Dennis Had Inspire Amps

[Analog Addict]

Scott/Bearcity came by to pick up his PSE when I happened to have a day off. (Greetings! Nice to meet you!) I got there earlier to have lunch and play with my new build. Ran both amps with my new 27 preamp all afternoon.



These are both awesome sounding amps, but my impression is that the Hot Rod is a little warmer and a bit more intimate in sound. The PSE throws a huge sound stage but Al Hirt's horn or Diana Krall's alto move back into the sound stage, kinda like the difference between a club and an arena. Personally, I'd rather have Diana sitting in my lap if that was possible. Anyway, I'm sure Scott will post his opinions eventually, but after a 4 hour drive home, I'm betting it will be tomorrow or later....

[FloridaBoy]

Originally Posted by Musica Amantem

Comzee: Let us know how you like the 6L6 vs KT66 in that same configuration. I love my 6P3S-E (6L6 variation) with the same Sophia mesh plate rectifier (274B). Thanks!

I think you would like the KT66. GL or KT66z. I run them with the same rectifier.

[FloridaBoy]

Originally Posted by Musica Amantem

Now that I read it again, you're right! I just meant, IMO the output tubes are to be picked from a limited family gravitating around the KT66 for easier achievement of an optimal setting (6V6-6L6-KT66-KT88).

All tubes in this amp matter, but the impact of choosing output tubes outside the proposed range makes it more difficult as the increasing power of larger Beam Tetrodes start trading transparency and detailing for sheer power and dynamics, in my limited experience. Sorry for the blabber!

It's not blabber, it's the engineer in you. I was just busting your chops.

[Rosco65]

Originally Posted by Analog Addict;

These are both awesome sounding amps, but [B

my impression is that the Hot Rod is a little warmer and a bit more intimate in sound[/B]. The PSE throws a huge sound stage but Al Hirt's horn or Diana Krall's alto move back into the sound stage, kinda like the difference between a club and an arena. Personally, I'd rather have Diana sitting in my lap if that was possible. Anyway, I'm sure Scott will post his opinions eventually, but after a 4 hour drive home, I'm betting it will be tomorrow or later....

AA - is this with the same tubes in each amplifier? I would be willing to wager you could find a tube combination that would warm up the PSE. An alternate explanation might be that the Hot Rod is running closer to maximum output compared to the PSE, which would imply an increased level of second order distortion that would sound warmer.

Back to the Infinite Impedance Power Supply:

I think we can accept that the key to this power supply design is the implied stability of screen voltage, and perhaps stability of the driver stage voltage as well. This is accomplished by isolating the B+ supply from the screen supply by a rectifier tube. B+ is supplied by a pair of solid state diodes for full wave rectification. In the PSE, this can be particularly advantageous: with four output tubes being fed from one rectifier we can expect instantaneous current demand that could cause a momentary sag in B+ voltage which would then be transmitted to the screen supply voltage. A solid state rectifier can pass current quicker (and pass a lot more current) while the tube rectifier isolates the screen supply from this momentary supply voltage variation. This tube is normally passing DC to DC with the vacuum isolating the input from the output. When the variations in B+ voltage occur under load, this rectifier tube now acts like an actual rectifier, converting the "dirty" B+ AC to "clean" DC in the screen supply.

This is a unique method of achieving this isolation, and an elegant one in that it can be done for the cost of a few small parts and can be retrofit into an existing circuit (at least this circuit). Other designers have taken different approaches to power supply isolation: Gary Dews of Border Patrol uses a "brute force" method. Each stage (input, bias, and output) receives a completely independent tube-rectified and regulated power supply. In his top line amplifier he uses a total of six independent tube power supplies, three for each channel. He's not the first one to do this. Naim Audio has long offered power supply upgrades for their solid state equipment, but rather than configure them as dual mono power supplies, they are configured with separate phono, preamp, and power stage power supplies.

An interesting consideration is if the sound of the PSE with IIPS could be improved with an additional tube rectifier for the B+ supply. This is obviously not a something that would fit in the PSE chassis, but something that may offer a higher level of performance.

Another consideration is the quality of the diodes used in the B+ supply: Jeff Day's interviews with Yakazi-san of the SPEC Corporation bring our attention to the ST Microelectronics STTH6110TV2 diode. They both rave about these relatively expensive ($27) diodes in tube equipment. I would be willing to pony up the extra cost for Dennis to use my amp as a guinea pig.

Finally a general consideration about output power: I've heard more than once that classical music can contains momentary peaks of 30dB. That is a lot, but if that is our objective we need to consider the amp/speaker relationship necessary to achieve this. If we have an efficient speaker of 93dB and we listen at two meters at 80dB, we would need 0.1 wpc. That is an easy load achievable with almost any amplifier. If we are using an Inspire PSE putting out 16 wpc, we have dynamic headroom of about 22dB - not too bad but not 30dB. Even at the lowish 80dB listening levels we can expect some compression. Now if we change any variable, the equation changes as well: if our speakers are 98 dB efficient we will now have 27dB headroom. Conversely, if we double our listening distance to four meters (e.g., in a larger room) we now have only 16dB headroom. Moving the other direction, if we listen near-field (1 meter) we now have 28dB headroom.

I think it is naive for most of us to assume that we do not regularly encounter compression when playing actual music. This may be a reason that the IIPS makes a significant difference even when listening at modest levels.

Edit: Tube rectifiers are often thought of as being more musical due in part to their voltage sag upon current demand. Their internal resistance means they cannot supply current fast enough and in a capacitor input power supply there is not typically enough energy storage to completely cope with transient peaks. This is at least partly responsible for damping transients and softening their edges a bit (in a good way). It occurred to me if the damping effect of the tube rectifier also happens at the voltage input. Would a B+ voltage change under current demand be damped by the tube rectifier as well, adding to the soft recovery aspects of the solid state rectifier? It may have the effect of damping some of the HF hash from solid state diode. Any ideas?

[Musica Amantem]

So, what prevents the PS to allow voltage disturbances ... or how do these unavoidable incidences are blocked from reaching the output stage through the rectifiers? I think I'm beginning to grasp the concept but I need answers to the above. Thanks!

PS: Sorry, I wrote this before reading Roscoe65's quite interesting last post. "This tube is normally passing DC to DC with the vacuum isolating the input from the output" I would agree in considering vacuum rectification in lieu of SS diodes. These would have different specs than the ones currently employed in the Inspire amps, of course, and may not be fast enough to react to a sudden high peak of voltage surge, but will take the SS "flavor" from the signal path. Amazing how much progress is taking place within a year of my amp's purchase ... Can we trade-in?

[Analog Addict]

The best tube combo I heard in the PSE was the one shown in the first pix. Two pair of 6L6GA variants with a 6SN7W metal base. We did put a quad of 6V6G in it right at the end, but I didn't spend enough time with this combo to get a good feel for it....

[BearCityUSA]

Another highly anticipated trip to Cary, NC has come and gone now and I have to say it lived up to my hopes and then some. I met a couple AAers and got to put faces to some personalities I have only known here online. Nice meeting you guys. If you are ever in the Asheville area do look me up. Back at the office now with the new PSE w/IIPS and I have to say WHAT AN AMP. More on that in a few days, or more, as I am able to digest and analyze.

In regards to my listening there at the Toy factory, we sat and listened to the two amps, the PSE and the new Hot Rod Analog posted pictures of above. I cannot give a concrete conclusion as to what I heard in that the listening session was short and as someone here inquired about, 'was the tube complement the same'. The answer to that, at least while I was there was no. I was not auditioning the Hot Rod so I did not even think to try that. I was mostly just enjoying what I heard and not focusing directly as to the differences/similarities of the two. Much of the time the Hot Rod was outfitted with vintage TS 6550. The first time I have heard them. They sounded great but I would not go and get some at their current price. Much of the time the PSE was outfitted with the new GL KT-77 (incidentally what Dennis sent me home with). Interestingly he has found that he likes the GL in the PSE where he preferred the JJ in the Fire Bottle. I have not spent enough time with them yet to make a judgement. My first impressions of the Hot Rod, a nice little amp that for those without an Inspire amp or looking for a second, you cannot go wrong with this one. More of a great thing Dennis is doing over in Cary.

Much discussion has been going on here about contemplating the new IIPS upgrade to previous versions of the Inspire line. I inquired with Dennis about maybe changing over to the new circuit. At the moment I have elected not to. My reasoning is that there is such a magical cohesion between Output and Rectifier Tubes that I am afraid to give that up with my 2013 model KT amp. I am sure you each have found those combinations. For me the Pope 6v6gt with Bendix RedBank 6106 for one, I just am not ready to abandon, even as much as I trust Dennis in his circuit advancement. I have my older KT and new PSE side by side currently and likely will for a while to come and I will do some comparisons maybe change my mind. If I do I will let you all know. If you are interested in an upgrade and you have an LP-2. Contact Dennis and get him to change it over to the LP-3a circuit. IMO you will not regret that choice. I am afraid I may, on some level, regret the new IIPS change over. As I right this with the PSE playing The Pros and Cons of Hitchhiking at pretty modest volume. I am hearing some of that Roger Waters' background layering that I have not heard on the KT. Is it the PSE or the IIPS,...I wonder? Some musical peaks are more pronounced as well. I know I sound as though I am already wavering.

Something we did this time which we did not last I was there in June was listen to the Inspire speakers. The shorter ones in the listening room there at the Toy Factory, the ones that Analog Addict may have a pair of which may be for sale. You may remember his posting on Audiogon a short time ago. A nice speaker I must say. Looks are great. The burl veneered fronts are striking and the proportions are very pleasing. They are not overly large so fitting them into smaller living spaces would be easy. The sound was a pleasure to listen to. Very balanced with he Inspire gear. Immense Soundstage coupled with a much larger listing area then I am used to with my Omegas. In fact I could not find a single place in the room where I was not impressed with the sound. This would be expected with the OB design compared to my single drivers here at my office. Anyway, without getting to blah blah with the lingo I can say that they are balanced, listenable for long periods of time and again, well suited for use with the Inspire pre-amp/amp combos. I am cataloging them for future reference as I plan to get some speakers for an addition to the house in 2017.

Enough for now. More to come as I get to know the PSE...

[Rosco65]

Originally Posted by BearCityUSA

As I right this with the PSE playing The Pros and Cons of Hitchhiking at pretty modest volume. I am hearing some of that Roger Waters' background layering that I have not heard on the KT. Is it the PSE or the IIPS,...I wonder? Some musical peaks are more pronounced as well. I know I sound as though I am already wavering.

That is an interesting and confusing statement. Are you saying that you do not like the sound of the PSE or that you cannot tell if the difference in sound from you KT is due to the PSE design or the IIPS? Are you saying you wished you had been able to hear if prior to the IIPS first?

[BearCityUSA]

Originally Posted by Rosco65

That is an interesting and confusing statement. Are you saying that you do not like the sound of the PSE or that you cannot tell if the difference in sound from you KT is due to the PSE design or the IIPS? Are you saying you wished you had been able to hear if prior to the IIPS first?

Sorry Rosco,

Definitely liking the PSE. A real improvement over my KT is apparent already. I am just not sure if it is the PSE or the IISP that is the driver of this improvement, and likely never will be. The option of hearing it before the IIPS was not offered and I did not inquire. I put my trust in Dennis on that one. He told me this is what he was installing and I just nodded my head with a glazed look of meager understanding at the time. At the moment I have no wishes or second thoughts except for the fact that I need to stop spending money on stereo gear for a while.

[Musica Amantem]

An interesting comparison would be the previous KT design vs the same with the IIPS mods (apples to apples). Of course, this would probably have to rely on sound memory.