Dennis Had Inspire Amps

[Musica Amantem]

Originally Posted by opnly bafld

Bought a KT88 sep from Mr. Had friday, should be here Wednesday.

You're on the right track ... I made the move last year and have not looked back!

[trackpad]

Originally Posted by Bombadil

Anyone ever try a new re-issue "Tung Sol" 6SN7 and give it time to break in? I see that one can order them tested for low-noise and having matched sections. Possibly the same tube as the Electro Harmonix.

I have heard them in my friend's Cary Preamp. I got a match quad. They sounded fine with nice tone and do call attention to themselves. No problems with reliability.

[pstrisik]

Originally Posted by opnly bafld

Bought a KT88 sep from Mr. Had friday, should be here Wednesday.

Glad to hear it! Welcome over to this forum. I can't recall if you have Omegas or not. What speakers will you be running with the Inspire?

[o]

Hi Peter,

Enjoyed your journey with your Omegas.

About 3 years ago I bought a Sweet 807 from Dennis and a pair of Super 3is (b stock) from Louis (both great guys in my experience).
Then around a year later with 8 tube amps and several speakers about I decided to sell most of them including the Inspire and the Omegas.

At the time my main system was a McAlister Audio SE32 15w pse tube amp (best amp I've owned; RIP) driving Legacy Audio Classics (Bill D's person Hot Rod pair).
I can't remember now why I thought it was a good idea to sell the Legacys 2 years ago.

Believe it or not, I'm going to try it with my ATC SCM 11v2s at 85 dB 1w/1m and 8 ohm "Flat impedance curve allowing easy load for amplifiers." according to ATC.
When I first got the speakers a year ago for fun I hooked up my 6 watt (set/sep switchable) EL84 based amp and was impressed with how well it did.

[Dream On]

Hi everyone,

I'll be reading with interest how the Inspire amp works for opnly bafld's ATC's.

I registered to ask for people's thoughts regarding Dennis' Fire Bottle 12 watt KT88 singled ended amp, which I am close to purchasing (either that or it will be push pull 30 watt tube amp). I have a pair of ProAc Studio 118 speakers. Similar to ATC they should present an easy load.

However, I can't help but think a push pull amp might be a better fit for the 118's, especially since I listen to mostly rock music at decent volume. That said, the system is in a small room and I sit fairly close (6' away). Volume seems to range from mid 70db (quiet parts) to around 90db for louder parts - at least that's what my spl meter tells me. I know theoretically that means an amp is outputting about 1 or 2 watts but I'm not sure I buy that it's quite that simple in practice. Really really want to try Class A single ended, but my head is telling me that I should buy the amp that is the best fit for the application and that it may not be the SE amp.

If anyone has any insights into this potential match I would definitely appreciate it.

[CoGT3]

Originally Posted by Musica Amantem

Any impressions you may want to share on the SET 45 from Dennis? Thanks!

A couple of people of asked, so here you go. (short version is, I sold a pair of $15K 845 SET mono blocks 2 months after getting the 45 SET).

We where fortunate enough to build a custom house about 4 years ago, in which I was able to squeeze out space for a dedicated listening room. I have 2 young children (some to be 3) so the room was built to be reasonably isolated for sound (most listening is done after they are asleep). The room is 19x15x10.5, floor is concrete slab with hardwood, walls double 5/8 gypsum with green glue floated with a isolation system, ceiling double 5/8 and green glue hung by springs. The point being, that even with a standard door, there is very little sound leaving the room, in general the bigger problem I have is controlling the sound trapped in the room. So given the moderate size room and isolation, I think I have had better luck than most would using the 2W 45 SET, I really don't have to crank it up that much to get "load" since the musical energy stays in the room.

At the time I received the amp, my system was made up of a Rega P7 with Ortofon Cadenza Black feeding a Thoeress Preamp with phono stage, Thoeress 845 SET mono blocks, and Horning Hybrid Aristoteles.

The Aristoteles are a back loaded Lowther design, using a heavily modified Lowther driver in a back loaded horn set up, it is rolled off to a horn loaded tweeter at around 12K with a simple cap, and acoustically rolled off below 200Hz by the cabinet design. Each speaker has 4 8" woofer in an isobaric setup firing into the back of the horn to cover from 200Hz down. By specs, they are 96dB/w efficient. But as you may expect given the complex woofer design, do benefit from some power with rock, bigger classical pieces, or more layered music. Despite this, the Thoeress 845's left and Dennis' 45 SET stayed.

Here is something I had sent back to Dennis after having the 45 SET for about 2 months:
"Dennis,
I wanted to give you a little bit of an update. I have had more time than expected to play around this week so i thought I would pass along my first thoughts.

Most listening was done with the same four tracks, all vinyl:

Lou Reed Transformer: Walk On the Wild Side-current release pressing
Nat King Cole The Very Thought of You: The Very Thought of You-45 rpm Analogue Productions reissue
My Brightest Diamond All Things Will Unwind: Be Brave-current release
Led Zeppelin Physical Graffiti: Kashmir-current reissue (unfortunately I was in med school when the Classic Record reissues happened, managed to score only 3 of them scrapping pennies together)

Started with the Philco globes and RCA 5Z3,
then RCA ST's with RCA 80,
finally back to the Thoeress 845's

Turned each combo on in the morning and let them warm up all day and listened in the evening

Started with the Philco Globes figuring lets see what this Type 45 tube thing is all about. Definitely lost about 1/2 an octave on the bottom across the recordings, but as always, sins of omission are the most tolerable. Either slightly rolled at top, or more tolerable of less than perfect recordings. Wasn't expecting this given the frequent description of "transparency" with the 45s. I found myself leaving the volume up during passages I previously turned down where the treble was bothersome. However, there was a certain "rightness" to all the tracks.

Lou Reed: Nice uniform bass line, full sound with good resonance of the bass notes. Vocals spooky real. Saxophone solo had more bite to it in a good way, just like a live player digging into a few notes. Played for my father in law. Was floored at the 1.8W at work, was walking around between the speakers afterwords pointing out the apparent locations of the instruments.
Nat King Cole: Nice underhand pitch for the 45's, as expected, knocked it out of the park, Nat is just there in the room. Vocal track blended better with backing orchestral tracks than before. Less congested in midrange. Nice ambient sounds even if a studio recording.
My Brightest Diamond: Probably haven't heard this before, but nicely mixes excellent vocals with mixed acoustic instruments, both rock and classical. Really noticed missing bottom 1/2 octave, bass clarinet missing a little weight. Again vocals are relaxed and real.
Led Zeppelin: Biggest surprise of all. Have only listened to this reissue twice as I have generally found the recording poorly done and sound at times quite irritating, thin, and generally lacking drive/weight. I don't know why I grabbed it, but I did. Certainly did not fill in the sense of hollowness. But I found myself very engaged finally. The louder sections that had been bright/irritating now came across as a realistic bite instead, especially the vocals and screams. Actually had one of those hair raising moments. Now it didn't make the recording magically superb, but it pulled me into the recording far more than ever before.

Next was ST/80 combo. The difference between the Globe/5Z3 combo where subtle at best but there. In general I think it lost a little of that "45" magic. A little more weight/heft in the lower end, lower 1/2 octave still not there but a fuller presentation. Treble a hair more extended also, but creeps ever so slightly back toward the "bright" sound the Globe combo had eased/eliminated. Little more drive on the Lou Reed/Zeppelin. Again this is really splitting hairs. Certainly would not confuse the presentation for anything other than a 45 SET.

Back to the Thoeress 845's. These are much in the vein of the Cary 805's, big monoblock SET, massive custom hand wound transformer (by the designer/builder), stacks of oil caps etc. As expected there was a fuller sound from top to bottom. Bottom 1/2 octave came back as well as a general fullness to the presentation. Soundstage a little bigger and much denser. However, midrange is a little too dense and congested in comparison (speakers are probably not it there final resting place in the room which may have some effect there also).

Lou Reed: Bass now sounds like you are in the studio with the bass player, more detailed resonance of the strings, powerful. Probably more accurate, but certainly not would you would hear live in a concert setting. Vocals are great but not as spooky at 45's. Saxophone now has a little edge at the crescendo.
Nat King Cole: Vocal still great, in the room again. More apparent of 3 track recording, vocal/orchestral doesn't blend as well. however larger sound from orchestra tracks.
My Brightest Diamond: Lower octave really noticed, more drive which suits music. Clarinet takes on more presence. But again, more like being in the studio with the performers.
Led Zeppelin: As alluded too, not my favorite track with this amp. Just a too thin up top and irritating at times. Definitely more weight, drive, fuller bass but still not drawn in as much as with 45's. Biggest surprise of all!

So that's my short take. Really interested in hearing your take on the EML 45's. If they can fill in that bottom octave and give a little more weight to the over all presentation my current amps are in trouble. The combo of the Globe and EML 45 could give the 1-2 punch to cover most musical tastes. Actually have already had the thought about selling the 845's to fund a planned turntable upgrade sooner than expected."

I did sell the 845's and rolled the money into the TT upgrade fund, new TT arrived this summer for my Bday.

A year later, my initial impression stay true, for almost all vocal music, simple acoustic arrangements, small classical/solo piano, and most of my jazz, the 45 SET is amazing given its 2W output. Most of the music that it really shins with is probably using the Lowther driver predominantly. At this point I will be adding a PSE in the next 6-8 weeks, should more than cover the musical types that tend to overwhelm the 45 SET and should compliment it nicely. Ultimately down the road (with surprise child 3 showing up for Xmas, really down the road), I will be trying out a 300b mono block made by my TT manufacture, albeit at a much higher price point than Dennis' fine work. Even if the 300b sticks around, the other amps will go nowhere, with a 5, 3, and T-16weeker around, how better for them to grow up with music than the nice glow of an Inspire amp!

[CoGT3]

Some pics:

45 SET as delivered



45 SET current state



Room current state (and far from complete, 703 will be covered with fabric, vertical slat diffusers along side walls between columns, media storage built into back wall stagged as diffuser)



Little man taking in some music (shelving across back is Ikea to hold be over till custom shelving built in. Hard to tell in pic, but they are staggered in depth from center to each side wall to act as diffusers).

[CoGT3]

Originally Posted by Analog Addict

Well, that is a question above my tech grade, but I do know that one of the beneficiaries of the new PS is the screen grid voltage. The screen grid’s purpose is to reduce capacitance that arises between the control grid and the plate. Such parasitic capacitance can cause the tube’s circuit to become self-resonant at some frequencies, and it will reduce the tube’s achievable gain at higher frequencies. This problem is called the Miller Effect, and the screen grid helps to resolve it. A triode amplifier will typically require some type of “neutralization” circuit outside of the vacuum tube to avoid the detriments of the Miller Effect. ((G6B10) Vacuum Tubes - Ham Radio School.com)
Any variance in the voltage at the screen grid will cause fluctuations in the electron flow, introducing unwanted variance in the signal.

From Dennis' comments...."What I discovered was when an output device, in my case a vacuum tube, became non-linear and produced various spurious distortion products back fed to the power supply. In the case of a basic power supply supplying both the output devices along with the driving front gain sections I was able to detect these modulated parasitic products in the driver stage compounding the problem of output distortion of the final product.

So what he is saying (I think) is that the clipping/distortion produced by a transient dynamic peak is compounded by bleeding into the (assumed) regulated power supply feeding the driver tubes and the output tube screen grids, causing even greater distortion. Call it unintentional negative feedback of the worst type.

So, in a flash of Inspire-ation he came up with the idea of using the elements of the rectifier tube to isolate the power supply from any distortion or variance produced by the output tubes. Think of it kinda like a isolation or interstage transformer in some ways. There is no direct contact linking the two ends of the circuit. Instead, Dennis is using the vacuum of the rectifier tube to isolate the regulated power supply from the rest of the circuit, hence the "infinite impedence" part of the circuit. The novel part of it is that he is running direct current through the rectifier, and not AC as would normally be applied to a rectifier.

Now with respect to the 45 amp, remember that there's no screen grid in the 45, so you would lose the benefit of this effect. However, any amp will use driver tubes, so they would benefit from this application. My undereducated guess is that the amp would benefit, but not so much as a tetrode amp.

Thank you for your detailed responses, definitely beyond my current understanding (did buy a book off Amazon recently on basic of tube amps, still got some reading to do.)

Given your description even without the grid to interrupt, I suspect it will have an effect on the 45 SET. In my case, I am using it with 96dB/w speakers and as you allude to probably inducing clipping more than I realize. If that is the case, cleaning up the power to the high Mu 6SL7s can't hurt.

[Analog Addict]

Originally Posted by CoGT3

A couple of people of asked, so here you go. (short version is, I sold a pair of $15K 845 SET mono blocks 2 months after getting the 45 SET).

We where fortunate enough to build a custom house about 4 years ago, in which I was able to squeeze out space for a dedicated listening room. I have 2 young children (some to be 3) so the room was built to be reasonably isolated for sound (most listening is done after they are asleep). The room is 19x15x10.5, floor is concrete slab with hardwood, walls double 5/8 gypsum with green glue floated with a isolation system, ceiling double 5/8 and green glue hung by springs. The point being, that even with a standard door, there is very little sound leaving the room, in general the bigger problem I have is controlling the sound trapped in the room. So given the moderate size room and isolation, I think I have had better luck than most would using the 2W 45 SET, I really don't have to crank it up that much to get "load" since the musical energy stays in the room.

At the time I received the amp, my system was made up of a Rega P7 with Ortofon Cadenza Black feeding a Thoeress Preamp with phono stage, Thoeress 845 SET mono blocks, and Horning Hybrid Aristoteles.

The Aristoteles are a back loaded Lowther design, using a heavily modified Lowther driver in a back loaded horn set up, it is rolled off to a horn loaded tweeter at around 12K with a simple cap, and acoustically rolled off below 200Hz by the cabinet design. Each speaker has 4 8" woofer in an isobaric setup firing into the back of the horn to cover from 200Hz down. By specs, they are 96dB/w efficient. But as you may expect given the complex woofer design, do benefit from some power with rock, bigger classical pieces, or more layered music. Despite this, the Thoeress 845's left and Dennis' 45 SET stayed.

Here is something I had sent back to Dennis after having the 45 SET for about 2 months:
"Dennis,
I wanted to give you a little bit of an update. I have had more time than expected to play around this week so i thought I would pass along my first thoughts.

Most listening was done with the same four tracks, all vinyl:

Lou Reed Transformer: Walk On the Wild Side-current release pressing
Nat King Cole The Very Thought of You: The Very Thought of You-45 rpm Analogue Productions reissue
My Brightest Diamond All Things Will Unwind: Be Brave-current release
Led Zeppelin Physical Graffiti: Kashmir-current reissue (unfortunately I was in med school when the Classic Record reissues happened, managed to score only 3 of them scrapping pennies together)

Started with the Philco globes and RCA 5Z3,
then RCA ST's with RCA 80,
finally back to the Thoeress 845's

Turned each combo on in the morning and let them warm up all day and listened in the evening

Started with the Philco Globes figuring lets see what this Type 45 tube thing is all about. Definitely lost about 1/2 an octave on the bottom across the recordings, but as always, sins of omission are the most tolerable. Either slightly rolled at top, or more tolerable of less than perfect recordings. Wasn't expecting this given the frequent description of "transparency" with the 45s. I found myself leaving the volume up during passages I previously turned down where the treble was bothersome. However, there was a certain "rightness" to all the tracks.

Lou Reed: Nice uniform bass line, full sound with good resonance of the bass notes. Vocals spooky real. Saxophone solo had more bite to it in a good way, just like a live player digging into a few notes. Played for my father in law. Was floored at the 1.8W at work, was walking around between the speakers afterwords pointing out the apparent locations of the instruments.
Nat King Cole: Nice underhand pitch for the 45's, as expected, knocked it out of the park, Nat is just there in the room. Vocal track blended better with backing orchestral tracks than before. Less congested in midrange. Nice ambient sounds even if a studio recording.
My Brightest Diamond: Probably haven't heard this before, but nicely mixes excellent vocals with mixed acoustic instruments, both rock and classical. Really noticed missing bottom 1/2 octave, bass clarinet missing a little weight. Again vocals are relaxed and real.
Led Zeppelin: Biggest surprise of all. Have only listened to this reissue twice as I have generally found the recording poorly done and sound at times quite irritating, thin, and generally lacking drive/weight. I don't know why I grabbed it, but I did. Certainly did not fill in the sense of hollowness. But I found myself very engaged finally. The louder sections that had been bright/irritating now came across as a realistic bite instead, especially the vocals and screams. Actually had one of those hair raising moments. Now it didn't make the recording magically superb, but it pulled me into the recording far more than ever before.

Next was ST/80 combo. The difference between the Globe/5Z3 combo where subtle at best but there. In general I think it lost a little of that "45" magic. A little more weight/heft in the lower end, lower 1/2 octave still not there but a fuller presentation. Treble a hair more extended also, but creeps ever so slightly back toward the "bright" sound the Globe combo had eased/eliminated. Little more drive on the Lou Reed/Zeppelin. Again this is really splitting hairs. Certainly would not confuse the presentation for anything other than a 45 SET.

Back to the Thoeress 845's. These are much in the vein of the Cary 805's, big monoblock SET, massive custom hand wound transformer (by the designer/builder), stacks of oil caps etc. As expected there was a fuller sound from top to bottom. Bottom 1/2 octave came back as well as a general fullness to the presentation. Soundstage a little bigger and much denser. However, midrange is a little too dense and congested in comparison (speakers are probably not it there final resting place in the room which may have some effect there also).

Lou Reed: Bass now sounds like you are in the studio with the bass player, more detailed resonance of the strings, powerful. Probably more accurate, but certainly not would you would hear live in a concert setting. Vocals are great but not as spooky at 45's. Saxophone now has a little edge at the crescendo.
Nat King Cole: Vocal still great, in the room again. More apparent of 3 track recording, vocal/orchestral doesn't blend as well. however larger sound from orchestra tracks.
My Brightest Diamond: Lower octave really noticed, more drive which suits music. Clarinet takes on more presence. But again, more like being in the studio with the performers.
Led Zeppelin: As alluded too, not my favorite track with this amp. Just a too thin up top and irritating at times. Definitely more weight, drive, fuller bass but still not drawn in as much as with 45's. Biggest surprise of all!

So that's my short take. Really interested in hearing your take on the EML 45's. If they can fill in that bottom octave and give a little more weight to the over all presentation my current amps are in trouble. The combo of the Globe and EML 45 could give the 1-2 punch to cover most musical tastes. Actually have already had the thought about selling the 845's to fund a planned turntable upgrade sooner than expected."

I did sell the 845's and rolled the money into the TT upgrade fund, new TT arrived this summer for my Bday.

A year later, my initial impression stay true, for almost all vocal music, simple acoustic arrangements, small classical/solo piano, and most of my jazz, the 45 SET is amazing given its 2W output. Most of the music that it really shins with is probably using the Lowther driver predominantly. At this point I will be adding a PSE in the next 6-8 weeks, should more than cover the musical types that tend to overwhelm the 45 SET and should compliment it nicely. Ultimately down the road (with surprise child 3 showing up for Xmas, really down the road), I will be trying out a 300b mono block made by my TT manufacture, albeit at a much higher price point than Dennis' fine work. Even if the 300b sticks around, the other amps will go nowhere, with a 5, 3, and T-16weeker around, how better for them to grow up with music than the nice glow of an Inspire amp!

Personally, I'm going to bet that the 300B won't do it for you now that you are "Inspire-d". But, I would add a few thoughts. Even though Dennis tends to poo-poo the 45 tube as an "old man's tube", there's a reason he's still got two of them floating around the shop. He and I both agree there's something magical in the old globe tubes as well. One thing I would also recommend to you is to roll a wide variety of driver tubes through your 45 amp. I can't tell if it's the SN or SL flavor, but you may very well notice a huge difference between driver tubes. I wouldn't hesitate to try either. My bet is that you will find something in an older tube that really does it for you.

I've been brainstorming with Dennis about my next project and originally it was going to be a PSE 71A amp for a grand total of 1.5 WPC, but the more we talk about it, the more I am leaning towards a PSE 45 build, with the new power supply. I may still use a tube rectifier, but I haven't started working on the schematic yet. Hopefully if it turns out well, and Dennis likes it, it may motivate him to try one for himself...

I've also been pushing him a little to build a limited run of phono pre amps. Maybe get 20 or 30 chassis made, and when they're gone, that's it for a good while. So far he hasn't bit. Will keep working on him....

[Bombadil]

Originally Posted by Dream On

I registered to ask for people's thoughts regarding Dennis' Fire Bottle 12 watt KT88 singled ended amp, which I am close to purchasing (either that or it will be push pull 30 watt tube amp). I have a pair of ProAc Studio 118 speakers. Similar to ATC they should present an easy load.

I am using an Inspire KT88 SE 17 wpc amp to drive a pair of Focal Aria 906 2-way monitors. Spec'ed by Focal at 89.5dB sensitivity, so very close to the ProAc Studio 118 spec of 88.5dB. My listening position is just 2M.

I have used my amp both with an without a powered subwoofer. I've used tube sets which produce 10-12 wpc, even lower with 6V6 tubes.

I have been quite satisfied with volume levels and bass output. With the 6V6s I preferred it with the subwoofer handling up to 80Hz, relieving the amp of trying to drive my moderately efficient speakers on low bass.

If I tried to push this setup to near concert levels, I doubt there would be sufficient power. But typical levels being in the low to mid 80s and peaks in the low to mid 90s, it works just fine. More than fine, it sounds wonderful in my setup. Perhaps if I tweaked up the volume another 3-4dB it would be a different story.

Actually, when using the subwoofer, I've had success driving the same system with my Inspire SE EL84 amp which only makes around 5 wpc. I've been careful not to push it too hard.