Not that simple (sorry). Most axial resistors are specified as 1/2W, and they have to fit a 0.5", or 12.5-mm spacing. I suspect 1/4W would work in some cases, but I would have to look at the circuit for each substitution made (too much time). The feedback resistors were recommended as 1/2W low noise. There are also some wire-wound resistors, some vertical power resistors, thick-film SMD resistors in different power ratings... not an easy BOM to sort out.
Thanks PMI,
I haven't looked at the BOM yet as it seems so much is in flux and many things are not settled yet. I'll wait awhile before I order any parts and see if any significant changes for the better happen or just availability makes the choice for us. Chasing unobtainium parts can be a real drag!
I haven't looked at the BOM yet as it seems so much is in flux and many things are not settled yet. I'll wait awhile before I order any parts and see if any significant changes for the better happen or just availability makes the choice for us. Chasing unobtainium parts can be a real drag!
No need to use hard to find low noise carbon film 1/2W, as Bonsai did, it's OK to use normal metal film 1/2 W instead. Also, it's possible to use normal 1/2W carbon film. Bonsai's pcb has resistor footprints for normal 1/2W carbon film for flexibility, it has enough space for them because they are bigger, but you don't have to use them, smaller 1/2W metal film are OK, as well as 1W metal oxide, which are same size as 1/2W metal film.
The Fairchild KSC3503ESTU is around $0.80-$0.90 in q 100-250 pieces, on cut tape, which in my opinion means there is reasonable assurance these are not rejects (but only until I change my mind, of course). US Source, repair stock.
Not sure I understand how price is calculated, there is an internal charge, plus the incremental piece price which makes up the per piece cost. After shipping twice, ~$1, give or take pennies. KSA1381E not available from same source, reason being it is still an active part available from distributors.
Fairchild KSA1381ESTU at Mouser, costs are as follows:
1: $0.47
10: $0.315
100: $0.176
1000: $0.131
So, assuming 100 pieces, cost per pair would be around $1.20 plus shipping. I do not have much more to contribute to the component discussion at this time.
I will leave it up to someone else to decide what is the best solution here. I am not really leaning one way or another.
(long time on the phone today, it is after 5 pm somewhere, and I intend to take my cue from that...
)
Not sure I understand how price is calculated, there is an internal charge, plus the incremental piece price which makes up the per piece cost. After shipping twice, ~$1, give or take pennies. KSA1381E not available from same source, reason being it is still an active part available from distributors.
Fairchild KSA1381ESTU at Mouser, costs are as follows:
1: $0.47
10: $0.315
100: $0.176
1000: $0.131
So, assuming 100 pieces, cost per pair would be around $1.20 plus shipping. I do not have much more to contribute to the component discussion at this time.
I will leave it up to someone else to decide what is the best solution here. I am not really leaning one way or another.
(long time on the phone today, it is after 5 pm somewhere, and I intend to take my cue from that...
)
PMI,
Thanks for doing all that hunting and searching and showing the prices. I am waiting until there is an official decision made here on the direction this build is going to take. Perhaps then it would be wise to make a group buy of the chosen transistors at least the ones you just found that are not easily available. I would have hoped for a modern tranny that would be available later and not something that we may get one time and then have to go through the whole process again to find a satisfactory part. If those are the selected transistors then I would be willing to put in let's say $35.00 towards a batch of them so I have more matched pairs for later projects.
Thanks for doing all that hunting and searching and showing the prices. I am waiting until there is an official decision made here on the direction this build is going to take. Perhaps then it would be wise to make a group buy of the chosen transistors at least the ones you just found that are not easily available. I would have hoped for a modern tranny that would be available later and not something that we may get one time and then have to go through the whole process again to find a satisfactory part. If those are the selected transistors then I would be willing to put in let's say $35.00 towards a batch of them so I have more matched pairs for later projects.
On the question of resistors couldn't we parallel two 1/4 watt resistors and by careful selection have very good precision in those position that is required?
The vertical power resistors are Ohmite 7 W types from Mouser or Digikey. I used these because I have a big stock of 0.33 Ohms, and I have found them to be very reliable.
The 4.7 Ohm gate stoppers are SMD thick film 2512 types from Mouser. I don't recall the brand, but Xircon, Panasonic, Yageo are all OK.
Spacing for the 0.5 Watt metal film resistors is indeed 12.5 mm 0.5 "
The most critical devices are:-
R12-R16 2.7 k feedback resistor
R28, R29 and R11
Use good quality low TC types in these positions.
I will add resistor part numbers to the BOM when I update it.
The 4.7 Ohm gate stoppers are SMD thick film 2512 types from Mouser. I don't recall the brand, but Xircon, Panasonic, Yageo are all OK.
Spacing for the 0.5 Watt metal film resistors is indeed 12.5 mm 0.5 "
The most critical devices are:-
R12-R16 2.7 k feedback resistor
R28, R29 and R11
Use good quality low TC types in these positions.
I will add resistor part numbers to the BOM when I update it.
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Kindhornman, the resistors I used are standard 0.5 W types from Mouser and DK. The only special ones are the DALE types - I used these because they are low noise, low voltage coefficients types.
For the PSU circuit U2 is listed as PDTC144ET in the schematic and bill of materials. The PC board silkscreen says PDTC143ET. Which is correct?
Let me conform test back to you when I get home later today. Thanks for catching this.
The Fairchild KSC3503ESTU is around $0.80-$0.90 in q 100-250 pieces, on cut tape, which in my opinion means there is reasonable assurance these are not rejects (but only until I change my mind, of course). US Source, repair stock.
Not sure I understand how price is calculated, there is an internal charge, plus the incremental piece price which makes up the per piece cost. After shipping twice, ~$1, give or take pennies. KSA1381E not available from same source, reason being it is still an active part available from distributors.
Fairchild KSA1381ESTU at Mouser, costs are as follows:
1: $0.47
10: $0.315
100: $0.176
1000: $0.131
So, assuming 100 pieces, cost per pair would be around $1.20 plus shipping. I do not have much more to contribute to the component discussion at this time.
I will leave it up to someone else to decide what is the best solution here. I am not really leaning one way or another.
(long time on the phone today, it is after 5 pm somewhere, and I intend to take my cue from that...
I'll take 20pcs KSC3503 ESTU from repair stock.
Bill_P
The correct part number is PDTC144ET
This is a NPN 100mA 47k RET (both the series current limiting and pull down resistors are 47k)
I have corrected the PCB component indication.
The correct part number is PDTC144ET
This is a NPN 100mA 47k RET (both the series current limiting and pull down resistors are 47k)
I have corrected the PCB component indication.
For the 0.33 Ohm power vertical resistors: They are Ohmite part #
TWW5JR33E
Here is the link to the Mouser Catalogue with all details:-
TWW5JR33E Ohmite | Mouser
Note - Mouser say they only have 143 in stock and lead time is 18 weeks - so I'd order quickly.
Newark/Element 14 have 600 in stock - but its not normally stocked
TWW5JR33E - OHMITE - RESISTOR WIREWOUND, 0.33 OHM, | Newark
For the 33 Ohm 2W wire wound resistors here is the Mouser catalog link
http://tw.mouser.com/ProductDetail/...VXvp%2biPirOpwtzDjAweWplESSCNuaOyquGAsNsxJA==
They say they have 15700 in stock.
Note: These are 5W resistors, not 7 W as I said earlier on
For all of the other thru hole plated resistors, except for the feedback resistor (see below) I used Xicon from Mouser. These are stock standard 0.5W 50ppm 1% resistors. If you can afford or want to use better types, then you can just make sure that dimensionally they will fit in the board. here is the link to the 10k Xicon 0.5W resistor for your reference:-
http://tw.mouser.com/ProductDetail/Xicon/273-10K-RC/?qs=sGAEpiMZZMu61qfTUdNhG/NICg4NOtz5wTWUkBCy22U=
TWW5JR33E
Here is the link to the Mouser Catalogue with all details:-
TWW5JR33E Ohmite | Mouser
Note - Mouser say they only have 143 in stock and lead time is 18 weeks - so I'd order quickly.
Newark/Element 14 have 600 in stock - but its not normally stocked
TWW5JR33E - OHMITE - RESISTOR WIREWOUND, 0.33 OHM, | Newark
For the 33 Ohm 2W wire wound resistors here is the Mouser catalog link
http://tw.mouser.com/ProductDetail/...VXvp%2biPirOpwtzDjAweWplESSCNuaOyquGAsNsxJA==
They say they have 15700 in stock.
Note: These are 5W resistors, not 7 W as I said earlier on
For all of the other thru hole plated resistors, except for the feedback resistor (see below) I used Xicon from Mouser. These are stock standard 0.5W 50ppm 1% resistors. If you can afford or want to use better types, then you can just make sure that dimensionally they will fit in the board. here is the link to the 10k Xicon 0.5W resistor for your reference:-
http://tw.mouser.com/ProductDetail/Xicon/273-10K-RC/?qs=sGAEpiMZZMu61qfTUdNhG/NICg4NOtz5wTWUkBCy22U=
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For the feedback resistors (these are the 2.7k R12-R16) I had available Dale CMF60 types, which I now see are not available on Mouser. I took particular care with these resistors since in a CFA the feedback resistor will dissipate quite a bit of power (you need to keep the value low as it forms part of the compensation). However, if you cannot find the Dale CMF60 types, I would go ahead and build with the Xicon - you can always update later on when they are available.
Here is a link to the mouser page where you can get high quality Dale resistors 0.5W from 2.49k to 2.8k
71-CCF60- Metal Film Resistors - Through Hole | Mouser
71-CCF60- Metal Film Resistors - Through Hole | Mouser
Other than the feedback resistors and high power resistors, does the dissipation exceed that of normal 1/4watt metal film resistors? I am asking because I want to try the nxAmp with through hole components on a single sided board which I designed a while ago. The changes I'd like to make now is to thermally couple the input transistors. Here is an image of the PCB. Thanks.
Attachments
4R7 base stopper resistors for output transistors are 1W. Other than that it seems that 1/4W resistors would suffice. Higher power 1/2W metal film resistors provide lower distortion and noise, if you want to keep it as low as possible.
Thanks, I did find the 2.74K (eventually) That link gives prices in TWD - that did wake me up... no need for coffee now...
The price in the US is $.10, so only $1 for ten pieces to cover both boards. That is only a bit more than a conventional 1% MF in small quantity.