I had calcualted 140,000uf/ ch , i have .......
Good boy!
Now go and take some pudding from the fridge.
Wayne, here's a workable model.
I won't go into much lenghty explaining, just a basic note. The topology is what I call a Hitachi bastard topology because it looks a lot like what Hitachi serves us in their HMA-7500 MkII MOSFET amp. FYI, that topology has since beome one of the standard topologies anyone talking about them will evetually mentio, and indeed, Bob Cordell makes a note of it. I say "bastard" because it generally looks like that, but there are several changes which do change the original into something different even though similar.
The one thing I felt obliged to do is to use an unusually elaborate front end CCS. There is no current mirror, which makes the front end have a lower Common Mode Rejection Ratio (CMRR) than I'm comfortable with. Some months ago, somebody posted here 10 or 11 types of CCS circuits with measurements of their CMRR factor, and showed that this can vary from a humble number of 42 dB to a much better number of 82 dB, no less than 100 times better. The version I used was not on that list, but it was clear enough that if a cascode circuit was used, the rejection would be much improved over the more common types.
As you can see from the attached schematic, as per your wishes (which I still feel are risky) all overvoltage and overcurrent protection has been removed, leaving only fuses for protection. I'd never do that for myself, but you wanted it just so.
As noted in a previous message, a rough calculation showed you culd get away with 7 pairs, so that's what i used, 7 pairs of 200W plastic pack devices. I have to say that as is, it is running at full power at the very limit of what the transistors can take for any reasonable period of time, as they will likely overheat and trip the overheat protection, which I did leave in because I don't want the transistors melting on you, nor will I ever deliver anything that has no DC protection. I cannot, I have seen in my own room what happens when something goes wrong and a burst of serious DC passes through, turning the bass driver into Kentucky Fried.
Note that amp is AC. It can be developed into a DC amp, all the more so because it has a FET input. Speaking of which, you are probably not going to need C20 if you are sure your preamp blocks DC, simply leave it out and connect the two holes with a bit of wire.
Also, note that in real life, you will need TWO output relays working in parallel, as one will limit you to 16A steady state, although it should pass aroud 24A in short term peaks.
As it turned out, the number of compromises I had to make was way less than I expected. Yes, I had to use more global NFB, but it's still around 31 dB only, still WAY below that "you can't have too much NFB" school limit.
But I did get what you wanted, reasonably low THD and IM specs even into 1 Ohm load. Here's a list of preliminary measurements, with input filter limiting at 200 kHz:
Open loop full power bandwidth - 42 kHz, THD 1.3% at 42 kHz
Open loop full power bandwidth at 20 kHz - output voltage 18Vrms, THD 0,8%
31 mV produces 20Vrms output open loop, OL gain 645:1 (56.2 dB)
1.1V produces 20Vrms closed loop, closed loop gain 25.2 dB
Output 1W/1 Ohms, 1 kHz - THD 0.003%
Output 20Vrms, 20-20,000 Hz, 1 Ohm - < 0.06%
Output 20Vrms, 20-20.000 Hz, 2 Ohms - < 0.05%
Output 20Vrms, 20-20.000 Hz, 3 Ohms - < 0.03%
Output 20Vrms, 20-20.000 Hz, 4 Ohms - < 0.02%
Output 20Vrms, 20-20.000 Hz, 6 Ohms - < 0.015%
Output 20Vrms, 20-20.000 Hz, 8 Ohms - < 0.012%
Obviously, by 4 Ohms, we are in fact reaching the limits of the topology.
Mote than this, the square wave perofrmance looks really good, controlled overshoots, no ringing to speak of.
Even more important, harmonic decay looks very promising as well, but still needs some work to meake it really good.
If you want to discuss it further, I suggest we switch to private post, so as not to throttle the whole forum with this one-off product.
FYI, I am chalking you up for an extra small bottle of an alternative chilli sauce, but one which must make me run on afterburners.
PS. I forgot - the bias current is 115 mA per transistor, currently a total of (7 x 115) 805 mA.
I guess you have no photos of a working prototype.....again?
I had calcualted 140,000uf/ ch , i have .......
What voltage and in what kind of configuration?
* "Calculated"
why this is common prejudice?Not adverse to anything but bad sound Dutchie, no preference at all .....
Yes , but neither is passing the signal thru miles of copper and transformer hysteresis an answer ...
who in the world would make fransformer iron from magnetic hard material ???
And why would I do that, Pierre?
For one thing, I've never heard an audio device requiring so many Amps of current which used a switchmode PSU, I only know from magazines that Chord does.
For another ,why complicate matters? A straight linear PSU is a known quantity, and if done well, it will perform as predicted. Very few unknowns, and those that do exist can be easily remedied.
Besides, please remember one and all, this is strictly a one-off essay, I don't even know anyone else with similar requirements of Wayne, and if by some strange chance you are such a person, Pierre, I feel absolutely sure you could do extremely well for yourself and you don't need me, even if only on basis of what you were doing back in 2003.
I believe Wayne picked that aspect from my previous posts, some months back.
Theory has it that we need 1-2 Joules of energy for ever 10W of dissipated power, depending on how complex and difficult that load is. It is assumed we know what our PSU voltages will be at full power on.
If so, then we make an assumption regrading load difficulty and calculate according to the formula:
Joules = /(+Vcc sq)C/:2
for symmterical +/- PSUs.
In Wayne's case, and according to my essay, supply is +/-42V and power is 400W/1 Ohm. Wayne was optimistic and opted for 1 Joule/10W, for a total of 40 Joules. So, we have:
Joules = /1764 x 0.14/:2 = 61.74
which corresponds to 1.5 Joules/10W dissipated. He obviously likes working with a good safety margin, because if you recall, he did say that it's the bass which is at 1 Ohm impedance, and that above the bass driver range, the impedance only rises, thus also reducing energy requirements.
Why dont we approach this as the best approach needed to build, 35 yrs at this and i have never heard a small amp sound better than big, small for me is 100@ 8 and delivers it voltages regardless of load or speaker type driven and yes not interested in Switchmode, not going to experiment with that...
@ Jacco ,
we had calculated some time back a min of 140K uf/ch, not 85K, some calculators gave me 240K/ch, of course it depends on how much ripple you are willing to put up with....
Oh Dear, me had 170K stuck in my head, I must be getting old and blind.
Hang on, I had my eyes lasered not so long ago, I demand a refund.
140K uf is 70.000uF per rail.
Ripple is calculated with the number of C's on the rail => c = 100/ω.r.p
What was the sensitivity of your monsters again ?
(I figured you might like to see another 1R capable amp. It's more modern little brother does a nominal 150/8 continuous and 1200W/1. Also fully balanced, balanced operation allows silly high output current levels. SOA and all that)
Sounds good, what brand is it , i do want to try and do a diy deal and eventually make the speakers active 3 way , amps in the panel would work ...
Sensitivity is 80db on a good day ...
@D ,
tried your email , chk on it ....
@Northstar...
Hang in their Bob ....
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I'm trying my very best Wayne; but I do have to admit that some of you guys here are way more advanced than I in some audio departments.
* I think that active powered speakers are a great way to go. ...Matching amps with their proper dedicated drivers and speaker's enclosures.
...Separate active crossovers?
* I think that active powered speakers are a great way to go. ...Matching amps with their proper dedicated drivers and speaker's enclosures.
...Separate active crossovers?
Ok, i know the amplifier very well , reliability is an issue with some levinsons at such a low load, never had a chance to try the specific one you are talking about thou ...
Edit: I did try one of those amplifiers when they were new and they were fantanstic, different speaker thou and new they were out of my price range ..
Mark Levinson No.33H monoblock power amplifier Measurements part 2 | Stereophile.com
It does look the part , the levinson I'm thinking of was another model (331) owned by a friend he had reliability issues with it on his Divas ...
Edit: I did try one of those amplifiers when they were new and they were fantanstic, different speaker thou and new they were out of my price range ..
Mark Levinson No.33H monoblock power amplifier Measurements part 2 | Stereophile.com
It does look the part , the levinson I'm thinking of was another model (331) owned by a friend he had reliability issues with it on his Divas ...
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Jacco, I don't think it's come to that stage yet. There are many issues to resolve before that, case dimensions and available real estate for one.
Then, what to use, a relatively smaller number of big caps, or a multitude of smalle caps. Bigger caps filter better, but are slower, smaller caps don't filter as well, but are faster. A mixture, then, but how to distribute?
Many issues to resolve yet.
Then, what to use, a relatively smaller number of big caps, or a multitude of smalle caps. Bigger caps filter better, but are slower, smaller caps don't filter as well, but are faster. A mixture, then, but how to distribute?
Many issues to resolve yet.
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