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Is class A bass light?

norriemal

norriemal

Hertz and Minds
Recently I've been unhappy with the light bass that I was getting from my Proac Super Towers and was pointing the finger at a refoam. By chance I changed the speaker cable from some solid core similar to DNM Reson to basic 74 strand. The bass opened up and I thought I had found the problem so I was happy.

I also had earthing issues with my pre being double earthed and power amp not. So last week I had a bit of a shuffle around of my stuff and replaced the AURA PA-200 power amp with an Audiolab 8000P. Both are rated at around 100WPC but the AURA is pure class A.

The difference was like night and day with what I would describe as really tight and in control bass slam. Hence my question is class A bass light in any way?

The only other thought is that in running an earth wire between the turntable earth post on the pre and the case of the power amp to overcome the hum problem I may have impacted the grounding and power in some way.

Maybe the Proacs are just not a good match with the power amp as in my study system I have an Audiolab CDQ running balanced cables to an Aura PA200 with no issues at all. The bass from my Allison CD8's goes deep and is effortless and airy with the open sound I like.

My third system now has Albarry M408's into Royd Minstrels and I am enjoying that pairing also.

Any insights welcome as I feel a bit more mixing and matching may be required.
 
I googled the Aura and a couple of comments come up from Wam members regarding its sound signature that may shed some light on your problem.
Bass light and mellow.
 
The set up I'm playing with just now with the Albarrys is an old Pioneer PD 9700 into the digital in of a Sony ESD1000. I had this set up to play with the parametric equalization into a pair of passive Linn Kabers to tame the HF ( ninka tweeter upgrade) and boost the bass.

I am about to try my old PS Audio passive control unit which is what I ran them with 30 years ago. Nostalgia rules.
 
I read somewhere that they are class A but could just be disinformation. I have just looked at the original manual and it only states 110W at 8 ohms and 250W when bridged. Certainly they are almost too hot to touch even in standby. I have 2 of them and was running them bridged for a while but thought it was overkill and was worried about the electricity destroying the planet. If they are not class A I may go back to bridged guilt free.

The Albarry's are great with the Allisons but I felt they were lacking with the Proacs. I will give them another go as it may have been the speaker cable that was limiting them.
 
A 100w pure class A amp would be huge and could well weigh almost 100lbs so perhaps as someone before has suggested, your amp isn't pure class A.

I run two class A systems, using Sugden and Accuphase amps and there's no lacking for bass so no, pure class A should not be bass light.

Incidentally, my Accuphase amps are paired with ProAc K6s and I find the match to be superb.
 
Must just be the character of the amps and getting the balance of the system sorted between the components. Anyway, I am happy that I have my Proacs sounding so in control now.

I'll drop Ramesh who serviced the amps a line and ask him about them as it would be nice to know for sure.
 
Arkless Repairs said:
. The Aura is not Class A BTW....
Click to expand...

I could be wrong but I seem to recall the Aura uses Hitachi Fets. These are normally run at 100mA bias and if there are 2 pairs running off +/-50V rails then each channel will dissipate 20W and achieve 1 or 2W in class A.
20W X 2 (assuming a stereo amp) will result in fairly hot running conditions if the heatsinks are smallish.
 
my 30WPC Class A is not bass light or bass shy at all.

on the contrary, they produce tighter and deeper bass than my Class A/B amp with higher power rating..
 
Singslinger said:
A 100w pure class A amp would be huge and could well weigh almost 100lbs so perhaps as someone before has suggested, your amp isn't pure class A.
Click to expand...

In another thread someone posted photos of an Electrocompaniet amp that was supposedly 250W/ch Class A, it had about enough heat sink for 30W/ch Class A.
 
From memory there are 8 output transistors per channel and the whole case is the heatsink.

aura3.jpg


AuraPA200.jpg


Hi Fi engine has the service manual and the bias is set to 320 - 340 mA and it says to check supplies 20V,-20V, 25V,-25V.

http://www.hifiengine.com/library/aura/pa-200.shtml
 
Just found my original info from Ramesh Ladd in Bradford who is the repair specialist for old B&W stuff. I had them serviced and the upgraded power modules fitted.

There are 8 Mosfet’s on each channel. Mosfet’s are priced £8 each. If it has outputs plus the little surface mounted power pcb on that channel being faulty or burnt then you will have to replace this and is fairly expensive. There was a fault with these original surface mounted pcb so when one of these is replaced with new upgraded version then you have to replace the one on the other channel to balance the outputs and you will also need to reset the bias to stop the pcb’s getting hot and burning up. Repair of Aura PA200 is a very specialised job and should only be handled by very competent engineer otherwise you will end up destroying other parts. When these amplifiers were first introduced by B&W Loudspeakers they you to retail at around £2000. They are very good amplifiers built to a very high specification and working in Class A with virtually zero distortion. Anyway let me know what you wish to do.
 
..........and if they are too hot to touch then summat is wrong. My amps have twenty pairs of output thingies per channel and two 1.2KVA xformers in the box. After a couple of hours listening at realistic spl the box is just lukewarm.

Cheers,

DV
 
To me most FET amps prior to the mid 90s sounded a bit bass light. a huge generalisation and i have not heard all... The Arcam delta 290 and Alpha 5 and 6 I think we're the first FET amps I thought had a bit of bottom thump.

Most FET amps to me always sounded powerful, quite smooth but lacking in mid insight and bottom end thump.
 
Darth Vader said:
..........and if they are too hot to touch then summat is wrong. My amps have twenty pairs of output thingies per channel and two 1.2KVA xformers in the box. After a couple of hours listening at realistic spl the box is just lukewarm.

Cheers,

DV
Click to expand...

But are your amps Class A?
I have a 30w per channel class A amp and it gives out a fair bit of heat from the heatsinking.
 
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