Bob Carver said what!?

HBombToo

Originally posted by rlw

The signal coming from your source/pre-amp is DC.
So, a power amp has an input stage that handles DC.

I feel like a friggen idiot over here! This is stuck in my short term memory and i can't shake it. What am I misunderstanding?

I thought an amp provided gain to the analog signal provided from the preamp out which is also analog.

analog being something like ~ SIN(W)...

DC being W=0 so SIN = 1 i guess?

Been a long time for the HBomb... so what does it mean a preamp is a DC source?

with respect

caseymou

got me thinkin a little here. I thought the incoming analog signal from either the tuner or other source was neither ac or dc but a distorted signal with peaks which vary with amplitude and frequency depending on the source. I think I have actually examined the fm signal on an o scope in class after building a fm receiver and this is what I saw.

Btw, does anyone have a link so I can read the "blind" test where the professionals were embarassed? I think this would be an interesting read.

TroyD

I don't have the link but here is what El Roma had to say about it and I'll bet he can recite it word for word:

The Carver M1.0t, rated at 200wpc @ 8 ohms, 350wpc @ 4 ohms, is an okay amp. Like BDT said, it was "transfer modified" by Bob Carver to sound like a pair of $5K C-J Premier 5 TUBE amps. This was NOT his choice. His challenge was to the hemaphrodites at Stereophile magazine. Specifically, "I can make my new 200wpc, $699 retail power amp sound INDISTINGUISHABLE from any other 200wpc you choose." The clever fellows at Stereophile decided to throw him a curveball. They chose tube monoblocs.

He performed this magic in a friggin' motel room in Santa Fe. He had 48 hours to accomplish it. After 24 hours, and serious listening, they agreed he was not quite there yet. HIS amp had better low end than the C-J's. So he sent them back home, muddied up the low end on his M1.0t, and when they came back 24 hours later, they had to agree, his amp was virtually IDENTICAL to the C-J's. But when they printed the results in the next issue of Stereophile, the scumbags HAD to dilute the mans success by saying "Well he may be able to do it in a motel room, but we doubt he can assure every one coming off the assembly line will be the same."

The article was in a 1985 issue of stereophile but it's one of the back issues that they won't sell you. Gee, I wonder why.

BDT

burdette

Stereo Review used to consistently test speaker wire using double-blind testing. They didn't attempt (nor therefore succeed) in embarrassing anyone, but they consistently found that people can't hear the difference between zip cord and esoteric wire.

The signal coming from a source component is voltage-varying AC. However, an amplifier can pass electrons in only one direction, i.e. DC, so the AC audio signal is placed on a DC offset. The amplifer output is current-varying DC. As this current varies through the voice coil, the magnetic flux varies and the magnet therefore moves the coil.. moving the cone.. moving the air.. producing sound.

Tubes tend to be slower reacting than transistors.. i.e. tubes have a lower damping factor, making them less able to handle transients, usually described by listeners as a mellow sound. What some tube-enthusiests describe as harsh sound from transistors is simply the transister amplifier reacting fast enough that it doesn't miss any of the signal, as the tubes do. On old source material without many fast transients, transistors can show the limitations of the source material. So, indeed, tubes might sound "better" due to their limitations.

As we've discussed previously, the different "sound" of different amplifiers, especially tube amplifiers, does not come from them being "better", it in fact comes from some limitation they possess that causes them to introduce distortion to the output signal. Given that this sort of distortion is pleasing to many people, they claim tubes are "better" amplifiers. The Carver example shows this... he actually had to *diminish* the performance of his amp in order to match the sound of the tube monoblocks. He had to introduce distortion that otherwise was not present in his design.

This is also why two decent transistor amplifiers operating within limits are indistinguishable. It is only when one produces distortion that they can be discerned. More expensive transistor amplifiers are less likely to distort, meaning they can produce a clean signal at higher volumes when a lesser amplifier would begin to clip, for example.

... if you care...

rlw

Originally posted by burdette


The signal coming from a source component is voltage-varying AC. However, an amplifier can pass electrons in only one direction, i.e. DC, so the AC audio signal is placed on a DC offset. The amplifer output is current-varying DC. As this current varies through the voice coil, the magnetic flux varies and the magnet therefore moves the coil.. moving the cone.. moving the air.. producing sound.

Are you *sure* about that?

I'm fairly certain that an amp's output is AC - not DC. In fact, I'm pretty sure that, at DC, the x-over's inductors are a dead short, and the x-over capacitors are an open circuit. Isn't that how caps and coils behave?

In fact, some tube amps include output transformers to prevent DC from going to the speakers. Sand amps typically include capacitors somewhere in the signal path to prevent DC from hitting the speakers - most power amps are NOT DC coupled.

You are, however correct in your correction of my brain-**** that line level is DC. Line level is AC too.

So...I think my original question needs rephrased: A power amp takes an AC signal, applies 30dB of gain, and outputs an AC signal. A preamp takes an AC signal, and typically applies no gain .

If all SS power amps sound the same, shouldn't all SS preamps sound the same? I mean, you can't really overdrive your preamp.

Do we think that all SS preamps sound the same?

HBombToo

Interesting is your position...

Liike I've said, I are an engineer.

Hmmmmmmm...........
is that too many?

faster100

For goodness sakes just listen and love what you can afford, everyone on here has his price point and it doesnt matter what 500.00 or 5000.00 dollar item sounds like until you can afford it and take it home. thats what is so fun about this hobby... no one person has listened to everything out there and even if they did, whats it matter unless they can actually purchase it and tell us all how it sounds, you like it keep it, you don't return it then.. testing is fun but at the end of the day i will never own a 20,000 system and someone else on here might. so why should i concern myself with that the 20 grand system sounds like compared to my couple grand system, its all apples to oranges, Its like if you can afford the best polk speakers all the sudden they are the best, then joe smoe can only afford the cheapest and he thinks they are the best ever....... I know we all like a good conversation but lets leave it up to the people like BOB carver who have made a life long job of audio gear to decide what they think about the amps they build, after all they should know right??

rlw

Originally posted by HBombToo
Interesting is your position...

Liike I've said, I are an engineer.

Hmmmmmmm...........
is that too many?

I'm just asking, honest. I'm only interested in learning/understand as much as I can about this stuff. Feel free to tell me my questions make no sense, just explain why to me, and let me ask more.

I figure the more I understand, the better. A friend of mine says that "It's a great day when we can learn something new", and I tend to agree.

RuSsMaN

Originally posted by rlw

Do we think that all SS preamps sound the same?

Well, just for **** and giggles, after another run through tonight, with limited gear to 'test', I still feel the preamp colors / changes the sound much more than the amp (hopefully will at least blind, if not double blind different amps tomorrow).

Sticking with my ADC16/2 cd, Signal Cable Interconns, MIT Term 5 speaker cable, and SDA CRS+ AND Kef Cresta 2's, I ran through some swaps with the m400a. I chose to stay away from the internal phono stages, and keep it as basic as I could - Line input stage, line output stage.

The pre's interchanged were a Luxman R-113, Yamaha C40, and NAD 1130. This was not a blind test, just me, and the gear. 2 runs were done, one at 85 db avg, one at 90 db avg. Music was South Hampton Dock, and The Final Cut from Pink Floyd.

Lux- Smooth low end, strong (but not forward) mids, laid back, but pleasing highs.

Yam- Smooth low end, but almost punchy, listenable midrange, highs a bit bright.

Nad- Smooth, but not as much authority as the Lux on the lows, strong (once again not forward) mids, detailed, but not overly bright highs.

The Nad and Lux were very very close, all adjectives above are used very lightly.

Even though the Kef's and SDA's are obviously different speakers, the pre's all seemed to stay consistent on either speaker, as far as the effect on the overall sound.

I'm keeping the cave setup with this gear for the weekend, and calling in some Yamaha, Nad, Nakamichi, and Marantz amps to test the original question.

How about passive preamps, or 'direct' switches (not only by-passing user adjustable tone controls, but actually re-routing the signal inside the pre). All tone controls add some sort of distortion, and the signal MUST pass through these (unless said 'bypass / direct switch is available). Is this why sand preamps sound different from each other?

What differs between a preamp's input stage, and an amp's input stage? Obviously the output stages are different, with the amp having to push much higher current on the speaker cables, than the pre on interconns.

Thanks for all your input guys, great read, keep it coming.

Cheers,
Russ (yes, I did this sober)

caseymou

Russ,
I think your "drunk" posts are much more entertaining.

rlw

Originally posted by RuSsMaN



How about passive preamps, or 'direct' switches (not only by-passing user adjustable tone controls, but actually re-routing the signal inside the pre). All tone controls add some sort of distortion, and the signal MUST pass through these (unless said 'bypass / direct switch is available). Is this why sand preamps sound different from each other?

What differs between a preamp's input stage, and an amp's input stage? Obviously the output stages are different, with the amp having to push much higher current on the speaker cables, than the pre on interconns.

Thanks for all your input guys, great read, keep it coming.

Cheers,
Russ (yes, I did this sober)

Interesting.

What about sand preamps that have no tone controls?

I think there's a lot of factors at play. In another thread, I posted an article by Nelson Pass about speaker cable. In there, Pass talks about his real-world experience of the nasty effects of oxidation on the amp/speaker connection.

Could it be that things like connector quality, parts quality, build quality, and parts layout all contribute to the sound of a preamp? What about things like background noise - in our world, there seems to be more and more RF, and crappier AC mains. Wouldn't a preamp that takes these things into consideration, making sure to shield the signal path from RF and internally generated noise have the potential for sounding better?

At the extreme, what about some of those silly-expensive preamps that actually have a power supply which take the mains AC, convert it to DC, then back to AC to get "clean" power have some sonic advantages with "dirty" AC power? Wouldn't any improvement of the power supply yield good results?

Wouldn't these same considerations apply to power amps? If I introduce RF into my signal path at the input stage of the power amp, that sucks just as bad as having it at the preamp. Likewise, if I have noise on my AC mains, and the amp power supply doesn't do much to filter it, isnt' that bad? What if I have a substandard connector or PCB?

The other thing I'm confused about by Carver's claims. He does claim that unless overloaded, SS power amps sound the same. Yet, in the same interview, in the previous statement, he says that he took one of his SS amps, and changed the way it sounds prior to production so that it sounded like his tube amp.

So do all other SS amps sound like the pre-production version, or the version after making sonic changes to [hopefully] improve it?

TroyD

This is just MHO, and in no way am I claiming to be an expert, but, I think that we have to look at the whole statement. I think what he is getting at is let's say you take a flat test tone at a reasonable volume then two SS amps will sound similar. It's when make the amp really work (and I don't think that you neccesarily have to push the amp that hard) that the differences come out in the details. It's how the amp reacts. Again, that's just the way I read it.

BDT

burdette

Originally posted by rlw


Are you *sure* about that?

Of course not. It made perfect sense when I wrote it.. I'll rethink it based on your comments and see what my brain tells me. Perhaps I was insane for a moment. Thanks.

rlw

Originally posted by burdette


Of course not. It made perfect sense when I wrote it.. I'll rethink it based on your comments and see what my brain tells me. Perhaps I was insane for a moment. Thanks.

LMAO!

rlw

Originally posted by TroyD
This is just MHO, and in no way am I claiming to be an expert, but, I think that we have to look at the whole statement. I think what he is getting at is let's say you take a flat test tone at a reasonable volume then two SS amps will sound similar. It's when make the amp really work (and I don't think that you neccesarily have to push the amp that hard) that the differences come out in the details. It's how the amp reacts. Again, that's just the way I read it.

BDT

Troy, this is somewhat of a smart-**** comment, but: I don't listen to test tones, do you?

So, if we're saying that real-world demands end up making amps sound different, well, I agree.

For the record: I'm making no claims on being an expert either. I'm just trying to understand this little hobby thing.

TroyD

Sure, don't we all listen to test tones? heh, heh.....

No worries, for the record, I do think amps are inherently different but my point is, and I think Bob's is, like you say, how the amps react that really differentiates.

BDT

mantis

I think thats why It's so hard to believe that SS amps sound alike.They certianly sound differnt to me.It's hard to find 2 brands to sound alike.Under real world listening,I would go as far as saying that maybe 50% of people can hear differences.It takes a sharp listener to hear it.Tones are tones,if people knew what they where listening for ,I bet the numbers would increase.Just my opnion.Alot of people don't have such cridical ears.Actually I think thats a good thing.Happiness can be found alot quicker.

This subject was interesting to read.I have found amps of all kinds to have there own personal way of expressing themselves(damn, that sounded sorta twisted).

As far as being an expert on amps.......I'm far from it,I just know what I can hear.........or not hear..
Dan

jcaut

Saying that Bob Carver is sharper than me concerning the workings of an amplifier would be something of an understatement. (Ha-ha) But reading it carefully, I'm not surprised about what he said.

provided neither one is overloaded in any fashion, they'll sound identical. That's a big if.

It's very easy to do this (overload, in some form) if you don't have a big juicy amplifier.

Point is (and I think it was already made above, but I'll just re-state) that it's not difficult to run up against the limitations of your amplifier. You might not even be aware that the amp is being overloaded but for the subtle sound differences-- that some people can hear. In other words, it's the way that the amp reacts to real-world (not gross, clipping-type) overload, that accounts for the differences we hear.

Assuming fairly capable amps (and unfortunately I think that excludes *most* receivers), driven completely in their "comfort-zone", being fed equal inputs, I think it would be difficult to hear the difference. I haven't had the opportunity to test this out, so I may be completely wrong. I'm inclined to believe Bob though.

joe logston

there is not that much difference in amp unless you run out of power, its mostly up to the speaker load and how lould you pay them its all in the power supply of the amp and how the amp handles the ohms of the drivers, a clean pre amp makes some differants in a clean gain and good valume control. clean power is the word.
im on bob carvers side