What is voltage under load? 35v seems to be the unloaded voltage for 25v ac secondaries. 25v x 1.41 = 35v. So that’s good. Under Class A load the voltage will drop a few volts and the cap multiplier will drop an additional 3v if you adjust the trimpot for max ripple regulation. So total drop could be as high as 5v to 6v and you would be at 29v to 30v rails at your amp while fully powered and driving a hot Class A amp.
Thanks for the reply xrk!
Yes, the 35V is without load. I don't really have a load to attach yet, I have to build it first. =) It will be a USSA-5, though, I have the PCB's and components at hand, but wanted to complete the PSU's before starting that build. Can I adjust the trimpots without load or should I do that when driving the load?
Once you have the load adjust it to have about 3v of drop and that will give you the best ripple reduction. We really should have just put a fixed resistor there because the range of adjustment under load is really only about 1v to 2v difference.
Should we just stick a 100 ohm resistor in there and be done with it? ‘Best’ ripple reduction is somewhat relative to current draw and value of the CRC capacitors. I’ve used 10mF capacitors and the ripple reduction continues to be quite good. 15mF of course is better. A single resistor is cheaper than a pot anyway…
Best,
Anand.
I am not sure if it is the midpoint 100R that is best. If someone who is using it now can check what their actual R value is and report back that would great.
Might be something for me to do in the future. Actually, I wonder if this changes based on current draw and requisite voltage rails. I can use a 3 pin header, attach pot, attach load, adjust pot for lowest ripple while viewing on scope for said load, remove + measure pot, and replace with fixed resistor.
Best,
Anand.
Thanks for the advice! I experimented with the trimpot and got no more than 0,5V difference between the extremes, although this was without load.
Sorry if I’m going on about obvious stuff, but I’m trying to wrap my head around this… I followed the advice above to choose the transformers, rounding to the next size up (25V) to be on the safe side. I figured that should give me around 28V in the end.
Now what I’m struggling to understand is where the voltage drops from the cap Mx and sag will come into play? If I’m measuring 35V without load will the “in use” voltage still come around 28V or so?
My amp contains components that are 35V rated, and the overall recommendation for max voltage is 32V. I’m trying to understand whether the 35V I’m measuring will be OK or are further measures required?
The load under Class A of 1.5A to 2.5A will cause a voltage drop of 2-3v from no load. That’s the so called ability of the trafo to provide regulation. The BJT in the cap Mx itself has about 3v drop. The CRC maybe 0.5v to 1v drop depending on current. You could be looking at 5-6v drop max. So 35v no load could be 29v to 30v.
Hy,
hopefully the SLB will be delivered to me. 🙂
i am go through all the pages and i found some alternatives for the "rectifier fets".
some devices are not easy to get now.
you can decide how much money you will spend. Tungsten audio (post 599) find the lowest rdson...but they are not cheap.😀
hopefully the SLB will be delivered to me. 🙂
i am go through all the pages and i found some alternatives for the "rectifier fets".
some devices are not easy to get now.
you can decide how much money you will spend. Tungsten audio (post 599) find the lowest rdson...but they are not cheap.😀
| STP110N8F6 | N MOSFET - 6,5mOhm , 9100pF | not available | |
| Texas Instruments CSD19501KCS | 6,6mohm 3900pF | 2,15 euro | not available |
| Toshiba TK56E12N1,S1X | 5mohm, 4200pF | 1,37 bei 50stk. | not available |
| TK5R3E08QM,S1X | 5mohm, 3980pF | 1,58 | not available |
| TK72E08N1,S1X | 5,3mohm, 3980pF | 2,35 | |
| STP140N8F7 | 4,3mOHM, 6340pF | 3,2 | |
| IRF3205ZPBF , 55V | 6,5mOhm, 3450pF | 1,99 | |
| FDP045N10A-F102 | 4,5mOhm, 5100pF | 4,2 | |
| STP130N8F7 | 5mOhm, 2600pF | 1,81 | |
| IPA037N08N3 | 3,7mOhm, 6100pF | 2,05 | |
| CSD19501KCS | 6,6mOhm, 3980pF | 2,15 | |
| IPP029N06N | 2,9mohm, 4100pF | 3,11 | |
| IPP050N10NF2SAKMA1 | 5mOhm, 3690pF | 3,05 |
the NTC is the Excense NTC-8D20 8ohm 6Amps. not available
i run out of the CL60 but i found smaller: B57238S0709M000 TDK 7ohms 6A
kr
chris
happy Christmas time
i run out of the CL60 but i found smaller: B57238S0709M000 TDK 7ohms 6A
kr
chris
happy Christmas time
No, it’s a specific vendor chip. On SLB it must be DIP8 variant.
Regarding what MOSFET to use: pick one that is rated for the voltage you need to use on your power supply rails (1.41x Vac of trafo) plus some safety margin. All of the ones above have a sufficiently low RDson (below 40mOhm is good). A TO-220 without heatsink can’t dissipate more than 0.5w. So for example, if you plan on 5A max current x 0.04ohm = 0.2w dissipation.
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I think one of them is compatible with an adapter as I recall a board that Prasi made accepts either DIP8 or one of the SMT’s.
It’s the DDIL-08 - a tiny part with belly pads and difficult to solder unless use paste and hot plate.
It’s the DDIL-08 - a tiny part with belly pads and difficult to solder unless use paste and hot plate.
If an SLB revision is planned, adding the MSOP12 package in between the DIP8 pads would be a nice safeguard against 'out of stock' issues.