate the smd equivalent. I found the BC850/BC860 but according to datasheet linearity is not as good as the BC550/560. 250mW is sufficient for this application.
Edit: I found another manufacturer datasheet of the BC850/BC860 which shows a more comparable gain plot against the BC550/560. The C grade appears more linear at 3ma than the B grade...
That are still a bit different but possibly suitable.
Fab
I could not locate the smd equivalent. I found the BC850/BC860 but according to datasheet linearity is not as good as the BC550/560. 250mW is sufficient for this application.
Edit: I found another manufacturer datasheet of the BC850/BC860 which shows a more comparable gain plot against the BC550/560. The C grade appears more linear at 3ma than the B grade...
That are still a bit different but possibly suitable.
Fab
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Thanks.
It seems every company stops manufacture pnp transistor day by day. No active manufacturer for 560c and for 860c nexperia is the only active one.
I attached the datasheets. Which graphic you look for linearity hfe vs dc current? (they dont seems apple to apple to me)
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Your BC560C datasheet is showing a different gain vs IC current curve than the one from the datasheet shown at Digi-Key distributor site -which shows a very flat curve for Hfe. In fact, I searched again tonight and have found 2 other BC560 datasheets showing different results but in different VCE conditions or temperature. Therefore at this point I can’t really confirm if the BC860C is better or worse than the BC560C.... They might be similar but I would suggest the same as I have indicated previously to use the BC548/558 B grade instead since they are TO-92 package that fit into the pcb. The later transistors are available at DIGI-Key At this moment and they work perfectly in this circuit.
Fab
Fab
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You mean USSA5 version 5B with bjt as output ?
If you look at USSA3B thread I haved switched between 2SC/2SA and MJL and found slightly better THD figure with the MJL. However, I have not investigated more to see if it was due to higher HFE of my specific transistors used....The MJW1302/MJW3281 are supposed to be even better according to simulation model findings from another thread.
No idea what the (Q) means but I suppose it is not related to performance.
Fab
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Thanks all - here is the reference to ‘Q’
2SC5200-O(Q) Toshiba Semiconductor and Storage | Discrete Semiconductor Products | DigiKey
Plenty of stock of MJW1302/MJW3281 (newer lead free version) as suggested, so since these are compatible with the design I’ll buy them.
Any feedback on the resistor tolerance - is it worth specifying better than 1%
2SC5200-O(Q) Toshiba Semiconductor and Storage | Discrete Semiconductor Products | DigiKey
Plenty of stock of MJW1302/MJW3281 (newer lead free version) as suggested, so since these are compatible with the design I’ll buy them.
Any feedback on the resistor tolerance - is it worth specifying better than 1%
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OK I will reply even though others have different views on resistor selection and will argue.
For power amps 1% is generally fine. If you like, you can match the resistors with the same value on the "positive" side to the "negative" side of an amp. In this amp I do not think that this is critical. Fab can confirm.
I generally use Vishay CMF or RN metal film resistors because Vishay uses good quality materials to make their resistors. Those cheap 0.5W or 0.6W resistors use impure recycled material and cannot be used anywhere near their rating.
Also Vishay do not use steel end caps in this series, so they are not attracted to magnets. That is important to *me*.
Other alternative brands are PRP, Takman, Shinkoh etc.
For surface mount Susumu, Vishay thin film or Vishay Melf.
Now to really annoy a few of you.... I don't like carbon composition or metal oxide resistors.
For power amps 1% is generally fine. If you like, you can match the resistors with the same value on the "positive" side to the "negative" side of an amp. In this amp I do not think that this is critical. Fab can confirm.
I generally use Vishay CMF or RN metal film resistors because Vishay uses good quality materials to make their resistors. Those cheap 0.5W or 0.6W resistors use impure recycled material and cannot be used anywhere near their rating.
Also Vishay do not use steel end caps in this series, so they are not attracted to magnets. That is important to *me*.
Other alternative brands are PRP, Takman, Shinkoh etc.
For surface mount Susumu, Vishay thin film or Vishay Melf.
Now to really annoy a few of you.... I don't like carbon composition or metal oxide resistors.
That is correct. Most important is temperature stability (low temperature coefficient) so the nominal value stay nominal
. Metal film suggested part in the BOM has a TC of <=100ppm/degC. 1% tolerance is good enough.Fab
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Hi
I suppose you mean temporary accidental « short circuit ». In the latter case the said « short « is not really 0 ohms but more a bad contact resistance range value thus limiting the current in output transistors and since accidental then for a short duration. Remember that this is the heat that damages the part and heat increase is relatively not fast....
By experience the lateral mosfet is quite resistant for bad contact shorts even for a few seconds provided you have a good heatsink dissipation capability. Therefore, as other lateral mosfet amplifiers in normal home installation you should not need additional protection than the diodes at gate of mosfet.
For the bjt output version there is no base protection and more quickly susceptible to damage in general due to “shorts”. In many amplifiers there would be usually a sensing circuit on the emitters of both the output transistors in the follower (common collector) configuration. However, in the USSA bipolar output version it is not a follower version and a sensing circuit would be needed for each output transistor. The pcb does not include it but you have the test points that can be used to install a circuit outside of the pcb. For example, a circuit could be an optocoupler circuit triggering a short on the load of the input stage giving no base voltage for the output transistors....
The PASS F5 schematics provides an over current circuit using transistors parts.
But since it is Diy and not commercial Diy I guess we can live with that
Fab
I suppose you mean temporary accidental « short circuit ». In the latter case the said « short « is not really 0 ohms but more a bad contact resistance range value thus limiting the current in output transistors and since accidental then for a short duration. Remember that this is the heat that damages the part and heat increase is relatively not fast....
By experience the lateral mosfet is quite resistant for bad contact shorts even for a few seconds provided you have a good heatsink dissipation capability. Therefore, as other lateral mosfet amplifiers in normal home installation you should not need additional protection than the diodes at gate of mosfet.
For the bjt output version there is no base protection and more quickly susceptible to damage in general due to “shorts”. In many amplifiers there would be usually a sensing circuit on the emitters of both the output transistors in the follower (common collector) configuration. However, in the USSA bipolar output version it is not a follower version and a sensing circuit would be needed for each output transistor. The pcb does not include it but you have the test points that can be used to install a circuit outside of the pcb. For example, a circuit could be an optocoupler circuit triggering a short on the load of the input stage giving no base voltage for the output transistors....
The PASS F5 schematics provides an over current circuit using transistors parts.
But since it is Diy and not commercial Diy I guess we can live with that
Fab
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If you are worried about DC getting on the speaker terminals of the amp, consider buying a speaker protection board/relay from ebay and installing it in the amp. If you have expensive speakers with drivers that cannot be economically sourced from a speaker supply house, or have older speakers where the drivers are not available, it makes sense to protect them from possible mishaps with DIY amplifiers.