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Old 29th August 2007, 08:26 AM   #1
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Join Date: Jul 2007
Default Class A does sound better!

Dear Pass Labs DIY's,

Two months ago I started a thread with the following subject: "Why Class A? Wasting power is something of the past "
Some people reacted a bit upset because they thought I was attacking Nelson Pass's designs and thereby himself. Others thought I was mere ignorant, lacking knowledge or just argumenting for the sake of it. Let's say I could have been more cautious more subtle in my approach.

I operate a Levinson ML-3 (Class AB2 amp) on a set of Acoustat 2 + 2. Recently I bought a pair of Levinson ML-2 Class Amplifiers for the resell. I hooked them up to establish if they work. You'll allready guessed it they outclassed the ML-3 in every parameter except for earbleeding soundpressure of course. I'm very familiar with the beautiful debut of Damien Rice O, (Song 'The blower's daughter' in the movie 'Closer') and the sound really purified with the ML-2 and not by a small margin.
The ML-2 is a complementary design biased for 25 Watts/8 Ohm and it consumes 400 Watts when idling. The design (completely modular) is originally from John Curl I believe (designated JC-3) but finalized by Thomas Colangelo. Mine are now almost 30 years old and a regulator card in one of the ML-2's (AP1) has a big black burning spot behind the three 10 Ohm parallel configurated rushin current limiting resistors. On that PCB there is a DC trimmer and I can't turn down DC-offset more then 35 mV with it because it's at the end of the turningcapability.
Three of the four Elmwood thermalsensors on the outputmodules (2 X NPN 2n5886, 2 X PNP 5884) were removed.
So I keep the ML-3 at hand because I'm not sure how long the ML-2's will operate properly.

So with ML gear my question/argument is answered. Yess Class A is worth it.
I have to make a apolagy to you (G. Rollins especially) for my stuborness.

A friend of mine was in search of a new amplifier. I advised him to listen to a Pass X-350.5 and X1 pre-amp. He bought the preamp allready and is waiting for a X-250 or 350.

Hope you forgive me all

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Old 29th August 2007, 02:42 PM   #2
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Location: Columbia, SC
Not a problem.
Yes, class A is a nuisance in the summer, but in the winter it's actually more efficient in this way: You'd be generating that heat anyway, just to keep your home warm, right? At least this way the energy is put to use twice, once creating music, then as heat to keep you warm.

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Old 29th August 2007, 06:01 PM   #3
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John Curl frequents the Solid State forum, and you might be
able to obtain needed information from him regarding service
issues on the ML-2.

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Old 29th August 2007, 08:46 PM   #4
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Location: Columbia, SC
If you want to undertake repairs yourself, the schematics for the ML-2 are available at, but be aware that the site seems to be offline a lot these days. If at first you don't succeed, try again an hour later.

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Old 29th August 2007, 09:44 PM   #5
Jaac is offline Jaac  Netherlands
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What i don't get is that the ML-2 sound significant better then the ML-3 but you keep the ML-3 ?? please repair the ML-2 !!!

And the X 350.5 is only class A for small amount of power. Go for the XA's
The right tool for the right job, a very nice Solarboat || Ready for a groupbuy ? CLick
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Old 3rd September 2007, 10:01 PM   #6
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Thanks for your replies.
I had the Schematics and servicemanual.
I intend to keep the ML-3 for reserve and when I want to play Sacre du Printemps from igor Stravinsky at a more realistic level then the ML-2's can offer.
The ML-2's are playing though as I concipate this entry so they're not broke yet.
Maybe I can substitute the old ST 2N5884/5886 tandem with a fresh sets of MJ21195/96 and the old oneturn DC, bias and regulator voltage 1K trimmers with new multiturn Spectrol or Bourns ones.
I'm intrested who with Levinson came up in the mid seventies (first ML-2's were delivered in August 1977) to built such a modular power-amplifier. To my knowledge the Audio PC Card was never updated though as like in the no. 20 series (20.5 & 20.6). But the concept seems pretty ok/forward thinking in those times and maybe for a servicing standpoint the modular construction comes in handy.

Greetings to you all
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Old 5th September 2007, 02:47 AM   #7
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It's been my experience that circuits built with a modular philosophy are always touted as something done for the customer "so the amplifier/preamp/etc. can be updated forever." The truth of the matter is that the vast majority of these circuits have about the same product lifespan as their non-modular cousins. Once the circuit is discontinued, no further updates are to be expected. So why do they do it? To make service easier. Not that there's anything wrong with making service easier, mind you, but it is a bit disingenuous to claim that it was done with the customer in mind.
Note that Audio Research (by way of comparison) does have an ongoing update program for just about everything they've ever produced, but to my knowledge they've never produced modular plug-and-play boards like Levinson did with the ML-2. Sure would make their lives easier if they would. On the other hand, given what ARC charges for their updates, I imagine it's a non-trivial addition to their bottom line to have all the updates done the hard way.
I always wanted to own a JC-2 and a pair of ML-2s. Time has passed and I'm fully aware that the phono stage in the JC-2 was flawed and that there are better ways of doing things. Nonetheless, if I ever win the lottery, don't be surprised if I snag a could of old ML units off of ebay. Some dreams die hard.

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Old 5th September 2007, 02:37 PM   #8
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Default Modular construction

You're probably right there.
To my knowledge there was no official update program with the ML-2 as with the no. 20, although the boards do differ over time.
Probably the same is through for the preamps of that era. I also have two LNC-2 crossovers with potted modules inside. Both units have startup problems with their PLS-151 outboard powersupplies and when the fault is in the potted modules of the main unit you which you can't repair them or buy a new one your practically lost. So there's a con for this kind of modular construction, if there potted you can't repair those old items on component level. Later incarnations of the LNC-2 and the successors of the ML1 and 6 the ML-7 and ML-6a used openframe L-modules which can be repaired.

Nice to here your enthousiasm for these old audio products.
Hope you win the lottery or snag a couple of dead dead one s which you, and I've no doubt about that considering the projects you're involved with here, can repair and upgrade them.

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Old 5th September 2007, 03:03 PM   #9
Westley is offline Westley  United States
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I have been upgrading the ML-2's for years. The first place to start with any Class A amp is the filter capacitors. GE and Cornell Dubilier have a 120,000 uf/50V capacitor that I use for the main caps and a 15,000 uf/50V for the rails. The original caps dry up due to time and heat. Replace all the caps on the audio and power supply plug-in modules especially the tantalums. I use the MIT multicaps in the audio board. Replacing the bridge rectifier with a new one or fast recovery bridge also helps.

There are many other things - better output jacks, etc but with these changes, this amp will hold it's own against many amps out there. The bass is better defined, midrange and top end is smoother and more detailed.

I have six of these and the open frame LNC-2 crossover you mentioned used with either a ML-7A or 26S. I have been using these amps since new in 1976. Many speakers, etc have come and gone but I still love these amps.
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Old 5th September 2007, 03:38 PM   #10
AndrewT is offline AndrewT  Scotland
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120,000 uf/50V capacitor that I use for the main caps and a 15,000 uf/50V for the rails.
are these the caps fitted as standard to a 25W amplifier?
+-120mF per channel or shared over two channels?
regards Andrew T.
Sent from my desktop computer using a keyboard
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