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Old 7th May 2015, 10:36 PM   #1
MatthewHorton is offline MatthewHorton  United Kingdom
diyAudio Member
Join Date: May 2015
Location: Leicester, UK
Default New to the forums

Hi everyone,

I have been reading the speaker forums on here for a while and i've just signed up for an account because I wanted to ask for some advice on amps.

I am from a studio background where neutral room and speakers are the most important for creating a balanced mix. We treat an amp as an amp. As long as it powers the speakers, we're happy.

I would like to build a simple low powered amp to power my 2.5inch full range drivers to prove to myself that a good amp can sound better than another amp. Ive never really been able to hear a difference in amps, probably because I'm concentrating on other things.

Which amp is quick, simple and cheap to build that would be good enough for me to hear an improvement over amps that I'm used to? I would prefer a kit to be honest. It doesn't have to be high power.

The amp that I'm using at the moment is a Rotel RA-04.

Many thanks for your help,
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Old 7th May 2015, 11:01 PM   #2
sreten is offline sreten  United Kingdom
Join Date: Nov 2003
Location: Brighton UK

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.
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Old 8th May 2015, 09:34 AM   #3
MatthewHorton is offline MatthewHorton  United Kingdom
diyAudio Member
Join Date: May 2015
Location: Leicester, UK
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.

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Old 8th May 2015, 10:55 PM   #4
Struth is offline Struth  Canada
Join Date: Aug 2012
Location: books at londonpower.com
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
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