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Rotel RB-1070 Amplifier Review

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 3 1.1%
  • 2. Not terrible (postman panther)

    Votes: 46 17.2%
  • 3. Fine (happy panther)

    Votes: 183 68.3%
  • 4. Great (golfing panther)

    Votes: 36 13.4%

  • Total voters
    268

pma

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I has predictably Higher noise and distortion at any frequencies. The fact that SINAD stays put as voltage increase is a bit of a concern no? It requires more digging. Does it means that the noise floor increase at the same rate as the volume? That would be a bit odd and not a good thing, If not it would mean that distortion start to increase as soon as you increase level, from zero. Also odd.
PSR is poor (or supply rail induced distortion) so the background noise (from ripple) increases with power and this makes THD+N constant with power. I have similar measurements in my prototype archives.
 

mdunjic

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This is a review and detailed measurements of the Rotel RB-1070 stereo power amplifier. It was released in early 2000. Can't find the cost then but I see it used for around $400 to $500.
View attachment 258672
I have always found Rotels to be most attractively designed power amplifiers. One look at that front panel and you immediately think of muscle and beauty in design. Alas, the extruded aluminum in front which gives it that look, is cosmetic. There are two others internally which do the job of cooling this classic AB design. In use the heastsinks got pretty warm to touch to give it some air to breath.

Not much news in the back other than nice inclusion of trigger input/output:
View attachment 258673

Rotel RB-1070 Measurements
The unit warmed up nicely without its performance changing much:
View attachment 258674

So let's see what our dashboard of 1 kHz tone does into 4 ohm load:

View attachment 258675
The amp is about 2 dB more sensitive than usual which likely accentuates the power supply noise a bit. I was able to reduce 60 Hz hum in one channel but not simultaneously in the other. That is exceeded however by the power supply noise at 120 Hz and multiples. SINAD is likely dominated by distortion to the tune of -80 dB. This lands the RB-1070 slightly above average of all amplifiers tested:
View attachment 258676

Despite the power supply noise, dynamic range is very good:
View attachment 258677

Frequency response is excellent and spec compliant:
View attachment 258678

Crosstalk is good:
View attachment 258679

Multitone shows no frequency dependence which is nice:
View attachment 258680

There is ample power available into 4 ohm:
View attachment 258681

The response is quite odd in that it doesn't slope down. Don't know if that is intentional, accidental or due to power supply caps aging, letting in more ripple as power goes up.

Regardless, lots of power is available:
View attachment 258683

Company only specs the power into 8 ohm at 130 watts. It certainly delivers that:
View attachment 258684
Putting aside noise floor which is rather high, the units transfer function is one of the best I have ever seen:
View attachment 258685

Sadly there is a significant power on pop:
View attachment 258686

Conclusions
As one of my favorite (looking) brands, I was very anxious to measure a Rotel amp, hoping it would not let me down. Fortunately it did not. No, the SINAD doesn't break new ground but the rest of the measurements are very good with plenty of power available. It is a great choice for people wanting good amount of power in an attractive package with competent performance.

I am going to recommend (used) Rotel RB-1070.

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Had Rotel RB-1050 for several years 20yrs ago … nothing wrong with it, sounded perfectly ok, except less power than I may have wanted. Then I moved to Quad 909 and now, after 15 yrs of Quad, now I am having combo of Hypex Ncore NC502MP based Class D stereo + Hypex NCORE NC500MP class D monoblocks, to biamp my speakers … loads of power, ultimate linearity and neutrally. Most likely one of the best values in hifi
 
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sarumbear

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It is predictable vs not. Audible difference?
What is not predictable. You measure you know. What is there to predict? Lower distortion is always a good thing, why bother if it’s changing along better and best?
 

Thomas_A

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I has predictably Higher noise and distortion at any frequencies. The fact that SINAD stays put as voltage increase is a bit of a concern no? It requires more digging. Does it means that the noise floor increase at the same rate as the volume? That would be a bit odd and not a good thing, If not it would mean that distortion start to increase as soon as you increase level, from zero. Also odd.
Sure but you are also comparing a 20 year old amp that you can get used for $250-350 vs an amp for $2000-2500. Power is essentially the same, perhaphs better for the Rotel dynamically, and distortion in real use inaudible. If distortion would swing the same pattern as the Purify at a higher base level, it would be bad.
 

Thomas_A

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What is not predictable. You measure you know. What is there to predict? Lower distortion is always a good thing, why bother if it’s changing along better and best?
If distortion would swing the same at a higher base level, it would be bad and perhaps audible. It does not, which is good. Neither of them, as measured, would be audible in practical use. Or?
 

PeteL

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Sure but you are also comparing a 20 year old amp that you can get used for $250-350 vs an amp for $2000-2500. Power is essentially the same, perhaphs better for the Rotel dynamically, and distortion in real use inaudible. If distortion would swing the same pattern as the Purify at a higher base level, it would be bad.
You made this comparison, not me.
 

Thomas_A

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You made this comparison, not me.
Yes I did. If distortion would be 10-20 dB higher for higher frequencies vs power of the Rotel, it would not be good.
 

sarumbear

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If distortion would swing the same at a higher base level, it would be bad and perhaps audible. It does not, which is good. Neither of them, as measured, would be audible in practical use. Or?
Have you looked at the two images I posted???
 

PeteL

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Have you looked at the two images I posted???
You posted 2 different graphs, the lower one is not ventilated with frequencies. I believe the main point of Thomas is the absence of frequency dependencies in THD spec. Which indeed is a bit more of the norm in class AB. It doesn't mean that I don't agree with your main point but let's compare graphs that evaluate the same metrics, else we confuse everything.
 

Thomas_A

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Have you looked at the two images I posted??

You mean this one?


Yes, I looked at that one. The comparison would be to this one of an old Rotel model (980BX this time but 980BX-981-1070 are basically the same with slight modifications over the years):

file.php

Amirs measurements of the RB-1070 is basically flat on the 0.01% line. (Reasons could be aging caps.) Despite that there was no rising distortion vs. frequency when power increased.
 
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restorer-john

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What you say is probably true because you are familiar with and have knowledge of amplifiers, but does it apply to all Rotel amplifier model/ series?

Pretty much. Rotel's basic power amp design has been recycled for a bit over 30 years. More devices, higher voltage- more power. Less devices, lower voltage, low power. Their integrateds are very good, but not 'SOTA'. But then, they know their market and their products are solid and dependable.

I use an early 90s RA-930AX as a test amp on my bench and a RA-970BX for TV sound duties.

A great vintage amp to find selling for peanuts is the ('87-'91) RB-850. Bridgeable into a very powerful little monoblock.

(internet pic)
2525077-5457c47a-rotel-rb-850-dual-mono-power-amplifier.jpg
 
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TimF

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It is possible that some of you specialists will determine that an Audio Alchemy DAC-in-the-box can be bested by a current generation device costing almost nothing. What the hell does 'bested' mean?

From a review of the Audio Alchemy DAC-in-a-box from Gramophone way back in the old days of 2012: "Despite the increasing climate of opinion which denigrates audio measurements and points to their inability to predict or even correlate reliably with the sound quality as heard, I never regard technical testing as a waste of time. At some stage, therefore, before or after the admittedly more meaningful listening sessions, I like to check the makers' specification point by point. Without 'testing to destruction' I can often get a better feel for the unit's ability to stand up to rough handling and the quality of construction and electrical alignment than is possible from mere music listening. There is the added benefit that objective tests can be carried out to international standards on an individual unit in isolation, whereas 'listening' to an amplifier, for example, is only possible when a CD deck or other source and chosen loudspeakers are hooked up, with their own idiosyncrasies. Then there is the effect of the listening room..."

The review, Rachel Cramond is concerned about rough handling.
 
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AdamG

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I will never understand why amps with so much real estate on the back have to put the speaker outputs so close together.
To make our lives miserable I suspect. You could park another amp in that unused real estate on the back. Little Finger from GOT likes it though :cool:
 

restorer-john

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I will never understand why amps with so much real estate on the back have to put the speaker outputs so close together.

It's actually good design. :)

The OV return/CT carries more current than any other single path in the amplifier. It carries the current from both channels combined. Getting that impedance as low as possible is only achievable by placing the common terminals as close to each other and the common Ov/E point. It's even more important with a bridgeable amplifier. This design uses a single CT (centre tapped) secondary, split to two (L/R) rectifiers and filters- one for each channel. Tying them together at 0V is important to preserve performance in BTL.

Also, keeping the path from the output devices to the 'hot' terminals as low impedance as possible is important. They can't be mounted right on the speaker terminals, so they ran solid copper bussbars and the shortest practical high current track paths they could.

1674354058694.png
 

dr0ss

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I have an A12, which is 1 better.

FWIW, I bought the Rotel (which I mainly use as a power amp) over a D amp because I wanted something that will likely still be functioning when I die. I'm pretty confident that the Rotel is that well built. It likely doesn't measure as well as something with Hypex or Purifi modules, but I'm sure I can't hear the difference.
 

Maginness

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I bought a used one of these in 2020. Kinda pandemic working from home fueled upgrade home office system kick I went on. Paired with a set of MnK S150 speakers I really liked the RB-1070. Then the pandemic kept going an I kept going on updating my home office system. The amp is in a box now waiting for future duty. Great performance for dollar value and I didn't want to sell it. Now I want to hook it back up and give it a listen.
 

capslock

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Probably the design with lower loopgain (lower feedback factor). Or CFA ( current feedback amplifier). Maybe intentionally resistor loaded VAS. Separate THD (not THD+N) measurement would reveal more, or spectrum measurements at various power. But, the 5W distortion is too high, I would expect lower distortion from this Rotel amplifier.

Nice to see 3 pairs of power transistors per channel, the SOA will be better than with similarly power rated commercial audio amplifiers, good for reliability.
The service manual is available, e.g. elektrotanya. I see little wrong with it. Symmetric diff amps (i.e. PNP and NPN pairs), VAS, EF3 with tripple output pairs, regular voltage feedback. What I don't like:
- no emitter degeneration on input pairs
- no miller compensation - the VAS is loaded to ground by a cap, there is also a resistor to ground in the schematic, but since no value is stated, it is probably unpopulated
- gain appears awfully low - (1 k + 560) / 560 so about 3x.

I still don't see anything that would result in level-independent distortion. Nor do I see where the high even order distortion comes from. With the symmetric input stage, I would expect cancellation of even orders.
 
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