The BOM for the SPP hasn't been refreshed in some time. New parts come and go, and even old parts get new numbers to justify price increases. In most cases any part that has the same or higher ratings than what's specified in the BOM will work.
In this case I searched for a 3 watt, 150K through hole resistor. Then I looked at the data sheet for the voltage rating and found 750 volts for the first part that Digikey showed and looked for the same part at Mouser. There are lots of other parts that will work here.
R2 can be any generic 3 watt resistor that's rated for the full expected B+ voltage. It is just the bleeder resistor that discharges the filter caps on power off. A quick search shows this 3 watt 750 volt part at both distributors for the same 37 cents for one part price:
Digikey:
https://www.digikey.com/en/products/detail/te-connectivity-passive-product/RR03J150KTB/2385201
Mouser:
https://www.mouser.com/ProductDetai...=sGAEpiMZZMsPqMdJzcrNwtkiCP/uZm62xteQWPdJkVA=
In this case I searched for a 3 watt, 150K through hole resistor. Then I looked at the data sheet for the voltage rating and found 750 volts for the first part that Digikey showed and looked for the same part at Mouser. There are lots of other parts that will work here.
R2 can be any generic 3 watt resistor that's rated for the full expected B+ voltage. It is just the bleeder resistor that discharges the filter caps on power off. A quick search shows this 3 watt 750 volt part at both distributors for the same 37 cents for one part price:
Digikey:
https://www.digikey.com/en/products/detail/te-connectivity-passive-product/RR03J150KTB/2385201
Mouser:
https://www.mouser.com/ProductDetai...=sGAEpiMZZMsPqMdJzcrNwtkiCP/uZm62xteQWPdJkVA=
Using a choke reduces the hum.
There has been a lot of discussion in this extensive thread about the value of B+.
There has been a lot of discussion in this extensive thread about the value of B+.
Finally stuffing the board and noticed that, although Wirewound power supply resistors 112,116,etc. resistors are discussed in George's intro to the design metal film arrived from the BOM. There's always been a lot of discussion on line about one vs. another, low noise vs. pleasing heightened DC passthrough for example.
In this particular design which suits better?
In this particular design which suits better?
Why do I always discover a missing part a few days before a holiday? Had to wait until yesterday for the latest to arrive and hopefully, by tomorrow I'll be listening to favorite albums like this one:
Likely tomorrow because I just discovered the excellent OPT wiring guides of Steve Morley, rknize, and Steve Graham. I really miss the wiring diagrams George had for the Simple SE. OPT's always elude me when PCBs are involved. Point-to-point, no problem.
Likely tomorrow because I just discovered the excellent OPT wiring guides of Steve Morley, rknize, and Steve Graham. I really miss the wiring diagrams George had for the Simple SE. OPT's always elude me when PCBs are involved. Point-to-point, no problem.
I mean .... is swinging while standing up really OK when you are just about to have a baby?
All of a sudden it doesn't seem like the most risky thing to be doing when sticking two probes into the insides of an amp while trying to keep my hands steady and read the meter I put in a silly place.
All of a sudden it doesn't seem like the most risky thing to be doing when sticking two probes into the insides of an amp while trying to keep my hands steady and read the meter I put in a silly place.
I ordered the SPP for George. I have been checking the build and schematic info while the PCB gets to me. I want to use a choke instead of the R1 resistor, but I there is not information about the ideal value for the choke. I understand a choke can raise the value of the voltage. Can someone point out what would be the ideal choke value to use in this build. Thnx.
u can use anything from 1.5H to 10H, make sure it has enough current rating (min. 200mA)
resistance will be lower the larger the choke is, it doesnt really matter IMO.
your B+ voltage will ultimately settle based on your AC mains, if u use a CL-90 thermistor in the primary, your chosen PT, tube vs SS regulator, etc.
for me, once the build is mostly finished, I'll adjust B+ with an additional high wattage resistor in series with the choke in the PS.
based on the other factors, it may or may not be needed.
I really like the hammond 193H for a fancy top-mount option.
under mount you can use anything here rated 200ma and above: https://www.hammfg.com/electronics/transformers/choke/153-159
or the toroidal option from AnTek like this: https://www.antekinc.com/lk-8h200-toroidal-power-choke/
resistance will be lower the larger the choke is, it doesnt really matter IMO.
your B+ voltage will ultimately settle based on your AC mains, if u use a CL-90 thermistor in the primary, your chosen PT, tube vs SS regulator, etc.
for me, once the build is mostly finished, I'll adjust B+ with an additional high wattage resistor in series with the choke in the PS.
based on the other factors, it may or may not be needed.
I really like the hammond 193H for a fancy top-mount option.
under mount you can use anything here rated 200ma and above: https://www.hammfg.com/electronics/transformers/choke/153-159
or the toroidal option from AnTek like this: https://www.antekinc.com/lk-8h200-toroidal-power-choke/
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I've used a Hammond 156R in my builds. It's 1.5H rated at 200mA. You may use a choke with more inductance and more reactance if you wish but as the current draw from the power supply will be about 150mA, a 200mA rating on the choke will allow some margin. If you will be using a tube rectifier, then a 300-0-300 power transformer secondary will likely keep B+ voltage within safe limits. If you are considering solid state rectification then something around 275-0-275 would likely be best.
I found a choke essential for removing the last little bit of hum. You also need to be careful positioning it with regards to the power trans so you don't get any induced hum.
Good luck with your build.
I found a choke essential for removing the last little bit of hum. You also need to be careful positioning it with regards to the power trans so you don't get any induced hum.
Good luck with your build.
I agree with Itsik and Steve, however, I have used an even lower cost Triad 1H reactor with good results. With a PP amp the ripple on the B+ is usually not a problem.
This one: https://www.mouser.com/ProductDetail/Triad-Magnetics/C-24X?qs=xrpI9KL/Xvsp8oLEd8wC/Q==
This one: https://www.mouser.com/ProductDetail/Triad-Magnetics/C-24X?qs=xrpI9KL/Xvsp8oLEd8wC/Q==
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George has mentioned this one for previous questions about the choke
Triad C14X
Good value when you order enough online to get free delivery.
Triad C14X
Good value when you order enough online to get free delivery.
Hi,
maybe someone can help me out. Today I replaced R1 with 270ohm (B+ was too high) with a Hammond Choke 159R (6H, 150 Ohm). The hum is now away but I can smell something weird. Looks Like something ist getting hotter than before. I didnt measure B+ up to now but is there a way to increase the Choke resistance or put an resistor before c1?
best regards
martin
maybe someone can help me out. Today I replaced R1 with 270ohm (B+ was too high) with a Hammond Choke 159R (6H, 150 Ohm). The hum is now away but I can smell something weird. Looks Like something ist getting hotter than before. I didnt measure B+ up to now but is there a way to increase the Choke resistance or put an resistor before c1?
best regards
martin
There are lots of posts asking about the gNFB feedback compensation cap.
I am building my third SPP, this time with Sowter OPTs (that seem to be of very high quality, BTW), and thought I'd share a FR graph of different cap values.
With this OPT, FR is pretty flat in the audio band, so I'm not even sure if a cap is necessary, but I experimented with 0pF-390pF.
With 0pF (no cap), the HF continues to rise and is likely truncated only due to my sound card sample rate?
With 390pF, the amp becomes unstable at max output power, so that is too high.
150-220pF seem to be the optimal capacitance, for this specific OPT.
I am building my third SPP, this time with Sowter OPTs (that seem to be of very high quality, BTW), and thought I'd share a FR graph of different cap values.
With this OPT, FR is pretty flat in the audio band, so I'm not even sure if a cap is necessary, but I experimented with 0pF-390pF.
With 0pF (no cap), the HF continues to rise and is likely truncated only due to my sound card sample rate?
With 390pF, the amp becomes unstable at max output power, so that is too high.
150-220pF seem to be the optimal capacitance, for this specific OPT.
