SETs and Horns

[Parsons]

Correct. I've played a bit with digital crossovers when I was trying a Lyngdorf TDAI-3400, but did not like the sound of the digital processing. I do use a miniDSP hd 2x4 on my sub units and it's really excellent (minus the low input impedance).

Also tough to bypass the passives in my speakers as I've got to get in there and cut wires just to try. Obviously this means my active crossover experience was sullied. Really just a way to remove the low frequencies from the 300b SET monoblocks I was also using at the time.

To your earlier points, it's definitely a head scratcher. As a non-engineer the only thing that pops to mind is to whether the top and bottom sections are different enough in impedance or efficiency that when running separated they are placing enough of a different draw on the individual amp supporting it vs. the combined draw of both, that something audible would be existent in one half when bi-amped. Seems unlikely to me but who knows. I'm not doubting your findings...merely interested to understand them a little more.

In most cases where I have bi-amped (or tri-amped), the sections were jumpered together from the factory so it was an easy back-forth to bi-amp or tri-amp then rejumper and retest. I had access to 3 identical stereo amps, and it was a decent step up in terms of transparency and perceived "ease" without a loss of cohesion. The combined costs of the 3 amps was over double the cost of the speakers, so I ultimately stuck with bi-amping (already owning the two identical amps) and returned the third to my friend without justifying the additional cost for only a modest gain over bi-amping. What was interesting is that I could hear a difference in which two parts of the 3-way I ran on the same amp vs. it's own, and so I ended up tweaking the sound that way.

I also currently use the MiniDSP to bi-amp my current open baffles and I think it works well (although I've only used them for bass). Its especially useful as I play around with different SET amps for the top sections that have different output levels from each other.

 

[acg]

@cal3713

Not saying this is the case, but it may be something to look into regarding the 'coherence' issue when bi-amping. When two amplifiers are paralleled their input impedance is also paralleled which means the load your preamp sees actually halves (when biamping). If you maintain the standard 47kOhm F4 input resistor, then the load that your preamplifier sees is now nominally 23.5kOhm when drving two F4's. I had a quick look at your preamp and although not specified in what I saw, it may have quite a high output impedance being single stage using a tube with Rp=4.5kOhm and output transformer coupled.

What may be happening is not an interaction between the amplifiers and speaker, but between the preamplifier and amplifiers via an impedance mismatch. If this is the problem then the solution is to use a preamplifier with lower output impedance or go back to single amplifiers...which you have done. Perhaps you could try swapping the F4 input resistors from 47k to 100k...that may also be acceptable.

 

[Atmasphere]

Agreed with high orders but I would point out that an all (or mostly) odd dominated spectrum will likely sound worse than a spectrum that has all harmonics in an exponential decay with increasing order. There is an article in Stereophile by Keith Howard where he adds distortion to a recording showed that, at least to his preference, the worst sounding addition he made was with all odd orders and the least offensive was an alternating even/odd pattern that decayed exponentially. The best overall of course was no added distortion...which he stated debunked the idea of "euphonic" distortion. This also fits with observations from earlier audio writers, like Jean Hiraga, who stated that a monotonic spectrum (meaning an exponential decay with increasing order) was preferrable (Cheever also made this claim). It turns out that only single ended circuits make such a pattern (unless a designer of a PP circuit deliberately unbalances the circuit to minimize the even order cancellation that PP circuits make).

IME electronic circuits tend to have variance that prevents them from having distortion of a really pure type. We try really hard to make sure our stuff is as balanced as possible, but being zero feedback its not going to be perfect- and so will have some even ordered harmonic content, which in fact is unavoidable. So far no-one has reported a 'hooded' sound- quite the opposite in fact. FWIW an amplifier that has the 3rd as its primary distortion product will certainly exhibit an exponential decay of harmonics as the order is increased.

Since we've been repairing equipment as well as making it, we've had opportunities to audition a variety of amps, using our own as benchmarks of course. Of a variety of tube amplifiers, the one that has sounded the most like ours was an SET, as opposed to an ARC or CAT.

 

[cal3713]

So far no-one has reported a 'hooded' sound- quite the opposite in fact.

Agreed here. My experience (and reading of Nelson Pass, so perhaps some expectation bias), is that 2nd dominance creates the impression of warmth and body, and 3rd dominance detail and clarity.

 

[cal3713]

@cal3713

Not saying this is the case, but it may be something to look into regarding the 'coherence' issue when bi-amping. When two amplifiers are paralleled their input impedance is also paralleled which means the load your preamp sees actually halves (when biamping). If you maintain the standard 47kOhm F4 input resistor, then the load that your preamplifier sees is now nominally 23.5kOhm when drving two F4's. I had a quick look at your preamp and although not specified in what I saw, it may have quite a high output impedance being single stage using a tube with Rp=4.5kOhm and output transformer coupled.

What may be happening is not an interaction between the amplifiers and speaker, but between the preamplifier and amplifiers via an impedance mismatch. If this is the problem then the solution is to use a preamplifier with lower output impedance or go back to single amplifiers...which you have done. Perhaps you could try swapping the F4 input resistors from 47k to 100k...that may also be acceptable

Agreed. These findings are actually from a different pre, Don Sachs' modification of the VTA SP14 6sn7 preamp. It has output caps, so I modified the F4's input impedance to 200k so I could use reasonable value duelund CAST caps on the output. It has an output impedance of 850 ohms.

Haven't gone back to test with with my current pre, but it's actually at 375 ohms: https://simplepleasuretubeamps.com/2020/12/30/shiny-eyes-eml20a-preamplifier/

 

[Parsons]

Agreed. These findings are actually from a different pre, Don Sachs' modification of the VTA SP14 6sn7 preamp. It has output caps, so I modified the F4's input impedance to 200k so I could use reasonable value duelund CAST caps on the output. It has an output impedance of 850 ohms.

Haven't gone back to test with with my current pre, but it's actually at 375 ohms: https://simplepleasuretubeamps.com/2020/12/30/shiny-eyes-eml20a-preamplifier/

I have a bunch of stuff from Radu...great stuff. Haven't heard a pre from him yet, however.

 

[cal3713]

Btw, it's real

I have a bunch of stuff from Radu...great stuff. Haven't heard a pre from him yet, however.

The difference in clarity and precision over my prior (and universally well-reviewed) 6sn7 pre is striking.

I just asked him to build me a second power supply so that I could make it a fully dual mono design and keep each channel completely separated after the volume control. Aside from small power supply modifications that I could do at home (like switching to a filament bias), that's basically going to max out the circuit's capability. The nice thing about working within the DHT framework is that the circuit is so well documented. Nothing magic to add from another designer here and once you've got a framework, it's easy to make small changes yourself. Radu did a great job with the build. It's beautiful and has no hum or microphonics. It'll look nice with the full symmetry of the three box solution.

 

[marslo]

Very interesting and very technical thread .I understand that for many audiophiles with technical approach this is important to understand why some elements may have and other not the synergy with each other.

But I am missing here more examples and pictures of real setups installed in our homes - there are only few of them in this thread.

Instead of understand I prefer listen to.
Because our choices are limited to the availiblity of brands and financial means.

Next we have to agree with our spouses about the budget and the look of the gear we want to buy, unless one lives alone.

As for myself I selected first horns because of difficult room acoustics where less efficient speakers suffered from reflections of big windows in empty space . Why Avantgardes ? Because only the AG dealer was willing to make a demo in our house on the countryside.

Then after trying over 10 different amps ( SS class A, AB and D) push-pulls , OTL and SEts available in our market for the price I considered "fair" I made a choice for one which had the best relation price/SQ/look .And sounded the best for me.

The gear is only the necessary instrument to listen to music available on vinyls, cds or files .

Would I change my mind after having read that the distortion on paper is too high and the material of the horn is not adequate ?
No , it does not work this way for me.

Sure, I could try to make a special room with perfect acoustic treatment and close myself for long hours there.

But we need to share life with our partners and music is one of best common hobbies.

So please, show your setups and tell how you adapted to your real life requirements.

 

[ArnoFenn]

But I missing here more examples and pictures of real setups installed in our homes - there are only few of them in this thread.



So please, show your setups and tell how you adapted to your real life requirements.

Some pics

 

[marslo]

Dear @ArnoFenn,

could you pls give us some comments about your horn/SET combo?
Your TT - is that Fat Bob?

 

[ArnoFenn]

Dear @ArnoFenn,

could you pls give us some comments about your horn/SET combo?
Your TT - is that Fat Bob?

If there are more specific questions, do let me know, but to make a general start..

Yep, Fat Bob S as TT. The horns (DIY) 40Hz Tractrix profile, mid-horn TAF TD2001 driver and lazy ribbon as tweeter. SET's (DIY), 300B and interstage transformer coupling between drive tube and 300B tube.
Tweeter is mouted on a slider to adjust the phase wrt mid measured at listening position (CLIO pocket)

 

[marslo]

If there are more specific questions, do let me know, but to make a general start..

Yep, Fat Bob S as TT. The horns (DIY) 40Hz Tractrix profile, mid-horn TAF TD2001 driver and lazy ribbon as tweeter. SET's (DIY), 300B and interstage transformer coupling between drive tube and 300B tube.
Tweeter is mouted on a slider to adjust the phase wrt mid measured at listening position (CLIO pocket)

How about the bass section? Is that driven with the same amp as mid horn and ribbon tweeter?

 

[ArnoFenn]

How about the bass section? Is that driven with the same amp as mid horn and ribbon tweeter?

Yes, high efficiency and the level of the mid/high had to be attenuated to match the woofer/horn

 

[morricab]

If there are more specific questions, do let me know, but to make a general start..

Yep, Fat Bob S as TT. The horns (DIY) 40Hz Tractrix profile, mid-horn TAF TD2001 driver and lazy ribbon as tweeter. SET's (DIY), 300B and interstage transformer coupling between drive tube and 300B tube.
Tweeter is mouted on a slider to adjust the phase wrt mid measured at listening position (CLIO pocket)

The 40hz horn is driven by a Fostex 208sigma?

 

[morricab]

Very interesting and very technical thread .I understand that for many audiophiles with technical approach this is important to understand why some elements may have and other not the synergy with each other.

But I am missing here more examples and pictures of real setups installed in our homes - there are only few of them in this thread.

Instead of understand I prefer listen to.
Because our choices are limited to the availiblity of brands and financial means.

Next we have to agree with our spouses about the budget and the look of the gear we want to buy, unless one lives alone.

As for myself I selected first horns because of difficult room acoustics where less efficient speakers suffered from reflections of big windows in empty space . Why Avantgardes ? Because only the AG dealer was willing to make a demo in our house on the countryside.

Then after trying over 10 different amps ( SS class A, AB and D) push-pulls , OTL and SEts available in our market for the price I considered "fair" I made a choice for one which had the best relation price/SQ/look .And sounded the best for me.

The gear is only the necessary instrument to listen to music available on vinyls, cds or files .

Would I change my mind after having read that the distortion on paper is too high and the material of the horn is not adequate ?
No , it does not work this way for me.

Sure, I could try to make a special room with perfect acoustic treatment and close myself for long hours there.

But we need to share life with our partners and music is one of best common hobbies.

So please, show your setups and tell how you adapted to your real life requirements.

 

[morricab]

View attachment 75918

Now driven by:

 

[ArnoFenn]

The 40hz horn is driven by a Fostex 208sigma?

Indeed. Before it was a Lowther but then it was still a 1 speaker horn

 

[cal3713]

Dear @ArnoFenn,

could you pls give us some comments about your horn/SET combo?
Your TT - is that Fat Bob?

Agreed. I'd like to see more pictures AND more explanation of how the horn and amplifier combos were chosen and fit into the listening space.

 

[Blue58]

Very quiet Sunday here and haven’t posted pics for a while so here’s my direct coupled mono amps using half 12ax7 (Raytheon JRP black plate) to Globe 45 (Emission Labs V4), Electraprint partial silver output transformers. Rectifier is 5AS4A.

Duo Omega, obviously, with their new crossover using Miflex copper cap bypassed with a Duelund Tin/copper cap and a Jensen copper foil inductor. Lots more upgrades done and the rest of the system is in my signature.

Still a work in progress with a few more upgrades planned and the latest replacement for the Java LDR preamp soon to arrive (after 12 months wait).

 

[cal3713]

@Blue58 Do you happen to have a build/design thread for your amps? As I've mentioned a few times, I'm considering buying horns and if so would be curious to try a 45-based amplifier.