Rotel RB-870BX vs class D (hypex/Purifi…)

[Vincia]

In this forum, I see many knowledgeable people willing to offer advice. I'm taking advantage of this opportunity: I need advice on whether to replace my power amplifier Rotel RB-870BX with a class D (hypex/Purifi…).

Current system (as of 2025)
- Streamer-DAC-Preamp: WiiM Ultra
- Power amp: Rotel RB-870BX (100W; purchased in 1991)
- Speakers: 2 PMC GB1 (tower transmission line; purchased in 2004)
- Subwoofer: KEF Kube 12B

Listening room: approximately 180 m3
Speaker position: near the wall
Listening point: 2.5 m from center of speakers
Level: 75 dB approx
Music genres: classical (50%), jazz, pop
My hearing: I have the normal hearing impairments of a 78-year-old and I don't use hearing aids.


What would I like to improve?
I recently introduced the streamer and the subwoofer (with an 80 Hz crossover) and have done some interesting experiments with WiiM's room correction. Compared to my previous system, listening to symphonic music has improved significantly, as I can now appreciate even full orchestral performances, even if the sound remains a little confusing (before, only small ensembles were satisfactory). I'm wondering if you think listening to symphonic music would improve further if I replaced the old Rotel, and what amplifier (and power) I could use instead.

I have no intention of replacing the speakers (small footprint), which for 20 years have been in a position that makes them acceptable to other family members.

The budget should be no more than €1,000-1,500, staying below that if possible.

Thank you.

 

[voodooless]

Assuming the amp performs still within spec, a new amp will likely not bring any sonic improvements. Now the amp is 35 years old, so likely some of the caps will be out of spec. This might degrade performance and be actually audible. The device should be inspected to find out.

Within your budget there are plenty of amps with modules from Hypex, Purifi or 3E audio, among others. Availability of specific models will depend on your location.

 

[Vincia]

What should I pay attention to: power, current, damping factor? I would like to remove that confusion that there is when the whole orchestra plays. Can old capacitors be responsible?

 

[Cote Dazur]

Changing the amp will not bring any improvement. The Rotel is all you need. That was easy.
What is not easy is to reproduce symphonic music in a room.
What you hear is due to your room, not your system. You want to keep your speakers, that is fair, but the solution to your problem is most likely due in great part to where the are positioned in that room at the moment.
Please share a picture of your set up and a simple drawing of the floor plan.
The good news is, it will probably cost you nothing to get a better symphonic music experience.
The bad news is that the solution might need you to convince your family that change is a good thing.

Congratulation on your great opening post, concise yet very detailed and precise.

 

[VMAT4]

Here's a amp that matches the look of your WiiM Ultra Preamp, IOM Brick Stereo 250W. Of course the WiiM Vibelink amp matches the WiiM Ultra as well.

 

[melomane13]

I recently introduced the streamer and the subwoofer (with an 80 Hz crossover) and have done some interesting experiments with WiiM's room correction. Compared to my previous system, listening to symphonic music has improved significantly, as I can now appreciate even full orchestral performances, even if the sound remains a little confusing (before, only small ensembles were satisfactory). I'm wondering if you think listening to symphonic music would improve further if I replaced the old Rotel, and what amplifier (and power) I could use instead.

I would be rather cautious about replacing the amplifier at this point.

With the subwoofer crossed over at 80 Hz, the power requirements for the main amplifier are actually significantly reduced. The amplifier no longer has to deliver the large amounts of power required for the lowest frequencies, and the main speakers — including their midrange drivers — are also relieved of some of that workload. This should improve their dynamic capability and reduce distortion.

Unless the Rotel is actually performing outside its specifications due to age or a fault, I don't think replacing it with a more powerful amplifier would bring any significant advantage. It is already powerful enough for the PMC GB1s, especially with the 80 Hz high-pass filtering.

My suspicion is therefore that the system may simply be reaching one of its limits. The remaining slight congestion with a full orchestra could be coming from the speakers, their dynamic limitations, room interaction, or distortion increasing at high listening levels, rather than from insufficient amplifier power.

Before changing the amplifier, I would therefore try to establish whether the Rotel is still operating within its original specifications.

 

[Vincia]

Changing the amp will not bring any improvement. The Rotel is all you need. That was easy.
What is not easy is to reproduce symphonic music in a room.
What you hear is due to your room, not your system. You want to keep your speakers, that is fair, but the solution to your problem is most likely due in great part to where the are positioned in that room at the moment.
Please share a picture of your set up and a simple drawing of the floor plan.
The good news is, it will probably cost you nothing to get a better symphonic music experience.
The bad news is that the solution might need you to convince your family that change is a good thing.

Congratulation on your great opening post, concise yet very detailed and precise.

Thank you. However, the room is very irregular to be able to easily represent it and in any case the position of the speakers allows everyone to enjoy the view to the outside while we listen. I like it too. The issue is that I had a great benefit by inserting two new components without intervening in the room and therefore I wonder if I can expect improvements by changing the final amplifier. However, I will do more precise tests with the Wiim correction; I believe that even correcting the response curve I could benefit.

 

[Matt_Holland]

In this forum, I see many knowledgeable people willing to offer advice. I'm taking advantage of this opportunity: I need advice on whether to replace my power amplifier Rotel RB-870BX with a class D (hypex/Purifi…).

Current system (as of 2025)
- Streamer-DAC-Preamp: WiiM Ultra
- Power amp: Rotel RB-870BX (100W; purchased in 1991)
- Speakers: 2 PMC GB1 (tower transmission line; purchased in 2004)
- Subwoofer: KEF Kube 12B

Listening room: approximately 180 m3
Speaker position: near the wall
Listening point: 2.5 m from center of speakers
Level: 75 dB approx
Music genres: classical (50%), jazz, pop
My hearing: I have the normal hearing impairments of a 78-year-old and I don't use hearing aids.


What would I like to improve?
I recently introduced the streamer and the subwoofer (with an 80 Hz crossover) and have done some interesting experiments with WiiM's room correction. Compared to my previous system, listening to symphonic music has improved significantly, as I can now appreciate even full orchestral performances, even if the sound remains a little confusing (before, only small ensembles were satisfactory). I'm wondering if you think listening to symphonic music would improve further if I replaced the old Rotel, and what amplifier (and power) I could use instead.

I have no intention of replacing the speakers (small footprint), which for 20 years have been in a position that makes them acceptable to other family members.

The budget should be no more than €1,000-1,500, staying below that if possible.

Thank you.

I’m afraid I have to agree with previous comments that the limitation are with the speakers, likely due to innate resonances, non-linear frequency response, directivity (and very common trait with PMC, I’m sorry to say) and inter modulation distortion due to 2-way speaker limitations.

Keeping a similar form factor to your PMCs would you consider the active Buchardt A700LE which can be controlled directly from your Wiim Ultra. These are 3-way speakers and are extremely well engineered. You may not need your sub with them, but you would certainly be able to cross the sub much lower than 80Hz and this could give you even better room Intergration and very very low distortion which is so important for symphonic music.

There is a link to a detailed review and forum discussion here: CLICK

I know this is an expensive option but I wanted to try and get you to consider the speaker upgrade option as it will give you what you want in terms of sound quality improvements.

At a lower price point, I can highly recommend the KEF Q7 Meta which is also a 3-way speaker and a fairly slim cabinet. It has a very neutral and smooth sound with incredible detail and can also handle low bass very well. They would match you sub well, although, again, I would cross them lower than 80Hz.

I hope this is food for thought.

 

[Cote Dazur]

I will do more precise tests with the Wiim correction;

I agree with you on that, when speaker cannot be moved, then this is a great alternative, pursuing the same goal of taming the bad influence of the room.
Are you sitting with the back of the seat against a bare wall?

 

[Matt_Holland]

I believe that even correcting the response curve I could benefit.

I agree this would be a good starting point. Allow the Wiim room correction to work at all frequencies rather than the usually recommended lower mid-range and bass frequencies

 

[Vincia]

I would be rather cautious about replacing the amplifier at this point.

With the subwoofer crossed over at 80 Hz, the power requirements for the main amplifier are actually significantly reduced. The amplifier no longer has to deliver the large amounts of power required for the lowest frequencies, and the main speakers — including their midrange drivers — are also relieved of some of that workload. This should improve their dynamic capability and reduce distortion.

Unless the Rotel is actually performing outside its specifications due to age or a fault, I don't think replacing it with a more powerful amplifier would bring any significant advantage. It is already powerful enough for the PMC GB1s, especially with the 80 Hz high-pass filtering.

My suspicion is therefore that the system may simply be reaching one of its limits. The remaining slight congestion with a full orchestra could be coming from the speakers, their dynamic limitations, room interaction, or distortion increasing at high listening levels, rather than from insufficient amplifier power.

Before changing the amplifier, I would therefore try to establish whether the Rotel is still operating within its original specifications.

I agree with you that the system (speakers, room,...) may have reached its limits. For the amplifier I don’t think about power, but about dynamics and damping, aspects of which I have no practical experience. Do you have any suggestions on how to check the functionality of the Rotel?

 

[Matt_Holland]

I agree this would be a good starting point. Allow the Wiim room correction to work at all frequencies rather than the usually recommended lower mid-range and bass frequencies

Just to add to this: it’s possible the PMC will benefit from anechoic correction at mid and high frequencies. PMC are usually tuned with a very Hot treble and this can result in impressive imaging and perceived detail recovery, but the downside is inconsistency and listening fatigue particularly during dense, dynamic passages

 

[Vincia]

Assuming the amp performs still within spec, a new amp will likely not bring any sonic improvements. Now the amp is 35 years old, so likely some of the caps will be out of spec. This might degrade performance and be actually audible. The device should be inspected to find out.

Within your budget there are plenty of amps with modules from Hypex, Purifi or 3E audio, among others. Availability of specific models will depend on your location.

I appreciate your answer: capacitors, now very old, could affect the sound quality. I should have the replacement done by a specialized laboratory as I am not capable. This has a cost and in addition I could find myself a poorly done job. For the power I need, I see that the prices, even if higher than a repair, could be affordable. However, I would not like to choose a product worse than the Rotel to replace.

 

[Vincia]

Just to add to this: it’s possible the PMC will benefit from anechoic correction at mid and high frequencies. PMC are usually tuned with a very Hot treble and this can result in impressive imaging and perceived detail recovery, but the downside is inconsistency and listening fatigue particularly during dense, dynamic passages

I really like the image and the detail that the PMCs return. However, it is possible that there is the downside that you say. Please, what do you mean by ‘anechoic correction’? Is it something different from the ‘room correction’ that I can do with Wiim?

 

[Vincia]

I agree with you on that, when speaker cannot be moved, then this is a great alternative, pursuing the same goal of taming the bad influence of the room.
Are you sitting with the back of the seat against a bare wall?

No. There are 3 meters behind me at least.

 

[VMAT4]

The Buchardt Audio Anniversary 10 looks interesting as well.

 

[Matt_Holland]

I really like the image and the detail that the PMCs return. However, it is possible that there is the downside that you say. Please, what do you mean by ‘anechoic correction’? Is it something different from the ‘room correction’ that I can do with Wiim?

Anechoic correction means correcting the speaker’s frequency response without the contribution from the room. Usually this is done on-axis from at least 1m, usually 2m or more. The problem though is that you need a reflection free zone to accurately measure lower frequencies. Not an easy task for you but might be worth trying a measurement from 1m with just one speaker connected to see how smooth the response is.

 

[Vincia]

Anechoic correction means correcting the speaker’s frequency response without the contribution from the room. Usually this is done on-axis from at least 1m, usually 2m or more. The problem though is that you need a reflection free zone to accurately measure lower frequencies. Not an easy task for you but might be worth trying a measurement from 1m with just one speaker connected to see how smooth the response is.

food for thought

 

[Spkrdctr]

Those are 22 year old speakers. Sometimes 22 year old speakers are perfectly fine, other times the crossovers need to be recapped. If the amp is functional than it is fine. Using correction is the best thing you can do. I would also listen to one speaker at a time and see how they sound. If they both sound great then you are good to go. Good Luck!

 

[melomane13]

Je suis d'accord avec vous, le système (enceintes, pièce, etc.) a peut-être atteint ses limites. Concernant l'amplificateur, je ne pense pas à la puissance, mais plutôt à la dynamique et à l'amortissement, aspects que je ne maîtrise pas. Auriez-vous des suggestions pour vérifier le bon fonctionnement du Rotel ?

Que signifie « dynamique » ? Un amplificateur se définit essentiellement par sa puissance de sortie (quelle que soit l'impédance de charge), son bruit de fond et la linéarité de sa réponse. Quant au facteur d'amortissement, tous les amplificateurs modernes offrent des performances satisfaisantes à cet égard. Si votre ancien Rotel présente un défaut (ce qui n'est pas certain), il s'agit probablement d'un problème d'alimentation.

Puisque vous ne pouvez pas mesurer l'amplificateur vous-même, vous pourriez en emprunter un à un ami pour le testeur, ou en acheter un neuf, le testeur, puis le retourner ou revendre le Rotel. Votre Rotel pourrait se vendre environ 400 €. Par exemple, voici un amplificateur nettement plus puissant que votre Rotel et offrant d'excellentes performances. D'autres modèles affichent de meilleures performances, mais les différences sont inaudibles. https://www.audiosciencereview.com/forum/index.php?threads/audiophonics-mpa-s250nc-amp-review.45306/ 471 € 250 W