Dennis Had Inspire Amps

[FloridaBoy]

Originally Posted by Bombadil

I have tried just about everything I can think of and my Inspire SE EL84 amp continues to produce a bass-lacking sound. Not totally absent of bass, but sounding like it is down 3 to 4 dB from 150 Hz and on down.

I have used three different 6DJ8-type tubes, including NOS Amperex JAN 6922 and 7308. Five different EL84 tube sets. And three different recitifiers, including the stock 274B and two different 5U4GBs.

I've used three different preamps into it, including a very warm sounding Conrad Johnson PV10A.

I've used it to drive 4 different sets of speakers, from relatively inefficient Spica TC60 & Von Schweikert VM2 small monitors, to 90dB Focal bookshelves to 91dB Von Schweikert tower speakers.

I've listened at several volume levels, but mostly with the average volume level at 75 to 80dB, as measured by an SPL meter at the listening position. which is just 7' from the speakers.

I've evaluated it vs a Korato KVA-20 amp, which is an 18-20 wpc, 6CA7-based, triode-configured design. And an older Cary SLA-30 EL84 amp. The Inspire produces a lot less power, but should have easily handled the volume levels I was using, which required well under 1 watt.

Both of the other amps reproduced lower piano notes with rich harmonics and authority. Through the Inspire they were weak and lacking.

The midrange and highs were quite nice. Good transparency, engaging vocals.

Just today I thought of testing to see if the speaker terminals were wired out of phase. Will test that soon. It kinda sounds like the bass cancellation that one gets with out of phase speakers.

Any other ideas?

A subwoofer or V-Cap copper/Teflon caps in the coupling spot. YMMV. However, It may be best to contact Dennis.

[Rosco65]

Originally Posted by nhparrot

Based on recommendations from Simon, Peter and others, I picked up a pair of EL84 tubes and socket adapters. Will be swapping them in today to give them a test drive in my system.

I did the same thing. The beauty about the Firebottle KT88 is that I can use any tube, from EL84 to KT88 (or KT150 for that matter), while an EL84 amp will only use EL84's. My [our] amp will output anywhere from 5 - 12 watts depending on tubes. Any "SE friendly" speaker should work in that range.

[Musica Amantem]

Originally Posted by Rosco65

I did the same thing. The beauty about the Firebottle KT88 is that I can use any tube, from EL84 to KT88 (or KT150 for that matter), while an EL84 amp will only use EL84's. My [our] amp will output anywhere from 5 - 12 watts depending on tubes. Any "SE friendly" speaker should work in that range.

Of course, the transformers ought to be on par with the requirements. My KT-88 amp came with over-sized (20 Watts) transformers, which ensure that range of possible output power as a function of tube types without any unreasonable headroom ceiling.

[timeout59]

Hi everyone. I just bought a Fire Bottle KT-88 Special Edition from Dennis via eBay. Pretty excited and looking forward to it!

I had a few tube amps over maybe a ten year period, SET and PP, paired with some Coincident Technology speakers. Really loved the sound and fun of tubes, but went in a different direction with Maggies and SS. Lately got interested in Spatial Hologram open baffle speakers, and contacted Clayton Shaw about buying a pair at the end of next month when I'll have plenty of time to make use of the 60 day trial. I bought the Inspire to use with those.

Dennis said "One of these amplifiers is in a listening room in southern California driving a pair of Maggie 1.7's. Great amp for sure." I find it hard to believe it could work at the levels I sometimes listen, 85 to 90 dB but will try it.

I love this thread and it's really re-kindled my desire for tubes again. So much useful info here. I've been copying a pasting into a word doc for future reference on tubes to try. Yeah, this is going to be fun!

Jeff near Tacoma WA

[Bombadil]

I will try integrating a sub. It wasn't until about a month ago that I had a preamp which has a sub output. So when I was evaluating the amp, I really didn't have a way to route deep bass to a sub.

As to speaker efficiency, I am quite well versed on that. My problem is that I've never heard a speaker which had a sensitivity rating of over 93db which I've liked. There may be something out there, probably fairly expensive, which might toot my horn, but I don't want to drop big dollars on a speaker to use with an amp which I picked up used for $500. I consider my 91db speakers to be pretty efficient, as the average speaker is around 87dB. My 18wpc amp drives these speakers to well beyond my typical listening level.

Perhaps I will give the Inspire a go in a bi-amp setup.

[Bombadil]

Originally Posted by Masterlu

Bombadil... Welcome to AA!

Thanks, but I've been on here before. Over a year ago. Lost my login information and had to register again. But I didn't post much then.

[nhparrot]

Originally Posted by nhparrot

Based on recommendations from Simon, Peter and others, I picked up a pair of EL84 tubes and socket adapters. Will be swapping them in today to give them a test drive in my system.

The EL84's were interesting and different. Crisp and airy, but lacked the body and mid bass and lower heft I enjoy with 6V6GT's in my system/room. Back to 6V6GT's for me.

[pstrisik]

Originally Posted by nhparrot

The EL84's were interesting and different. Crisp and airy, but lacked the body and mid bass and lower heft I enjoy with 6V6GT's in my system/room. Back to 6V6GT's for me.

That is consistent with my findings. In my system, the bass isn't as important as I have biamped with 8" woofers and variable active crossover - plus a sub for very low freq. That airiness was the attraction for me.

That said, I've still moved back to EL34's (Mullard Xf2).

[Simonatsea]

Originally Posted by pstrisik

That is consistent with my findings. In my system, the bass isn't as important as I have biamped with 8" woofers and variable active crossover - plus a sub for very low freq. That airiness was the attraction for me. That said, I've still moved back to EL34's (Mullard Xf2).

I have swapped my 6v6's back in a few times, but in my system the EL84's are keepers, they do everything at the moment, and push as much bass as I've heard outta my Kef LS50's.
Every system is different.

I am tempted to look at the KT88 SE HO, 17 watts and three huge Trannies! Interested to hear the thoughts on it.

[Bombadil]

Getting back to my Inspire SE EL84 amp. Yesterday I used a recently acquired Marantz AV8003 preamp/processor to filter bass frequencies being sent to the Inspire at 100Hz. Routing those off to a SS amp driving a passive subwoofer.

Wow! What a difference that made! The Inspire no longer goes into clipping at volume levels in the mid-80s. The sound is much more dynamic. I'm very much looking forward to re-evaluating the amp vs my other amps.