Need amp for speakers measurements

[Hendrixon]

Hi,

The itch to measure speakers, crossovers, components, room acoustics and ultimately designing speakers got me.
I bought the dayton audio DATS V3 and Omnimic 40k and right now use an SMSL SU-1 with Fosi P4 preamp into Fosi V3 mono to output test sweeps.
What I didn't think about is that class D amps are not really +20kHz friendly (and most of them even below that have issues), and if I want to get the most out of that 40k mic I need something class A or A/B that is flat from bottom Hz up to 40kHz.

Dayton audio has their own recommended amp (APA150) which they claim is "Ultra linear frequency response from 10 Hz to 40 kHz".
It now costs $210 which is fine, but with shipping to the other side of the world and local customs on all of that it will easily be +$600 at my doorstep.

I do have an old Luxman M-2000 power amp that was given the re-youth treatment (new caps and other stuff), it will do the job easily, but that thing is a behemoth to move around.
Can anyone recommend some class A/B monoblocks (or stereo with bridge mode) that are table top friendly and measure well to 40kHz?

Thanks

 

[terryforsythe]

I think the Fosi V3 mono will be fine. If you want very precise measurements, you can use feedback to compensate for any load dependencies that may be in the amplifier's frequency response (which are small for the V3 Mono from my understanding based on a conversation I had with another member in another thread).

I built and used an ARTA box to provide feedback the last time I took a suite of outdoor measurements using an old Dayton Audio class D amplifier. The VituixCAD documentation explains a more simple solution using a computer soundcard. See pg. 2 here: https://kimmosaunisto.net/Software/VituixCAD/VituixCAD_Measurement_REW.pdf
EDIT: I just looked at that documentation again. It is not as robust as using something like an ARTA box. Nonetheless, I think it will be fine for use with the Fosi V3 Mono, assuming it is as linear with real world speaker loads as has been asserted in this forum.

I'm not sure you really need something flat to 40kHz unless you are very concerned about tweeter harmonic distortion. 20kHz bandwidth would allow you to measure the second harmonic of up to a 10kHz fundamental frequency, and the third harmonic of up to a 6.66kHz fundamental frequency.

 

[terryforsythe]

If you really are set on using class A/B, a Topping B100 or B200 should work well.

 

[DVDdoug]

Measuring speakers accurately isn't trivial and the amplifier is probably way-down on the list of things to worry about.

If you are measuring high frequencies in a room moving the mic a few inches will change the reading by several dB, and the room messes-up response over the whole range

But you'll have to be selective if you really want to go to 40kHz. It's not hard to make an amp that goes way beyond the audio range many do, but usually they are only measured & specified to 20Khz (or sometimes slightly higher).

It's also not unusual for an amplifier to intentionally filter-out DC (zero Hz) and the ultrasonics to keep the "junk" out and to avoid side-effects. Without filtering a solid state will likely go higher than 100kHz, but depending on the design it may not go down to DC.

You probably want to avoid high-power amps so you don't accidently blow a speaker. A "100W" speaker is designed for an amplifier hitting 100W on program peaks. You can fry it with constant 100W test tones and tweeters can't handle nearly as much power as woofers so you can fry a tweeter with tones that don't sound that loud, or that you can't hear, or that the tweeter can't reproduce.

Understanding Speaker Measurements (Video by Amir)

 

[Hendrixon]

I'm not sure you really need something flat to 40kHz unless you are very concerned about tweeter harmonic distortion. 20kHz bandwidth would allow you to measure the second harmonic of up to a 10kHz fundamental frequency, and the third harmonic of up to a 6.66kHz fundamental frequency.

At this early stage, where 96.4% of the info on loudspeakers design is still beyond me, I don't think I have a "need"
I'm just used to in anything I do that when I lay the first building blocks, to have them built well.
Simply thinking that if I bought this mic and it was designed to be flat to 40kHz, there is abviously a reason for that, which maybe now is still beyond me, but later on it will be usefull, so why limit this.

If you really are set on using class A/B, a Topping B100 or B200 should work well.

Only because looking on measured amps, I see all/most class D amps have issues at high frequencies and issues with different loads, unless they employ some NF and even then they are filtered above 20kHz.

Thanks for the direction on Topping, I wasn't aware of those.
The B100 is class B? and it measured so well by Amir, I don't remember ever seeing a hifi class B amp.
They seem like nice amps for the price but then I read comments on YT reviews where at least two guys reported that one of theirs failed. one guy reported that he listens to music pretty quit so there was no stress on the amps. that made me hesitant.
I know there were few Fosi V3m that were toasted on YT reviews, but those where tested to constant full power into resistive loads and without any care for heat dissipation.

Also that they are not discrete built, so local future repairs is out of the questions
My Luxman M-2000 power amp is almost my age, works better than me, can be serviced by any competent local tech, no unobtanium parts, and it will 100% out live me

The B200 IS discrete and look much better, but the price...
Maybe I'll order a B100 after all, it's size is table top friendly, measures supereb, power I guess is enough for measurements and price is managable. we'll see.

 

[Hendrixon]

Measuring speakers accurately isn't trivial and the amplifier is probably way-down on the list of things to worry about.

No argue on any of that lol

If you are measuring high frequencies in a room moving the mic a few inches will change the reading by several dB, and the room messes-up response over the whole range

Sure, but we try to do our best with what we have, like gating the IR, leveling the mic, have the tweeter at mid 3D room etc.
And sure in the end of this a measurement is relative to the measured speaker... as long as you don't move it lol

You probably want to avoid high-power amps so you don't accidently blow a speaker. A "100W" speaker is designed for an amplifier hitting 100W on program peaks. You can fry it with constant 100W test tones and tweeters can't handle nearly as much power as woofers so you can fry a tweeter with tones that don't sound that loud, or that you can't hear, or that the tweeter can't reproduce.

As for power, the Omnimic 40k comes with a feature that makes it idiot proof (yup like me) to set the signal to 2.83Vrms.. which is also one of the reasosns I decided to buy it.
Btw I've seen a tweeter or two that got fried by small amps that got pushed too hard (not by me).

 

[DSJR]

I can't link to it, but Klippel did once publish a list of suitable amps to use with performance and hopefully durability to suit many connection/disconnection cycles, possible shorts etc. and so on. One UK maker who published the list on their forum a couple or so years back (one has to be signed in to view), chose a Samson model which isn't expensive and seems to take more punishment without failure than the domestic-popular Quad amps they also use(d) for various jobs in the factory.

Klippel now recommend QSC (there may be a beneficial tie-up perhaps?)

Amplifier

www.klippel.de

https://www.klippel.de/fileadmin/klippel/Bilder/Our_Products/R-D_System/PDF/PLX2_spec_eng.pdf

Not sure on availability, but here's an ad with good pic -

QSC PLX1804 Power Amplifier (Factory Re-Certified)

The PLX2 series is a range of premium quality, high-power amplifiers designed for the most demanding live performance uses. Built on the third generation of QSC PowerLight® technology, PLX2 amplifiers combine light weight, superlative audio quality and proven QSC reliability. With high power...

www.avbyfp.com

Darn it, looks as if their stand alone amps are currently discontinued. Well, I tried

 

[terryforsythe]

At this early stage, where 96.4% of the info on loudspeakers design is still beyond me, I don't think I have a "need"
I'm just used to in anything I do that when I lay the first building blocks, to have them built well.
Simply thinking that if I bought this mic and it was designed to be flat to 40kHz, there is abviously a reason for that, which maybe now is still beyond me, but later on it will be usefull, so why limit this.


Only because looking on measured amps, I see all/most class D amps have issues at high frequencies and issues with different loads, unless they employ some NF and even then they are filtered above 20kHz.

Thanks for the direction on Topping, I wasn't aware of those.
The B100 is class B? and it measured so well by Amir, I don't remember ever seeing a hifi class B amp.
They seem like nice amps for the price but then I read comments on YT reviews where at least two guys reported that one of theirs failed. one guy reported that he listens to music pretty quit so there was no stress on the amps. that made me hesitant.
I know there were few Fosi V3m that were toasted on YT reviews, but those where tested to constant full power into resistive loads and without any care for heat dissipation.

Also that they are not discrete built, so local future repairs is out of the questions
My Luxman M-2000 power amp is almost my age, works better than me, can be serviced by any competent local tech, no unobtanium parts, and it will 100% out live me

The B200 IS discrete and look much better, but the price...
Maybe I'll order a B100 after all, it's size is table top friendly, measures supereb, power I guess is enough for measurements and price is managable. we'll see.

I have two B100s. I have not had any issues with them. But, I don't push them hard; they power my tweeters.

 

[Hendrixon]

I have two B100s. I have not had any issues with them. But, I don't push them hard; they power my tweeters.

Funny, I thought about that my self if I'll end up buying the B100
That's because I also bought a minidsp eight to easily design crossovers, and while not doing that to use it as active crossover for tri ampping my main system.

How do you like the B100s? what amp/s you have there to compare them too?

 

[terryforsythe]

Funny, I thought about that my self if I'll end up buying the B100
That's because I also bought a minidsp eight to easily design crossovers, and while not doing that to use it as active crossover for tri ampping my main system.

How do you like the B100s? what amp/s you have there to compare them too?

For over 20 years I had an Adcom GFA-5802. I liked it a lot. It was large, though. When I decided to go all active with my speakers, I had no room to fit additional amplifiers in my stereo cabinet. So, I put it up for sale and I purchased a Hypex Nilai500DIY Stereo amplifier. I briefly compared the two before the Adcom sold and before removing the passive filters from my speakers (not a controlled, blind comparison), and did not hear a difference. I use the Nilai to power my woofers.

I have two Topping LA90 Discrete amplifiers powering my midranges, and two Topping B100s powering my tweaters. To me, it sounds fantastic. One interesting note is that I do not hear any noise, even when putting my ear immediately next to the tweeter inside the concentric driver. With my Adcom, if I put my ear that close to the tweater I could hear a little bit of noise, but it certainly was not audible at my listening position.

As another comparison, in my other system I have KEF LS60 speakers, which are active. With those I can hear a little bit of noise when I put my ear right next to the concentric driver. But again, it is not audible at my listening position.

 

[DSJR]

Here's the Klippel list -

https://www.klippel.de/fileadmin/klippel/Bilder/Support/Product_Support/KLIPPEL_Amplifier_Requirements.pdf