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RE: 3B SST...

Morricab: Triodes versus Bipolar from Humble


You may be interested to learn young man that between Disbeliever and myself there amounts to over 100 years of listening to both valve & transistor amplifiers , we do not essentially disagree with you about sound quality and can concur that many amplifiers that measured well were largely overrated. However you appear to be widening the goalposts, originally stating that triodes had less distortion than bipolar transistors being a blanket statement without any circuit references, so I had to challenge you. You then go on to rubbish any form of feedback as if it were the bane of any design concept in the audio domain.

So firstly allow me to clarify a few points, it is true that taken as as an individual device transistors do have more intrinsic distortion than say a high mu triode but the point I have re-iterated is that a solitary transistor is rarely used in isolation as a straight amplifying device in a high quality amplifier, so the point about distortion becomes irrelevant , simply put, a circuit topography is used because the way in which transistors work allows it to be used to cancel out the very distortion that nonlinearities produce, but in such a way that it essentially still remains within the domain of a single device, meaning no phase anomalies an increase in speed thus widening the bandwidth and significant reduction in all distortions, yes it is essentially within the realms of current negative feedback, but the electrical reaction within the topography is without detriment , it,s now a symbiotic unity. The simplest of which is the longtailed differential pair to the more complex Current mirror load and constant current source, the same CCS is often used to feed the next stage the VAS to improve its linearity.

Now it is also true that with this type of topography very high intrinsic gains are achieved and further distortion from the output devices and drivers are also reduced by negative feedback, however many articles have been written about the proper use of feedback and all those other artifacts of SID, TID etc. which includes nested feedback to reduce phase anomalies , but you can not rule out the fact that many very good amplifiers have been designed with both high & low amounts of feedback, and some like Onkyo with no Global feedback which still produce relatively low amounts of distortion because the circuits are an amalgam of topographies used to reduce the additive stage distortion and if I remember correctly the Onkyo produced around 0.02% that Company believing as you do that an amp with limited distortion sounded better but in fact did,nt.

Referring to Geddes and Lee have you considered what happens when when say an audio amplifier of the transistor variety uses differing devices throughout the amplifying stages , for instance a J.Fet front end with it,s slope character followed by a standard B.polar VAS stage then followed by by say Mosfets, here you have three different slopes all adding their own particular distortions , feed all these back into the early stage and you have a disparity of control which results in both odd and even harmonics but more importantly some of the harmonic intervals are not amplitude consistant meaning some harmonics in the higher reaches have a larger than those proceeding, perhaps this is one reason why feedback can have rather unpleasant sounds with some designs , but is not generally known as a casual link,.. but in the end preferences will always be the deciding factor, however for proof of the proverbial pudding just take a well respected modern amplifier of each variety , in the case of the transitor version remove the input filter if it has one , then feed it with a square wave set at the same level as a valve version , then monitor the output into a dummy load , I think you will be very suprised at the result, because all the other factors of the amps will come into play which include the reaction by capacitors in the signal path and the interelectrode capacitance of the triodes CGK+(A+1)CAG, this then becomes a measure of accuracy not necessarily distortion, because it is measuring the filtering effect of both types of amplifier .

I have already conceded that there are many amplifiers of the valve variety out there which sound very sweet, so essentially we are not in any conflict whatever, I simply believe that a properly designed Transistor amplifier will give very satisfactory and pleasing results and can be blameless, I have had many debates with well regarded audio engineers , consultants and other speaker designers. Everyone has a preference for their particular beliefs and experiences , but they would all tell you that sound quality is of paramount importance but more often than not are convinced that their way is the only way forward and so sometimes get caught up in a negative feedback loop. ha ha.

Humble



Edits: 04/09/14 04/09/14 04/09/14 04/09/14
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