Tube amps and speaker matching

[cawleym]

Newbe here but I have Galileo Ispohon speakers matched up with 2 VTL amps (IT85 and ST85) It is a bi-amp setup as the speakers have 2 pair of terminals each

Otherwise pretty basic, Monster speaker cables, AR interconnects with RCA plugs. Trip lite surge protector for just the amps. Amps just serviced with contact cleaning and all tubes tested OK

Basic SonyCD player

Issue is NO bass!. Not from the CDplayer, nor the Blue tooth DAC streaming my Iphone. Mid and high range is sharp and crisp, very bright

I can turn the amps up to about half way and get plenty of volume but no bottom

Any ideas?

 

[lovinthehd]

Content with more bass? Better speakers? A sub? Gear that can help integrate a sub? Several ways to go overall. Why are you passively bi-amping? Just because the speakers have terminals isn't a good reason to do that (altho I know nothing about your speakers' passive network, never heard of the speaker brand either for that matter). As long as the cables are adequate they shouldn't matter. What are you listening to to judge this by?

 

[cawleym]

I listen to a wide range of music. Classical, acoustic, jazz, blues. I just know it sounds weak at the low end.
I had it hooked up without bi-amp (when I just had one amp in the beginning) that that was worse as they were under powered (to my ear) low volume and a thin sound.

The amps are matched for a bi-amp set up per the user manual. So each frequency range is powered at the same level

The Galileo are decent (though discontinued) I got them from Needle Doctor in MInneapolis as left overs since they never really took off in the States but I've read some good reviews and he is a good friend so I trust his advice on the gear

Overall I Iike the set up and hope it just needs a tweak. Subwoofer for more bass would be fine perhaps but with the bi-amp set up, I already used the pre-out jack. Maybe new speakers?

I'm not really that knowledgable about all this but did spend some real money here and would love to get it right

Thanks for any help

 

[TLS Guy]

Well you won't get good sound out of that rig. The fact you have no bass is explainable. The issue is your amp/speaker combo.

Someone has told you that tube amps are the last word in audio perfection haven't they? Well that is a myth and a gigantic lie, especially for a lot and your amps in particular.

Let me explain your problem

Let us start with your speakers. Your speakers are from a defunct, boutique and not very good Swiss vintage speaker manufacturer, Isophon Werke. Your speakers are a bookshelf 3 way with a 7" bass driver, 4" midrange and dome tweeter. Crossovers are at 160 Hz and and 3200 KHz. Now this is where the boutique idiocy comes into play. The crossovers are first order 6db. Nominally the speakers are 4 ohm. However since first order crossovers have such a low attenuation of the drivers there is huge overlap between them. This results in a 2 ohm load over a broad frequency range around crossover. This I find understandable. I can not find a graph, but descriptions of people who have measured them.

Now unlike solid state amps tube amps have a high output impedance and are basically a voltage source and not a current source, the latter being much better for driving loudspeakers. In your case the output impedance of the amps is 1.08 ohms. So that means the output impedance of your amps is over 50% of the load presented by the speakers in the bass octaves.

The significance of this is that that the output of tube amps follows the impedance curve of the speakers. Impedance curves of speakers are full of peaks and troughs.

Now this graph shows your amp driving a constant resistance source on the bench and a typical 4 ohm speaker.

There is more bad news to come. The distortion of your amps becomes outrageously high driving low impedance loads like your speakers present.

This is accompanied by enormous levels of distortion into 4 and especially 2 ohm loads even at low power.

So I suspect you have fallen victim to a boat load of nonsense and false information spouted by some idiotic "Audiophool" guru. These idiots abound. The result is that the technically uniformed end up laying out enormous amounts of cash for a very Low-Fi system and not the highest of Fi audio nirvana system they expected. They fall victim to ignorant opinionated fools, of which far too many are high end dealers.

To sum up all I can tell you is that to get any improvement you have to ditch what you have and start from scratch. Unfortunately that rig is not salvageable. The fact you have not a lick of bass is explainable from simple physics and there is nothing that can be done to change or ameliorate those immutable laws. I'm sorry but that is the way it is and it would be irresponsible for me to give you false hope.

 

[shadyJ]

Something else, check to see if the jumpers are in place and properly connecting the binding posts. If not, they may only be amplifying the midrange and tweeter with the bass driver getting nothing.

Here is an impedance measurement of the Isophon speakers. As TLSguy says, that is a brutal load for a tube amp.

 

[cawleym]

There are no jumpers in place as the Bi-amp set up has separate cables to each pair of posts (Instructions were to remove them in such a set up)

Anyway, lot to absorb here and perhaps I may have been sold a "bill of goods" by the tech. And I sure did spend some $$$.

I suppose people buy tube amps for a reason (other than nostolgia!) but maybe not.

Any way to make best use of the amps with a new speaker set up or something. Also, is there a guide to the physics of all these specs? I'd like to really understand the significance of crossover levels and impedance. A forum or book anyone can recommend ?

 

[Kvn_Walker]

Well... a lot of tube lovers buy high efficiency, high impedance horn speakers (mid or upper- 90s sensitivity, generally 8 ohm). Just about everybody on the Klipsch forum with the Heritage line runs tube amps.

Have heard a lot of good about Spatial Audio Triode Masters as well. Search for "tube-friendly speakers" and you will find a lot of options. Be warned that many of them are quite large speakers.

 

[TLS Guy]

Something else, check to see if the jumpers are in place and properly connecting the binding posts. If not, they may only be amplifying the midrange and tweeter with the bass driver getting nothing.

Here is an impedance measurement of the Isophon speakers. As TLSguy says, that is a brutal load for a tube amp.

Thanks Shady, yes, the impedance curve is brutal. I actually suspect the curve is below the DC resistance of the drive units. It would be interesting to have the OP measure the DC resistance of the speakers with an ohm meter. If the reading is higher than any points on that impedance curve, then the design is totally incompetent and the speaker crossover in resonance which is awful for any amp, and actually would probably blow up or send into protection many solid state amps.

 

[PENG]

Thanks Shady, yes, the impedance curve is brutal. I actually suspect the curve is below the DC resistance of the drive units. It would be interesting to have the OP measure the DC resistance of the speakers with an ohm meter. If the reading is higher than any points on that impedance curve, then the design is totally incompetent and the speaker crossover in resonance which is awful for any amp, and actually would probably blow up or send into protection many solid state amps.

The OP did not provide the model number. Since you seem to have seen the impedance curve, did Galileo Isophon make just one model or you just made an assumption on a particular bookshelf model.

One thing the OP can check just to make sure is that the speakers are wired in phase. Is the center stage (stereo mode) stable? Based on specs and Stereophile measurements, those amps are obviously not for neutrality or accuracy, and would do better with high impedance speakers, assuming they have high enough output voltage.

 

[TLS Guy]

There are no jumpers in place as the Bi-amp set up has separate cables to each pair of posts (Instructions were to remove them in such a set up)

Anyway, lot to absorb here and perhaps I may have been sold a "bill of goods" by the tech. And I sure did spend some $$$.

I suppose people buy tube amps for a reason (other than nostolgia!) but maybe not.

Any way to make best use of the amps with a new speaker set up or something. Also, is there a guide to the physics of all these specs? I'd like to really understand the significance of crossover levels and impedance. A forum or book anyone can recommend ?

As I suspected you got bamboozled by a dealer. Unfortunately the dealer probably believed all the nonsense he spouted at you.

Those speakers have to go, they are no good for any decent system and potentially lethal to amps.

The tube amps are a difficult issue. Unfortunately those amps are not very good as tube amps go. They have enormous amounts of distortion even when not pushed. They generate a totally unacceptable amount of harmonic content.

Really they need a speaker with 8 ohm impedance and a very flat impedance curve. About the only speaker that will do that is a full ranger without crossover. The 1.08 ohm output impedance of those tube amps is a huge problem when it comes to speaker selection.

Next point is, you do not need two of those amps. Passive biamping is not going to help you. It does not make more power available for one thing, as all of the power is required on the bottom end largely.

Now modern properly designed speakers have what is known as baffle step compensation. This is the point where a speakers transitions from being a monopole to an omnipole. That means going from a half space to a full space radiator. If a speaker lacks this it has a very thin lack of bass character. The frequency at which this occurs is higher the narrower the front baffle. The only way to make a passive speaker do this is to have it draw more power below this transition frequency by dropping the impedance at this point so that the appropriate 6db or so boost below the transition frequency can be applied. This does not fit well with tube amps because of their high output resistance as a group. As I said all tube amps are adverse to high current demands, and won't provide it.

The above is why the profile of speakers has changed since the hey day of tube amps. In days passed the fronts of speakers were much wider. The more modern narrow front baffle speaker have better dispersion characteristics as they have less diffraction (scatter with highs and nulls of output) in their frequency response.

So to use those amps with a "modern" concept speaker would really need a custom design. To use both amps would require active biamping and not passive. That means designing a two way speaker or at least a three way hybrid, with electronic crossover ahead of the power amps inserted between your pre amp and the power amp.

This would be a lot of work and effort. I will be honest and state that from what is have seen of those amps they are not worth that effort.

So if you keep those amps you are looking at specialist exotic speakers again.

The speakers that most come to mind here are Lowther horn loaded full rangers. Lowther are the worlds oldest high fidelity loudspeaker company by far, going back pre WW II. Common Sense Audio in MO have handled Lowther's US interest for 50 years or more.

My final thoughts are though that you are likely a music lover and not a "techie". Please correct me if I am wrong. You, I feel want a good plug, play and go solution. If you hang onto any of the rig you have now, that is not going to happen. If my assessment is correct then my honest advice to you is to liquidate what you have.

Then we can talk budget and design for something more suitable for your needs.

 

[TLS Guy]

The OP did not provide the model number. Since you seem to have seen the impedance curve, did Galileo Isophon make just one model or you just made an assumption on a particular bookshelf model.

One thing the OP can check just to make sure is that the speakers are wired in phase. Is the center stage (stereo mode) stable? Based on specs and Stereophile measurements, those amps are obviously not for neutrality or accuracy, and would do better with high impedance speakers, assuming they have high enough output voltage.

His speaker is the Isophon Galileo. Galileo is the model. I spent more time than I should have digging up the details on this speaker. As soon as I knew it was a three way with first order crossovers with one at 160 Hz with a four ohm rating I knew this was a kamikaze design. The speaker is pretty much certain to be two ohm as the woofer and mid are essentially in parallel over are large frequency range around 160 Hz. That is what I found. Actually are more honest spec for that speaker would be 2 ohm rather than 4 ohm. That is disaster for an amp with an output impedance of 1.08 ohms. So you can be certain the OP is correct that his system sounds as if it does not have a lick of bass.

I have done this long enough I can easily hear in my head the sonic signature of a rig like that.

 

[PENG]

His speaker is the Isophon Galileo. Galileo is the model. I spent more time than I should have digging up the details on this speaker. As soon as I knew it was a three way with first order crossovers with one at 160 Hz with a four ohm rating I knew this was a kamikaze design. The speaker is pretty much certain to be two ohm as the woofer and mid are essentially in parallel over are large frequency range around 160 Hz. That is what I found. Actually are more honest spec for that speaker would be 2 ohm rather than 4 ohm. That is disaster for an amp with an output impedance of 1.08 ohms. So you can be certain the OP is correct that his system sounds as if it does not have a lick of bass.

I have done this long enough I can easily hear in my head the sonic signature of a rig like that.

Thanks, I thought Galileo Isophon is the brand name. Still, in a small room, an good SS 50 W amp may be able to do a decent job at lower spl (say up to 75-80 dB average) with good bass/mid/treble balance, but not those VTL amps for sure.

 

[Kvn_Walker]

I bet if the OP got a pair of BMR's and a pair of Outlaw 2200s (or a good SS integrated), he'd be in 7th heaven. It won't be as sexy looking, it won't have the "audiophile cred", but I'm a function over form kind of guy.

 

[ryanosaur]

It won't be as sexy looking

I prefer to think of it as “industrial chic,” thank you.

 

[TLS Guy]

Thanks, I thought Galileo Isophon is the brand name. Still, in a small room, an good SS 50 W amp may be able to do a decent job at lower spl (say up to 75-80 dB average) with good bass/mid/treble balance, but not those VTL amps for sure.

Thanks, I thought Galileo Isophon is the brand name. Still, in a small room, an good SS 50 W amp may be able to do a decent job at lower spl (say up to 75-80 dB average) with good bass/mid/treble balance, but not those VTL amps for sure.

I'm really no sure about that. The whole design concept of those speakers is bad. It comes from the era of minimal phase shift as the overall priority of the design.
So the woofer is not 24 db down until 720 Hz. The mid range will have a falling acoustic response pretty much starting at crossover and so will roll off third order. So even if you discount any break up peaks in the woofer, the roll off below crossover will be two orders steeper than the roll off above. This is pretty much bound to result in a rising response above 160 Hz. Then we have the issue of the size of inductor to roll off the woofer at 160 Hz. Even under the most optimistic scenario there is going to be a significant DC resistance in series with the woofer, calculated to blow box tuning right out of the water. Honestly I do think that design is terminal.

This really is the worst case of dealer audiophoolery to have come onto these forums that I can remember. This is an absolutely egregious case study. I feel sorry for the OP. He should absolutely never have been pressured into buying that rig.

I can't think of anything else, other than doing careful measurements on those drivers. That means carefully measuring the TL parameters of those drivers and their acoustic responses, and then designing a new crossover from the ground up. Then at this time we don't even know if they got the box tuning correct.

That whole project would be an absolute labor of love and certainly not an economic proposition for anyone to undertake. At then end of the day, he has a lot invested in those amps. If he has the room then getting speakers of 8 ohm impedance, truly 8 ohm, then that is the way to solve it. Although the amps are rated at 70 watt, they perform very poorly into loads less than 8 ohm and even then have unacceptable levels of harmonic distortion long before reaching max power. So in reality they are very low powered amps and require very sensitive speakers. This really is a sad situation, but there is no point leading the OP on with solutions that will not solve his problem. If he is a plug and play music lover as I suspect, there is no point in having him spend good money after bad. If I surmised his situation correctly his best and cheapest solution is starting from scratch. I know that may be a bitter pill to swallow.

 

[Swerd]

Thanks, I thought Galileo Isophon is the brand name. Still, in a small room, an good SS 50 W amp may be able to do a decent job at lower spl (say up to 75-80 dB average) with good bass/mid/treble balance, but not those VTL amps for sure.

I agree with TLS Guy. With 1st order crossovers at 160 Hz, these speakers could be a kamikaze design. I blew up the impedance curve from the link shadyJ provided, and added a yellow line marking 4 Ohms (below).

The reviewer says, "Measured sensitivity is 86 dB, with average measured impedance being 4.8 Ohms. Not too bad, but this dips to a minimum of just over 2 Ohms at around 150 Hz, meaning the Galileos will be a difficult load to drive, and require an amplifier with a good current delivery and ability to drive low impedances."

 

[Swerd]

Assuming a high current solid state amplifier could be found that is stable at such very low impedances, I wonder how much it would cost. Those tube amps were probably expensive, and it is possible they could be sold at a price good enough to make it worthwhile for the owner.

I doubt if those speakers could be sold at nearly as good a price. Their bass performance is not there. I blew up that review's frequency response graph, which shows bass below 70-80 Hz falling off rapidly. Below about 200 Hz, bass performance is weak. The impedance curve (above) indicates the cabinet was tuned at 70 Hz. So, it's no surprise that the owner complains of weak sounding bass. He's right. And his vacuum tube amps can't handle the very low impedance, which makes matters worse.

And all this assumes that the 1st order crossovers don't introduce other problems, as TLS Guy also described. In my opinion, much better stand-mount 2-way speakers are available in the price range of $1000 to $1500 per pair. Such speakers wouldn't require heroic big iron amplifiers.

 

[PENG]

I agree with TLS Guy. With 1st order crossovers at 160 Hz, these speakers could be a kamikaze design. I blew up the impedance curve from the link shadyJ provided, and added a yellow line marking 4 Ohms (below).

The reviewer says, "Measured sensitivity is 86 dB, with average measured impedance being 4.8 Ohms. Not too bad, but this dips to a minimum of just over 2 Ohms at around 150 Hz, meaning the Galileos will be a difficult load to drive, and require an amplifier with a good current delivery and ability to drive low impedances."
View attachment 30119

I know what you guys are saying. I just feel that it is worth pointing out the fact any well designed/built low power amps such as 50 WPC 8 ohms, 70 WPC 4 ohms, can do a good job on low impedance (yes even 2 ohms) and/or not too sensitive speakers if the room is small enough, sit close enough, and the user (like me) cannot stand spl much higher than 75 dB average. Math don't lie, don't exaggerate!

I also agree with TLS that regardless my above comments, that VTL amp is not going to do it, that's just too obvious !!

The reason I tried to make this point using a 50 W amp is because his VTL amp is rated 60 W, but again, based on specs it is not one of those low power amp I would consider adequate for the Galileos in a general sense.

Below is an example of under what conditions a good SS 50/70 W 8/4 ohm rated amp can work. I assumed the amp can do 25 W into 2 ohms for typical music programs.

 

[TLS Guy]

Assuming a high current solid state amplifier could be found that is stable at such very low impedances, I wonder how much it would cost. Those tube amps were probably expensive, and it is possible they could be sold at a price good enough to make it worthwhile for the owner.

I doubt if those speakers could be sold at nearly as good a price. Their bass performance is not there. I blew up that review's frequency response graph, which shows bass below 70-80 Hz falling off rapidly. Below about 200 Hz, bass performance is weak. The impedance curve (above) indicates the cabinet bass was tuned at 70 Hz. So, it's no surprise that the owner complains of weak sounding bass. He's right. And his vacuum tube amps can't handle the very low impedance, which makes matters worse.

And all this assumes that the 1st order crossovers don't introduce other problems, as TLS Guy also described. In my opinion, much better stand-mount 2-way speakers are available in the price range of $1000 to $1500 per pair. Such speakers wouldn't require heroic big iron amplifiers.
View attachment 30122

Thanks for that Swerd. So you can see the lower crossover is not correct. The top one is OK, and that is because both the mid and Tweeter would have a satisfactory out of band response at the 3.2 KHz. Actually in terms of subjective loss of bass a response like that makes a speaker sound far more bass deficient then a roll off at 80 KHz. So subjectively those speakers would have a very lean sound. The trouble is that the impedance is still too low for that amp until 5 KHz.

I have had another idea though if he is prepared to ditch those tube power amps. If he could get a sub with a decent response to about I KHz, then he could place passive subs right next to those speakers and crossover at 500 Hz with an external active crossover between his preamp and new 4 ohm stable solid state amps. These are not hard to find. I think I would start with fourth order electrical slopes as both mid and the right sub would be in band for an octave either side of crossover.
The problem is the sub might have to be a custom build, but that would not be difficult or overly expensive. I think the crossover splits are a far enough apart split that there would not be a band pass gain issue, or at least not an issue bad enough to have to remedy.

However one still has to look at the cost of a pair of amps, an electronic crossover and the building of two subs, which in effect would be subs plus, versus starting from scratch. We need to hear the OPs thoughts.

You are right about one thing though Swerd. There is always a ready market for tube amps, even if they are lousy ones. I agree there will not be a ready market for those speakers.

 

[PENG]

Assuming a high current solid state amplifier could be found that is stable at such very low impedances, I wonder how much it would cost. Those tube amps were probably expensive, and it is possible they could be sold at a price good enough to make it worthwhile for the owner.

I doubt if those speakers could be sold at nearly as good a price. Their bass performance is not there. I blew up that review's frequency response graph, which shows bass below 70-80 Hz falling off rapidly. Below about 200 Hz, bass performance is weak. The impedance curve (above) indicates the cabinet bass was tuned at 70 Hz. So, it's no surprise that the owner complains of weak sounding bass. He's right. And his vacuum tube amps can't handle the very low impedance, which makes matters worse.

And all this assumes that the 1st order crossovers don't introduce other problems, as TLS Guy also described. In my opinion, much better stand-mount 2-way speakers are available in the price range of $1000 to $1500 per pair. Such speakers wouldn't require heroic big iron amplifiers.
View attachment 30122

Seems like a good little project, to modify the crossover.