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-   -   Curent Vs Voltage amplification in Alephs (http://www.diyaudio.com/forums/pass-labs/48090-curent-vs-voltage-amplification-alephs.html)

AR2 20th December 2004 12:41 AM

Curent Vs Voltage amplification in Alephs
 
I cannot make up my mind on the problem that I have, so what better place than this forum to ask.
I am sure many people are having the same problem, so I hope we could come with some answers for many of us.
In my three way active system, my bass speakers - sealed Lambda SB12 drivers are not very sensitive – 87dB and are having pretty flat 3 ohm impedance across the range. Upper part is very sensitive and I am able to drive it with very low powered amps.
It doesn’t matter what I do, or how much power I dump into bass units, it just doesn’t drive them well. The power just disappear like in the black hole. I tried several amps, and it is just not what I need. These amps are suffering.
So I concluded that with such a low impedance I need amp that will produce more current especially in the low freq. range. I am thinking of maybe Aleph 1.2 or some Super high powered version of Aleph X. I played with Aleph X calculations, I read all Aleph X and Aleph X high powered treads but I am not sure that I am finding what I need. High powered Aleph fall short in power that I need. Aleph 1.2 seems OK power wise (even more would be fine) but I do not know if it does what I need. I would like to have 200W at 8ohm and 300 - 400W at 4ohm.
Maybe I do not need to hunt for total power, but for Aleph X circuit that is optimized for high current. If that is the case I would like to ask for help in choosing the right values.
Is this a good rout – class A for bass only? Dou you have any other suggestions?
Thank you and Happy Holidays
AR2

GRollins 20th December 2004 01:59 AM

If you're running a 3 ohm impedance--especially if you intend to play loud--it would be a good idea to go for high bias current. A high powered amp, say 200W, will not do you much good if it current limits into a 3 ohm load. You'll get thin, anemic sound and no dynamics.
You're going to need a very big transformer and lots of heatsinks, and that means money. Start saving your pennies.

Grey

BDP 20th December 2004 03:45 AM

May I suggest building the A75 if you need to sink some current into a low impedance load. You can get the PCBs and a great construction article. This is the area where I think the A75 outperforms the Aleph and since its for the lower frequency range it shouldn't effect the voicing. On the other hand it might just be the driver that doesn't mate well with your mid. It might be less expensive to try a different driver.

BDP

AR2 20th December 2004 07:21 AM

2 Attachment(s)
I do agree with your comments. Currently I am using Mosfet Class AB 200W in 4 ohm and 400 W in 4 ohm and it does sound anemic. Only after heavy equalization I am able to achieve little bit better results. Amazingly, even Ampeg SVT2 Pro – 300W of tubes in 4 ohms has a hard time driving it.
I have to admit that I am responsible for the aquard match, 86-87dB sensitivity in sealed box, and 101 dB for the mid and 100dB for the ribbon. I was going for high sensitivity in upper end in order to use my 2A3 amp and because I love ribbons. That combination works perfect. On the bottom I was going for the lowest extension I could get in the sealed box. Lambda’s Fs is 23Hz and in the box it is flat until 30Hz. I did achieve all of my goals, and I like the sound...
It is sort of.. late to change speaker now since I already have box and veneering done. As well as sound is great as long as there is something to drive it with. The mid PHL is driven by 18W 2A3 amp and ribbon with Brian’s GC. By the calculation I would roughly need 200W to balance out difference in dB. (Without taking in account load)
If I do not find an amp solution I will eventualy change speaker.
After all my experimenting I am afraid that 75W wouldn’t balance it out with my upper part. I certainly could be wrong because I am judging just on Watts, and not by Amps. I will do some research and reading to learn more about this amp.

Quote:

Originally posted by GRollins
You're going to need a very big transformer and lots of heatsinks, and that means money. Start saving your pennies.
Grey

I already started collecting. I have 48 tightly matched IRF 240s, and Aleph X boards. I now that it will take a lot, but after I'm done I am sure that I will achieve a lot as well as enjoy. I am afraid to do callculations on my own, because I wouldn't be sure that I did everything right. Aleph callculation spread sheet is excellent tool, but I do not have enough experience to be sure that I did all correctly. If you could help me with this or suggest any other path I will appreciate it a lot.
THANK YOU

AR2 20th December 2004 07:22 AM

2 Attachment(s)
This one didn't go trough in the first post.

uli 20th December 2004 07:36 AM

Quote:

Originally posted by AR2
I do agree with your comments. Currently I am using Mosfet Class AB 200W in 4 ohm and 400 W in 4 ohm and it does sound anemic. Only after heavy equalization I am able to achieve little bit better results. Amazingly, even Ampeg SVT2 Pro – 300W of tubes in 4 ohms has a hard time driving it.
I have to admit that I am responsible for the aquard match, 86-87dB sensitivity in sealed box, and 101 dB for the mid and 100dB for the ribbon.

Keep in mind that for 14 dB difference you need 25 times (!!!) the power to achieve similar output. High efficiency systems like 100dB/1W/1m are not suitable to lo efficiency woofers.

IMHO the cheapest way is to swap that woofer to a more efficient one. Even using a JBL woofer will be less costly that implementing a weird solution for that unsuitable woofer!

Active driving the woofer only in Class A makes no sense, as the benefits of Class A are in the mid hi region. Every well constructed Class A/B will be better for the woofer. I once biamped my system with Aleph2 for midhi and X250 for the lo end as the X amp had a somewhat tighter bass.

Uli

:nod: :nod: :nod:

pro 20th December 2004 02:59 PM

Can your active crossover increase the bass of 14:bigeyes: dB? It means that for 100mV input of output on mid ans high, it must put out 2,5V on the bass, that it is not a joke. Can it?

uli 20th December 2004 03:16 PM

Quote:

Originally posted by pro
Can your active crossover increase the bass of 14:bigeyes: dB? It means that for 100mV input of output on mid ans high, it must put out 2,5V on the bass, that it is not a joke. Can it?

Not quite correct, 25 times the power means 5 times the voltage
14 dB equals 5 times!

Uli

:nod: :nod: :nod:

ingvar ahlberg 20th December 2004 07:39 PM

Hi
The most obvious solution to Your problems seems to get a better lf driver. The cabinet looks like 50-70 litres, closed or vented?, a Gamma la1231 for instance would make an enourmous difference, same extension 96dB sensitivity, alnico magnet and almost for free , around 100$ in Sweden. If You want to keep present driver maybe the Zen v5 can be a path to try. I use this as amp for my RCF L12P48, better efficiency and further extension but resembling matching disturbances. Also the RCF presents a nicer load to the amp. Running the v5 at 35V rails produces something like 60W at 8 ohms but biased at 2A per output device the subjective impression of power is awesome. When reaching max output voltage swing it ofcourse starts compressing but quite unobtrusive. Have tried to bridge this amp as can be seen in the " power hungry Zen v5 builders" thread. This produced maybe the most powerfull and dynamic bottom end i´ve heard but was almost impossible to get to stay adjusted regarding DC output, will probably require extensive component matching. Also needs balanced input signal. The long nordic winter has settled upon us here so i´ll give it another try.

GRollins 20th December 2004 09:25 PM

Have you actually measured the woofer, or are you assuming that the simulations were correct? It's quite possible, maybe even probable that the low frequency response is not flat. I don't know about Lambdas, but it's true for Shivas, Titanics, and the like; it takes EQ to get flat low end out of them.

Grey


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