200W mosfet Amplifier

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The Signal Ground (sig IN -) is connected to the power ground trace between the Medium Frequency local decoupling. This will ruin the amplifier.
This PCB has not been thought through.

I don't like the idea of running the LTP at <500uA, the Vas @ 8mA and direct driving the outputs from the low current Vas stage.

And the LTP is running right up at the Vce max rating of the devices (is it beyond the max rating?).
 
With 200W / 8 Ohm (given the supply rails) there's too few output pairs, you want at least 3 pairs. The VAS current is indeed rather low, but it's doable. With those current settings you shouldn't expect a very high bandwidth though, which sorta shows by the applied Cdom of 10pF in conjunction with a relatively high ohmic feedback of 33K.

Edit Vce of the input transistors is reduced some by the series restances in the circuit. When operating normally Vce is honoured, however during startup Vce is dishonored briefly for most of the transistors.
 
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BONE, your right it was published by sc and more so it was de-rated to this 200w watt @ 4 ohms and 140 ish @ 8 ohms (it's a pro sound amp design)

Having build this amplifier and using double die fet's plus adding a transistor within the bias circuit to track the o/p stage.. it gave a good performance..
 
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In a word - No. It is intended to be cheap and robust for pro sound or PA use. I know of 2 examples at work in my area and that is their purpose and end use. Only one has needed service over 10 years, due to being dropped in transport between gigs.

There is more than a little resemblance to the UK Maplin module kits of many years ago and since this published design is inspired by the kit retailer, Altronics, you might see why it could be considered marginal to the conservatives here but rest assured, it works fine in PA.
 
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Hi Ian,
would you concur that would also apply to the Goldmunds and many other cheap amps using the same topology. :rolleyes:
Nico, I don't believe that topology alone is any guarantee of sound quality, or even technical performance. The devil is in the detail as you know, better than I. Many folk here are also aware that this "balanced" VAS mosfet design has been commonly used since Hitachi popularised it long ago in their original TO3 Lateral Mosfet app. notes.

Assuredly, there have been as many c**p sounding amps based on that topology as any other. In fact, the first EA Mosfet kit amplifier here in 1980, which followed the app. notes very closely, sounded abominable, even with increased bias. Though I've never tried to clone Goldmund or other high-end products with the topology, I've custom built more than 30 units and variants in FET and Bipolar versions and bench tested and auditioned a small batch of these particular amplifiers as dual mono pairs in 2U cases, so I have a little experience with the design to back my comment in reply. It sounds clean, neutral and is tough as a pro. amp should be but I don't think it makes the grade as a 140W hi-fi amplifier. There are some other SC BJT versions that sound markedly better, in my view.

The OP has asked about the amplifier as he posted it, with the illustrated construction details. Considering he has been busy posting the same questions about every amplifier over 100W that was visible on the forum, I thought it would be sensible to restrict a reply to just the available details rather than enter into a generalised design merit discussion. This might make a good educational platform but let's see whether it will mean anything yet.
 
Nico, I don't believe that topology alone is any guarantee of sound quality, or even technical performance. The devil is in the detail as you know, better than I. Many folk here are also aware that this "balanced" VAS mosfet design has been commonly used since Hitachi popularised it long ago in their original TO3 Lateral Mosfet app. notes.

Assuredly, there have been as many c**p sounding amps based on that topology as any other. In fact, the first EA Mosfet kit amplifier here in 1980, which followed the app. notes very closely, sounded abominable, even with increased bias. Though I've never tried to clone Goldmund or other high-end products with the topology, I've custom built more than 30 units and variants in FET and Bipolar versions and bench tested and auditioned a small batch of these particular amplifiers as dual mono pairs in 2U cases, so I have a little experience with the design to back my comment in reply. It sounds clean, neutral and is tough as a pro. amp should be but I don't think it makes the grade as a 140W hi-fi amplifier. There are some other SC BJT versions that sound markedly better, in my view.

The OP has asked about the amplifier as he posted it, with the illustrated construction details. Considering he has been busy posting the same questions about every amplifier over 100W that was visible on the forum, I thought it would be sensible to restrict a reply to just the available details rather than enter into a generalised design merit discussion. This might make a good educational platform but let's see whether it will mean anything yet.


I would agree with you on that one..
 
Hi Ian,

I did not intend a dig at you, what I am advocating is that it is really hard to tell what is good for home or audiophile or professional, purely by looking at a schematic.

Simulation tells you a litttle more, not a lot, but may make one feel a little more comfortable with a particular design. Making it and listening is virtually the only way that can influence such a decision.

Ian, please do not feel offended, it was not meant to be.
 
Ian/Amptech,

I have personally never heard a Goldmund, but there was a hype about it and still is. Its topology was similar, by looking at it one cannot say whether it even sounds acceptable, but given its price tab it has to the best sounding amplifier in the world.(I read about this in the particular DIY thread).

I use this particular topology in almost all of my designs with some variations many of them perform phenomenally successful but some variant turns out absolutely junk.

Forgive the remark but this is a difficult topology to predict because it is not critical at all to make it work. However, to make it work great could mean changing a single component from one value to another.
 
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...I did not intend a dig at you, what I am advocating is that it is really hard to tell what is good for home or audiophile or professional, purely by looking at a schematic.
No real problem Nico, but thanks for your concern. I just took the opportunity to rant about my involvement with this design which, when there are the physical clues of having it in your hand and in a test set-up, was less convincing to me than other, electrically similar designs. 'Agreed that you can't see this in a schematic but you can put it down to the issues raised about the PCB layout, parts choices and the power supply, though these may be unimportant to sound reinforcement, which is another game altogether.

By "Hi-fi", I mean in the literal sense where the specification and personal listening impression we get is of flawless sound reproduction for the home environment. Usually, objective measurements fail to distinguish what we are really looking for here, yet we can all have the ability to agree what may sound more natural, accurate, harsh or fatiguing etc. in our personal comparisons.

You can be sure that is the principal interest of the OP and almost everyone on the forum when a new design for personal entertainment is posted. Oddly, when we discuss pro. sound, clock radios, ipods, even home theatre amplifiers, sound quality in these terms rarely gets a mention. ;)
 
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Hi Sakis nice to see you lurking around. I would say that you probably seen this topology in many amplifier brands that you repaired listened to or upgrade and I can bet that each one sounded very different. :)) This is a cameleon kind of topology with its double differential pair, with the right component values it could sound stunning with different ones it can sound awful, the problem is that it takes years of persistent tweaking before you find what you are looking for.
 
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