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Class D (and general) amplifier related questions

mk05

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#1
Hello, I have been researching the Hypex, Modulus, and Purifi Class D amps. Unfortunately, some parts are too technical for me to understand with way too many models, and I was wondering if I could ask for some advice. I am currently looking to drive a pair of KEF R5 floor standing speakers rated at 15-200w at 8Ohms, but the speakers are at 3.5-5Ohms from 100-1kHz.

1) The speakers have 4 posts, and I assume that means HF/LF plugs, which I will call AB(HF) CD(LF), +/- respectively for the Left speaker and EF(HF) and GH(LF) for +/- Right speaker. For this setup, which models of the three brands above would suffice?

2) In a regular listening session for those "8Ohm" rated speakers, and I understand that term is relative for everyone, what is the range of WPC that would be used: 15-30WPC, 20-50WPC, 35-75WPC, etc?
2b) What is "reference level listening volume" WPC for a 200w rated speaker?

3) I believe I read that the range where impedance drops lowest, is a very important range of frequency for human ears, so would I be rather looking at 4Ohm performance metric over the 8Ohm?

4) At some point, I will upgrade to a pair of KEF Reference 3 or Tekton's. When I upgrade to those speakers, I figured that I would add another of the same amp to "monoblock." This is where things get even more confusing for me. It seems those speakers should be "paired" with a 4Ohm amplifier. How do I "switch" the power for 4Ohm, or is that done automatically?
4b) How would I know that I am getting the 4Ohm driven sound which - allegedly - is a smoother experience, if there is no independent "4Ohm tap?"

5) If I "monoblock" the amp, and lets say that it is a Modulus-286, will I be "bridging" it, "bi-wiring" it, or "vertical-amping" it? Please feel free to correct to the most relevant amp for my cause.
5b) What are the drawbacks or benefits in changing the stereo amplifier from original configuration into a single speaker function? I don't know if those 3 brands allow for such a function. I figure, AB goes into HF of left speaker, and CD goes into LF of left speaker, while the EF goes into HF of right speaker, and GH goes into the LF of the left speaker. Please let me know if I have that very wrong.

6) Again, if you look at Modulus-286, it says 65w at 8Ohm or 125w at 4Ohm. Is that for both channels?
6b) What is that in 1 channel (monoblocked)?
6c) In case of the higher grade speakers needing 400+WPC, will my minimum WPC used for "normal listening" increase from the above metric to a lot more, ie 100-200WPC? And since they need 4Ohm, actually 200-400WPC spec?

Thank you in advance and I apologize if this makes all your brains hurt from utter incompetence. Trust me, I know how you feel. Imagine your level of distaste, as that is the level of my confusion after months of trying to decipher things. And if the forum could, please try to dumb it down to a layman speak so that I can takeaway some meaningful parts. I appreciate any insight and advice you guys could offer.
 

CDMC

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#2
Without going into answering your questions, I will make a suggestion. Get a Purifi stereo amp. It will provide plenty of power for your current speakers and your potential future speakers as listed. It is technically the best of the three options.

Many of your questions have incorrect assumptions and conflate different concepts. I am unsure of where to point you to information that would help you better understand the issues you raise, someone else may be able to.
 

RayDunzl

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#3
What amplifier are you using now?
 

pjug

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#4
It's not clear, but it sounds like you are considering only Class D. The Neurochrome Modulus amps are not Class D.
 

pozz

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#5
Hello, I have been researching the Hypex, Modulus, and Purifi Class D amps. Unfortunately, some parts are too technical for me to understand with way too many models, and I was wondering if I could ask for some advice. I am currently looking to drive a pair of KEF R5 floor standing speakers rated at 15-200w at 8Ohms, but the speakers are at 3.5-5Ohms from 100-1kHz.

1) The speakers have 4 posts, and I assume that means HF/LF plugs, which I will call AB(HF) CD(LF), +/- respectively for the Left speaker and EF(HF) and GH(LF) for +/- Right speaker. For this setup, which models of the three brands above would suffice?

2) In a regular listening session for those "8Ohm" rated speakers, and I understand that term is relative for everyone, what is the range of WPC that would be used: 15-30WPC, 20-50WPC, 35-75WPC, etc?
2b) What is "reference level listening volume" WPC for a 200w rated speaker?

3) I believe I read that the range where impedance drops lowest, is a very important range of frequency for human ears, so would I be rather looking at 4Ohm performance metric over the 8Ohm?

4) At some point, I will upgrade to a pair of KEF Reference 3 or Tekton's. When I upgrade to those speakers, I figured that I would add another of the same amp to "monoblock." This is where things get even more confusing for me. It seems those speakers should be "paired" with a 4Ohm amplifier. How do I "switch" the power for 4Ohm, or is that done automatically?
4b) How would I know that I am getting the 4Ohm driven sound which - allegedly - is a smoother experience, if there is no independent "4Ohm tap?"

5) If I "monoblock" the amp, and lets say that it is a Modulus-286, will I be "bridging" it, "bi-wiring" it, or "vertical-amping" it? Please feel free to correct to the most relevant amp for my cause.
5b) What are the drawbacks or benefits in changing the stereo amplifier from original configuration into a single speaker function? I don't know if those 3 brands allow for such a function. I figure, AB goes into HF of left speaker, and CD goes into LF of left speaker, while the EF goes into HF of right speaker, and GH goes into the LF of the left speaker. Please let me know if I have that very wrong.

6) Again, if you look at Modulus-286, it says 65w at 8Ohm or 125w at 4Ohm. Is that for both channels?
6b) What is that in 1 channel (monoblocked)?
6c) In case of the higher grade speakers needing 400+WPC, will my minimum WPC used for "normal listening" increase from the above metric to a lot more, ie 100-200WPC? And since they need 4Ohm, actually 200-400WPC spec?

Thank you in advance and I apologize if this makes all your brains hurt from utter incompetence. Trust me, I know how you feel. Imagine your level of distaste, as that is the level of my confusion after months of trying to decipher things. And if the forum could, please try to dumb it down to a layman speak so that I can takeaway some meaningful parts. I appreciate any insight and advice you guys could offer.
1. You do not need to consider the speaker binding posts. Any amplifier is compatible when the top and bottom posts are linked with a shorting bar. There is no benefit to biwiring (which you may have heard about before) or biamping (unless you bypass the crossover to design your own).

2. Wattage requirements are hard to pin down since they depend on listening distance, room volume, level and speaker sensitivity. 2b has the same answer. Check out this post and the comments below it.

3. You are mistaken about what impedance indicates. Speaker impedance measurements show an electromechanical plot from which you can learn a lot about the characteristics of the drivers, enclosure and their combination (mechanical resonances show up like wrinkles, for example). When it comes to amp requirements, the lowest point on the Y axis represents where the amp has to supply the most current. All you really need to take from this is that some amps fall apart when trying to power speakers with really low impedances, and that a one-number nominal impedance (as in an "8 ohm speaker") is a nonsense since impedance is different across the frequency spectrum. Manufacturers often misrepresent this figure.

4. Err... this isn't what you're looking for but I would avoid the Tektons. They are "one person/one chair" speakers. That aside, regarding 4 ohm taps or switches: this is another mistaken notion. I hope the above answer cleared it up. Don't expect any characteristic or different sound. Amps will have a "sound" only if they clip (run out of power), have egregiously high distortion (0.1% or -60dB H2 or 2nd harmonic is hard to hear and could even be called undetectable depending on the frequency; 0.1% H10 or tenth harmonic is unbearably bad, but also rare) or are badly designed. Before you ask, distortion audibility is so variable in terms of level and frequency, but also so easily masked by music, that you can ignore the subject altogether. The main reason we are obsessed with it on ASR is because we generally define the "best" by the boundaries of engineering quality.

5. A monoblock amp is a single channel amplifier. "Bridging" means combining outputs. A bridged mono output is pretty common for stereo (i.e., two channel) amps. This is a special connection and will be indicated as such (look at the back of the Benchmark AHB2 for an example). Don't try bridging using random methods if the amp wasn't designed for it.

5b. Using bridged mono produces more power at the cost of noise. How much more has to be measured. Other disadvantages are cost, bulk (since you have two boxes instead of one) and potential for ground loops.

6. Others can step in to answer your questions about specific brands. For Hypex and Purifi, you can choose both channel count and wattage as you need it in various configurations which aren't too expensive.

Most of the time you'll be drawing puny amounts from your amp, but if you ever get inefficient speakers or want to rock the house then more watts is better.
 
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mk05

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Thread Starter #6
What amplifier are you using now?
Hi Ray - for the R5, I have nothing. I am not in a hurry, so still learning and trying to catch up for the past 15+ years.

On another note, I am learning that I can't play Master tracks from Tidal, now that I was given TIDAL HiFi access. It appears that there's another hand to feed - seemingly, another "entry fee" for a...free codec? Reminds me a lot of mp3 battles. Everyone's always trying to build a box and sell a console...isn't monthly subscription enough? This is getting tiresome. Help me VLC...you're my only hope.
 

Blumlein 88

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#7
Without going into answering your questions, I will make a suggestion. Get a Purifi stereo amp. It will provide plenty of power for your current speakers and your potential future speakers as listed. It is technically the best of the three options.

Many of your questions have incorrect assumptions and conflate different concepts. I am unsure of where to point you to information that would help you better understand the issues you raise, someone else may be able to.
Agree with pozz. Just get a Purifi and don't worry.
 
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CDMC

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#8
1. You do not need to consider the speaker binding posts. Any amplifier is compatible when the top and bottom posts are linked with a shorting bar. There is no benefit to biwiring (which you may have heard about before) or biamping (unless you bypass the crossover to design your own).

2. Wattage requirements are hard to pin down since they depend on listening distance, room volume, level and speaker sensitivity. 2b has the same answer. Check out this post and the comments below it.

3. You are mistaken about what impedance indicates. Speaker impedance measurements show an electromechanical plot from which you can learn a lot about the characteristics of the drivers, enclosure and their combination (mechanical resonances show up like wrinkles, for example). When it comes to amp requirements, the lowest point on the Y axis represents where the amp has to supply the most current. All you really need to take from this is that some amps fall apart when trying to power speakers with really low impedances, and that a one-number nominal impedance (as in an "8 ohm speaker") is a nonsense since impedance is different across the frequency spectrum. Manufacturers often misrepresent this figure.

4. Err... this isn't what you're looking for but I would avoid the Tektons. They are "one person/one chair" speakers. That aside, regarding 4 ohm taps or switches: this is another mistaken notion. I hope the above answer cleared it up. Don't expect any characteristic or different sound. Amps will have a "sound" only if they clip (run out of power), have egregiously high distortion (0.1% or -60dB H2 or 2nd harmonic is hard to hear and could even be called undetectable depending on the frequency; 0.1% H10 or tenth harmonic is unbearably bad, but also rare) or are badly designed. Before you ask, distortion audibility is so variable in terms of level and frequency, but also so easily masked by music, that you can ignore the subject altogether. The main reason we are obsessed with it on ASR is because we generally define the "best" by the boundaries of engineering quality.

5. A monoblock amp is a single channel amplifier. "Bridging" means combining outputs. A bridged mono output is pretty common for stereo (i.e., two channel) amps. This is a special connection and will be indicated as such (look at the back of the Benchmark AHB2 for an example). Don't try bridging using random methods if the amp wasn't designed for it.

5b. Using bridged mono produces more power at the cost of noise. How much more has to be measured. Other disadvantages are cost, bulk (since you have two boxes instead of one) and potential for ground loops.

6. Others can step in to answer your questions about specific brands. For Hypex and Purifi, you can choose both channel count and wattage as you need it in various configurations which aren't too expensive.

Most of the time you'll be drawing puny amounts from your amp, but if you ever get inefficient speakers or want to rock the house then more watts is better.
Great explanation. It would have taken me hours to come up with something 1/4 as good.
 
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mk05

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Thread Starter #9
Agree. Just get a Purifi and don't worry.
I certainly know that I can do one of the above and not "worry" for now. Yet, I am interested in learning more (if you guys will let me) to correct all my mistaken beliefs. I don't want to assume any of the above, and make compounding mistakes further down the road. I'm constantly reading the measurement guides and other threads to takeaway meaningful aspects even though I'm not an engineer by trade.

Without going into answering your questions, I will make a suggestion. Get a Purifi stereo amp.
Will the stereo configuration, at some point, be able to turn into mono with acceptable loss of fidelity - I believe the NCore can? In the Purifi measurements thread, it doesn't seem like anyone has tested/experienced Purifi bridged like the AHB2 and confirmed it working within acceptable boundaries (perhaps this is what @pozz meant) - is Purifi not designed for it?
 

CDMC

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#10
Hi Ray - for the R5, I have nothing. I am not in a hurry, so still learning and trying to catch up for the past 15+ years.

On another note, I am learning that I can't play Master tracks from Tidal, now that I was given TIDAL HiFi access. It appears that there's another hand to feed - seemingly, another "entry fee" for a...free codec? Reminds me a lot of mp3 battles. Everyone's always trying to build a box and sell a console...isn't monthly subscription enough? This is getting tiresome. Help me VLC...you're my only hope.
An entirely different subject that is an entire rabbit hole unto itself. Here is my short synopsis. Tidal has chosen to go down the MQA path for "hi rez" files, which requires a MQA decoder, either software or hardware. MQA is a bunch of mumble jumbo that most agree is nothing more than an attempt by Meridian to, as you put it, be another hand to feed. The only real potential upside to MQA is it allows compression for less data usage.

This brings up another issue, hi rez. The difference between 320kbs MP3 and Redbook (44.1/16) is small enough, that most people cannot distinguish the two in blind testing. People cannot distinguish between between Redbook and higher sampling and/or bit depths. Compound this with the fact that 90%+ of "hi rez" recordings are nothing more than upsampled Redbook (you cannot create what does not exist) and it becomes nothing more than MQA, i.e. a way for music companies to sell/rent the same product for a higher price.
 

Thomas savage

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#11
Iv lived with @March Audio amps for awhile now , the case is beautiful and you need not worry about the internals .

Honestly, iv mono amps , they've sat in my lounge for awhile and just are wonderful to live with . Invisible but if you want to look they will reward with elegance abundance.

I will never think about amps again, what a relief.
 

CDMC

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#12
I certainly know that I can do one of the above and not "worry" for now. Yet, I am interested in learning more (if you guys will let me) to correct all my mistaken beliefs. I don't want to assume any of the above, and make compounding mistakes further down the road. I'm constantly reading the measurement guides and other threads to takeaway meaningful aspects even though I'm not an engineer by trade.


Will the stereo configuration, at some point, be able to turn into mono without loss of fidelity? I have read the long Purifi thread here, but it doesn't seem like anyone has tested/experienced Purifi bridged like the AHB2 and confirmed it working within acceptable boundaries. Perhaps this is what @pozz meant, is Purifi not designed for it?
Purifi modules cannot be bridged, they only come in a single channel rated at 225 watts into 8 ohms and 425 into 4 ohms and can drive a 2 ohm load. A stereo Purifi amplifier is simply two mono modules in a single case.

Again, unless you purchase highly innefficient speakers, listen at extremely high levels, and/or have a very large room, you are unlikely to run out of power with the Purifi. Remember, each time you double amplifier power, you only get 3db more volume. With an average speaker sensitivity of 87db/w and the Purifi at a 12 foot listening distance, you get peak SPL levels of 105db, or really, really, loud. Here is a calculator you can play with to get an idea for your room.

https://myhometheater.homestead.com/splcalculator.html

Keep asking away, the posters on this site are very friendly and glad to answer questions.
 
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mk05

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An entirely different subject that is an entire rabbit hole unto itself. Here is my short synopsis. Tidal has chosen to go down the MQA path for "hi rez" files, which requires a MQA decoder, either software or hardware. MQA is a bunch of mumble jumbo that most agree is nothing more than an attempt by Meridian to, as you put it, be another hand to feed. The only real potential upside to MQA is it allows compression for less data usage.

This brings up another issue, hi rez. The difference between 320kbs MP3 and Redbook (44.1/16) is small enough, that most people cannot distinguish the two in blind testing. People cannot distinguish between between Redbook and higher sampling and/or bit depths. Compound this with the fact that 90%+ of "hi rez" recordings are nothing more than upsampled Redbook (you cannot create what does not exist) and it becomes nothing more than MQA, i.e. a way for music companies to sell/rent the same product for a higher price.
Interesting! Thanks for taking the time for the tangent. Is there a downloadable or stream-able sample of the same recording (here or elsewhere) of each sample-rate and bit-depth ie 44.1/16, 48/24, 192/24, and 32-bit??
 

CDMC

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#14
One thing to keep in mind when you are looking at Hypex v. Purifi. The amplifiers modules were designed by the same engineer, Bruno Putzeys. While at Hypex he developed the first generation UCD modules, then the second generation nCore modules. He left Hypex and started Purifi which launched the 1et400a, which is essentially a third generation Hypex module. It improve high frequency distortion, but it is questionable if the improvements are audible. If you want the latest and greatest and are willing to spend a bit more than the NCore modules, then you go Purifi.
 

CDMC

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Interesting! Thanks for taking the time for the tangent. Is there a downloadable or stream-able sample of the same recording (here or elsewhere) of each sample-rate and bit-depth ie 44.1/16, 48/24, 192/24, and 32-bit??
Yes. If you search around, you can find links to perform double blind ABX testing using Foobar and files of different resolutions. Someone can likely post a link to the actual files and test, as there was someone who did all this and tracked the results.

Keep in mind when looking at bit depth you are looking only at the maximum sound to noise ratio. 16 bit gets you 96db, 24bit 144db. While 24 bit is best practice for recording and mixing as it gives extra latitude, it serves zero purpose for playback.

https://benchmarkmedia.com/blogs/application_notes/14949345-high-resolution-audio-bit-depth

https://en.wikipedia.org/wiki/Audio_bit_depth

Similarly, once you get above 44.1khz, you are simply getting the ability to record and playback frequencies above 22khz. This is assuming your speakers would play it and you could hear it. Most children can hear to 20khz on a good day, it only goes down from there as you age.

I suggest you may want to go through the articles on benchmarkmedia's website. They are a wealth of knowledge, written to non-engineers, and contain no fluff or pseudoscience.
 
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Xulonn

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#16
The main reason we are obsessed with it on ASR is because we generally define the "best" by the boundaries of engineering quality.
Excellent comment!

Those who are not technically inclined can be confused by the obsession with specification ratings by technophiles - some of those ratings are far beyond the limits of human audibility. Fortunately, there are many friendly technically-oriented ARS members around who can - and do - step in to try to explain the difference between audibility thresholds and engineering efforts to test theoretical and practical limits.

Keep asking away, the posters on this site are very friendly and glad to answer questions.
This thread and the questions asked by the OP are a very good example of what elicits friendly and helpful responses, even though the questions are very basic.

Contrast this with posts based on blatherings of ego-driven commenters who are clueless about science and make claims that are verifiably false. - and then whine and complain when they are called out. But that is life on the internet where anyone is free to either look informed and intelligent, or flail about like an ignorant fool.

And as far as amplifier recommendations, without going into details, my recommendations are based on three levels of measurements and performance. All of them have lots of power, plus noise and distortion that are below the threshold of hearing. They are listed by price and budget ones are first:

1: Lowest cost: Easy to assemble Ghent Case / ICEpower modules kits. The stereo amp is available for a bit higher price as a "solderless" version. $320 for a [email protected]Ω, [email protected]Ω stereo amplifier with either RCA or XLR inputs. Or for $440, you can get a pair of monoblocks with switchable RCA/XLR inputs.

These modules have been used by well-known audio manufacturers in the past including Jeff Rowland, Bel Canto and Cary. Supposedly they are much better than some of the less expensive ICEpower and lower power module which have been criticized for performance issues. (I already have a Ghent stereo XLR case, with a monoblock case on the way, and the ICEpower modules coming when PartsExpress gets them back in stock.)

2. Middle tier: Stereo amp with a Hypex NC252MP module from either VTV (N. America) for $499, or Audiophonics (Europe) for $390 (w/o VAT). Or monoblocks with the NC250MP modules, which ends up being a fair bit more expensive for two channels.

3. Best in class: Great sound plus bragging rights: Purifi 1ET400A monoblocks from VTV or Audiophonics in the $1,200 - $1,400 range per pair. And, of course, there are more expensive versions of Ncore and Purifi amplifiers from Nord, Apollon and others)

4. There are many other good options that are too diverse to include here - some tested/measured by Amir, and many not. But don't fall for the B.S trap that "more expensive is better" because there is lots of expensive junk out there that does not perform well, and budget gear that performs extremely well.
 
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mk05

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1. ...biamping (unless you bypass the crossover to design your own).
I think I will be doing this, most likely. A very nice member advised purchasing miniDSP's SHD to streamline, since it will do roomEQ and allow me to x-over in the future for bi-amping. But with the TIDAL MQA problem...I am faced with another conundrum. One problem at a time though. :/

2. Wattage requirements are hard to pin down since they depend on listening distance, room volume, level and speaker sensitivity. 2b has the same answer. Check out this post and the comments below it...Most of the time you'll be drawing puny amounts from your amp, but if you ever get inefficient speakers or want to rock the house then more watts is better
I will ask in a different subforum.

4. Err... this isn't what you're looking for but I would avoid the Tektons. They are "one person/one chair" speakers. That aside, regarding 4 ohm taps or switches: this is another mistaken notion. I hope the above answer cleared it up. Don't expect any characteristic or different sound.
That is surprising to hear as my friends and I immensely enjoyed the Tekton DIs at a holiday party - and the room was pretty big - yet I do understand that enjoyment (and the factors comprising it) differs for everyone. As for 4Ω vs 8Ω, I was told 4Ω tap sounds richer and more lush, like a I-4 vs V-8 engine going up a hill. I wonder if I can test this for myself - or if you guys have a thread to refer to.

5b. Using bridged mono produces more power at the cost of noise. How much more has to be measured. Other disadvantages are cost, bulk (since you have two boxes instead of one) and potential for ground loops.
I was curious if bridging will cause meaningful amount of fidelity being lost...although I also heard that there were positives of bridging vs negatives. I don't mind monoblocks, because I planned on bridging the stereo amps to turn into monoblocks in future (if feasible and/or advantageous). I decided against the Emotiva PA-1s since the ASC300 SINAD is apparently ~86dB according to Amir. I need 96dB to get the 16-bit resolution, otherwise why even use TIDAL or equivalent HiFi source, right?

Thank you guys again, and please let me know if you have different perspectives or experiences - even if a bit unrelated to OP. Whether relevant to OP or not, member inputs are extremely helpful because it provides contextual support. Each post I read on ASR lets me know that my current belief set is inaccurate, and why that is (well this part can be a bit too complex at times).
 

somebodyelse

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#18
Interesting! Thanks for taking the time for the tangent. Is there a downloadable or stream-able sample of the same recording (here or elsewhere) of each sample-rate and bit-depth ie 44.1/16, 48/24, 192/24, and 32-bit??
http://www.2l.no/hires/index.html
If you really want to know the effect of sample rate and bit depth you might be better starting with the highest resolution version and converting it yourself using something like sox - that way you know it hasn't been altered in any other way. You can then see if you can hear the difference using one of the players with ABX capabilities.
 

CDMC

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I think I will be doing this, most likely. A very nice member advised purchasing miniDSP's SHD to streamline, since it will do roomEQ and allow me to x-over in the future for bi-amping. But with the TIDAL MQA problem...I am faced with another conundrum. One problem at a time though. :/


I will ask in a different subforum.
Note that you can do DSP equalization in Roon or JRiver without using a MiniDSP. MiniDSP is a powerful tool, but personally I had a hard time with MiniDSP and gave up on it.

That is surprising to hear as my friends and I immensely enjoyed the Tekton DIs at a holiday party - and the room was pretty big - yet I do understand that enjoyment (and the factors comprising it) differs for everyone. As for 4Ω vs 8Ω, I was told 4Ω tap sounds richer and more lush, like a I-4 vs V-8 engine going up a hill. I wonder if I can test this for myself - or if you guys have a thread to refer to.
This is the most important thing, you like the speakers. We are not listening to them, you are. Just remember every room is different and the room has has by far the largest effect on sound of anything. Speakers that work great in one room may sound terrible in another. If you can try a set in your room, that is the best of all.

Taps are something that only exist on 1) tube amps, and 2) some McIntosh amps, and are related to the transformer used in tube amps. Tube amps have a high output impedance, which interacts with frequency response, and using different taps changes that response. Taps do not apply to solid state amps (except the McIntoshs that use output transformers for some weird reason). There are also some tube amps that do not have taps (OTL amps).


I was curious if bridging will cause meaningful amount of fidelity being lost...although I also heard that there were positives of bridging vs negatives. I don't mind monoblocks, because I planned on bridging the stereo amps to turn into monoblocks in future (if feasible and/or advantageous). I decided against the Emotiva PA-1s since the ASC300 SINAD is apparently ~86dB according to Amir. I need 96dB to get the 16-bit resolution, otherwise why even use TIDAL or equivalent HiFi source, right?

Thank you guys again, and please let me know if you have different perspectives or experiences - even if a bit unrelated to OP. Whether relevant to OP or not, member inputs are extremely helpful because it provides contextual support. Each post I read on ASR lets me know that my current belief set is inaccurate, and why that is (well this part can be a bit too complex at times).
Bridging halves the impedance an amp sees and doubles the distortion (roughly). Keep in mind bridging a stereo amp is different than a monoblock.

Most of us have inaccurate beliefs about a multitude of subjects. Some choose to lock in those beliefs as the only correct belief, others choose to remain open to the concept that their belief may not be accurate (or like often happens, even correct beliefs become incorrect as available information changes) and continue look at further information to establish whether to keep the belief of modify it.
 
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mcb

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Purifi modules cannot be bridged, they only come in a single channel rated at 225 watts into 8 ohms and 425 into 4 ohms and can drive a 2 ohm load. A stereo Purifi amplifier is simply two mono modules in a single case.
I am considering a class D amplifier, quite possibly Purifi-based. I own a set of Thiel 2.3 speakers which have a challenging impedence curve - see attached image from the Stereophile review. The impedence is between 2 and 4 ohms from 85 Hz to 1 KHz. I currently use a Krell KAV-300i integrated amp which claims 150W into 8 ohms and 300W into 4 and I'm relatively happy with it (except maybe idle power consumption). Would a Purifi amp be a meaningful upgrade? And is there anything intrinsic better or worse about class D amps with low impedence loads compared to a quality class AB amp?

Thanks for any insight!
 

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