Dennis Had Inspire Amps

[Musica Amantem]

Originally Posted by nhparrot

In my Inspire amp, a 6BX7, 6SN7 and 6SL7 are interchangeable as input tubes.

I get it the 6BX7 is apparently quite similar to 6SN7 and 6SL7, and in most conditions interchangeable? The 6BX7 came stock in my LP-27a preamplifier. I had no idea it could be used as an input tube in the amplifier also.

[x3workshop]

That is correct with 'most conditions' being the key term here. Operating parameters of a 6BX7 are slightly different than a 6SN7 and are very circuit design dependent. Dennis's design is able to accommodate the swap.

[Musica Amantem]

Originally Posted by x3workshop

That is correct with 'most conditions' being the key term here. Operating parameters of a 6BX7 are slightly different than a 6SN7 and are very circuit design dependent. Dennis's design is able to accommodate the swap.

Understood. Thanks! Yet another game variable ...

[FloridaBoy]

Originally Posted by x3workshop

That is correct with 'most conditions' being the key term here. Operating parameters of a 6BX7 are slightly different than a 6SN7 and are very circuit design dependent. Dennis's design is able to accommodate the swap.

My LP27a came with a 6BX7 and Dennis said it could also use a 6BL7. Good to know that a 6SN7/6SL7 can also be used.

[Etunes]

Will you please share with me what speakers are working well for you with his gear? I have 91db efficient speakers but still not experiencing what is being described here. I recently purchased his KT88 SE and want to love it but its struggling with my current setup. Running with KT150's has been best of far.

[pstrisik]

Originally Posted by Etunes

Will you please share with me what speakers are working well for you with his gear? I have 91db efficient speakers but still not experiencing what is being described here. I recently purchased his KT88 SE and want to love it but its struggling with my current setup. Running with KT150's has been best of far.

Welcome to the club Etunes!

Questions:

What speakers do you have? What is their impedance? My understanding is that lower impedance is harder to drive even if sensitivity is the same.

What is your source and are you running a preamp? Some sources will have lower output - I think 2volts is pretty typical and probably a minimum. A preamp should give you more gain.

My speakers are Omega Super Alnico Monitors. Louis, the designer/builder, had them spec'd at 93db/8ohm. He has recently changed that to 95db. My KT150 powers them just fine. I found that my vintage AR2ax' needed a bit more than the Inspire could offer even though they sounded great up to about 75db in a large room. Those speakers are ~87db/8ohm and sealed (acoustic suspension) and may be a bit harder to drive without being ported.

[nhparrot]

Originally Posted by Etunes

Will you please share with me what speakers are working well for you with his gear? I have 91db efficient speakers but still not experiencing what is being described here. I recently purchased his KT88 SE and want to love it but its struggling with my current setup. Running with KT150's has been best of far.

I have a small room and can drive a pair or ProAc 1SCs or a pair or ADS L520's to a satisfying level for me. I usually am running 6V6GT's, and drive the ProAc's 95% of the time.

ProAc's - Impedance: 8 ohms nominal. Sensitivity: 86dB/W/m.
ADS - Impedance: 6 ohms nominal. Sensitivity: 92dB/W/m

[FloridaBoy]

Originally Posted by Etunes

Will you please share with me what speakers are working well for you with his gear? I have 91db efficient speakers but still not experiencing what is being described here. I recently purchased his KT88 SE and want to love it but its struggling with my current setup. Running with KT150's has been best of far.

I use Klipsch Heresy III's 98db of so. No complaints. Are you using a preamp?

[robert_kc]

Originally Posted by Etunes

Will you please share with me what speakers are working well for you with his gear? I have 91db efficient speakers but still not experiencing what is being described here. I recently purchased his KT88 SE and want to love it but its struggling with my current setup. Running with KT150's has been best of far.

IME the Inspire single-ended-pentode amp is more finicky about speaker synergy than a push/pull (PP) tube amp, or solid state.

I use Klipsch RF-7 II (101dB, 8 ohm, 2 way) and RF-7 (102dB, 8 ohm, 2 way) in my basement system where my Inspire “Fire Bottle” SE Stereo Tube Amplifier HO is installed. My Inspire amp doesn't work as well with my Klipsch Palladium P-37F (96dB, 4 ohm, 3 way) in my TV room. The Inspire also doesn’t work well with my Snell Type CV (90dB, 8 ohm, 3 way) in my living room. Surprisingly the Inspire does OK with my JBL L880 (91dB, 8 ohm, 4 way) in my very small office. (I have 5 systems (different rooms), and a total of 26 amps, and I’ve experimented quite a bit with amp/speaker compatibility in my systems.) I think this shows that a few published specs don’t fully characterize how easy a speaker is to drive. (And room size matters.)

I listen mostly to classical music (ranging from chamber music to large scale orchestral) and opera, plus occasionally big band music. I listen at moderate sound level – not extremely loud. My unfinished basement is a large room (22’ x 30’ x 8’) with “live” acoustics (concrete floor and walls). One speaker is 4 feet from a rear wall; the other speaker is in the middle of the room. My listening position is 13 feet from each speaker.

I connect the Inspire directly to an older model Oppo DV-980H SACD/CD player (i.e., no preamp) and use the Oppo’s volume control. I increase the output level of my Oppo by adjusting its “trim levels” for the l/r speakers to their max value (i.e., +10dB vs. 0dB). As pstrisik said, a preamp will increase the gain – however I choose to use the Inspire amp in a “minimalist configuration” without a preamp. (I can use a McIntosh MX110Z tuner/pre-amp in this system if I wish.)

My Inspire amp was originally equipped with KT88, 5U4, 6CG7. I decided on GT6L6 GE, 5AR4, 6DJ8 based on extensive tube rolling, and based on my goal of recreating the natural timbre of orchestral instruments and human voice (i.e., the full range of male and female singers). My bias is that I don’t like bright sound. Of course my selection of tubes is based on Klipsch RF-7, my listening room, and what I remember hearing in my local symphony hall and opera house (which both have excellent acoustics). (For brighter sound the KT88 would be indicated.)

With the Inspire / RF-7 II combination I realize sound that I would describe as “natural”, “full”, and “rich”, with adequate volume, good dynamics, and good bass. With that said, I’ve recently become a convert regarding subwoofers. (I can activate a Klipsch R-115SW in my basement system with the Inspire and RF-7s.) I can set parameters in my Oppo player so that it provides a crossover and off-loads deep bass from the Inspire amp and main speakers, thereby increasing dynamics and bass. Nonetheless, even without a subwoofer, my Inspire “Fire Bottle” SE Stereo Tube Amplifier HO (with the tube compliment I described above) delivers excellent sound quality with my RF-7 II for everything except the lowest pedal notes of a pipe organ. A big subwoofer is also indicated if you want to experience a mighty whack of the bass drum the way it sounds in the symphony hall.

To put things in perspective, here’s a list of the other amps in my basement system that I can compare to my Inspire “Fire Bottle” SE Stereo Tube Amplifier HO: Scott 272 (PP EL34 integrated amp), Scott 222C (PP 7189 integrated amp), McIntosh MX110Z pre-amp, Fisher KX-200 (PP 7591 integrated amp), Marantz 2325 solid state receiver (125 wpc), Pilot SA-260 (PP EL34 power amp), Scott 210F (PP EL34 mono integrated amp), Fisher TA 500 (PP KT66 mono receiver), and Scott LK150 (PP KT88 power amp). For large scale orchestral music (e.g., a high resolution digital recording of Mahler Symphony No. 2) the Inspire amp doesn’t deliver the dynamics of the McIntosh MX110Z pre-amp paired with the Scott LK150 (PP KT88 delivering 58wpc). Nonetheless the Inspire amp always sounds good, and sounds fabulous with smaller scale music. I would be satisfied to have the Oppo / Inspire / RF-7 II / R-115SW as my only system, and I think this combination represents a great-value hi-fi system (for an average size room). In other words, IMO additional investment would result in dramatically diminishing returns (assuming an average room size and reasonable listening levels).

I hope that you get your system optimized. What speakers are you using? What deficiencies are you hearing when using the Inspire amp? Where do you live? Perhaps you could hear someone else’s Inspire amp paired with different speakers.

[pstrisik]

Nice post Robert.

I've not had an Oppo, but it sounds like the Oppo acts like a preamp if default gain is middle and you can turn it up from there. My Cambridge Audio streamer/DAC has a preamp mode, but it is just attenuation, not gain. I can't recall the voltage output. I do use that mode for volume control and into the LP-2 then KT150 Inspires.