Power Supply Voltage - NAP180, NAP250 & NCC200
- Thread starter misterc6
- Start date
Somewhere there is my NAP180 upgraded with two minicap6's and that same transformer I believe. I wont put a link because its absolutely horrid! (grrrr Les, make me sick 
)
But if I get a PM I'll see if I can help Misterc6. I did mine the less tidy way to get the thing running - and have little inclination to tidy up its great! I'd happily talk you through it.
Regarding voltages, my boards are running over 50V - like LesW I think I get some extra volts at home. I think it helps the sound though, nout like a bit more potential when a kick drum hits! Sounding awesome tonight At the minimum the cap6/minis are the way to go, but the bigger voltage traffo tops it right off.
Out of interest, whats the maximum you can run Naim boards without breaking them (assuming not playing loud and murdering them with heat)?
)But if I get a PM I'll see if I can help Misterc6. I did mine the less tidy way to get the thing running - and have little inclination to tidy up its great! I'd happily talk you through it.
Regarding voltages, my boards are running over 50V - like LesW I think I get some extra volts at home. I think it helps the sound though, nout like a bit more potential when a kick drum hits! Sounding awesome tonight
At the minimum the cap6/minis are the way to go, but the bigger voltage traffo tops it right off.Out of interest, whats the maximum you can run Naim boards without breaking them (assuming not playing loud and murdering them with heat)?
misterc6
Wasted and wounded, it ain’t what the moon did
Thanks Trancera I'll maybe take you up on the offer when the parts arrive from Les. He is now certain that the Cap6s will fit along with the 750 VA AST trafo in the 180 case, so I've ordered those with the amp board refurb kit. This should give me 50v power rails.
I've still got a couple of questions regarding the exact routing of the various ground cables and if whether or not I should remove the thermal trip. It strikes me that it does nothing and the existing wiring to it will be tight under the new trafo.
Les should perhaps put up the correct pictures which are amazing. I like the musicality of the 180 but am looking for a little more oomph.
malcolm
I've still got a couple of questions regarding the exact routing of the various ground cables and if whether or not I should remove the thermal trip. It strikes me that it does nothing and the existing wiring to it will be tight under the new trafo.
Les should perhaps put up the correct pictures which are amazing. I like the musicality of the 180 but am looking for a little more oomph.
malcolm
Oh they definetly fit ;-) and yes I see about 51V.
Its not a 180 when its done really. Its a Naim that has serious power and ability. I still have the thermal trip fitted, caused me no problem at all.
I hadnt done a power amp, hence serious voltage and current before so i wanted to do the minimum of messing at the time and drill the least holes, worked well for me.
Its not a 180 when its done really. Its a Naim that has serious power and ability. I still have the thermal trip fitted, caused me no problem at all.
I hadnt done a power amp, hence serious voltage and current before so i wanted to do the minimum of messing at the time and drill the least holes, worked well for me.
I was concerned about rail voltages on my NAP boards because the front-end LTP trannies see full rail voltage at the collector, giving a total Vce of (+ve) + (0.6V). In my case, the rails are +/-50V from a 35-0-35 trafo, so TR1 has +50.6V Vce. The standard-fit transistors on my boards are BC239 (now replaced with hand-matched BC547C) that have a datasheet-recommended absolute max rating of 45V Vce... yet nothing has blown up yet.
What gives?
My other question to which I've never completely been 100% sure on is: if I have 2 NAP180 amps (or 250s, 140s, NCC200-based amps, whatever), one with +/-50V rails, the other with +/-42V rails, do both of them produce the same level of output for a given input signal, or does the +/-50V amp produce a louder output than the +/-42V?
What gives?
My other question to which I've never completely been 100% sure on is: if I have 2 NAP180 amps (or 250s, 140s, NCC200-based amps, whatever), one with +/-50V rails, the other with +/-42V rails, do both of them produce the same level of output for a given input signal, or does the +/-50V amp produce a louder output than the +/-42V?
martin clark
pinko bodger
They produce the same output. Gain in a feedback amp is set entirely by the f/back network.
This why exact DC voltages , or balancing voltages on split-rail circuits (including opamps) really doesn't matter. It' s only the dynamic (i.e AC properties) that definitely do.
[yes I'm ignoring PSRR, but problems at -80dB level aren't exactly going to upst the gain match when the average volume pot struggles to maintain a 2dB balance ]
This why exact DC voltages , or balancing voltages on split-rail circuits (including opamps) really doesn't matter. It' s only the dynamic (i.e AC properties) that definitely do.
[yes I'm ignoring PSRR, but problems at -80dB level aren't exactly going to upst the gain match when the average volume pot struggles to maintain a 2dB balance
]
martin clark
pinko bodger
PS Carl you might just be getting away with running over the rated Vce because the tail current is closely defined (limited) by the LTP tail curent source.
Think I'd go looking for something rated for the application though! BC546 / 556 would do it, to stay in the same family. Unfortunately, as Vce goes up, hfe usually goes down...
Think I'd go looking for something rated for the application though! BC546 / 556 would do it, to stay in the same family. Unfortunately, as Vce goes up, hfe usually goes down...
misterc6
Wasted and wounded, it ain’t what the moon did
They produce the same output. Gain in a feedback amp is set entirely by the f/back network.
This why exact DC voltages , or balancing voltages on split-rail circuits (including opamps) really doesn't matter. It' s only the dynamic (i.e AC properties) that definitely do.
[yes I'm ignoring PSRR, but problems at -80dB level aren't exactly going to upst the gain match when the average volume pot struggles to maintain a 2dB balance
Of course the higher the voltage is the lower the current needed to produce the same pwoer.
martin clark
pinko bodger
Not here.
If you have an amp running on, say, 60v rails, and an amp running on 40v rails, and they are both delivering the same power into a given load then dissipation inside the first amp is (60/40)^2, two-and-a quarter times as much as the '40v' amp!
That's because, for a given load and power, the amp output current will be identical from either amp: so the higher power amp wastes more internally as heat (whether that's partly in regulators or not doesn't matter at all)
Linear amplifers do not behave anything like perfect transformers!
If you have an amp running on, say, 60v rails, and an amp running on 40v rails, and they are both delivering the same power into a given load then dissipation inside the first amp is (60/40)^2, two-and-a quarter times as much as the '40v' amp!
That's because, for a given load and power, the amp output current will be identical from either amp: so the higher power amp wastes more internally as heat (whether that's partly in regulators or not doesn't matter at all)
Linear amplifers do not behave anything like perfect transformers!
Yeah, it must be the current because my Naim factory fitted parts are rated the same as BC547: 45V Vce. I think I'll buy a crap-load of BC546 and hand match for high hfe and tolerance.
It's good news about the volume, because my upcoming 3-way active speaker project will be powered by six monoblocks: the bass from drivers from 500VA 50-0-50VDC each, and the mids/tweeters from 230VA 42-0-42VDC each.
It's good news about the volume, because my upcoming 3-way active speaker project will be powered by six monoblocks: the bass from drivers from 500VA 50-0-50VDC each, and the mids/tweeters from 230VA 42-0-42VDC each.
This 547 seems to have higher voltage and keep the higher hfe?
http://uk.farnell.com/nxp/bc547b/transistor-npn-to-92/dp/1097288
546 drop to about half this hfe.
http://uk.farnell.com/nxp/bc547b/transistor-npn-to-92/dp/1097288
546 drop to about half this hfe.
That's a mistake on Farnell's site - the manufacturer's site says 45V: http://www.nxp.com/pip/BC847_BC547_SER_7.html If you're looking for higher hfe then try the C variant instead of the B. Looks like for high voltage rails we'll need to use the BC546C after all. If you buy enough I'm sure you'll get some with nice high hfe, that's what I'm gonna try.
martin clark
pinko bodger
No but it might take out a speaker if the LTP unbalancing itself that way leads to a nice DC offset when the amp output 'rails'... which would not ncessarily trip any protection if your amp is one with regulation (eg NAP250)
hmm thats worse, i like my Linns as they are and theres no crossovers to help at all
I take it you get the usual turn-on thump from the amps? Do you have any protection for your tweeters?
Les/Zener - I dont think 546's are the issue - rated 65V and is what we would change to.
Its 547s (and other originals Bc239) in Naim boards we are worried about that are rated 45V.
I realise even then they will have some safety factor on the component and are being run at low current. Still a concern running at 51V though.
Should they be changed quick smart?
Its 547s (and other originals Bc239) in Naim boards we are worried about that are rated 45V.
I realise even then they will have some safety factor on the component and are being run at low current. Still a concern running at 51V though.
Should they be changed quick smart?