Rotel RB-1070 Amplifier Review

[laudio]

Sometimes meters are overrated

 

[oldsysop]

Excellent amplifier and best of all, it is not of the infamous class D.
Thanks Amir for review !

 

[Dmitri]

Sometimes meters are overrated

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The PA-7 was originally a Darth Vader “ArtHaus” design. Fun fact…Nakamichi turned the on power led from Vader’s proprietary ”Sinister Red” to the less controversial green shown here to avoid confusion and PTSD flashbacks amongst their customers. ; )

That is one gorgeous piece of eye candy….

 

[D700]

Sometimes meters are overrated

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You found the controls for the tractor beam Obi-Wan

 

[pieterv1]

I recently picked up a Rotel RB-06 to match my RC-06 preamp.

I noticed that the amplifier board actually has 4 spots for the large output transistors that are not populated (so it has 4 per channel instead of 6). The same board is probably used in a different model with more power, even though the RB-06 with its release didn't have a heavier sibling. Maybe the RB-1552 which came out 2 years later? Unfortunately I can't find a service manual of that one.

The topology is very similar to many other Rotels, including this RB-1070 so I'm wondering if maybe I could add these additional transistors. Not sure if it'll just add power or also just better performance/precision, some change in sound...

And maybe the power supply might not be able to handle the extra power. Just veeeeery curious

 

[Martin_320]

Definitely not normal. Whether it is the house wiring or the amp is hard to say.

Maybe that's a characteristic of Rotel high-current amps. My 5-channel RMB-1075 (pictured in post 194 above) makes the lights in my room 'blip' momentarily when I turn that on.

 

[restorer-john]

I recently picked up a Rotel RB-06 to match my RC-06 preamp.

I noticed that the amplifier board actually has 4 spots for the large output transistors that are not populated (so it has 4 per channel instead of 6). The same board is probably used in a different model with more power, even though the RB-06 with its release didn't have a heavier sibling. Maybe the RB-1552 which came out 2 years later? Unfortunately I can't find a service manual of that one.

The topology is very similar to many other Rotels, including this RB-1070 so I'm wondering if maybe I could add these additional transistors. Not sure if it'll just add power or also just better performance/precision, some change in sound...

And maybe the power supply might not be able to handle the extra power. Just veeeeery curious

It's common with many brands to share the power amp board through a few models in a range. Yamaha have done it for decades.

The differences are not just a few extra OPTs. The transformer/s are more capable, higher voltages, the rectifiers are upgraded as are the filter capacitors, along with changes to bias currents and sometimes driver transistors as well. And, the protection circuit values all change as well.

So, just leave the RB-06 the way it is, is my suggestion.

 

[pieterv1]

So just leave the RB-06 the way it is, is my suggestion.

Woops

 

[RenSong]

Maybe that's a characteristic of Rotel high-current amps. My 5-channel RMB-1075 (pictured in post 194 above) makes the lights in my room 'blip' momentarily when I turn that on.

It's super quick but my room light will do it. Hasn't tripped the breaker in months though

 

[AnalogSteph]

Woops

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I always hate it when people whack in these huge crossover film caps in places where they clearly don't belong. It looks silly, not to mention the parasitics - you can even make an amplifier oscillate in some cases. If you must use a film cap, please, get some decent WIMAs or something. MKP4 4.7µ/100V are not outrageously large at least (13 x 24 x 31.5 mm, lead spacing 27.5 mm).

 

[restorer-john]

I always hate it when people whack in these huge crossover film caps in places where they clearly don't belong.

And mucking around with bridge rectifiers. (look at that bodge with the matrix board)

 

[pieterv1]

And mucking around with bridge rectifiers. (look at that bodge with the matrix board)

Maybe some extra context is necessary

I only got this amp 2 weeks ago and most of the mods had already been done by the previous owner, including those rectifier bridges.. Many of the mods I would've never thought of and some I have reverted in the meantime. The diodes are definitely not cheap and they do the job so I'm just going to leave them be. At least the aluminum piece offers some decent cooling. He also had added 2 AC line filters which didn't make any sense to me. One was sticking out at the back and he had also completely changed the wiring around the transformer/power switch...

As for the film caps: he had installed some cheap 600V LCR monsters (see pic). His reasoning was that this capacitor position was in the signal path. I did consider Wima's, but can't install them at this position with their short leads. The smaller 160V Mundorfs, for audio use, seemed like a good compromise. They're not much larger than the 100v Wima's and they have long leads which made them easy to solder (with the necessary isolation on the leads of course)

I must say, when I just received the amp, I was a little disappointed compared to my Quad 405-2 which I had just sold. The Rotel sounded pretty harsh.

I only just finished working on it yesterday. I got rid of the outboard ac filter, did a full recap - this time including the power filter caps and reverted all the wiring to original, according to the service manual.

This is going to sound very cliché, but after all the work it does sound in fact sound remarkably better. It has more body and the harshness has been reduced into nice presence & sparkle. All in all I'm very happy with the way it sounds now so no regrets about the Quad anymore.

I'm still thinking about replacing the small orange pp caps with polystyrenes. Any other suggestions welcome!

!! Old picture of the state I received it in

 

[pieterv1]

I always hate it when people whack in these huge crossover film caps

I see where you're coming from.
See previous comment!

Is there really a disadvantage to using axial PP caps (used mostly in speaker crossovers) instead of PP Wima's apart from physical aspect? I don't hear/measure any oscillation. The caps sit right after the rca input, in the audio path. I can always just revert it to the original electrolytic, but also at work, my colleagues told me it doesn't hurt to have a filmcap at this position.

 

[Joffy1780]

Always loved the look of these big Rotels Brilliant review and, as others have said, Amir has just increased the value of these, no doubt!!

 

[restorer-john]

Is there really a disadvantage to using axial PP caps (used mostly in speaker crossovers) instead of PP Wima's apart from physical aspect?

Due to their size and placement, they can actually pick up noise- moreso than a physically tiny cap mounted on the PCB. The left channel axial PP is sitting right up against the PSU filter cap- I would expect some coupling of ripple noise under load.

Personally, I would return the entire amplifier to stock, measure and determine what, if anything, is on the table for improvement.

 

[pieterv1]

Due to their size and placement, they can actually pick up noise- moreso than a physically tiny cap mounted on the PCB.

Interesting! Thanks for the info!

The left channel axial PP is sitting right up against the PSU filter cap- I would expect some coupling of ripple noise under load.

Are you talking about the picture with the white Mundorfs or the one with the big black film caps standing upright? The mundorfs I got instead, are substantially smaller already.

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When I install the polystyrene capacitors, I'll put back a 4,7uF electrolytic cap as well and try to hear if there's any difference.

 

[cybernaut667]

I got the pre amp RC-995
and I would like to match it with class D purifi through XLR.
Nice phono stage .
It would be good to see some measurements of this

There was some concern about these Rotel models being made in China, however a friend of mine has the RB-991, a more powerful predecessor of this, it still works very well after 20+ years now.

 

[notsodeadlizard]

In the FFT, odd harmonics are much smaller and a beautiful monotonous decline in amplitudes is visible.
If someone is interested in “tube sound”, then this is a completely tube sound, the main thing is not to drive the amplifier into clipping.
It's the right amp.

 

[JktHifi]

I like this amp because no sub-out.

Everything Should Be Made as Simple as Possible, But Not Simpler​

 

[Beave]

I like this amp because no sub-out.

Everything Should Be Made as Simple as Possible, But Not Simpler​

Are there *any* stand-alone two-channel power amplifiers that have subwoofer outputs?