Dennis Had Inspire Amps

[Rosco65]

Thanks Peter,

The suggestion I made to you on AC is my current solution, but being able to A/B a speaker level cap vs. a line level cap is interesting to me. The crossover point on the 802D functions both to fill in the high frequencies (>4khz) and to partially level match with the 414A. It's sensitivity is about 108 dB at 1000hz but falls to 100dB at 15khz or so. Bringing it in high at 6dB would make the effective crossover point about 4khz.

I'm curious about Dennis' response - pin #6 on the KT88 or KT150 are unused.

[Coltrane1]

Originally Posted by Rosco65

I remember seeing the seller reference the original Ebay ad when he bought it from Dennis. If memory serves, he paid $1,350 for it.

For reference, Dennis most recent sale for a KT88HO with IIPS was for $1,434 including shipping. I'm still scratching my head at the seller's asking price.

Hi Rosco,

Much obliged! I looked at the price and thought can that be appropriate?

Originally Posted by pstrisik

Hi Greg,

Been a while! I am still enjoying my KT150 big time. Dennis upgraded it a couple of months ago to employ his infinite impedance power supply and Jantzen Z-Silver caps. Very significant improvement.

That is the amp I saw. He lowered the price twice. Down to $1450 about the time we talked about it here. Hasn't sold so far, so the price still is on the high side. Still might sell at that price, but you're right, Dennis' current offerings are a better deal than that one used at that price. The price for mine in early 2014 was $1650 shipped. That was $1550 plus $100 for custom powder coating color. Since he is charging for shipping, it is very close to the $1550 new price at the time I bought mine.

Hi Peter,

A while yes. Last time I recall being here there were something like 130 pages. You all have been busy!

Wow, so Dennis is still hard at it making improvements. I'm thinking of selling mine and going for the KT150. Jantzen Z-Silver caps sounds like a nice addition to an already great amp. But we know amps or preamps are all about the power supply.

What does Dennis' "infinite impedance power supply" mean in real world language. Does it allow the amp to retain a reserve of power, or does it make the amp a better impedance match to both preamps and loudspeakers?

Congratulations on the upgraded amp! How much break in time for the new caps?

Cheers,
Greg

[Coltrane1]

Originally Posted by Simonatsea

Anyone tried thier Inspire amp with Quad ESL 57's?

Hi Simonatsea,

Thinking of acquiring Quads? I love Quad's, but have never owned a pair. I've owned Martin Logan's and other electrostat's for 35 years.

Here's a youtube of an Inspire KT88 and LP2 pre driving a pair of Martin Logan Theos. Sounds pretty good, in spite of the video phone upload.

www.youtube.com/watch?v=jlR9B22kOiM

[x3workshop]

Originally Posted by Rosco65

Does anyone know how I (or Dennis) could limit the bandwidth of a KT88HO amp to function as a tweeter amp? I know some people use Harrison Lab FMOD filters that are 12dB/octave inserted ahead of the amp. I am looking to limit the amp to above 6 to 8khz, 6dB/octave.

One option is to insert a capacitor of the correct value in line with the amp. This would require me to know the input impedance. Another option would be to choose a smaller coupling capacitor value in the amp itself to limit LF response.

I'm toying with crossover options for my Altec 414A/802D setup. Current options include Joe Esmilla's crossover, Joe Roberts' recommendation of a single cap at 6-8khz with attenuator (l-pad or autoformer), or and active/passive solution using two amplifiers. I have an LP-27a preamp (two outputs), a PSE amp (15 wpc or so), and a KT88HO (5 wpc with 6V6 to 12wpc KT88). I could use one amp with a speaker-level crossover or both amps by limiting the low frequency response of the "tweeter" amp. The power difference between the two would almost perfectly match the sensitivity difference of the drivers (99dB vs. 105dB).

Any thoughts or suggestions?

Interesting question. I've been using the high pass F MOD REDs to great result. Allows the Inspire to just work >100Hz. Everything else goes to the sub.

You may have tried this already, but I wonder if an easy and relatively inexpensive experiment would be to use the orange or green high pass F MODS to see how well it does?

[pstrisik]

Originally Posted by Coltrane1

Hi Peter,

A while yes. Last time I recall being here there were something like 130 pages. You all have been busy!

Wow, so Dennis is still hard at it making improvements. I'm thinking of selling mine and going for the KT150. Jantzen Z-Silver caps sounds like a nice addition to an already great amp. But we know amps or preamps are all about the power supply.

What does Dennis' "infinite impedance power supply" mean in real world language. Does it allow the amp to retain a reserve of power, or does it make the amp a better impedance match to both preamps and loudspeakers?

Congratulations on the upgraded amp! How much break in time for the new caps?

Cheers,
Greg

Can't say about break in. It sounded at least as good as I remembered (a week without listening to it) so any break in was gravy and I wasn't on the look out for it since I was already happy!

There seems to be a number of aspects to describe about the IIPS, some of which are beyond my understanding at this point. Below is a quote from Dennis, by way of an earlier post by Analog Addict. But the heart of the mod, in my way of understanding is the mod provides a way to eliminate some distortion introduced into the power circuit by running it through the rectifier tube which makes for a decoupler in the circuit so the distortion elements are not transmitted beyond that point.

"...a new circuit I have recently developed to prevent power supply distortions caused by the output tubes pushed into high and even higher non linear levels of output power. These distortions show up as a parasitic modulation products even on the smallest forms of the power supply. The actual sonic audible indications are sharp high frequency lisps on vocals and instruments becoming strident and for a better word ear piercing. I normally let me ear be the design chain but in this case I went to test equipment spectrum displays for analysis of the power supply wave form along with the output wave for and harmonic content. My goal was to limit odd order products in the output signal and in turn discover the source of many over load distortions. 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.

I was surprised to find the nasties invading even the regulated power supply circuit I use for the input driver tube and output tube screen grids. My thought process, (dangerous!!!) took me to figure on a high impedance decoupling device of the power supply between the output and input devices with a shared power source. Well, since I gotta lotta time to think about circuits and not banks and employees … bingo … the light went off. How about the good ole two element vacuum rectifier vacuum tube. Yea, like and indirectly heated 5AR4, GZ34 and variants …. use the vacuum between the elements and see if the good ole rectifier tube could transfer the positive going DC voltage from the high B+ output tube potential to the lower (+250 VDC) regulated driver and screen grid supply. With some additional parts and old man soldering, it works and works well. I can now drive the you know what out of a single-ended amplifier and create a listenable signal even in complete over load with the 2nd order harmonic masking the third and fifth order nasties. How does it sound …. smooth, with honey flowing from the loudspeakers. "

[Musica Amantem]

Originally Posted by x3workshop

Interesting question. I've been using the high pass F MOD REDs to great result. Allows the Inspire to just work >100Hz. Everything else goes to the sub.

You may have tried this already, but I wonder if an easy and relatively inexpensive experiment would be to use the orange or green high pass F MODS to see how well it does?

Hi x3workshop,

This seems like a great and easy to implement tweak to allow only higher than 100 Hz frqs going to the amp. I just need to see if I'm getting this right:

1. Connect an FMOD on each male RCA from the preamp out to the amp.

2. Use the SUB pre outs to feed the line-level SUB input and set the SUB's crossover at 100 Hz.

The described arrangement should allow nothing under 100 Hz at the amp and the SUB will take over from 100 Hz and under, easying the amp's amplification from the burden of the really low frequencies.

If this is correct, I should use the Low-Pass (Black) FMOD, which in the FMOD site's color scale says "None" (i.e., no color) for the 100 Hz Low-Pass mark.

Another question is if this added stage in the signal path may possibly affect sound negatively? What is your opinion in this aspect?

I may be misinterpreting this because you mentioned high-pass RED FMOD and I understand it should be LOW-PASS Black?

Thanks for your valid feedback.

[x3workshop]

Originally Posted by Musica Amantem

Hi x3workshop,

This seems like a great and easy to implement tweak to allow only higher than 100 Hz frqs going to the amp. I just need to see if I'm getting this right:

1. Connect an FMOD on each male RCA from the preamp out to the amp.

2. Use the SUB pre outs to feed the line-level SUB input and set the SUB's crossover at 100 Hz.

The described arrangement should allow nothing under 100 Hz at the amp and the SUB will take over from 100 Hz and under, easying the amp's amplification from the burden of the really low frequencies.

If this is correct, I should use the Low-Pass (Black) FMOD, which in the FMOD site's color scale says "None" (i.e., no color) for the 100 Hz Low-Pass mark.

Another question is if this added stage in the signal path may possibly affect sound negatively? What is your opinion in this aspect?

I may be misinterpreting this because you mentioned high-pass RED FMOD and I understand it should be LOW-PASS Black?

Thanks for your valid feedback.

MA,

Yes, your are correct, Pre to FMOD to amp input. Preamp to subwoofer. However, you actually want a High Pass going into your amp. It let's all freq >100hz through. A low pass would only let sub 100Hz through. Please be aware that these are 12db/octave slopes. They were available in 18 & 24/db slopes, but it seems they are discontinued.

When I mentioned "RED FMOD" the labels of the High Pass filter labels are red, low pass labels are black. Each frequency roll off has a designated color band. The 100hz High Pass (and low pass) has no color band.

I've been using them for about 3 years with all of my amps. Early on I didn't have loudspeakers that I felt reproduced the very low end without getting muddy at higher volumes so they solved that issue for me.

I have much better loudspeakers now, but I do use them when running the Inspire and some of my low watt UL PP amps to take that <100Hz strain off of them. The subwoofer takes care of those frequencies leaving the low power amps to shine in the upper bass & midrange. Makes a massive improvement to me.

I will honestly tell you that, in my application(s), they have no ill effect on sound quality. I've a/b tested with others present and no one could detect a negative change. They have many fans, but of course some people will poo poo them because they don't cost several hundreds/thousands of dollars. I love them and recommend them. I'm not affiliated.

Absolute sound reviewer likes them too:

http://www.hlabs.com/testimonials/

I was going to hard wire a set in under the hood of my LP-27a on the subwoofer outputs, (I had Dennis install a third set of outputs for this purpose.), That's how much I like them.

Here's a shot using them on my MC240's -

[Musica Amantem]

Originally Posted by x3workshop

MA,

Yes, your are correct, Pre to FMOD to amp input. Preamp to subwoofer. However, you actually want a High Pass going into your amp. It let's all freq >100hz through. A low pass would only let sub 100Hz through. Please be aware that these are 12db/octave slopes. They were available in 18 & 24/db slopes, but it seems they are discontinued.

When I mentioned "RED FMOD" the labels of the High Pass filter labels are red, low pass labels are black. Each frequency roll off has a designated color band. The 100hz High Pass (and low pass) has no color band.

I've been using them for about 3 years with all of my amps. Early on I didn't have loudspeakers that I felt reproduced the very low end without getting muddy at higher volumes so they solved that issue for me.

I have much better loudspeakers now, but I do use them when running the Inspire and some of my low watt UL PP amps to take that <100Hz strain off of them. The subwoofer takes care of those frequencies leaving the low power amps to shine in the upper bass & midrange. Makes a massive improvement to me.

I will honestly tell you that, in my application(s), they have no ill effect on sound quality. I've a/b tested with others present and no one could detect a negative change. They have many fans, but of course some people will poo poo them because they don't cost several hundreds/thousands of dollars. I love them and recommend them. I'm not affiliated.

Absolute sound reviewer likes them too:

http://www.hlabs.com/testimonials/

I was going to hard wire a set in under the hood of my LP-27a on the subwoofer outputs, (I had Dennis install a third set of outputs for this purpose.), That's how much I like them.

Here's a shot using them on my MC240's -

Thanks for clearing this up. My confusion stems from the semantics involved: to me it is just intuitive to assume a High Pass filter would filter high frequencies and viceversa, when in reality it is the other way around. I'm clear about the frequency color bands on each group.

Please be aware that these are 12db/octave slopes - Could you kindly explain what the implications are?

This is all good news and a find for me. My loudspeakers are good at reproducing bass, but the Inspire is still a "flea" amp and releasing it from tough low frequencies is a big benefit, as you pointed out. I don't listen at high volumes, so my interest is more aimed at increasing headroom reserves and hopefully improve the SQ from a less stressed amp.

Since your experience shows no detracting effects on sound, I'll get me a pair of these very soon. Thanks again for a great tip! BTW, you have nice audio pieces in your system.

[x3workshop]

Originally Posted by Musica Amantem

Thanks for clearing this up. My confusion stems from the semantics involved: to me it is just intuitive to assume a High Pass filter would filter high frequencies and viceversa, when in reality it is the other way around. I'm clear about the frequency color bands on each group.

Please be aware that these are 12db/octave slopes - Could you kindly explain what the implications are?

This is all good news and a find for me. My loudspeakers are good at reproducing bass, but the Inspire is still a "flea" amp and releasing it from tough low frequencies is a big benefit, as you pointed out. I don't listen at high volumes, so my interest is more aimed at increasing headroom reserves and hopefully improve the SQ from a less stressed amp.

Since your experience shows no detracting effects on sound, I'll get me a pair of these very soon. Thanks again for a great tip! BTW, you have nice audio pieces in your system.

Simply put, the 12db/octave means that if you have a 100Hz crossover @ 50Hz (1 octave) the signal is attenuated by 12db and then at 25hz it will be reduced by another 12db. This is the slope or rolloff that people often discuss in xovers.

Some good info here: http://www.audiomasterclass.com/shou...-db-per-octave

I think your setup sounds like 12db/octave would be fine. I've used 12 & 18db in mine and I prefer 12db/octave. Not too steep of a handoff of frequencies and the sub blends in well.

If you implement something like this you will notice a big step up in your Inspire's overall perceived performance.

Thanks for the gear comment. I wish it was all I had. I just finished the complete rebuild of that MC225 on the left last night. So fine. Putting it into rotation today.

Onto the Citation II restore that's been waiting for 6 months for attention. That'll take me to into March.


On another note, I just picked up several pairs of Ei KT90's at an amazing price. Going to be giving them a listen very soon.

[Musica Amantem]

Thanks for the explanation and reference. I guess a high pass at 100 Hz won't leave much room for slope differences to be noticed given the limited incidence of such low frequencies in the usual frequency distribution anyway.

Congrats on your so much more technical audio hobby. Looking forward to your impressions on the Ei KT-90's in the Triode-strapped Inspire we share. In my system, these would probably be too bold and less revealing, but you never know. BTW, this may be another potential benefit from the High Pass tweak, hopefully reducing detail-masking from the low frequency emphasis of larger tubes like KT-88 and up.