Yes, the chassis is quite heat efficient. I used the same chassis for my Aleph-J, which is running at 200 W idle dissipation. It's no problem to keep my hands on it for as long as I want.
Arranging the PSU transformer, 2 x Smooth Like Buttah boards, 2 USSA-5 boards, 2 x DC protection boards, etc. all into this chassis is going to be a 3D Lego challenge. It's going to be tight in there! Let's see how this works out... I have ordered parts, and it will be a while until I can get this going.
Any recommendations on input coupling caps with a low profile? 20 mm height / diameter would be great.
Arranging the PSU transformer, 2 x Smooth Like Buttah boards, 2 USSA-5 boards, 2 x DC protection boards, etc. all into this chassis is going to be a 3D Lego challenge. It's going to be tight in there! Let's see how this works out... I have ordered parts, and it will be a while until I can get this going.
Any recommendations on input coupling caps with a low profile? 20 mm height / diameter would be great.
Indeed that is quite a challenge to fit all that.
For input coupling cap, the one mentioned in the BOM is surely not bad. However I know other builders have used many different caps but sometimes quite big....
I hope some peoples will jump in for a good input cap meeting your indicated size profile
Polypropylene cap is in general most appropriate.
There is also the no cap option but this is not my preference if you are not sure your connected source is always free of DC...
At least the feedback cap prevents the amplification of DC presence.
Fab
For input coupling cap, the one mentioned in the BOM is surely not bad. However I know other builders have used many different caps but sometimes quite big....
I hope some peoples will jump in for a good input cap meeting your indicated size profile
Polypropylene cap is in general most appropriate.
There is also the no cap option but this is not my preference if you are not sure your connected source is always free of DC...
At least the feedback cap prevents the amplification of DC presence.
Fab
Last edited:
Question about the input transistors. The BOM states:
Q1, Q4: NPN BC547C OR B (OR BC550x) x:B or C (C is better)
Q2, Q3: PNP BC557C OR B (OR BC560x)
I don't have the background why these particular parts were chosen for the USSA-5, so I wonder if BC547/BC557 are preferred over BC550/BC560? My parts order is stuck because BC547C+BC557C are out of stock. I could replace them with BC550C+BC560C or look elsewhere for BC547C+BC557C.
What do you think?
Q1, Q4: NPN BC547C OR B (OR BC550x) x:B or C (C is better)
Q2, Q3: PNP BC557C OR B (OR BC560x)
I don't have the background why these particular parts were chosen for the USSA-5, so I wonder if BC547/BC557 are preferred over BC550/BC560? My parts order is stuck because BC547C+BC557C are out of stock. I could replace them with BC550C+BC560C or look elsewhere for BC547C+BC557C.
What do you think?
Argh! I can't find a supplier that has 550C+560C or 547C+557C (except China parts from eBay, but lets not go there). It seems these parts are getting scarcer these days...
I also forgot the trimmers P1, P2, P3 and P4 (Bourns 3299W-1-102 and 3299W-1-103) in my last order, so I will add those to my next Mouser order. It would be cool if I could add the input transistors to this order too -- however Mouser (and the other big suppliers) don't have the BC547C/550C+BC557C/560C parts. What would be suitable modern replacements that are available from Mouser etc.?
I also forgot the trimmers P1, P2, P3 and P4 (Bourns 3299W-1-102 and 3299W-1-103) in my last order, so I will add those to my next Mouser order. It would be cool if I could add the input transistors to this order too -- however Mouser (and the other big suppliers) don't have the BC547C/550C+BC557C/560C parts. What would be suitable modern replacements that are available from Mouser etc.?
It seems that C grade HFE is harder to get in the P type. But, as the manual indicates you can use B grade HFE instead and it would be without noticeable effect ( C is only better in theory). Digi-Key has many thousand units of 547B/557B. BC546B/556B is the higher voltage version and can also be used. Finding a replacement to this BC transistor in the circuit is not a simple task and could be done in case of obsolescence but it is not the case.
Fab
Fab
Last edited:
The other ones (A992) you previously mentioned are good but not as good as the BC for the linearity.
A970 has an excellent linearity comparable to the BC but pin out is reversed. For transition frequency it is 100Mhz instead of 300Mhz but this is still acceptable.
Fab
C grade BC transistors have higher HFE then more gain thus with local feedback applied the resulting local feedback factor is slightly higher for the input stage. However, grade B has already a high HFE compared to many other small signal transistors. And most important this BC transistor is very linear over a wide range of operating current.
Fab
Fab