Rotel surround pre = crap.

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hi everyone,

just a general FYI. Rotel surround sound preamps sound like crap.

some of you may know that i started the Son of Dork project a while back, a purist yet flexible multichannel preamp to use with new formats (SACD/DVD-A) and integrate with a surround sound controller. work has gone in spurts and i'm not very far along so i decided in the mean time, i would upgrade my old Denon AVD-2000 surround sound controller, which doesn't even have DTS decoding.

so i got a used Rotel RSP-966, which has been recently replaced by the 1066 (has newer formats like DTS EX and Pro Logic II but otherwise identical). like the denon, it has a direct 5.1 channel analog input which i use for multichannel SACD. i was hoping it would sound at least as good as or better than the analog section (volume control) of the Denon. well, it sounds pretty disappointing to say the least.

before i even listened to it, i popped the hood to see what's inside. i could only really see the power supply and main audio boards, but the main board had all sorts of digital and analog circuits mingled together - Crystal DSP, AKM DACs, cheap JRC opamps, all clumped together into a fairly small area. it appears to be only a 2 layer board and the ground planes aren't all that big. the 5.1 channel inputs have to pass through all kinds of crap before even getting near the output jacks, where there are electrolytic coupling caps, more cheap opamps, and solid state mutes. yuck.

and the sound... worse than my old Denon that i paid $150 for used! the Denon actually has a much nicer layout internally, although it doesn't have anywhere near the switching capability of the Rotel so it's a little easier. also, the control flexibility of the Rotel sucks - you need a TV monitor to adjust anything more than volume, and it does not memorize separate level settings for each input like my Denon did. and it has non-defeatable tone controls! agh!

anyway, i thought i got a good deal on this thing ($699 mint used) but it turned out to be a hunk of $%^@! it doesn't even sound good for movies! Dolby Digital sounds marginally better than the old Denon in some aspects, worse in others (the Denon has a smoother, fuller sound, though with less detail). and DTS was not much better either.

anyway, this is totally unrelated to DIY except for the very loose connection to Son of Dork, but just needed to vent some frustration. :mad: this thing's going back on the used market pretty soon, hell, i think i'll build my own DD/DTS decoder as an add-on module to Son of Dork!
 
Retired diyAudio Moderator
Joined 2002
I have the same denon decoder that you have. I am content with it. I paid $150 off ubid about 5 years ago.

How do you propose to make your own DD/DTS decoder? I haven't been able to obtain the chips needed. I was considering integrating it into the pre-amp that I am building now. So far, all that I have for my pre-amp is a circuit with a pga2310 controlling the volume, and I ordered the display vfd from Noritake:

http://www.noritake-elec.com/7000.htm

I bought the GU140X32F-7002. It has sync serial, assync serial and parallel interfaces. You can order direct from Noritake for $96.

If you are looking for a beautiful display with a lot of features, check out the Noritake.

Datasheet posted at:
Datasheet

I am using a PIC18F452 microcontroller.

Let me know if you have find anyway to decode DTS. I would like to add this to my pre-amp project.

--
Brian
 
wow, that's a great looking VFD brian, thanx for the info. i will check it out for Son of Dork.

i'm not sure how i'll do the DD/DTS decoding. i said i would make it myself out-of-the-blue, sort of out of a mix of frustration with crappy/overpriced commercial products and pure DIY bravura. i would think we could get the same Crystal or Motorola DSP chips that the big boys use, but i'm not sure how the codec licensing works... i think not only the semiconductor manufacturers but equipment makers have to pay royalties to Dolby etc. are those the chips you've tried getting?
 
Peter Daniel said:
Denon surround receivers are highly regarded and supposedly sound very good.

from the design of my old AVD-2000, i'd have to agree they are definitely above par. the circuit layout isn't purist but it's not all that bad either; i think Denon has a litlte more audiophile sensibility than most. you would think Rotel, with its pretensions to audiophile quality, would be at least as good, but the Denon unit is far superior in execution.

considering that $800 buys you a receiver with the latest decoding features, spiffy remote control, AND 5 channels of amplification to boot these days, i wish one of the big Japanese firms would make a decent quality surround sound preamp for around $1k. but i guess there isn't much market for that.
 
Retired diyAudio Moderator
Joined 2002
Yeah, it is the newest in VFDs that are out now. Look over the datasheet and check out all of the features that it has. My roommate has taken a class in Microcontroller design with the PIC18F452, and he will help me interface with it.

As for the DD/DTS chips, I e-mailed a couple of companies who provided chips (crystal and motorolla), and they wouldn't provide any chips for use, due to licensing issues. I was told that I had to pay large licensing fees in order to buy the chips. I just gave up with the effort. I considered taking the chips out of old broken equipment, and using them, but I haven't followed through with that.

How is your pre-amp progress going? (I guess this should be continued in the appropiate thread....)

--
Brian
 
Son of Dork is on hold at the moment, been busy reviewing some equipment for the magazine i write for and tending to other things. but i hope to get back to prototyping more circuits soon, my work tends to come in spurts. the JFET buffer i built as a first step of the project is holding up very well though, it sounds great and has become my reference preamp of sorts.
 
Peter Daniel said:
Denon surround receivers are highly regarded and supposedly sound very good.
Well, why not buy one of the mid-range units second hand, and redo all the audio signal electronics after the DAC outputs in a seperate case? That saves you all the greif of trying to get/make function a DD/dts chipset, and only involves a small amount of soldering and drilling in the Denon. I doubt you'll be able to get chipsets or even samples of DD/dts ICs due to licensing agreements.

When I find a second hand receiver cheap enough, I might just do this myself. But it's <i>very</i> low on my priority list to do.

Ciao
 
That's the inside of my Citation 7 Home Theatre preamp. I don't think I would like to built anything like that myself. Bought it used for $600 two years ago, still didn't have a chance to use it.;)
 

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I think it is somewaht unfair to say something sounds like crap in comparisson to something else arbitrarly. I have a Rotel 1080 it is a 200 Watt Stereo Amp and sounds very good, it has had some great reviews. I bulit a 200 Watt MOSFET Amp using the new Motorola matched output FET's and a reference design I came across on the internet. The Amp I built sounds much better, why I thought, I did not use exceptional parts as a rule. What I did do was build a really big *** power supply, much larger capacity than Rotel's. I think the Rotel amp is still a good Amp, but I do not have to answer to the same cost engineers that a Rotel design Engineers has to. I do not have to worry about using parts that are always available for consistency. I do not have to worry about customer complaints due to fried parts from pushing the envelope of design.


So that's have a little respect for those companies that make it possible for us DIY'ers to do what we do, because if there is no mass market, there is no market at all.

Anthony
 
i never said anything about Rotel amps. they are above average. no need to defend your purchase here. however, this preamp sucks. there is no 2 ways about it. i'm not sure if it's reasonable to expect much more at this price but the design of this one is pretty poor, and it is reflected in the bad sound. that is why i was so disappointed, because i had expected a little more from Rotel. i would have thought they would at least match Denon. the comparison is not arbitrary at all as they are similar types of products of similar calibre; if anything, the rotel should have outdone the Denon.

p.s. the fact that a product has had great reviews means almost nothing, particularly in a forum such as this one. there are plenty of mediocre products that get rave reviews in the audio press for reasons other than sound quality.
 
on second listen...

yes, the preamp section still sucks for music, but the DTS decoding is not as bad as i thought. i had originally tried Gladiator on DVD and the sound was not very good, but that disc has pretty awful sound anyway. i stuck Rush Hour 2 in (DTS ES 6.1) and it sounds quite a bit better, cleaner and more dynamic than dolby digital. so i'm on the rocks now whether to re-sell the unit, or maybe try to modify it a bit.... maybe i'll see if i can get a service manual first... i want to get those infernal tone controls out of the circuit!
 
Yes, death to tone controls. Interesting comment about how your preamp has lack luster performance for music but DTS is acceptable. I hate to point out the obvious but it seems the analogue section may be at fault or inferior as the case may be.

Crappy resistors, cheap caps, or the ADC itself? Are you using digital in from a CD source or Analogue? I find the power supplies in these low end units to be the biggets culprits myself. I will try to dig up schematics for my Amps.

Anthony
 
when i refer to the Rotel as a preamp, it is when used in purely analog mode with the multichannel inputs. they pass through volume and tone controls and the output stages, but not an ADC or anything. (if the signal were converted to digital i would not bother holding any hope for signal fidelity.) there are problems too numerous to list, but for starters: crappy resistors/caps at the input stage, long wiring harness to the mixed signal board where there's digital and analog stuff strewn all over the place, long signal traces, most likely an IC volume control chip (don't know what type), more long traces, electronic switching, tone controls, lots of cheap opamps, electrolytic coupling caps, muting transistors, etc. etc. and yeah, the power supply is not so hot either. i'm hoping once i get a service manual i can figure out some points of improvement, though this one may be beyond tweaking.

i think the DTS suffers from the same problems as music; it has to because it passes through the same analog stages etc. however the decoding quality itself (purely digital) is better than i originally gave it credit for, and i like the AKM DACs used. movies tend to be a little more forgiving than music; the failings are just that much more obvious when using, say, my SACD source material through the analog inputs.
 
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