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In Reply to: Transistor/tube amps are not linear, inject noise to the signal, have imperfect gain bandwidth's the list goes on.... posted by Ugly on March 6, 2007 at 09:39:40:
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No but as few active stages as possible is usually a good idea. For example, my system with cd has a total of 4 active gain stages (one in the DAC and 3 in the integrated amp). No op amps only 2 tubes and 2 transistors and no negative feedback. For phono I have to add two more active stages to have sufficient gain.
Hi.I share the same 'less means more' idea with you.
Since I love LPs more than my DVD-audio & CD, a good phono premap is needed for me. I use both SS & tube.
My tube pre-amp is a basic two-stage phonostage plus a programme selector, followed by a non-reactive passive volume attenuator. I so designed-built this simple pre-amp to accept MM cartridge, DVD-audio & CD inputs WITHOUT any grounding loop isolation device, e.g. I/P transformer (very popularly used to kill ground loop hums due to multi inputs), & yet neglegible hum at phono I/P full volume.
My SS 'pre-amp' is only a two-stage phonostage employing two NPN bi-polars. Fully monoblock design with 17V battery power supply. I always try not to use any chips. The SS phonostage, being my second phono source, is hooked up to my tube phono-preamp occasionally. Frankly, I prefer my tube phonostage better.
I never got the problem of not enough gain even on playing LPs though many worry about not enough drive with passive linestages. More headroom makes music sound more engaging & more enjoyable.
If you want to cut down on opamps and such in your cd player/DAC then try the Monarchy Audio M24 DAC. I am using it and its fantastic. The analog output stage is a passive IV conversion followed by an SRPP tube output stage. It also has a full tube preamp that I don't use because I really don't need it and it adds an extra stage (it is also SRPP and very good sounding though with a normal power amp). This is how I get only 1 gain stage in the cd player. My amp (kr audio VA350i) uses 3 stages because the "preamp" is passive. So JFET input, MOSFET driver and KR audio T-100 output tubes (1 per channel good for 30 watts). Yep a MOSFET driving an output tube and it works better than any tube driver I have yet heard.I am using a Silvaweld SWH650 phonostage. Its tube rectified and tube regulated (the only transistor in the whole darn thing is the one for the MC input). Simple passive RIAA equalization means no negative feedback here either.
My TT rig is a Voyd "The Voyd" (3 motor concept with big ass power supply making pure sine waves) with Helius Cyalene arm and Benz Micro H2 cartridge (weakest link IMO).
Hi.Better than tubes-driving-tubes? That's news to me.
My experience was reversing yours. The very best power amp I ever heard so far, dollar for dollar, is the Belgian desinged but
Canadian built Tenor Audio 75WP 75W all-triode OTL-OCL power amp monoblock. It was famed a very fine sounding amp beating amps cost many times more, by critics worldwide.It uesd the cheapest tubes imagineable, with SS regulators throughout, yet its sound was good musical & yet so powerful I was very impressed.
Unfortunately, this affordable sonic jewel was discontinued & now replaced by a tubes-driving-MosFETs power monoblock, being more powerful & "less adjustment than the older all-tube model" per the amp distributor.
I was saddened as I missed bigtime the musically being-there from the new hybrid amp.
c-J
"Better than tubes-driving-tubes? That's news to me."Glad I could be the first to break it to you. It shocked me too, believe me. However, I started reading about how difficult it is to really get the driver of the output stage right and where a couple of guys claimed that this was the primary source of distortion in many tube amps. This high voltage MOSFET really controls the output tube such that there is NO sloppiness in the bass (also great output trannies) and yet the mids and highs sound like pure SET. The secret I think is that there is no feedback and the fets are running single ended class A with no feedback, which should produce mostly low order products like a good tube stage (actually according to Boyk and Sussman's model it should produce only 2nd and 4th harmonics due to the quadratic nature of the mosfet).
I know the Tenor OTLs. Fantastic sound and you can really hear how the regulation tightens up the sound compared to some other OTLs. I know this because I had a pair of Silvaweld OTL Tube Reference amps using a similar tube complement to the Tenors. The sound was crystal clear and extremely dynamic. Truly a beautiful sounding amp; however, they were not as well regulated and as a result the bass was somewhat sloppy. The mids and highs were nearly perfect (when biased correctly...too low bias and they began to sound a bit cold). I only sold them though due to the unbearable heat they generated (500 watts per monoblock all the time). The room went up at least 5 degrees C in a couple of hours!!
However, the KR hybrid is just as dynamic and clean sounding as the Tenors with even better bass. Hard to believe but at least to my ears true. Here is a link to the smaller brother of the amp I own. You will see that it has pretty nice measurements for a tube amp in general (let alone a SET).
http://www.vi-fi.nl/assets/s2dmain.html?http://www.vi-fi.nl/xtrartikelen/testen/100000982d090451e/index.html
The one I have gets about 10 more watts. Notice the linearity of the output vs. frequency (no sharp rise in the bass due to tranny saturation big key to good bass performance). Notice also the -3db point is 80Khz...without negative feedback! Distortion at 1 watt has only to the 5th harmonic at about -105db. At 10 watts some higher harmonics but all below -110 db. Even a decent damping factor (always above 5).
The Tenor at 10 watts looks like this:
http://www.soundstagemagazine.com/measurements/tenoraudio_75wi/
Not too bad either but there are more higher order harmonics and there is more power supply noise in the distortion spectrum. Also, the progression is not as smooth probably for two reasons, 1) it is essentially a pushpull amp and 2) it uses negative feedback. Also running in Class AB it will perhaps have a bit more mismatch in the zero crossing (a SET has no discontinuity there). Finally, it has a more complicated circuit which means more active stages with each adding some distortion.
Honestly much of this is made up for by not having the output transformer. OTLs really do sound amazingly transparent and the KR is first tube (output) amp that I have heard that really measures up in this regard. I have found that the OTLs though that are using negative feedback (this means Graaf, Tenor, Silvaweld, and some Atmasphere) to lower the output impedance to a reasonable level do sound a bit less rich harmonically than the best zero feedback tube amps. Not so cold as most solid state and a bit different but not perfect either. Call OTLs my second favorite amps :), with "normal" hybrids my third favorite (I still love the tone of my Sphinx Project 14 hybrid...tubes in Mosfets out). I have heard one, from AcousticPlan, that is very close to sounding like a good OTL.
Right now electronic state of the art is these active devices which have these nonidealnesses built in, ie tubes/transistors. Unfortunately I don't believe there is a such thing as an passive electronic gain stage (don't know of any in any other physcs disciplines either). I have not researched the possibility of using some other class of gain stage and so can't say if the electrical approach is best but one might guess that for example a hydraulic gain stage would have tradeoffs of its own. It is an interesting line of questioning...Whether or not our audio system designers have indeed isoated and implemented the "best" approach that technology allows.My post was not intended to imply anything other than what I believe is the answer to the original posters question. Although you could say that in general I believe when active stages can be avoided in favor of passive stages often times this will yeild meaningful improvements in maintaining a lower distortion of the original signal.
Hi.No gain no 'pain' sonically.
Even the best amp design employing active devices like tubes, discrete bi-polars & chips, there is always distortion due to non-linear transfer of the signals.
Passive topolopy is the better evil than active provided there are enough gain & power to drive the loudspeakers properly.
So keep the active stages minimum to prevent too much gain to overload the headroom needed for the powerstage to swing.
As I posted here last week, even a 2051 chip can be built into a fine sound power amp winning the "Best of 2006" award. The designer
built the simple amp more simple by employing a simple non-inductive
stepped volume attenuator.Less can deliver more.
c-J
Good luck trying to drive any speakers that exist today with a phono cartridge output for example. Even if you can hear it through some ultra efficient mutations of speakers it likely wouldn't be very satisfying volume wise. You see in this day and age the state of the art IS these electronic gain stages that I have listed some of the downsides of.BTW
I don't understand why I am being lectured here. Did I not demonstrate a sufficient understanding of the downsides of the existing commonly used electronic gain stages? Is there something specific that I said which is incorrect?
Hi.I said passive linestage to drive power amps, both tube & SS, that in fact, I am doing since day one, driven by LP phonostage, & DVD-auido & CD player direct. I am still a very happy camper. No audiophile vistors who auditioned my set-up ever complained about not enough guts & juices.
I never hinted a phono cartridge or even via a phonostage with say 0.5V O/P could drive a loudspeaker direct. This is your incorrect impression.Let me tell you a real story in line of your thinking
Years back when I was en-route back home stopping over Vacouver, Canada, I popped in probably the largest hi-end audio boutique in town.
The store manager brought me into one of the audition rooms to listen to some of the very best stuffs. What caught my eyes was a full range of large & tall colourful pair of twisted horn speaker systems with subwoofers (out of my head I forget this pretty famous brandnme). He said if speakers one day could make so highly efficient, he would like to drive direct from a CD player without any amp in between. He said who needed any amps if the source can drive the speaker direct, ideally the best sound.
He did try to drive the horn speakers direct with a high-end CD player & we could hear thinny low low sound coming out from the horn speakers !!! Of course, this was only a trial to show this audio expert's die-hard philosophy of less-deliver-better music.
I don't see why you sound sorta upset?
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