I'd say you're ready to test it with some speakers. Cheap ones for the first few minutes if you've got some.
Works just fine ... other than nasty thump at power up. That sort of makes up my mind that the soft start and protection board is essential to enjoying this amp safely.
My apologies, I hadn’t looked at the more recent posts closely, didn’t see the bleeder resistor recommendation.
After looking at the picture however, you might want to make sure the circuit board isn’t getting scorched under that tacked on part, can’t tell if there’s an air gap or not...
After looking at the picture however, you might want to make sure the circuit board isn’t getting scorched under that tacked on part, can’t tell if there’s an air gap or not...
That was just temporary. I think it's safe to move forward with planning next steps:
1) pull output boards to write up parts list
2) source new PS caps 85V - 100V
3) price out DIY Audio Soft Start/Protection Kit
I will most likely start a thread just for the "rebuild" so I can get suggestions on parts, and mods that will make this amp safe. I'd like to order parts within the week, but it's not urgent. Now that I know the amp works, and that MOSFETs aren't blown, I'm a happy camper.
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Remove the bleed resistors you added to the capacitors in the thump will probably go away. I was afraid of that.
B&K ST-202 Plus :: Parts & Upgrades
Hey guys, I should mention this thread could only start because of some very helpful members who helped me diagnose this amp. At one point, I thought it would become a parts amp. Instead, it turns out one end of the R channel fuse holder on the PS board was not holding the fuse in tight enough.
So now, I want to get a parts list together for the output stage, ps caps (screw top), and possible mods. My intention is to get links and prices so that if any other ST-202 Plus owner needs to do the same, maybe this will help.
I should add the caveat that I may do this in phases. I don't yet know what the diyAudio Soft Start / Protection kit will cost once components are sourced out ... but I'm guessing it's north of $100 for two kits on this 2 channel amp. If anyone can give me a better estimate, feel free to post now. I may not get around to doing this until the weekend.
To start off, I'm looking for ps caps first. These could be a big cost and there aren't many options available.
The stock ps cap value is:
15,600 uF -10 + 75%
75 VDC 95 Surge
85C Max Ambient
Lead spacing is about 33mm
Height ~107mm
Width ~76mm
Mouser has Kemet caps that look like they could work, and not too pricey.
ALS80A163KF100 KEMET | Mouser
Another option I may not be able to afford, or even justify for this amp, is from Musical Design. They recommend using their PS board, which I'm sure would require more modification than I want.
This makes the diyAudio kit the most realistic option.
Hey guys, I should mention this thread could only start because of some very helpful members who helped me diagnose this amp. At one point, I thought it would become a parts amp. Instead, it turns out one end of the R channel fuse holder on the PS board was not holding the fuse in tight enough.
So now, I want to get a parts list together for the output stage, ps caps (screw top), and possible mods. My intention is to get links and prices so that if any other ST-202 Plus owner needs to do the same, maybe this will help.
I should add the caveat that I may do this in phases. I don't yet know what the diyAudio Soft Start / Protection kit will cost once components are sourced out ... but I'm guessing it's north of $100 for two kits on this 2 channel amp. If anyone can give me a better estimate, feel free to post now. I may not get around to doing this until the weekend.
To start off, I'm looking for ps caps first. These could be a big cost and there aren't many options available.
The stock ps cap value is:
15,600 uF -10 + 75%
75 VDC 95 Surge
85C Max Ambient
Lead spacing is about 33mm
Height ~107mm
Width ~76mm
Mouser has Kemet caps that look like they could work, and not too pricey.
ALS80A163KF100 KEMET | Mouser
Another option I may not be able to afford, or even justify for this amp, is from Musical Design. They recommend using their PS board, which I'm sure would require more modification than I want.
This makes the diyAudio kit the most realistic option.
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The thump at power up went away. Thanks!
The first time I tried and got a nasty thump was due to the preamp. I'm using a PS Audio 6.1 that has a "straightwire" function, which "removes all line level electronics from the signal path, and directs the signal through only the volume and balance control en route to the power amplifier." This function also reduces the volume level to the speakers. I had first powered up with this "on" and got the thump. I disengaged the "straightwire" function and the amp powered up quietly. Hmmm. Anyway, the amp seems fine and sounds really good through my test speakers (Optimus ProX77).
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I did start a parts build thread, and posted these ps caps. They are $22 each, and the measurements look like they will work.
ALS80A163KF100 KEMET | Mouser
The first time I tried and got a nasty thump was due to the preamp. I'm using a PS Audio 6.1 that has a "straightwire" function, which "removes all line level electronics from the signal path, and directs the signal through only the volume and balance control en route to the power amplifier." This function also reduces the volume level to the speakers. I had first powered up with this "on" and got the thump. I disengaged the "straightwire" function and the amp powered up quietly. Hmmm. Anyway, the amp seems fine and sounds really good through my test speakers (Optimus ProX77).
---------
I did start a parts build thread, and posted these ps caps. They are $22 each, and the measurements look like they will work.
ALS80A163KF100 KEMET | Mouser
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I think so, but it wasn't as much as with the bleeder resistors. As it stands now, the hum is way down to what I would expect, and it powers up quietly. There is a little sound, not sure if it's even a micro thump ... but it is behaving the way I would expect.
Now you just need to get the bias set properly. 🙂
Did you ever get a killawatt meter? I'd be interested in how much wattage its drawing from the wall at idle. That should give a good idea of how much bias current its running.
Did you ever get a killawatt meter? I'd be interested in how much wattage its drawing from the wall at idle. That should give a good idea of how much bias current its running.
The PS board in your amp has holes for narrow spacing capacitor posts and wider spacing posts to allow some flexibility in cap choice. Are you sure the wider spacing is only 22mm? For a 76mm diameter capacitor its usually 1.125" or 1.25". With a 1.25" post spacing you can get a 100V capacitor of 30k uF or more in the same physical size. Personally I think 16k uF X 2 is a bit small for a 200wpc amp.
You are correct on the lead spacing. Thanks! The narrower spacing is about 23mm.
I was wondering about the uF rating on the caps. How much higher is safe? And I assume increasing the value of the PS caps, does not require other value changes on the output boards? Although, when I recap gear, I'm usually doubling the voltage rating.
I was wondering about the uF rating on the caps. How much higher is safe? And I assume increasing the value of the PS caps, does not require other value changes on the output boards? Although, when I recap gear, I'm usually doubling the voltage rating.
I have a P3 Kill A Watt ... plugged into my surge protector shows 123.6V
I was going to wait on dealing with bias since my plan is to replace components, including new Bourns trimpots.
Can I just plug the amp in, without connecting to anything else, in order to check the draw from the wall. I'm about to call it a day on this and go veg downstairs ... 🙂
Just plugged amp in with nothing connected ... doesn't change the reading, but maybe down to 123.4-123.5V, so drops by 0.1V ...
I was going to wait on dealing with bias since my plan is to replace components, including new Bourns trimpots.
Can I just plug the amp in, without connecting to anything else, in order to check the draw from the wall. I'm about to call it a day on this and go veg downstairs ... 🙂
Just plugged amp in with nothing connected ... doesn't change the reading, but maybe down to 123.4-123.5V, so drops by 0.1V ...
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There's probably an inrush limiter somewhere in the amp on the incoming AC power its a small black disc approx 1" diameter that looks like a ceramic capacitor and it should be in the main incoming AC power line. This affords a bit of protection to the switch when used in conjunction with an arc protection cap across the power switch contacts.
An amp with 50 - 60K uF total (both caps combined) is fairly common place any longer. For higher capacitance values you may need to also look into putting a higher amperage rated bridge rectifier if the original is 25A or less. 35A and 50A rectifiers are only a couple of bucks. My Hafler XL-600 has 72k uF from the factory.
An amp with 50 - 60K uF total (both caps combined) is fairly common place any longer. For higher capacitance values you may need to also look into putting a higher amperage rated bridge rectifier if the original is 25A or less. 35A and 50A rectifiers are only a couple of bucks. My Hafler XL-600 has 72k uF from the factory.
Thanks phase.
I need to decide if I feel the need to add the soft start/protection kit now. Is that something that is easy to add later?
I ask because my bro-in-law has been using his ST-202 Plus, in stock form, for a few years now with no issues. He's driving Vandersteen 2C's and they sound great. While I see the value in this type of kit, I just don't have the money right now. Updating the output boards with quality parts is simple and affordable.
In comparison, I have a Sansui BA-3000 that I restored with Mundorf ps caps. I love the sound, and am a fan of Mundorf. For me, they are the sweet spot of quality/cost. For that reason, I'd be tempted to put Mundorf caps in ... but I would need a smaller mounting ring, and I'm not sure if getting the ps board that close to the transformer is a good idea? Their 10,000uF Mlytic HC is only 76mm high, putting the ps board too close to the transformer. I'm not sure it would fit without customization.
KC, I may go ahead and pull an output board today so I can see what values I need. I'll post a pic so we can arrive at a good parts list. I appreciate your input. I don't see an inrush limiter like that, but there is a poly cap on each board ... if it's possible to modify the boards to add the inrush limiter, I'm up for that.
I need to decide if I feel the need to add the soft start/protection kit now. Is that something that is easy to add later?
I ask because my bro-in-law has been using his ST-202 Plus, in stock form, for a few years now with no issues. He's driving Vandersteen 2C's and they sound great. While I see the value in this type of kit, I just don't have the money right now. Updating the output boards with quality parts is simple and affordable.
In comparison, I have a Sansui BA-3000 that I restored with Mundorf ps caps. I love the sound, and am a fan of Mundorf. For me, they are the sweet spot of quality/cost. For that reason, I'd be tempted to put Mundorf caps in ... but I would need a smaller mounting ring, and I'm not sure if getting the ps board that close to the transformer is a good idea? Their 10,000uF Mlytic HC is only 76mm high, putting the ps board too close to the transformer. I'm not sure it would fit without customization.
KC, I may go ahead and pull an output board today so I can see what values I need. I'll post a pic so we can arrive at a good parts list. I appreciate your input. I don't see an inrush limiter like that, but there is a poly cap on each board ... if it's possible to modify the boards to add the inrush limiter, I'm up for that.
Removing output boards.
Is it best to simple remove the hex head screws holding the MOSFETs in, and then replace thermal pads on reassembly?
OR
Leave the MOSFETs in place and desolder legs on output boards?
Is it best to simple remove the hex head screws holding the MOSFETs in, and then replace thermal pads on reassembly?
OR
Leave the MOSFETs in place and desolder legs on output boards?
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