Hello guys,
I have a pair of rega rs3 speakers which are 6ohm, 89db sensitive speakers currently by powered by a rega brio 3r amplifier. I am looking to build a better amp and would like to go with a class a design.
I am having some difficulty deciding the amount of power I need for these, the brio is 50w into 8ohm/73 into 4ohm for comparison so it should be something like 60w into the 6ohm.
How much power could I expect from an f5 into 6ohm? Rega says these speakers can work with as little as 30w of power but I'm afraid that would be somewhat lacking.
I am more inclined for the turbo version as it would have some more headroom.
It is my understanding that the turbo version would easily output 50w into 6ohm with appropriate Transformer and biasing, am I correct? I have been reading and I would go with a cascoded input stage, 34v/12A secondaries, 600VA transformer, 4 MOSFET per channel, so a mix of v2 and v3 versions.
Please let me know your opinion.
Manuel
I have a pair of rega rs3 speakers which are 6ohm, 89db sensitive speakers currently by powered by a rega brio 3r amplifier. I am looking to build a better amp and would like to go with a class a design.
I am having some difficulty deciding the amount of power I need for these, the brio is 50w into 8ohm/73 into 4ohm for comparison so it should be something like 60w into the 6ohm.
How much power could I expect from an f5 into 6ohm? Rega says these speakers can work with as little as 30w of power but I'm afraid that would be somewhat lacking.
I am more inclined for the turbo version as it would have some more headroom.
It is my understanding that the turbo version would easily output 50w into 6ohm with appropriate Transformer and biasing, am I correct? I have been reading and I would go with a cascoded input stage, 34v/12A secondaries, 600VA transformer, 4 MOSFET per channel, so a mix of v2 and v3 versions.
Please let me know your opinion.
Manuel
First,sorry for my english,is so poor!: (
However,i believe that 50w into 6 ohms is really loud,but your loudspeaker dont have sensitivity.What inches are?
Maybe,if you change the speaker,have better results!.
50watt is a good power.Good luck
However,i believe that 50w into 6 ohms is really loud,but your loudspeaker dont have sensitivity.What inches are?
Maybe,if you change the speaker,have better results!.
50watt is a good power.Good luck
34v transfo way too high for two pairs.
2 x 25v transformer / 33vrails / twin pairs delivers about 75w into 6ohms. Enuff?
Be aware of heatsink size if you choose more.
2 x 25v transformer / 33vrails / twin pairs delivers about 75w into 6ohms. Enuff?
Be aware of heatsink size if you choose more.
Last edited:
Tailoring to 6 ohms.
Even a 2 x 22v AC transformer would give about 50w / 6 ohms.
This allowing a deeper bias without excessive dissipation / heatsink size.
That would give about 29v rails.
For 50w full class A you have to bias at 1.2 amp per pair.
dissip per device:1.2 A x 29 v = 34.8 watts.( little bit more than standard F5)
So each channel have to dissipate about 140w.
Which is Already considerable.( about twice standard F5)
If that is too big heatsinks, you could consider biasing less and leave class A sooner, which is not really a problem.
Many dyers, when they come to class A for the first time, do not realise the heatsink size needed.
A 50w class A amplifier is huge and heavy. (and expensive)
Even a 2 x 22v AC transformer would give about 50w / 6 ohms.
This allowing a deeper bias without excessive dissipation / heatsink size.
That would give about 29v rails.
For 50w full class A you have to bias at 1.2 amp per pair.
dissip per device:1.2 A x 29 v = 34.8 watts.( little bit more than standard F5)
So each channel have to dissipate about 140w.
Which is Already considerable.( about twice standard F5)
If that is too big heatsinks, you could consider biasing less and leave class A sooner, which is not really a problem.
Many dyers, when they come to class A for the first time, do not realise the heatsink size needed.
A 50w class A amplifier is huge and heavy. (and expensive)
Last edited:
Sorry, my math are so bad.
That is 1A and not 1.2A bias
Formula is P = (2xIbias)^ x Rload/2 When Ibias is total bias.
dissip about 30w /device
total 120w
22v transfo is OK
That is 1A and not 1.2A bias
Formula is P = (2xIbias)^ x Rload/2 When Ibias is total bias.
dissip about 30w /device
total 120w
22v transfo is OK
Last edited:
Hi Manuel,
I have an F5 running at home with a pair of Mordant short 89bB speakers.
My main system uses Orion Active speakers so i haven't gotten arround to getting good speakers for the F5 yet but these small ones from MS are surprisingly good for the price although a far cry from what the F5 deserves.
Anyway if you want to hear the F5 with them send me a PM and I'll offer you a beer...make sure to bring your favorite music .
You might even bring your speakers/cables to get a good sample of what to expect.
😎
Last edited:
My " Standard" F5 with PD boards and standard PSU as per Firstwatt has a 12cm high case( sinks ) 350mm deep and 439 wide , heatsinks are 8cm deep with 1cm tick base.
This is essentially fin area papa's Firstwatt uses, the operating temperature of the heatsinks, after about an hour stabilizes at circa 55ºC in Lisbon Summer.....after that you will need ZMs babysitter which i made just in case 😉
This should give you a good subjective reference to choose what to build.
This is essentially fin area papa's Firstwatt uses, the operating temperature of the heatsinks, after about an hour stabilizes at circa 55ºC in Lisbon Summer.....after that you will need ZMs babysitter which i made just in case 😉
This should give you a good subjective reference to choose what to build.
A sensitivity of 89dB/2.83V/m implies that ~18V continuous would be sufficient to reach 105dB sound pressure.
The RS3 handles 100W Max (is continuous power), minimum impedance of the RS3 is ~4 Ohm : means that more than 20V continuous at the terminals will destroy the drivers.
18V continuous makes ~40W in 8 Ohm, a transformer with 22Vac secondaries instead of 18V would get there.
22Vac transformer secondaries would boil down to ~29.5V rails.
The J74 handles a max Vds of 25V on the datasheet.
Official max numbers are figures at which 1000 out of 1000 will survive.
In reality, 999 of 1000 may survive at 30V, 99 of 100 at 40V, 9 of 10 at +40V.
According to Paps, Toshiba spec'd the J74 very conservatively at 25V, so 10 of 10 may easily live to see 35V all day.
Easy to check if a J74 handles +30V before soldering it on a board, worst case you'll burn a few bucks before you have two J74 that are up to the higher rail task.
Doesn't require cascoding, or multiple output devices in parallel.
Your choice would cost twice as much transformer, twice as much parts, and twice as much heatsink/case.
Interesting if you plan to dump the Regas in the near future, not sound economics if you intend to keep them.
(but what do i know, i'm so Dutch i turn over a slice of cheese on a sandwich so that i can eat it twice)
Last edited:
Jacco,
i think 20v transfo and 1.6 bias will do 40 watts/6ohms.
40 w dissipation per device.
Twin pairs more on the safe side and sound better.
(to my ear)
I am one of those fraidy cats.
i think 20v transfo and 1.6 bias will do 40 watts/6ohms.
40 w dissipation per device.
Twin pairs more on the safe side and sound better.
(to my ear)
I am one of those fraidy cats.
Last edited:
Hi Manuel,
i have very low efficient speakers (about 82/83dbs) in my small room (10m2) and i am running my prototype fan cooled F5 for about a year and a half without problems.
So my opinion is , it depends on the size of your room and how loud you like listening to music.
If your room is not to big, F5 should be good for you.
Um abraço
i have very low efficient speakers (about 82/83dbs) in my small room (10m2) and i am running my prototype fan cooled F5 for about a year and a half without problems.
So my opinion is , it depends on the size of your room and how loud you like listening to music.
If your room is not to big, F5 should be good for you.
Um abraço
My opinion is that first one need to decide what output voltagge is needed in each personal circumstancies.
There is an easy test that require a known signal at low frequency and a voltmeter.
Set your volume to play your faworite music as laud as you are likley to get
with the volume at that setting play a signal at -12 dB low frequency with your CD player and mesure the V rms with the multimeter
Multiply by 4 and that is the hieghes voltagge you are likley to demand out of your speaker
Search for the tread started by Pano all you need is there (unfortunatley there is a lot of dross) I would concentarte on the first few post .
I have been running a cascode twin mosfets F5 since August and I am realy happy with it.
my speakers are 87 dB 4 hom Polk LS15i in a 12 X 22 foot room the maximum voltagge I have measured out of the F5 is about 12 V
rails are at about 36 V and F5 can go to about 2 volts of the rails before voltagge clipping.
I had at first the standard F5 but newer managed a back to back comparison
Both version of the F5 I have eard sound realy realy good the cascoded Turbo official version is to joung to realy say. As far as I know Nobody has realy listened to the Papa design so far.
Another thing to keep i mind is the kind of music you listen to
If you play CD and recent stuff it is quite poor in dinamics
If you play classical music you need 20dB head room.
And another thing I use to have a 150 W amplifier bougt from the shoop
since I have the F5 I play much louder (It still suprise me) and with much less listening fatigue.
IMO either version of the F5 is well worth a try
Last edited:
So I have decided I will use the v2 boards being developed right now, with 4 output devices to spread the load between them, possibly cascoded input to use 30v secondaries (using a nice schuro.de or toroidy.pl transformer). Case will be home built around a pair of 300-350x 200x 80mm heatsinks which acording to research will have around .15/.20 w/c. This will allow to heavy bias the mosfets.
I am also considering building it as an integrated amplifier, with either a b1 (no gain) or an a20(AMB Laboratories DIY Audio Site, allows user set gain) buffer and some sort of relay based attenuator and source selection. The pre amp section would be mounted on the back panel. However the close proximity to the large toroidal could be an issue.
I am also considering building it as an integrated amplifier, with either a b1 (no gain) or an a20(AMB Laboratories DIY Audio Site, allows user set gain) buffer and some sort of relay based attenuator and source selection. The pre amp section would be mounted on the back panel. However the close proximity to the large toroidal could be an issue.
why not go for 400 x 150 x 80mm sink? it is better to build it deeper then higher. and you will need the space on the bottom plate🙂
just make sure the baseplate of the sinks are thick🙂 about 10mm+ for 200mm🙂 thicker the better.
- Status
- Not open for further replies.