Hello all - I am new to this forum and to DIY audio and it looks like I’m in the right place for a little help and advice. So, I’ve managed to gather everything I need (I think) and will soon begin my first build, the First Watt F5. It’s taken some time acquiring everything, including the two 250va toroids and dual unregulated PSU boards for the project. I went this way because A., DIY Audio was out of stock for the boards at the time, B., I wanted to have plenty of power as a foundation for this initial build and C., I couldn’t readily find a 5-600VA toroid with called for specs at a reasonable price. So “dual-mono” PSUs seemed the way to go.
My questions - which are surely elementary and easily answered, although several hours spent searching this forum hasn’t been fruitful. So here goes:
1. I plan to connect both primaries of the xfmrs to the common input line, with both hots running through the same switch and through the same soft start module I intend to use, which specs more than ample capacity for this application. The soft start circuit will, in addition to managing initial cap charging inrush current, allow me to use a momentary “standby” push-button on the front of the amp. I’m not sure whether using this device will negate the need for the CR60 thermistors at the input - aren’t these also intended to limit current during startup?
2. Are there any other commonalities between the two xfmrs/psus I need to consider for this scheme? I am assuming that grounds will be common between the two psus, is there anything else I need to consider with respect to, I don’t know...keeping the psus in “sync” or something like that, maybe to compensate for slight irregularities between the two xfmrs or psu circuits? I suppose I had just planned to treat each amp channel/psu as completely separate entities (so to speak) with the only commons being at the high side input and the common DC grounds.
Anything else I might should be thinking about with regard to the power supply scheme for this amp? I’m using 80kuf per side for filtering, which I hope will be more than sufficient - I’m not inclined to do all the ripple math and stuff, in favor of just going big on the filtration!
Thanks in advance for any guidance or advice you could provide here!
R, Phil
My questions - which are surely elementary and easily answered, although several hours spent searching this forum hasn’t been fruitful. So here goes:
1. I plan to connect both primaries of the xfmrs to the common input line, with both hots running through the same switch and through the same soft start module I intend to use, which specs more than ample capacity for this application. The soft start circuit will, in addition to managing initial cap charging inrush current, allow me to use a momentary “standby” push-button on the front of the amp. I’m not sure whether using this device will negate the need for the CR60 thermistors at the input - aren’t these also intended to limit current during startup?
2. Are there any other commonalities between the two xfmrs/psus I need to consider for this scheme? I am assuming that grounds will be common between the two psus, is there anything else I need to consider with respect to, I don’t know...keeping the psus in “sync” or something like that, maybe to compensate for slight irregularities between the two xfmrs or psu circuits? I suppose I had just planned to treat each amp channel/psu as completely separate entities (so to speak) with the only commons being at the high side input and the common DC grounds.
Anything else I might should be thinking about with regard to the power supply scheme for this amp? I’m using 80kuf per side for filtering, which I hope will be more than sufficient - I’m not inclined to do all the ripple math and stuff, in favor of just going big on the filtration!
Thanks in advance for any guidance or advice you could provide here!
R, Phil
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You might get more response posting this in the Pass Labs forum but some answers to your questions:
- if you are using a soft start module then you don't need the CL-60 inrush current limiters
- you do not need to 'synchronize' anything between the 2 PSUs and they can share only AC from the soft start and chassis earth safety connection. You do not need to join DC GND between them.
I think 80mF per channel is plenty (160mF total)
- if you are using a soft start module then you don't need the CL-60 inrush current limiters
- you do not need to 'synchronize' anything between the 2 PSUs and they can share only AC from the soft start and chassis earth safety connection. You do not need to join DC GND between them.
I think 80mF per channel is plenty (160mF total)
Hi twitchie thanks a bunch for your reply, I’m pretty sure you’ve answered my main questions, much appreciated! And I did think about posting in Pass Labs forum, but since these were psu questions I flipped a coin. I think you’ve given me something I can work with now