New to the forums

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hi,

Rotel have a good track record in amplifier designs.

I doubt you could build a clearly better cheap amplifier.

2.5" FR's are no way to judge an amplifier. You need
a proper hifi system to illustrate the differences.

There is nothing cheap about building amplifiers.
My favourite budget amplifier, the Pioneer A300X,
can be picked up for £60, and it would cost a small
fortune to build an amplifier of the same quality.

rgds, sreten.
 
From my experiences, my little 2.5 inch full-range drivers 'colour' the sound less than other speakers and therefore I would have expected them to allow a good amp to shine through. I've listened to a lot of speakers and these little full-range drivers are the clearest I've ever heard. Including some that get a lot of hype on this forum. Night and day better than anything else. They just don't go loud or deep.

I was hoping that similar compromises would be available for amps if I don't need it to go loud.

Thanks,
Matt
 
Hi Guys

It is often assumed that a low-power amp should be considerably simpler than a high-power one, however this is incorrect. All of the techniques that give a high-power amp its good performance - or that can improve its performance - also improve the performance of a low-watt amp.

One thing that is easy to do is to use much higher supply rails than are required for the power level you desire. For example, lots of guys build 100W amps. At 8R, 100Wrms is 200Wpk and thus 40Vpk. You could squeak by with sub-50V rails and maybe get acceptable performance. But... if the circuit is designed with 80-90V rails, the THD20 at 40V output is much lower than the low-voltage amp.

On the other hand, you can purposely design a low-voltage amp for low power output that has phenomenally low THD. For example, I designed an amp to drive 4R in balanced mode, i.e. bridged, as there are sonic advantages to doing this. Anyway, because I only needed about 1-2W maximum, I could design it to operate class-A to eliminate crossover distortion, and keep dissipation down by running the output stage at +/-8V. The front-end runs off 24V rails. THD20 at 4V into 2R is 1ppm. In bridge mode, this would be 8Vpk at 4R, so 16Wpk - waaaaay more than I can ever stand or use. At 2V per side, 4V total, THD20 drops to 90ppb. THD at 1kHz is 1800ppb at 4V per side and 20ppb at 2V per side. For my speakers, these are power levels I will never approach, and at the levels I do use THD20 is <10ppb. This amp has 14 Qs and could readily drive my speakers single-ended with similarly low THD. The board for each block is only 3.4 x 2.5" or so, so doubling them to run balanced is no big deal. This is further doubled by the fact I have a sub-sat system.

There are 2" drivers that have fantastic near-FR performance, such as the Jordan 92s, now replaced by the larger Eikona 60. You need a sub that can go up to about 160Hz with the original modules, or about 80-100Hz with the Eikonas.

Proper assessment of speakers and amps happens at low and medium SPLs. You do not want your ears compressing or getting tired - if they do either then you are not hearing things accurately. I often turn things down if I want to hear everything. Bass sounds better quieter; everything does.

Also, if you want a really good performing amp kit, check out Doug Self's Compact Blameless on his site: Signal Transfer Company.

Have fun
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.