Give me an Amp Crash Course

[killdozzer]

Another one for you to judge:

I know XTZ are well famous for their Room EQ equipment, do you know anything about their amps? I have a chance to buy a second hand a100d3 for 750$ (this would be a solution in a longer run if you say it is a quality build).

It features a built-in DAC and a Sub out. No USB, but you can't find a lot of these, so what the hell... Strangely enough, being so strong in Room EQ business, they don't state the cut-off freq for the sub out in the manuals. I have to check that, but if everything else is OK, I might consider it. It lets you switch between A and AB Class mode of operating, but since I'm interested in more power; it states 110Wpch into 8ohms and 180Wpch into 4ohms.

XTZ A100D3

It seems it has a lot of what I need combined with good looks.



killdozzer

Update on the short run: I have my eyes set on a aprox. 90$ second hand Yamaha with 75Wpch, sub out (100Hz cut off), and a DAC (once again only optical and coaxial input for the digital signal). This is probably what I'll get so that I can even do all the experiments with a sub before I decide to buy one. I'll take one for a tryout and try to set it up. In about 10 to 15 days.

 

[killdozzer]

I've send an e-mail to XTZ asking about the sub-out port. I'll let you know.

killdozzer

 

[Swerd]

@killdozzer
I have no first hand knowledge about XTZ. Thanks for providing the manual.

It seems good, and is more than powerful enough. 110 watts per channel at 8 ohms is plenty for you. If you like the price and the looks, I see nothing wrong. What does this model cost new and how does that compare to $750?

I like that it has pre-amp out jacks as well as amp input jacks. That allows you maximum flexibility for the future. You can use this as a preamp with an external amp, as an amp with an external preamp, or you can install another external device (such as a parametric equalizer) between the XTZ preamp and amp. That's the proper way to build it.

The user switchable class A - AB business is novel. Many amps are built with class A/AB operation, where at low watt power it runs as class A and above a certain power level, it switches to class AB. I wonder if people really can hear a difference. If I had the XTZ, I would set it on Auto and forget about it.

If the manual says nothing about a cut-off frequency for the sub out jack, I would assume there is none.

You should be able to find some type of dongle at a low price that converts USB digital audio from a computer to digital coaxial (4 on the XTZ) or optical (1 on the XTZ). Maybe you can find a sound card for your laptop that does this.

Of course, I like that $90 Yamaha better .

 

[killdozzer]

Thanks man!

90$ Yamaha is coming regardless of XTZ. It'll get me through . I see it as a great cheap way to check all the setups. It has a lot of options (considering price/year of the model):
Second hand Yamaha

I think the XTZ model is discontinued. I'll try to find the price, you got me interested.

killdozzer

 

[killdozzer]

(Philips, although the tray is not opening...)

Nothing I couldn't fix with a nice glass of wine


The tray opens like heaven for good people

But the sound is terrible. Terrible! I don't know what's the problem.

killdozzer

 

[killdozzer]

Never heard back from XTZ, but I might give up on that amp because the guy is asking too much. It sold for 880$ when it was new. I would expect a bigger drop in price. But these Swedes were famous for trying to make a cheap, powerful and well built amp. That's probably why it doesn't loose value easily, but I don't intend to pay 800$ for a discontinued unit, warranty expired, used and it was 880$ new.

So long term search is still on.

 

[KenM10759]

I can't fix anything with a glass of wine.

It takes good ol' American Bourbon to do the trick for me!

Best of luck in the amplifier search.

 

[killdozzer]

I can't fix anything with a glass of wine.

It takes good ol' American Bourbon to do the trick for me!

Best of luck in the amplifier search.

Thanks! Here's one to keep me company until I'm back on my feet. Could you help me with the impedance settings, please?

What should I choose for LS50's:


I'm guessing it should be the answer in the right end column second from the bottom, but I would like to double check this.

 

[KenM10759]

I'd pick that one too. While the LS50's can dip to 3.2Ω, it's a very brief transient thing and shouldn't cause any issues.

 

[killdozzer]

What is confusing for me is when they simply write 'higher'. In Croatian impedance is translated the same as resistance (otpor), so since it's harder for the amp to work with a lower number, does that mean it is higher or lower?

 

[killdozzer]

I'd pick that one too. While the LS50's can dip to 3.2Ω, it's a very brief transient thing and shouldn't cause any issues.

So you wouldn't go for 4 because of that drop? (One more ignorant question, should you hear the difference in sound when toggling this?)

kd

 

[KenM10759]

I'm not knowledgeable enough about the subject to give an educated answer. All I can tell you is that my R500/R200c/R100 set are all rated by KEF the same minimum 3.2Ω and I haven't had any problems at all turning up the volume to reference level on my 60w/ch NAD receiver for short periods at a time. I can't stay in the room for more than a minute or 3 at that level, and your integrated amp is more powerful.

That means even at full volume your speakers will be louder (a wee bit) and I really doubt there would be any issues.

Most amplifier specifications do show more distortion at 4Ω than 8Ω, though I don't have the trained ear to be able to hear the difference.

 

[killdozzer]

I'm not knowledgeable enough about the subject to give an educated answer. All I can tell you is that my R500/R200c/R100 set are all rated by KEF the same minimum 3.2Ω and I haven't had any problems at all turning up the volume to reference level on my 60w/ch NAD receiver for short periods at a time. I can't stay in the room for more than a minute or 3 at that level, and your integrated amp is more powerful.

That means even at full volume your speakers will be louder (a wee bit) and I really doubt there would be any issues.

Most amplifier specifications do show more distortion at 4Ω than 8Ω, though I don't have the trained ear to be able to hear the difference.

Great, thanks!
Yesterday evening I just brought the Yamaha home, so i was a bit impatient, I admit. I wanted to hear what it sounds like but didn't want to cause any damage.

I have to poke around some more to check everything that this receiver has to offer. It sounds notably "warmer" which is strange to me. I have a feeling some effect somewhere is still on and I have to find it.

Other than "warmth" I have no other observations and don't see the benefit of almost double the strength from the previous amp. Do you ever go over the middle on the volume knob? When do you ever need that?

killdozzer

 

[Alex2507]

What is confusing for me is when they simply write 'higher'. In Croatian impedance is translated the same as resistance (otpor), so since it's harder for the amp to work with a lower number, does that mean it is higher or lower?

Resistance and impedance ... and otpor. I think of otpor as resistance to disease and for sure I haven't heard that word in forever. Resistance is used to describe the resistance to direct current. Impedance measures that plus the resistance offered by the magnetic field created by moving electrons (current) and capacitance. I think the key search term there would be 'inductive reactance'. Impedance is frequency dependent as you can see with a speaker's impedance graph. I think the LS50 dips low (3.2 Ohms) around 1 or 2 hundred Hz. The way I think of that is that the speaker offers little resistance to the flow of current coming from the amp. That dip occupies a narrow region so while that can tax an amp at loud volume when those frequencies are being reproduced, it won't kill the amp. A test tone right at the dip played at loud volume for 2 days straight would not be good.

Lower impedance draws more watts. Way oversimplified and open for correction: An 8 Ohm speaker playing at 100 db draws say 100 watts. A 4 Ohm speaker at the same volume draws 200 watts. The capacitors in an amp store power for those spikes in draw. So that applies to the variations in impedance all through a speaker's frequency response.

Lots of people can explain that better and they're invited.

Think of the volume control as distortion control. When an amp's output is maxed out for loud parts in music, the distortion is also at it's highest point then. If a drum beat draws more than the rated power for an instant the distortion rating is also exceeded however briefly. The benefit of clean power at high volume is at first fleeting but as the volume goes higher and higher the distortion becomes audible. Then you need to know if your speaker or your amp is distorting so you know what to upgrade first.

 

[killdozzer]

Think of the volume control as distortion control.

You're the man! Thank you for this reply. I remember I first found audioholics long time ago when I decided to understand impedance. There were some links to some articles and I remember one being from PhD engineer, who tried to make uninformed buyers understand how it works. He said it is, rather than thinking of an amp as horse powers (so less resistance the faster it goes), better to think of it as a water pump with a task of creating a pressure in side a narrow pipe (more resistance, higher impedance, 8Ohm) and a wide pipe (less resistance, lower impedance, 4Ohm). In order to create the same pressure in a wider pipe (although the water flows more easily) the water pump has to work a lot harder.

This did the trick for me for the most part. But now, since it is a bit upside down in the mind of an average Joe, when someone simply says "higher", I wonder "higher" what? Would you consider a lower number to be higher impedance since it is harder for the amp to work?

But I think I got it now. Thanks!

 

[Alex2507]

Would you consider a lower number to be higher impedance since it is harder for the amp to work?

NO !!!

A lower number is lower impedance or a wider pipe. More water. Same pump. Pump works harder.

 

[Swerd]

Alex2507 has got it mostly right. The definitions of impedance and resistance I had learned says that resistance is for direct current (DC) electricity, and impedance is for alternating current (AC). The electrical music signals that speakers get are AC, so we say impedance. His water pump analogy is good.

In the past, Audioholics had an article that dealt with your question. I found it, and, in brief, it says put that selector switch at 8 ohms and don't worry.

https://www.audioholics.com/frequent-questions/connecting-4-ohm-speakers-to-an-8-ohm-receiver-or-amplifier

Connecting 4-ohm speakers to an 8-ohm receiver

Receivers: Most midfi Receivers may have problems adequately driving a 4 ohm load. However, many of the better Receivers today have a large enough power supply, heat sink area, and current capability in the amp sections to handle 4 ohm loads. You are usually safe running these speakers on the Flagship Receiver models from: Yamaha, Denon, Onkyo, Harman Kardon, NAD, Nakamichi.

NOTE: Some Receivers have an impedance selector switch. In most cases we recommend the 8-ohm or more setting. The manufacturer puts them there for UL/CSA approvals as well as easing consumer concerns about driving low impedance loads. These switches step down voltage feed to the power sections which will limit dynamics and overall fidelity. Keep the switch set for 8 ohms regardless of the impedance of your speakers and ensure proper ventilation of the Receiver.

For a detailed explanation on how to set the impedance switch on your receiver, read: Setting the AV Receiver Impedance Switch

 

[Swerd]

For what its worth…

KEF says the LS50 is an 8 ohm speaker.

In Stereophile's review, they say:

"Somewhat optimistically specified at 8 ohms, the LS50's impedance (fig.1, solid trace, use the vertical scale on the left side for impedance) drops to 4 ohms at 200Hz and to 5.4 ohms at the top of the audioband. The electrical phase angle is generally mild, but the combination of 5.3 ohms and –41° at 135Hz, a frequency where music often has high energy, will make the speaker work at its best with a good, 4 ohm–rated amplifier."​

I read those words as saying the KEF LS50 is an easy load for most receivers and amps.

 

[Alex2507]

Alex2507 has got it mostly right.

I pulled the "impedance is frequency dependent" on a pretty sharp electrician and got a lesson and a half. Most of it was out of my depth but I came away thinking that impedance could be measured on d/c to factor in capacitance and the induced magnetic field.

We need PENG for a ruling.

 

[Swerd]

I pulled the "impedance is frequency dependent" on a pretty sharp electrician and got a lesson and a half. Most of it was out of my depth but I came away thinking that impedance could be measured on d/c to factor in capacitance and the induced magnetic field.

We need PENG for a ruling.

That's the trouble with those science types, you never can get a simple answer.

It would be like asking me, 'just what is cancer anyway?', in 10 words or less .