How inexpensive could a pre-pro be? (1 Viewer)

[Ricky T]

Great discussion guys! I'd also be more interested now these points apply to $1000-1500 receivers, as opposed to $500 receivers.

 

[chung]

What if it was 95dB in the receiver, and improved to 100dB by taking the amps out. Would that be significant?

I don't think the difference between 95dB and 100dB is significant at all. In the old days, a great phono preamp may get close to 70dB S/N (not including surface noise from the LP). An analog Dolby cassette deck may get to 80dB, if everything is done right. The CD format allows 96dB S/N best case, but it is just about impossible to find programming with that kind of dynamic range. The best FM receiver is probably around 80dB in mono. As far as I am concerned, anything above 90dB is only of academic interest. By the way, you really have to screw up bad as an electrical engineer to achieve

 

[chung]

What % of the $500 rcvr cost do you think these mnfgrs spend on the amps...could that money do anything to upgrade the dac's ?????

If you are talking about a street cost of $500, the actual bill-of-material cost will be much less. I don't know, but just to make a wild guess, I think the BOM cost is about $150 or less. Assembly and testing probably costs $20. The box, shipping, manuals, remote, etc probably add another $30. So the receiver costs about $200 to build.

That $200 cost will probably be reduced to $140 or so if all the amps were taken out. My guess is based on the fact that the chassis is smaller, the transformer is much smaller, and the 5 or 6 power amps are removed, and there will be fewer connectors.

The DAC cost is a small portion of that $140. DAC's are integrated circuits that have good yields, and I don't know if it's worth it to buy DAC's with tighter specs, if such things exist. I would put the money instead on gold plated connectors, nice front bezels, a better remote control, etc. These are things that do not show up on the data sheet, but make for a better product.

Again, I may be off quite a bit with my estimates. Take these figures with a huge grain of salt. The $200 cost may be $250, or it may be $150. I know it's not going to be $350, or less than $50.

Yes, the receiver is a surprisingly good deal. At the Denon 5800 level, of course the profits are much higher, since the sales volume is so much lower.

 

[Saurav]

As far as I am concerned, anything above 90dB is only of academic interest.

Well, I listen to vinyl through a kit-built tube line stage, tube amps and kit-built speakers, so for me, SNR becomes academic well below 90dB. I don't listen to music with my TV on though, but I see your point for HT.

 

[Richard Burzynski]

Chung wrote:

"By the way, you really have to screw up bad as an electrical engineer to achieve

 

[MatthewJ S]

S/N AT 89 ? WHO?

 

[Mifr44]

"S/N AT 89 ? WHO?"
He might be talking about this one, although it has been brought up that this might be a typo.
Michael

 

[MatthewJ S]

back of the avr307 manual lists s/n as 98

 

[Samuel Des]

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[AjayM]

Well, I have a B&K Ref 20, which is listed on both the manual and the website as having a SNR of 89db. Which also sounds better (not by leaps and bounds, but is an improvement) than the Denon 3300 reciever which was used as a pre-pro (which for the most part had much better specs all around) that I had before I bought the B&K.

Andrew

 

[MatthewJ S]

That certainly is one of the questions...while, I find that the pre-pro section doesn't draw too much current itself and the noise problems ,according to others, can be engineered around, it is the need for better and better, hence bigger and bigger, amps that have many people entering the seperates market.....It is a bit of a size issue for flagship rcvrs to keep putting in stronger and stronger amps....What I was thinking was ,given that this market/hobby is growing,wouldn't it be nice if there were more low priced pre-pro units so that enthusiasts w/ a budjet would be able to have new technology with their existing amps...Many people on this forum pay close attention to the least expensive pre-pro available at any given time while others just look at rcvrs w/pre-outs...

I understand that right now this may be a pipe dream, but it would be nice to give people more options for better bang for their buck

 

[Larry B]

Saurav, Chung, and others:

I read with interest your many comments, one of which (quoted below) got me wondering.

Companies like Sony and Denon have been building receivers for over 50 years. Don't you give them credit for understanding all these issues and having engineering solutions for them? Do you hear hum at the outputs of modern receivers?

I should point out that (as I think Saurav knows) I have spoiled myself with high-quality stereo equipment, but lack formal electrical engineering training. So here's my question: Is "hum" all that matters. In other words, can't the proximity of the amplifier to the preamp cause problems other than hum?

Thanks in advance - - -

Larry

 

[Saurav]

Well, I did respond that I did hear an audible hiss at my speakers when I used a receiver, and now that I use tube hear, there's even more of that hiss.

In other words, can't the proximity of the amplifier to the preamp cause problems other than hum?

It could, but I think I agree with Chung here: even for other radiated noise, the effect of the pre-pro on the amps will be much more than the effect in the reverse direction. Of course, that addresses the question "is it worth it to remove the amps", which is probably a better question to ask than what was asked in the beginning, which is "will there be an improvement by removing the amps". I still think the answer to the second question is "yes", and I agree with Chung, the answer to the first question is "no". In my opinion, of course.
Another thing that you might be interested in - the SNR number will cover all kinds of noise - hum, hiss, buzz, what have you. It measures the noise level of the equipment, the floor above which the signal must exist. This noise can be at any frequency, it doesn't have to be just at 60 Hz (which is the noise most commonly described as hum).
The point I'm trying to make is, a good SNR figure will indicate low levels of noise at any frequency.
And again, personally - I don't give too much importance to numbers, but that's a whole different discussion

 

[Larry B]

Saurav:
Thanks for the info. Out of curiosity, how do you think the folks at Levinson, or Linn, or Naim (to name three examples; there are of course many others) would respond if asked about the benefits of keeping amp and pre-amp separate?
Larry
P.S. I take it you ddn't yet sell the wife, kids and car for the Lamm equipment.

 

[chung]

So here's my question: Is "hum" all that matters. In other words, can't the proximity of the amplifier to the preamp cause problems other than hum?

When I was asking the question does one hear hum from a receiver, I was making the point that layout issues around the transformer in a receiver are understood and solved, and that was made in response to Saurav's observation that he could pick up hum if he was not careful with the dressing of the wires. Hum is noise at AC line frequency and its harmonics (60Hz, 120 Hz, 180Hz, etc.).

Hum is not the only kind of noise. There is broadband noise that manifests itself as hiss. The CMOS DSP circuits generates a lot of broadband noise on the power supplies that need to be filtered, and they also could radiate noise via magnetic and capacitive coupling. Again, these problems can be solved satisfactorily, and if a pre-pro has a S/N >90dB, then these noises are not audible. There is also noise from the DAC, from quantization errors and from the noise floor of the DAC, but that noise is irrelevant to this discussion.

By the way, hum is more often a result of ground loops in connection of equipment, and not because of internal pickup from transformers. In fact, if you use the optical connection between your CD/DVD player to your receiver, you minimize the likelihood of ground loops. Here is one instance where a receiver has an inherent advantage, since the pre-pro has the same ground as the power amp.

I can't think of any noise that can be generated just because the pre-pro is close to the power amp. The power amp carries audio frequency signals when driving speakers, and those signals do not radiate out easily.

 

[Dan Harding]

Most people here seem to think that receivers don't sound as "musical" or otherwise as nice as separate pre-pros. How much of that is due to the amplifiers in the receivers? If you use those receivers, like the HK-AVR320, or Sony DA3ES/DA5ES, or Denon 2802/3802 as prepos, and use the built-in amps for the surround channels and add a stereo or 3-channel power amp, you should get great results.

I just did this very thing over the weekend. After lamenting how music has never quite been the same after going from 2-channel to 5.1, having dropped a Rotel/B&K 2-channel for a Denon AVR-3200 (several years ago), I wanted the music back without forsaking home theatre.

I obtained a pair of Carver Silver 7T monoblocks and am using them to drive my front mains, using the preamp outs on the 3200.

The difference is truly astounding. I had hoped there might be a difference, but I didn't think it would be anything like this. Louder, cleaner volume notwithstanding, even at normal listening volume I'm hearing more pronounced and deeper bass, more depth of soundstage.

I'm now considering myself a complete dumbass for having done without for the last 3 years.

-Dan

 

[Saurav]

I was making the point that layout issues around the transformer in a receiver are understood and solved

Is it just around the transformer? I don't know the current draw of solid state non-amplifier circuitry. For tubes, the heaters draw a pretty heavy current, so you need to watch your heater wiring dress even if you're running DC to the heaters from a separate transformer. Take my case, for instance - my preamp has two power supplies. It originally had one transformer supplying both the B+ and the heater, but now the heater current comes from a separate wall-wart transformer. And since a Radio Shack transformer has only so much filtering, I've had to play with that cable and make sure it doesn't interfere with the signal lines.

But, point taken, and in solid state devices, I doubt there's anything other than the amps which are drawing more than tens of milliamps of current. So again, this is pretty much a non-issue in a receiver/pre-pro.

 

[chung]

I obtained a pair of Carver Silver 7T monoblocks and am using them to drive my front mains, using the preamp outs on the 3200.

The difference is truly astounding.

Yes, the power amps are the weak link in most receivers, especially ones from Japan. I have proven this many times over the years to myself.

Unlike in the case of the stereo preamp, the power amp is harder to spec. And a power amp with good-looking specs may not sound good. The main reason is because the speaker is not an ideal 8-ohm load, and the power amp specs are measured into an 8-ohm load. How well the power amp controls its output impedance, over frequency and output level, has a direct effect on how the speaker sounds. Unfortunately that is not an area where amps are spec'd clearly.

When I choose a power amp, I want one that is close to being an ideal voltage source. That is, I want it to output twice the power into 4-ohm loads compared to 8-ohm loads. Very few Japanese power amps, especially those in receivers, can do this. The great power amps will output 4 times the power into 2-ohm loads, too, and that is a direct result of the reserve of the power supplies.

In contrast, a stereo analog preamp can be specified very precisely, and there should be great correlation between specs and performance.

 

[Samuel Des]

Great thread.

Yes, the power amps are the weak link in most receivers, especially ones from Japan. I have proven this many times over the years to myself.

Hi Chung, I'm curious. What tests have you done? What sort of results did you get?

 

[chung]

What tests have you done? What sort of results did you get?

When I was with HP, I had access to huge resistive loads and distortion analyzers, and I was able to make THD measurements at varying output levels and output loads. On the cheaper amps, THD would be excellent at 8 ohm loads, but rapidly degrade as you lower the load impedance. Also one can easily observe signs of clipping early on. Note that a good sign of a power amp is a large torroidal transformer. It's simple physics that larger transformers can pass larger currents before running into saturation.

Recently I have been doing only listening tests. The power amps in a lot of receivers cannot keep up with demanding material at high listening volumes. I use mostly classical music and voice for listening test. The most notable results are listening fatigue, and the general harshness of the sound. It is not a very subtle effect, either. This kind of problem is much worse than what one can discern among different CD players or preamps. I think Harman Kardon probably does the best job among receiver manufacturers as far as the power amps are concerned, but I have not listened to the new Denon, Yamaha or Pioneer Elites.

Now I have pretty good speakers and they are not very efficient. It is very possible that the power amps in receivers are prefectly adequate in driving some speakers. You need to do some listening tests to determine that. The center and the surrounds do not have to deliver as much sound level, so the receivers amps should do well with those speakers.