I need more power

[OttoMatic]

You will need two switching places, at the output of the bd30 and the two amps or at the speakers from the two amps.

I see why you might say that I'd need to switch at the BD30, but do I really? If I send use both the optical and coax digital outputs (one to each preamp), should that not suffice? Those outputs, interfaces and cables are different, yes, but those differences should be zero, right? (bits is bits, cables don't matter, etc.)

I think that .1V mentioned may be too high, I think you need to do no more than 1% voltage variation.

OK, I'll see what I can do. How would you go about this? Currently, I'm at the mercy of the volume controls or channel trims, which are probably limited to 0.5dB resolution. I can create a voltage divider between the preamp and that amp, but I'm not sure that's the way to go. What would be AH approved?

It would be a good idea to check he levels at 100Hz and 10kHz too, just to be sure.

I should be able to do that. I can probably get hold of an oscilloscope if needed.

Not sure if I follow you that the wife will not be in the room? After she makes a switch so you can compare one and the other? That may work but she certainly needs to keep proper track which one is connected for each trial. Then you write down your guess and compare at the end.

Yeah, scratch that, you're right. Not sure what I was thinking of. However, now that I realize she'll have to be involved in this process for what will probably be hours, I think I'll need to find another volunteer.

 

[OttoMatic]

I am going to say here, probably with much criticism, that the test itself is not along the lines of what I was stating in this thread.

This particular thread is about adding an amp to the 3808.

So the 3808 will be the pre-pro in any situation.

With the 3808 as the pre-pro, in the same room, with the same speakers.

Any amp added will not have any audible difference, unless a tube amp is used.

This is my position.

I don't have any criticism of that position. I agree that swapping amps only will have zero to minimal (yes, probably inaudible) change to the sound of the system (with tube amps excepted, as you note). Yeah, I probably couldn't hear a difference between two amps.

I admit that I'm changing a bunch of things at once: front end outputs, cables, DACs, preamps and power amps. However, we must admit that here at AH, each and every one of those things are regularly claimed to have no audible effect on the final sound. So, although I'm changing a lot of things, there should be no difference in sound.

I'm also doing it to see if I can hear a difference with changes of those magnitude. Just to see if if I can. And to justify my separates over a receiver, etc. (Jeez, what if I can't hear a difference? Will I be trading my separates in? Well, I guess I never claimed that I can hear a difference, just that I like what I have.)

Supposing I am able to hear a difference, will I be separating out all the changes until I find out where the difference lies? Not sure. I'll see how much work it is.

A speaker change will yield the most audible difference in every aspect.

Agreed.

 

[zumbo]

After you do your test, will you start a new thread about it.

This is a pretty big deal.

 

[OttoMatic]

After you do your test, will you start a new thread about it.

This is a pretty big deal.

I will, but it might be a while.

I did get my DMM out tonight to see what type of measurements I get at the speakers (with sine waves, with the intention to perform the level matching. So I guess that's a first step.

 

[fmw]

Otto, I'm not aware of anybody having done what you are planning to do. These kinds of tests are usually done to compare a single component to another, not an entire system (less speakers.) I'm genuinely interested in the results.

 

[highfigh]

I will, but it might be a while.

I did get my DMM out tonight to see what type of measurements I get at the speakers (with sine waves, with the intention to perform the level matching. So I guess that's a first step.

If the DMM isn't made for this kind of thing, AC voltages won't necessarily be accurate. You'd be better off using an SPL meter. You can get a free version of TrueRTA and it has SPL, RTA, Oscilloscope and 1 octave resolution but you can upgrade to 1/6 or 1/24 octave at their website.

 

[OttoMatic]

If the DMM isn't made for this kind of thing, AC voltages won't necessarily be accurate.

Please elaborate. I'm using a Fluke DMM that can read AC RMS voltages. Why would this not work? Measurements last night showed solid readings at various volume levels. (e.g., at -25 dB on my preamp, I got 0.422 VAC at the speaker terminals with a 1kHz sine wave as generated from my PC using REW. Changing volume levels would increase or decrease the DMM's reading, but it would return to 0.422 VAC when I returned the volume knob to -25 dB).

You'd be better off using an SPL meter.

I can do that, and I would do it as a double check after setting voltages at the speaker terminals. I have a Galaxy CM-140.

You can get a free version of TrueRTA and it has SPL, RTA, Oscilloscope and 1 octave resolution but you can upgrade to 1/6 or 1/24 octave at their website.

I can probably borrow a real oscilloscope from work if that helps.

I'm more concerned with being able to get the voltages to match in the first place. I believe I'll be constrained by a resolution of 0.5 dB from the preamps. It will not surprise me if that is too coarse to get levels close enough. Do we have any proposals as to how to address this? I suggested a voltage divider between the preamp and the amp. Is that acceptable?

 

[highfigh]

Please elaborate. I'm using a Fluke DMM that can read AC RMS voltages. Why would this not work? Measurements last night showed solid readings at various volume levels. (e.g., at -25 dB on my preamp, I got 0.422 VAC at the speaker terminals with a 1kHz sine wave as generated from my PC using REW. Changing volume levels would increase or decrease the DMM's reading, but it would return to 0.422 VAC when I returned the volume knob to -25 dB).



I can do that, and I would do it as a double check after setting voltages at the speaker terminals. I have a Galaxy CM-140.



I can probably borrow a real oscilloscope from work if that helps.

I'm more concerned with being able to get the voltages to match in the first place. I believe I'll be constrained by a resolution of 0.5 dB from the preamps. It will not surprise me if that is too coarse to get levels close enough. Do we have any proposals as to how to address this? I suggested a voltage divider between the preamp and the amp. Is that acceptable?

Ya didn't say what DMM you have and I said "AC voltages won't necessarily be accurate", not that they won't be.

I think the best thing would be to find the output of each, so you'll know how close they are, relative to the .5dB. Using a scope, you can see how close they are better than using a DMM, IMO. Your ambient noise level and hearing are the other main factors as to whether this will be an issue. Since you're listening for a difference, an SPL meter/scope will probably be the easiest way to synch them.

As far as a voltage divider, that will definitely do the job, but you'll have to determine how many dB it needs to be attenuated. Get the schematic for each and look at the resistance at the input, then calculate the necessary resistance. I had to do this last year, in order to drop the level to an Audio Research amp so it would match the level from the Mac MC300. I had a way to do it with their remote control but that preamp doesn't use discreet commands for everything and it could have easily been controlling Z1 when Z2 was the one that needed adjustment.

As far as that being acceptable, they used resistors at the input of the amp, so I guess the answer would be "Yes". You'll need several to test with but they're not that expensive.

 

[OttoMatic]

Ya didn't say what DMM you have and I said "AC voltages won't necessarily be accurate", not that they won't be.

Sorry, I think my post wasn't worded well. I should have asked "under what circumstances will it not work."

You'll need several to test with but they're not that expensive.

I should be able to use a good pot, right?

 

[zumbo]

Did someone say good pot?

 

[highfigh]

Sorry, I think my post wasn't worded well. I should have asked "under what circumstances will it not work."



I should be able to use a good pot, right?

You might be able to use a pot but it'll be more expensive and may not track equally on both channels, or may add/subtract something. How you connect the resistance it up to you but whether it's in a different cable or a circuit that you connect the cables to, it's adding a variable to that amp's configuration. That's one of the reasons I recommended using an SPL meter. Nothing it added or subtracted with either amp and .5dB won't be terribly noticeable unless the reference level is where you're most sensitive or some other odd thing makes it obvious.

 

[OttoMatic]

That's one of the reasons I recommended using an SPL meter. Nothing it added or subtracted with either amp and .5dB won't be terribly noticeable unless the reference level is where you're most sensitive or some other odd thing makes it obvious.

I'm fine with level matching using an SPL meter, as long as it won't be used against me to negate whatever results.

I was thinking, and if I have resolution to set levels at 0.5 dB, I should be able to level match with a difference no greater that 0.25 dB.

 

[selkec]

The same. The same. My answer was too short for the forum.

I totally disagree with it sounding the same. I just got my xpa-3 to run my polk rti150's and they came to life. The bass sounds so much cleaner and the total sound is 100% better. And goes way louder with no distortion. Maybe this is because my rti's are just under 5ohms :even though the specs state other wise and its been proven on the polk site, plus I measured for myself" So all in all I think it will sound way better than any receiver. Just my opinion along with all my friends that hear it.

 

[mtrycrafts]

I don't have any criticism of that position. I agree that swapping amps only will have zero to minimal (yes, probably inaudible) change to the sound of the system (with tube amps excepted, as you note). Yeah, I probably couldn't hear a difference between two amps.

I admit that I'm changing a bunch of things at once: front end outputs, cables, DACs, preamps and power amps. However, we must admit that here at AH, each and every one of those things are regularly claimed to have no audible effect on the final sound. So, although I'm changing a lot of things, there should be no difference in sound.

I'm also doing it to see if I can hear a difference with changes of those magnitude. Just to see if if I can. And to justify my separates over a receiver, etc. (Jeez, what if I can't hear a difference? Will I be trading my separates in? Well, I guess I never claimed that I can hear a difference, just that I like what I have.)

Supposing I am able to hear a difference, will I be separating out all the changes until I find out where the difference lies? Not sure. I'll see how much work it is.
Agreed.

This published test of just what you are proposing, two different systems except for the speakers, with a number of listeners. Although the switching was anything but instant, the outcome was predictable perhaps with instant switching, it may have been different

Nousaine, Tom "To Tweak, or Not to Tweak?" Stereo Review, Jun 98, pg 79-81.

 

[mtrycrafts]

Otto, I'm not aware of anybody having done what you are planning to do. These kinds of tests are usually done to compare a single component to another, not an entire system (less speakers.) I'm genuinely interested in the results.

Then here you go

Nousaine, Tom "To Tweak, or Not to Tweak?" Stereo Review, Jun 98, pg 79-81.

Our buddy Tom has done exactly what he is proposing, a few days ago.
Everything was different except for the speakers, of course.

 

[fmw]

Then here you go

Nousaine, Tom "To Tweak, or Not to Tweak?" Stereo Review, Jun 98, pg 79-81.

Our buddy Tom has done exactly what he is proposing, a few days ago.
Everything was different except for the speakers, of course.

How was the test conducted and what was the result?

 

[OttoMatic]

This published test of just what you are proposing, two different systems except for the speakers, with a number of listeners. Although the switching was anything but instant, the outcome was predictable perhaps with instant switching, it may have been different

Nousaine, Tom "To Tweak, or Not to Tweak?" Stereo Review, Jun 98, pg 79-81.

Cool, thanks. I can't find it online, unfotunately. Do you know where I can get a copy? If anyone has a hard copy, I'd be happy to pay for the magazine + shipping.

Thanks again.

 

[mtrycrafts]

Cool, thanks. I can't find it online, unfotunately. Do you know where I can get a copy? If anyone has a hard copy, I'd be happy to pay for the magazine + shipping.

Thanks again.

Try your local library first for a inter library loan and they will search a library holding that issue and mail a copy for next to nothing, usually.

Tom Nousaine has a web page, didn't bother to bookmark it and he has some of his articles available to buy or something.
All else fails, send me a PM

 

[mtrycrafts]

How was the test conducted and what was the result?

It was DBT, but he swapped the systems, covered up the wiring and the listeners came in, one at a time to evaluate or guess, rather
Long time difference for a proper comparison but the listeners didn't want to use the ABX box, if I recall. The results? The usual null

 

[fmw]

I appreciate your sending it to me. There wasn't anything unexpected in it. It was a pretty good description of a competently conducted bias controlled test. I'm sure the believers would hate it.