So, I am specing up a project for the future and have come to the conclusion that a Pass F5 amp build looks like the one for me. But before I go firm on any plans I have a few questions to ask the forum.
Outline plan is to build effective F5 monoblocks which will be mounted in some the sands for some stand/bookshelf speakers (another project) along with the crossovers.
Questions I have are -
1) For mounting the amp (amp boad, power supply and transformer) I am looking at making the back of the stand (effectively rectangular (speaker) wood box with vent holes top and bottom) from plate aluminium (22cm x 52cm = approx. 1150sq.cm) i.e. making it into a mono plate amp. I can get 5083/N8 plate from 5mm to 12mm in thickness and also add a traditional finned heatsink on the back with heat transfer cement if needed. The question is - is it possible to get get away with a thick block of aluminium plate or is it better to go with a thinner plate with a 200 x 150 x 50mm finned element on the rear opposite to the amp board?
2) I plan on using the Diystore F5 v3 boards. For the power supply again using the Diystore Universal Power Supply Boards which I believe can be split in half. In terms of transformer and capacitors I plan on using a 300 or possibly 400VA toroidal on each side but what is the best capacitor size to use - the spec says 30000uf per side, the boards have 4 x 35mm positions so will 4x100000uf be enough or should I go up to 4x22000uf (the cost different is not too much)?
3) I currently run active monitors directly from a passive "preamp" (actually just an latter attenuator, M-Patch v2) and a dac that outputs 2.5V (Audio GD NFB3.1). For the front end can I stick with this arrangement or do I need a preamp that actually amplifies the 2.5V signal ? (for info the speakers will be Statement Monitors which are approx. 85dB sensitivity). I do not need to listen at very loud level as the room is quite small.
Sorry for the length of the post but hopefully you can all help before I start to spend cash.
Thanks in advance.
Outline plan is to build effective F5 monoblocks which will be mounted in some the sands for some stand/bookshelf speakers (another project) along with the crossovers.
Questions I have are -
1) For mounting the amp (amp boad, power supply and transformer) I am looking at making the back of the stand (effectively rectangular (speaker) wood box with vent holes top and bottom) from plate aluminium (22cm x 52cm = approx. 1150sq.cm) i.e. making it into a mono plate amp. I can get 5083/N8 plate from 5mm to 12mm in thickness and also add a traditional finned heatsink on the back with heat transfer cement if needed. The question is - is it possible to get get away with a thick block of aluminium plate or is it better to go with a thinner plate with a 200 x 150 x 50mm finned element on the rear opposite to the amp board?
2) I plan on using the Diystore F5 v3 boards. For the power supply again using the Diystore Universal Power Supply Boards which I believe can be split in half. In terms of transformer and capacitors I plan on using a 300 or possibly 400VA toroidal on each side but what is the best capacitor size to use - the spec says 30000uf per side, the boards have 4 x 35mm positions so will 4x100000uf be enough or should I go up to 4x22000uf (the cost different is not too much)?
3) I currently run active monitors directly from a passive "preamp" (actually just an latter attenuator, M-Patch v2) and a dac that outputs 2.5V (Audio GD NFB3.1). For the front end can I stick with this arrangement or do I need a preamp that actually amplifies the 2.5V signal ? (for info the speakers will be Statement Monitors which are approx. 85dB sensitivity). I do not need to listen at very loud level as the room is quite small.
Sorry for the length of the post but hopefully you can all help before I start to spend cash.
Thanks in advance.
I found this calculator for plate: Free Flat Plate Heat Sink Calculator. It gives about 2ºC/W for 12mm, which isn't nearly enough. You're going to need the finned element.
The factory Firstwatt F5 uses a single 300VA toroid (so roughly 150VA is available per channel), and 120,000uF total (60,000uF per channel). While a lot of folks go bigger, you don't want to get too out of sync between the transformer and the caps or you'll over-stress the transformer. So if you wanted to do 88,000uF per channel (4 x 22,000), something on the order of 200VA toroids would work well.
The Statements are 4 ohms? My sim shows it needing about 3.3V to develop full power (~50W class AB) into 4 ohms, and topping out at about 30W with 2.5V. It looks like it's leaving class A around 15W (depending on bias) when driving a 4 ohm load.
Cheers,
Jeff.
The factory Firstwatt F5 uses a single 300VA toroid (so roughly 150VA is available per channel), and 120,000uF total (60,000uF per channel). While a lot of folks go bigger, you don't want to get too out of sync between the transformer and the caps or you'll over-stress the transformer. So if you wanted to do 88,000uF per channel (4 x 22,000), something on the order of 200VA toroids would work well.
The Statements are 4 ohms? My sim shows it needing about 3.3V to develop full power (~50W class AB) into 4 ohms, and topping out at about 30W with 2.5V. It looks like it's leaving class A around 15W (depending on bias) when driving a 4 ohm load.
Cheers,
Jeff.
Many thanks @JeffYoung, much appreciated.
Happy to drop the thickness of the back plate to probably 5-6mm and then mount some finned heatsinks (min (8" x 6") 150x200x40 as specified) on the rear.
Good news about the caps and transformer, looks like I was in the right ball park.
Please can you explain a bit more about your last para, are you saying that the 25W/channel of the F5 is OK or not ? or will I need an active preamp to add gain to the 2.5V to get it up nearer the 3.3V stated.
(These are the speakers for info - Statements_Monitor)
Many thanks, much appreciated.
Happy to drop the thickness of the back plate to probably 5-6mm and then mount some finned heatsinks (min (8" x 6") 150x200x40 as specified) on the rear.
Good news about the caps and transformer, looks like I was in the right ball park.
Please can you explain a bit more about your last para, are you saying that the 25W/channel of the F5 is OK or not ? or will I need an active preamp to add gain to the 2.5V to get it up nearer the 3.3V stated.
(These are the speakers for info - Statements_Monitor)
Many thanks, much appreciated.
I think when you split the diyaudio PS PCB you only get a single polarity. So if
you are looking for a more compact solution for 4 caps for each monoblock, then
you may need something else.
The gain of the F5 is quoted at 15dB. If your dac max output is 2.5V (RMS)
then the max voltage swing out of the F5 is a bit under +/-20 V, which corresponds
to 25W into 8 ohms.
What is the impedance of your passive? I would definitely give it a try first.
you are looking for a more compact solution for 4 caps for each monoblock, then
you may need something else.
The gain of the F5 is quoted at 15dB. If your dac max output is 2.5V (RMS)
then the max voltage swing out of the F5 is a bit under +/-20 V, which corresponds
to 25W into 8 ohms.
What is the impedance of your passive? I would definitely give it a try first.
To followup on Jeff's point, you might want to try this test:
A Test. How much Voltage (power) do your speakers need?
A Test. How much Voltage (power) do your speakers need?
Many thanks all again.
The room is 10ft x 10ft with 8ft ceiling so will be sitting about 7ft from the speakers max.
Using this calculator - Peak SPL Calculator
I get 98db at 7ft from 2 speakers at 85db sensitivity and 25W. I typically listen at about 85db which is plenty loud enough.
Comparison to my current set up is not very good as I have a pair of Mackie HR824 active monitors that have 250W Class AB per speaker but they are turned down to about 1/4 on the rear and the passive preamp is again turned down to less than half so probably about 1/20 of the power at normal listening levels assuming the pots are linear (unlikely).
On the heat sinks I re-read the F5 Manual by NP which says "An example of this would be a chunk of finned aluminium, with a series of 2” fins attached to an 8” by 6” base. You will need two per channel". This gives an area of 96 sq.in or 620 sq.cm. So a 20cm x 30cm with 5cm fins would be pretty close given the extra material in the main plate. Will look out for some this size as a minimum.
I will also look into the power supply side of things.
The DIYAudioStore power supply Universal Power Supply – diyAudio Store
info says - "Capacitor section can be snapped off lengthwise regardless if the Diode section is still attached or snapped off for more build flexibility (0.2mm V-Cut both sides)" which seems to suggest you can divide it down the middle to make it into two mono supplies. Will have a read of the build manual to get more info and google some build F5's to see what they did. EDIT - Dennis, looks like you are correct - one side give you V- and the other V+ so either I need one board per monoblock (8x10000uf caps) or another solution. Splitting is only for packaging convenience.
Thanks again.
The room is 10ft x 10ft with 8ft ceiling so will be sitting about 7ft from the speakers max.
Using this calculator - Peak SPL Calculator
I get 98db at 7ft from 2 speakers at 85db sensitivity and 25W. I typically listen at about 85db which is plenty loud enough.
Comparison to my current set up is not very good as I have a pair of Mackie HR824 active monitors that have 250W Class AB per speaker but they are turned down to about 1/4 on the rear and the passive preamp is again turned down to less than half so probably about 1/20 of the power at normal listening levels assuming the pots are linear (unlikely).
On the heat sinks I re-read the F5 Manual by NP which says "An example of this would be a chunk of finned aluminium, with a series of 2” fins attached to an 8” by 6” base. You will need two per channel". This gives an area of 96 sq.in or 620 sq.cm. So a 20cm x 30cm with 5cm fins would be pretty close given the extra material in the main plate. Will look out for some this size as a minimum.
I will also look into the power supply side of things.
The DIYAudioStore power supply Universal Power Supply – diyAudio Store
info says - "Capacitor section can be snapped off lengthwise regardless if the Diode section is still attached or snapped off for more build flexibility (0.2mm V-Cut both sides)" which seems to suggest you can divide it down the middle to make it into two mono supplies. Will have a read of the build manual to get more info and google some build F5's to see what they did. EDIT - Dennis, looks like you are correct - one side give you V- and the other V+ so either I need one board per monoblock (8x10000uf caps) or another solution. Splitting is only for packaging convenience.
Thanks again.
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Been looking at mono power supply boards that give +/-v plus ground out.
Would this work, one per channel fed by a 200-300VA toroidal transformer with 2x18v outputs -
https://www.ebay.co.uk/itm/DIY-Scho...869756?hash=item3f627673fc:g:CacAAOSw5HJXLJlm
And
2 Output Toroidal Transformer, 225VA, 2 x 18V ac | RS Components
Plus 6 of these each channel, these seem to be a mid price us it worth going up or down from here?
MAL205658103E3 | Vishay Aluminium Electrolytic Capacitor 10000μF 63V dc 35mm Snap-In 56 Series, Through Hole Electrolytic, +-20% | RS Components
Would this work, one per channel fed by a 200-300VA toroidal transformer with 2x18v outputs -
https://www.ebay.co.uk/itm/DIY-Scho...869756?hash=item3f627673fc:g:CacAAOSw5HJXLJlm
And
2 Output Toroidal Transformer, 225VA, 2 x 18V ac | RS Components
Plus 6 of these each channel, these seem to be a mid price us it worth going up or down from here?
MAL205658103E3 | Vishay Aluminium Electrolytic Capacitor 10000μF 63V dc 35mm Snap-In 56 Series, Through Hole Electrolytic, +-20% | RS Components
That PSU board is just a C filter. A CRC, which has much better ripple rejection, is normally used with the F5. As an example: CRC 6 Capacitors Rectifier Filter Power supply PCB for Class A Pass Amplifier | eBay. (I've no experience with that seller.)
The RSPro transformer looks the job, although FWIW most of us in the EU use Toroidy (Transformatory toroidalne - Producent transformatorow Toroidy.pl).
When picking a cap you want to make sure it has enough voltage (with a bit of wiggle room), but for 24V rails 35V or 40V capacitors should do the job. 63V will just be larger (and more expensive).
The first caps get hammered with ripple from the transformer, so you want to make sure that they have enough ripple current handling. Each 18V secondary in a 225VA transformer is on the order of 6A, so you want your capacitors before the resistors to add up to a decent buffer above that. The example board above has 2 caps before the resistors on each rail, so you're looking for something in the region of 4A (or better) each.
The RSPro transformer looks the job, although FWIW most of us in the EU use Toroidy (Transformatory toroidalne - Producent transformatorow Toroidy.pl).
When picking a cap you want to make sure it has enough voltage (with a bit of wiggle room), but for 24V rails 35V or 40V capacitors should do the job. 63V will just be larger (and more expensive).
The first caps get hammered with ripple from the transformer, so you want to make sure that they have enough ripple current handling. Each 18V secondary in a 225VA transformer is on the order of 6A, so you want your capacitors before the resistors to add up to a decent buffer above that. The example board above has 2 caps before the resistors on each rail, so you're looking for something in the region of 4A (or better) each.
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