2006 vintage upgrade?

Hi Miguel,

I've been reading your updates and although I'm very pleased how your fellow head-fiers have been enjoying the Solo SRG, I have felt frustrated that I'd not delivered to their full expectations - the comment similar to "I could have used a little extra bass" as you know, I not only take on board, but jump through hoops to correct.

Unfortunately I am unable to make a simple modification to deliver the tad required. Instead it's been the usual case of a few hundred hours research and development, and the same again regarding burn-in time.

The result should actually be known as a completely different model because there is only the faintest similarity to the SRG, that being that it's still an op-amp voltage amplifier with a transistor output stage.

So what had to be changed? It would be easier to list the things that were not changed.

At this point I will have to leave you all in suspense for a little longer as the days chores are pressing right now, but very soon I want to be able to offer all Solo users since spring 2004 a full upgrade service, or a DIY upgrade card.

More info to follow in this thread sooner than it's been going so far.

...while we are waiting for Solo upgrade kit...

There is quick&dirty way of squeezing more bass from Solo driven K701:

Get the AD823 out and swap in AD8397 (heatsinked and mounted on SOIC to DIL adapter).

Please see this link

Although announced to the contrary at the time (some 6 months ago) a rumour has emerged that we still use the AD823 in the SRG. The AD823 was dropped early in production as the financial crisis threatened to wipe out Analogue Devices Inc. (please feel free to look up ADI stocks quotes history). Since then things recovered but the AD823 has not been used in the SRG since.

As a responsible manufacturer (unlike some I could mention) we are highly equipped on the test and measurement gear front. Unlike Mr Pease ex of National Semiconductor who frowns on simulators, I use one of the best on the market and even without modelling in parasitics it can easily be seen that some op-amps are unsuited to some applications.

Even without any test gear or simulation it can be seen what it says on Data Sheets and for the LM4562 and LME49860 which is the same in every respect apart from its supply voltage, both data sheets clearly show a 16% overshoot for a 100pf capacitive load.

Although no capacitors can be seen between the output of the Solo opamp and its output transistors they exist! Those who don't see them don't know electronics, and shouldn't really be making any performance claims (sorry to be so harsh - you'll have to forgive this blunt Yorkshireman).

Bipolar, FET or valve, they all have input capacitance, and even in follower mode feature Cie or the equivalent notation. This is because all devices have a transition frequency at which their gain falls to unity.

The result I'm afraid to say, is oscillation if the equation doesn't balance and if an opamps overshoot is 16% into 100pf, what is it at 10 times that capacitive load? Yes gross distortion at HF (quite possibly beyond our hearing but there is a phenomenon known as mixing which brings in alias frequencies). Now, place that inside a negative feedback loop and even Mr Pease will tell you it oscillates because he knows his stuff!

Edit: I don't really like pulling rank because I'm not arrogant - blunt maybe but not arrogant. Well before the internet and all these opinions my job was to design line drivers and receivers. They were used to transmit live feeds via a BT line from an outside venue back to the studio for FM stereo broadcasting. The BT line from one of these venues was a mile long (Peace Gardens to the Star newspaper building top floor where Radio Hallam in Sheffield lived at the time). Because of the galvanic isolation required by BT (British Telecommunications) there were 1:1 audio transformers either end, but these were essentially transparent to the devices driving them (apart from the excitation current) - they "saw" the 1 mile cable. Those devices were NE5532's!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Pause for the "WI ladies" to vomit....

What a shock! How could that be? Technique! It's not the opamp but the way it's used.


Edited by Graham Slee - 22 Jul 2009 at 2:31am