Are you using a passive X-Over or active X-Over?
If passive you already have one in place... besides I don't think the Vifa are that sensitive of a tweeter. Ribbons are notorious for being easily damaged, the capacitor just add a small degree of protection at the cost of slight colouration of the sound.
If passive you already have one in place... besides I don't think the Vifa are that sensitive of a tweeter. Ribbons are notorious for being easily damaged, the capacitor just add a small degree of protection at the cost of slight colouration of the sound.
hopefully there will be more stories and photos of application and listening impressions in the coming weeks/months, so dont write the thread off, but its a GB thread and the GB was finished within 24hrs, few have built the amp yet as about half of the PCBs that were sold have been waiting on heatsinks and parts, so theres a lot of filler.
Anyone who has heard them is impressed, as much as you can be impressed with distilled water, if you catch my meaning. on the whole most members of the GB are pretty objectively biased, so you wont find any talk of maidens performing 'miracles' on 'members' here
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most tweeters are rated for 100-200W just so they can cope without being overloaded/burned. with a digital XO, particularly without a cap, I would be very surprised if you use more than 5W for HF perhaps with transients up to 10W, I cannot foresee any situation where you will run out of power
Anyone who has heard them is impressed, as much as you can be impressed with distilled water, if you catch my meaning. on the whole most members of the GB are pretty objectively biased, so you wont find any talk of maidens performing 'miracles' on 'members' here
. most tweeters are rated for 100-200W just so they can cope without being overloaded/burned. with a digital XO, particularly without a cap, I would be very surprised if you use more than 5W for HF perhaps with transients up to 10W, I cannot foresee any situation where you will run out of power
I have active crossover and scanspeak 6600 aircirc which is electrically pretty similar to the xt25 (main difference between the two is low frequency distortion is lower on the 6600, I have a pair of xt25 that I may test out for giggles in my speakers too). My plan is to test with a cap then remove it.
What crossover are you using? I just say this because I know what transients the minidsp 2x4 produce (I have one) and you don't want to omit the cap if you're using a minidsp.
You should be ok.
Which active crossover design are you using?
[OT tangent, that's just how we tend to roll in this thread ...]
With the xt25 you want to make sure you get the notch filter included even if you are using reasonably steep crossover slope. Have a read of zaph's zd5 article on the HF crossover he's used there which appears to me to be of the most thoroghly documented crossovers using this tweeter.
Which active crossover design are you using?
[OT tangent, that's just how we tend to roll in this thread ...]
With the xt25 you want to make sure you get the notch filter included even if you are using reasonably steep crossover slope. Have a read of zaph's zd5 article on the HF crossover he's used there which appears to me to be of the most thoroghly documented crossovers using this tweeter.
Hi Guys,
Just a note of caution... these little amps don't have a large enough startup/shutdown transient to worry about with pretty much any tweeter, but if anything else in your system does, then you could be in trouble. Only omit the cap on the tweeter when you've tested the entire system for power loss behaviour.
If you don't have a scope, then you can use a larger scrap driver and hook it up in place of the tweeter. Plug the entire system into a power bar and try a series of power-loss scenarios... sometimes systems behave differently each time they shutdown.
As for the transient current, it is indeed true that these little buffers can deliver significantly more transient current than the RMS value I listed here. This is only really true for impedances lower than 8 ohms since driving an 8 ohm speaker will be voltage limited. Into 4 ohms however, you should be able to get over 30W under transient conditions.
Cheers,
Owen
Just a note of caution... these little amps don't have a large enough startup/shutdown transient to worry about with pretty much any tweeter, but if anything else in your system does, then you could be in trouble. Only omit the cap on the tweeter when you've tested the entire system for power loss behaviour.
If you don't have a scope, then you can use a larger scrap driver and hook it up in place of the tweeter. Plug the entire system into a power bar and try a series of power-loss scenarios... sometimes systems behave differently each time they shutdown.
As for the transient current, it is indeed true that these little buffers can deliver significantly more transient current than the RMS value I listed here. This is only really true for impedances lower than 8 ohms since driving an 8 ohm speaker will be voltage limited. Into 4 ohms however, you should be able to get over 30W under transient conditions.
Cheers,
Owen
since my system is very similar to your system (for this driver anyway) it should be ok, particularly with relay switching for power. i'll try a cap first though still. of course one of the bonuses of balanced input shows itself here too. so you confirm that as far as the amp itself goes, theres no trouble yes? in my system the amp will be the last thing to go on, sequenced that way.
with 6 ohms sounds like i'll get a bit more, but not a whole lot more transient power delivery too, which is nice.
with 6 ohms sounds like i'll get a bit more, but not a whole lot more transient power delivery too, which is nice.
Thanks for confirming that the short circuit rating of the buffers will contribute to the transient power for lower impedance loads Owen!
I will sleep more easily now that I am confident the tweeter isn't going to be a limitation when I have the urge to listen to a some tunes at properly neighbourhood-engaging levels!
I will sleep more easily now that I am confident the tweeter isn't going to be a limitation when I have the urge to listen to a some tunes at properly neighbourhood-engaging levels!
Thanks abraxalito for prompting me to think this through properly, I've been thinking about this a few different ways for a while now and obviously I hadn't got my head around it properly - there was quite a few things I've forgotten while designing power systems and not electronics since my uni days. This is the first power amp I've built so haven't had to think this through previously (hence asking in earlier post if it is fair to include Iout-sc in the power calc). Now I've done the calculations myself I see what's going on a lot more clearly!
I think it has all finally made sense now.
Hopefully people can correct the below logic if I've lead myself astray again.
With this amp into a 4ohm load the current output is the limitation for power produced by the amp, not voltage. ['voltage limited' gives 32W, 'current limited' gives 8W therefore we're calling the power rating 8W]
But under transient conditions on a lower impedance load (in my case 4ohm) the buffers Iout-shortcircuit can give up to double the output current. From datasheet Iout-sc = 500mA vs Iout = 250mA.
A 4ohm load at full voltage swing (assuming 16V voltage swing from18V rails) needs 2.8ARMS therefore ~350mA per buffer.
The point of all this rambling is that with a driver sensitivity SPL given in dB @ 2.83V because the amp is current limited I cannot just calculate max SPL with full voltage swing unless I am confident the amp can handle the corresponding current.
With an 8ohm load, as Owen has said, the current and voltage limits of this amp are about even in terms of power output so the above is of little concern.
I think it has all finally made sense now.
Hopefully people can correct the below logic if I've lead myself astray again.
With this amp into a 4ohm load the current output is the limitation for power produced by the amp, not voltage. ['voltage limited' gives 32W, 'current limited' gives 8W therefore we're calling the power rating 8W]
But under transient conditions on a lower impedance load (in my case 4ohm) the buffers Iout-shortcircuit can give up to double the output current. From datasheet Iout-sc = 500mA vs Iout = 250mA.
A 4ohm load at full voltage swing (assuming 16V voltage swing from18V rails) needs 2.8ARMS therefore ~350mA per buffer.
The point of all this rambling is that with a driver sensitivity SPL given in dB @ 2.83V because the amp is current limited I cannot just calculate max SPL with full voltage swing unless I am confident the amp can handle the corresponding current.
With an 8ohm load, as Owen has said, the current and voltage limits of this amp are about even in terms of power output so the above is of little concern.
Yes, I think this is a crucial insight.
Another line of approach is that driver sensitivities are given typically for '8ohm-watts' (i.e. the voltage that would give a 1W input into an 8R load). But then when a unit is 4R we either need to subtract 3dB to give its efficiency per watt (so the 91dB figure for 2W in goes down to 88dB for 1W) or ensure that the amp is a pure voltage source - its output voltage needs to be reasonably load-invariant.
When I did the estimations for the Rickie Lee Jones torture track that Bob Cordell cites, I used 8ohm watts in my amplifier power estimations, not actual power into the units (which can be other than 8R).
Started work putting together the amps last night - I have all the smd components and the voltage regs in. I should have the them up and running tonight.
Quick question, I have two currently 12V-0-12V toroids. Will these be ok or should I pick up some 15-0-15 transformers after work tonight?
Cheers,
Jake
Quick question, I have two currently 12V-0-12V toroids. Will these be ok or should I pick up some 15-0-15 transformers after work tonight?
Cheers,
Jake
For you (assuming you're still using it with the xt25 tweeter) it is less critical to have highest possible voltage rails.
To achieve 8W output into 4ohm you'd can get away with much lower voltage rails.
This is because 0.25A per buffer is reached with only 5.66V RMS output.
So for your 4ohm driver your required rail voltage depends on your listening habits and if you think you'll need extra voltage swing for transients.