Rotel RHB-10 : New life of my "Michi Kokoro"

[Martynka]

Hi,

I like hard and heavy speakers, I had in my system many of big Infinity like RS2.5, RS2B, Kappa 9, Kappa 8, Kappa 7, Re90 and many other. Now I have first Martin CLS with first "crossover". All of this speakers need strong power supply, all eats ampers.

I had tried Yamas like old M2, biamped M4 strongest MX10000, Krell's, Accupase's, Nakamichi.... and more. Now I discovered this:

Rotel RHB-10... it's Rotel only in name, inside no budget construction, zero compromises, zero "steryle sounds" like from Rotel. I bought it for try. I need something strong to play with my hungry for current CLS.

First I opened it:



Really good construction, full dual mono, two 1kVA transformers, two PCBs with rectifier circuits, capacitors in all circuits are oversized NIchicon GreatSupply and Rubycon BlackGate, good copper grounds. I check DC-offset and regulated bias and connected to my system.



Sounds in "Japan style", high tones and mids were great with little leak of bass. It's completely opposite my Krell but if you have electrostatic or ribbon speaker high and mids are like miracle and you need more and more. I decide to use "Michi Kokoro" in my main system....

... but like all my parts in perfect conditions:

I dissasembly power amplifier and decide to change all caps, maybe about BG I will decide after measure with RLC bridge

 

[Martynka]

All Sanken transistors were checked ( eight per side)



and I was very surprissed. All had almost the same Beta, like I meassured still one transistor not all.









I was shocked. All sixteen like one.

Capacitors look good but I left only BG, rest were chenged.

In a rectifying system I replaced GreatSupply 6800uF with 10000uF Mundorf M-Lytics





I put 1500uF M-Lytic in place old 1000uF





after assembly all to one and checked that Rotel still play I changed main power caps too.

Big GreatSupply 22000uF



were measured it electrically and with dimmensions. I needed to know what biggest caps I can put inside. I decided to use 4 x 39000 uF Nippon caps.

 

[Martynka]

Last part was outside, behind front panel. All caps in protection layout are new



All relays were in the same good conditions, need only to be clean



New look inside:



In the meantime, I also took care of the visual side of the amplifier.

I have black and wooden part in my system - Michi is silver with red side ( Kokoro means heart ). I decide to changed it... like in The Rolling Stones song " I see a red door And I want it painted black No colors anymore I want them to turn black "

Front goes for new varnish



and I prepare new side... from natural oak

 

[Martynka]

I finished all work and it was one off the best audio surprice. All mids and highs are still on the place but with more details, really clear and analytics but without blood from ears. Bass start to be heard. Very strong wide bass, stronger than Krell. I tried to turn off Rotel via protection listenning CLS and Infinity but no way. Can play with under 1 ohm impedance with full power without problems !!! I checked protection one more time and raelly work maybe my speaker start to be not that hard. I connected Nakamichi PA-7 and in 1/3 of power start blinking overload, turn pre further to 1/2 and Nak stop plays. It's not problems with protection or speakers but incredible good construction of Rotel RHB-10. Rest of parameters are the same good.

After 2 weeks played without front a pick up it from painting.



try with oak parts



and put it on place:

 

[Martynka]

And here is close up for my RHB-10 (at beginig and end of video )

 

[Ds2000]

You upped the inrush diodes value for the bigger mains caps, yes?

 

[Martynka]

You upped the inrush diodes value for the bigger mains caps, yes?

No, in this Rotel everything is oversized. Main power supply voltage is about 65V, main capacitors are rated 100V, diode briges are BR154: 400V DC, 280Vrms and
Peak Forward Surge Current 300A , Average Forward Rectified Current 15A.

15A average with this voltage give me about 1000VA, the same are transformers value and 300A peak is enough to protect BR with even bigger caps.

Do you think that I need to change it ?? In my opinion, no.

 

[Ds2000]

No, in this Rotel everything is oversized. Main power supply voltage is about 65V, main capacitors are rated 100V, diode briges are BR154: 400V DC, 280Vrms and
Peak Forward Surge Current 300A , Average Forward Rectified Current 15A.

15A average with this voltage give me about 1000VA, the same are transformers value and 300A peak is enough to protect BR with even bigger caps.

Do you think that I need to change it ?? In my opinion, no.

Maybe not in this one. I had this amplifier back when it was only about 9 years old, along with the active preamp.
I mentioned because it is often considered good practice to up the rating on those when going above 10% higher mains cap value.

 

[Martynka]

good practice to up the rating

I was surprised with all parts inside. I renewed few Luxman and Accuphase constructions and always voltage rating on caps was to low to safetly work in Europe. Always works few volts above limit ( 66 V in 63 V limit line , 74 V in 71 V line, etc ). The same with diodes ratings almost on limit. Here all limits are much higher.

I should have 230V AC but with fuc.... photovoltaic instalation all around in sunny day I have about 250 - 250 V AC in line and this measured about 65 V on main in Rotel is in this worster AC condition, today ( cloudy winter weather) is few volts lower inside RHB10.

 

[technic11]

Hello , How is the sound quality of the sound lets say in comparison to the RB 990 BX amps they made before ? is this amplifier similar sounding or much more musical ?

 

[Martynka]

in comparison to the RB 990 BX amps they made before

You need to know that RHB10 is not like Rotel. Rotel is only on plate. Zero sterile sound - pure melody and harmony.

 

[technic11]

How are the matching preamps in terms of quality ? have you tried them ? Or the amplifier is magical only unit not the matching preamp ? thank you

 

[KiM3Ce]

Congratulations on your project! I had the RHT-10 tuner and it was very good!

 

[Martynka]

have you tried them

Yes, I tried and... stay with my Restek Vector. RHA-10 sounds like standard RC-9xx.

 

[ALEXND]

Hello, please tell me where did you buy the NIPPON capacitors? Can't find them for sale.

 

[Martynka]

where did you buy the NIPPON capacitors

Schraub Elko Kondensator Radial 39000µF 80V 85°C E36D800HPN393MDA5U d63,5x105mm 39000uF | IT-005045

www.it-tronics.de

 

[ALEXND]

Thank you. In general, I have a problem with RHB 10 - I turned off the power, and now it does not turn on. Fuses are intact.

 

[Martynka]

Thank you. In general, I have a problem with RHB 10 - I turned off the power, and now it does not turn on. Fuses are intact.

You need to check Power On button. Check PCB for crack or burnt PIN. I have the same in my RHB-10 few months ago.



I cleaned it and re-solder

 

[ALEXND]

Good time! Modified his Rotel RHB 10. He is now the same in oak.)))

 

[Spacebulb]

No, in this Rotel everything is oversized. Main power supply voltage is about 65V, main capacitors are rated 100V, diode briges are BR154: 400V DC, 280Vrms and
Peak Forward Surge Current 300A , Average Forward Rectified Current 15A.

15A average with this voltage give me about 1000VA, the same are transformers value and 300A peak is enough to protect BR with even bigger caps.

Do you think that I need to change it ?? In my opinion, no.

This is a beautiful thread, congrats on your amazing work! I have recently acquired one of these amps, and i noticed there is slight hum coming from the amplifier which also can be heard in the speakers. Just wondering if that's considered normal or if that means i should have the amp checked out? Would appreciate any advice, since clearly you are the master! Incredible work you've done here, thanks for sharing.