Hi Guys,
A while back, Carlos challenged me do an A/B test with one of his amps and any other amp. I have been doing comparisons between the amps I have built for long time but always using two separate preamps and two sets of speakers but no matter how I hooked it up it was difficult to make quick enough switches to be able to really hear the subtleties. So I went about to make some equipment to be able to better tell what exactly was going on. So, the first thing I did was build a speaker switch. This allows me to switch between two amps and listen through the same set of speakers. I suppose it would also allow me to use one amp and two different speakers is I were A/Bing speaker cabinets.
Anyway, once I got the speaker switch finished I was still using two different preamps so I could adjust the volume of each amp due to the fact that different amps have different gain. Even with this I could never be sure if the differences I was hearing was the amps or the preamps. So, I decided to build a volume control box using two 50K "DACT Type SMD Stepped Attenuator 21 step" pots that I bought on Ebay. This setup, give a very good sound and I have pretty much quit using a preamp at all, even when just listening to music.
Now for the real kicker. I have found that once you get the volumes equalized between a pair of amps, the audible difference is almost indistinguishable. I was absolutely floored by how similar the amps all sound. You can look in my signature to see all the amps I have been A/B'ing. The differences are very, very subtle. The high powered amps gain a little advantage once you get the DB's up there, but for normal listening volumes, you would be amazed how close they are.
I am attaching a pic of my setup.
Blessings, Terry
A while back, Carlos challenged me do an A/B test with one of his amps and any other amp. I have been doing comparisons between the amps I have built for long time but always using two separate preamps and two sets of speakers but no matter how I hooked it up it was difficult to make quick enough switches to be able to really hear the subtleties. So I went about to make some equipment to be able to better tell what exactly was going on. So, the first thing I did was build a speaker switch. This allows me to switch between two amps and listen through the same set of speakers. I suppose it would also allow me to use one amp and two different speakers is I were A/Bing speaker cabinets.
Anyway, once I got the speaker switch finished I was still using two different preamps so I could adjust the volume of each amp due to the fact that different amps have different gain. Even with this I could never be sure if the differences I was hearing was the amps or the preamps. So, I decided to build a volume control box using two 50K "DACT Type SMD Stepped Attenuator 21 step" pots that I bought on Ebay. This setup, give a very good sound and I have pretty much quit using a preamp at all, even when just listening to music.
Now for the real kicker. I have found that once you get the volumes equalized between a pair of amps, the audible difference is almost indistinguishable. I was absolutely floored by how similar the amps all sound. You can look in my signature to see all the amps I have been A/B'ing. The differences are very, very subtle. The high powered amps gain a little advantage once you get the DB's up there, but for normal listening volumes, you would be amazed how close they are.
I am attaching a pic of my setup.
Blessings, Terry
Attachments
Hi,
Interesting observation, have you found Class A (e.g. KSA 50) and Class A/B (e.g. VSSA or Symasym) to sound different, i.e can you pick them blind folded?
I found Class A amps to sound much fuller than Class A/B's. Also Class A amps sound much closer to tube amps than Class A/B's.
Interesting observation, have you found Class A (e.g. KSA 50) and Class A/B (e.g. VSSA or Symasym) to sound different, i.e can you pick them blind folded?
I found Class A amps to sound much fuller than Class A/B's. Also Class A amps sound much closer to tube amps than Class A/B's.
It is surprising how similar they all sound to each other. One of the things about comparing Class A and AB is that unless you are pushing them, most AB amps are running in Class A or close to it. I definitely wouldn't discribe my Class A amps as being fuller. They have a little less "edge" to their sound. For some things that is good but some things sound dull because of it. I suppose it is a matter of taste. One thing I have noticed since I made up this volume control box is how much just increasing or decreasing the volume one notch changes the sound. It is no wonder I was chasing my tail trying to A/B stuff before. For folks who are truly interested in hearing the difference between amps I highly suggest making something like this. You will be amazed at what you hear.
I had built a JLH 1969 a few months ago because I wanted to try using a server power supply to power an audio amp and the JLH being single voltage fit the bill. It worked fine but I was disappointed in the sound and the heatsink I had it hooked to got very hot so I just put it away feeling the sound didn't justify the heat. Today on a whim, I got it out and mounted it on a couple of heatsinks I had lying around and hooked it up to my test setup. Wow, it held it's own against the SKA GB150 I just finished as well as a VSSA and the Super A. I had misjudged it and all because I didn't have way to really A/B it before.
Pretty cool!
I had built a JLH 1969 a few months ago because I wanted to try using a server power supply to power an audio amp and the JLH being single voltage fit the bill. It worked fine but I was disappointed in the sound and the heatsink I had it hooked to got very hot so I just put it away feeling the sound didn't justify the heat. Today on a whim, I got it out and mounted it on a couple of heatsinks I had lying around and hooked it up to my test setup. Wow, it held it's own against the SKA GB150 I just finished as well as a VSSA and the Super A. I had misjudged it and all because I didn't have way to really A/B it before.
Pretty cool!
Good stuff! That is something I have tried to be conscious of when evaluating an amplifier, the level of output that is. I can see where even slight differences can skew an evaluation.
Are you applying a test signal and measuring the output voltage prior to listening? Just curious as to your method for ensuring a match in output level. Most of my DIY builds were actually built to the same closed loop gain so there is almost nil difference to start with but level matching is needed to compare to a commercial offering.
I don't know about you, but I have found a general preference to my DIY builds in comparison to many commercial products.
Are you applying a test signal and measuring the output voltage prior to listening? Just curious as to your method for ensuring a match in output level. Most of my DIY builds were actually built to the same closed loop gain so there is almost nil difference to start with but level matching is needed to compare to a commercial offering.
I don't know about you, but I have found a general preference to my DIY builds in comparison to many commercial products.
Hi Jason,
No I am using my ear. With the speaker switch, it is instantaneous from one amp to the other. I simply listen with my eyes closed and press the button in and out and adjust the volume controls until the "sound" is as close as I can get it. This is a listening test after all, not a measurement test. We have equipment for that. For those interested, these are the parts I used.
Speaker switch
Stepped attenuator
You can see the attachment for how I wired the volume controls.
Blessings, Terry
No I am using my ear. With the speaker switch, it is instantaneous from one amp to the other. I simply listen with my eyes closed and press the button in and out and adjust the volume controls until the "sound" is as close as I can get it. This is a listening test after all, not a measurement test. We have equipment for that. For those interested, these are the parts I used.
Speaker switch
Stepped attenuator
You can see the attachment for how I wired the volume controls.
Blessings, Terry
Attachments
Oh, don't misinterpret me, I understand it is about the listening. However, if you are looking for a difference in sound then accurate matching of the output from each amplifier may be advisable. If one exhibits slightly more sibilance you may end up playing it at a slightly lower level than one that exhibits less sibilance for example. Just feed in the same test signal to both amplifiers and adjust the controls to read the same output voltage on a DVM, then listen. If you hear a difference in 'loudness' it may indicate a difference in the character of the amplifier.
That is the funny thing about perception, subtle queues can alter it but an instrument won't lie. Try this for curiosities sake:
Set the amplifiers to the same subjective loudness with music and then apply a test signal and measure the output. How close are you? A simple DVM test can likely get you to within 0.1dB, the ear may be up to 1dB different.
Unless you feed in pink noise or something similar the DVM is going to just read the frequency you are feeding and if one amp has a little bump in that range it will end up being dialed too low. How is that different than your ear hearing sibilance? I'll stick to listening.
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Set-up would be done with a pure tone mid-band, generally assumed to be 1kHz. This is conveniently where virtually all amplifiers are dead flat in frequency response and are not exhibiting any phase shift. If the amplifier isn't flat at 1kHz then it belongs in the trash. Also, most DVMs are able to provide a meaningful reading - it doesn't have to be accurate to reality, but it just provides a reference so the amplifiers have the same level.
The point of doing it this way is that if there are variations in frequency response or phase from one amplifier to the other that result in a difference in the way they sound that difference will be more noticeable. Shifts such as these occur out near the extremes of low and high frequencies. When tuning by ear you risk subconsciously compensating with a slight level adjustment, making the amplifiers sound more alike than they might otherwise be.
Anyhow Terry, I'm not saying you are wrong. I'm just trying to offer a somewhat more clinical methodology to actually showcase wether or not differences are there from one amplifier to the next.
Happy listening and have a Merry Christmas.
The point of doing it this way is that if there are variations in frequency response or phase from one amplifier to the other that result in a difference in the way they sound that difference will be more noticeable. Shifts such as these occur out near the extremes of low and high frequencies. When tuning by ear you risk subconsciously compensating with a slight level adjustment, making the amplifiers sound more alike than they might otherwise be.
Anyhow Terry, I'm not saying you are wrong. I'm just trying to offer a somewhat more clinical methodology to actually showcase wether or not differences are there from one amplifier to the next.
Happy listening and have a Merry Christmas.
Hi Jason,
I know what you are saying. We just love to measure things don't we? I guess the point I was trying to make is that the two amps can sound quite different and then with one click of the stepped attenuator, they are all but identical. I'm not saying they "measure" the same, only that they "sound" very, very similar. I urge anyone who is curious about how different amps stack up, to build a simple dual volume setup and speaker switch like this and give it a go.
Merry Christmas!!!
I know what you are saying. We just love to measure things don't we? I guess the point I was trying to make is that the two amps can sound quite different and then with one click of the stepped attenuator, they are all but identical. I'm not saying they "measure" the same, only that they "sound" very, very similar. I urge anyone who is curious about how different amps stack up, to build a simple dual volume setup and speaker switch like this and give it a go.
Merry Christmas!!!
It is not for the 'love of measurement' that Jason is making his suggestion. When switching between amplifiers it is very common that the louder one will sound better (a common trick for salesmen). I know you are trying to get them very close to the same volume by your listening method, but doing it the way Jason has suggested is the best way to ensure that they are as close to the same volume as possible (to within 10ths of a db).
Again, at the frequency it is set at. Not necessarily throughout the spectrum. It's all good, pick your poison. 😀
Well designed and properly built solid state amplifiers employing generous negative feedback will have a flat frequency response over the audio band, and often well beyond either extreme. This is representative of most amplifiers. This means the frequency chosen for the level setting is really academic and generally of no consequence; we would normally use 1kHz just because there are about as many octaves below that point as there are above it, making it approximately mid-band. Other factors will however influence your overall experience and dictate the character of the amplifiers being auditioned. This is what accurately measured level matching is supposed to showcase.
My opinion is stated and I'm not looking for any argument from this point forward. You will hear no more from me regarding this, but I do thank you for allowing my participation.
I like the look of those DACT style stepped attenuators and may just have to order up some for myself. Certainly can't beat the price. I should also cook up some sort of amplifier / speaker switch as well since I have been doing as you were doing prior - play, swap, play... Makes your 'memory' of the way something sounds unclear. A set up like this would make comparisons more meaningful.
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So far, the speaker switch has been working flawlessly. I'm not sure if it will eventually develop contact problems but so far so good. It sure makes switching between amps simple and seamless. Without the dual volume control box my findings were still a little skewed because I had to use two separate preamps to control the loudness of each amp. With the dual pot box it is very simple to feed each amp the exact same signal. I did add a 12K pot between the sweeper and ground of each pot as seen in figure #1 on this page.
ESP - A Better Volume Control
Jason, your comments are always welcome and informative.
Blessings, Terry
ESP - A Better Volume Control
Jason, your comments are always welcome and informative.
Blessings, Terry
Good idea Terry - I'm going to build an AB box since my amp collection is starting to resemble yours.
Your results aren't too surprising - all your amps are properly designed and I presume built correctly. I'd expect nothing but subtle differences unless you were comparing to a cheap receiver. As long as the amps are operated within their limits, loads are reasonable and you stay away from tripping the protection circuits they should be clean. Even my LM3886 app note amps sound pretty good when mounted on a proper heat sink. Low level details and imaging seem to be the differences I hear.
Your results aren't too surprising - all your amps are properly designed and I presume built correctly. I'd expect nothing but subtle differences unless you were comparing to a cheap receiver. As long as the amps are operated within their limits, loads are reasonable and you stay away from tripping the protection circuits they should be clean. Even my LM3886 app note amps sound pretty good when mounted on a proper heat sink. Low level details and imaging seem to be the differences I hear.
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