ETI 5000 MOSFET Power amp

[The Saint]

Hi Suzy

Great to hear you amp is working...

IMHO I have found that it is important to balance the speed
difference between the N-chn and P-chn fets. this is best achieved I believe by increasing the N-channel get resistor value
with respect to the P-channel. You see the P-chn fet is quite a bit slower that the N-channel fet, so the n-channel fet will need to be slowed down to the same speed of the P-channel.
This I have found will rid of the oscillation and helps to get rid of cross conduction issues.
My NX150 and NX400 Amplifiers do not cross conduct even at 200khz and have no oscillation issues at all.

also when testing the amplifiers into a dummy load try loading
the amp with a 2uf MKP in parallel with an 8 Ohm load this will show up any instablity issues if any. 2 Ohms load have habit of doing this as well.

Anyway good luck with you amp. Very impressed with your eye for detail.

[Samuel Jayaraj]

Suzyj, try out my recommendation of gate resistors values. I am sure they will help almost eliminate oscillation issues and improve sonics as well. These were Randy Slones favoured values when using 2SK1058 and 2SJ162 mosfets. I have used them and have been mighty pleased. However, if you are using the 2SK133,134,135 and 2SJ74,75,76 types values may differ.

[johndiy]

this amp has been built to high levels of sophistication
just think this-if it all turns out bad sounding what a
contrast of objectivist misinformation

i am just waiting to see this rf-audio-amp really come
to completion including casing etc the designer is keen
to push the limits of performance with some rf know
how lets see

suzyj no1

cheers

john

[suzyj]

Originally posted by The Saint
IMHO I have found that it is important to balance the speed
difference between the N-chn and P-chn fets. this is best achieved I believe by increasing the N-channel get resistor value
with respect to the P-channel. You see the P-chn fet is quite a bit slower that the N-channel fet, so the n-channel fet will need to be slowed down to the same speed of the P-channel.

Originally posted by Samuel Jayaraj
Suzyj, try out my recommendation of gate resistors values. I am sure they will help almost eliminate oscillation issues and improve sonics as well. These were Randy Slones favoured values when using 2SK1058 and 2SJ162 mosfets. I have used them and have been mighty pleased. However, if you are using the 2SK133,134,135 and 2SJ74,75,76 types values may differ.

Thanks guys.

I thought at first that increasing the gate resistors would destroy the intermod performance, but on simulation I find that there's only a very modest increase in intermods (by a dB or two).

However the improvement in stability is remarkable.

I'm now running with 470 and 680 Ohm gate resistors, 2 x 15pF miller caps on each of the driver transisrors, and x16 gain, and my monoblocks are as solid as a rock.

I've done all sorts of horrid things to them - driving them hard into clipping at 20KHz, putting a 2u2 cap across my dummy load, you name it. They just work.

Awesome. Now that I'm satisfied that they won't take off, I can hook them up to my good speakers and do some listening tests.

Again, thanks heaps for your help.

Cheers,

Suzy

[janusz]

Hi Suzyj,

Congratulations!!! Now you can built two or four more units plus active crossovers and go active all the way. It is the most significant improvement heard by all who can still hear something.

Maybe you could post a final cuircuit diagram of your achievement?

One additional note: I keep my power supply for my active system in a separate box. No hum problems in my amps whatsoever. Costs many times less than your board expenditure.

cheers,

[suzyj]

Hi Janusz,

It's certainly tempting. I've got another couple of PCBs, sitting on my bench, looking awefully lonely...

What's the usual deal with active crossover systems? I imagine the woofer needs most of the power, so do you use a thumping big amplifier for the woofers, and smaller ones for mid and tweeters, or just use lots of big ones?

It adds some interesting flexibility, come to think of it. If there's no need to be able to drive large powers at high frequency, one could optimise the amplifier for the tweeters for slew rate, and end up with much better system performance.

So do you put the amps with the speakers, or with the sources?

On another note, I think I've found a reasonable sound card. It's the M-Audio Audiophile USB. Looks like it has reasonably good distortion specs, at any rate. I've been working on my hubby to convince him that I really need one. "But darling, I can use it in the HTPC that I want to make..."

Cheers,

Suzy (married to a saint)

[johndiy]

-------------------------------------------------------------------------------
susyj:
I'm now running with 470 and 680 Ohm gate resistors, 2 x 15pF miller caps on each of the driver transisrors, and x16 gain, and my monoblocks are as solid as a rock.
------------------------------------------------------------------------------
i'd suggest you increase the miller caps to at least 100pf!on the other hand leave em and take the risk

john - class-a guru

[jacco vermeulen]

Originally posted by suzyj
M-Audio Audiophile USB.

Miss Jackson,

You could ask Janneman how he likes it, he uses it.
(thinking of getting one myself too)

Traditional power distribution for a 3-way is: 2-1-1
So say 100 watts for the woofer, and 50 for mid and high.

Going to post some pictures of the finished work ?

J(Just another devil)

[janusz]

Hi Suzyj,

Jacco already replied on power requirements for a three way system. If I remember correctly, on the average, there is only about 15% of sonic energy above 3kHz but it is good to have ample headroom in all amps.

My power amps are in boxes and speakers are connected by thick speaker cables. You may attach power amps to speaker boxes if you wish. Each solution has advantages and disadvantages. I prefer boxed amps close to their preamp and active crossover. Connecting small signal cables are short and amps are not exposed to direct speaker vibrations.

The current system I'm stll building has active 600Hz crossover (4th order Bessel, low pass is all pass minus high pass) but midrange and tweeter are crossed passively (simple first order crossover). All four amps are identical - about 150W RMS into 8 ohms. As my woofers are 6ohm (2x12ohm parallel), while midrange and tweeter are 8 ohms each, my woofers see a 200W amp.

The system will have separate active servo subwoofers crossed at about 120Hz. There will be two subwoofers. These are my intentions. Maybe they will come true. I also intended to keep my old car for the next 2-3 years but three weeks ago it was terminated on an intersection by a student from India. Luckily, no one was hurt.

cheers,

[ralphs99]

Hi Suzy,

I'm sure you'll be very happy with the M-Audio card. I've got a Soundblaster Audigy NX USB card that is also very good and has been an extemely useful tool for me. I use it for just about all of my audio measurements.

Soundblaster products have a mixed reputation, but this particular card is pretty good. I've measued residual THD+N at -90dB (0.003%). By looking at the individual harmonics I can resolve distortion products down to about -94dB, which is usually enough for me.

The M-Audio card will probably do even better.

With regard to active crossovers; I'm a big fan! Rather than repeat the advantages here, I suggest you have a look at Rod Elliot's site. He's got an excellent article on active crossovers and loads of other great information. A clever guy who really tells it like it is. And he's a local!
http://sound.westhost.com/biamp-vs-passive.htm

Cheers, Ralph