Well ultimately I settled on a not dissimilar answer, too. Though in my case it happens to be by Rotel. I've always liked their build quality and general design, layout etc. and drooled over them in my younger years. So, if nothing else I shall own something that I have quite a fondness for!
I plumped for an RB-970BX, which is a power amp from (I believe) the mid/late 90's. Much simpler and more spacious inside without all the pre-amp gubbins that I don't need,. So I stand a fair chance of being able to maintain and repair such a thing, it has fewer contacts etc to go wrong to begin with, and measures better without an unnecessary pre-amp stage- which overall are the things I wanted.
To begin with I'll probably just look at replacing any old electrolytic capacitors and leave it as is. Maybe add a pair of balanced inputs, but could make an external converter instead. That seems like a level of DIY that I've got time for at the moment, with a fair chance of success, and in total it really shouldn't cost very much at all. I hope to pick it up later in the week 🙂
I plumped for an RB-970BX, which is a power amp from (I believe) the mid/late 90's. Much simpler and more spacious inside without all the pre-amp gubbins that I don't need,. So I stand a fair chance of being able to maintain and repair such a thing, it has fewer contacts etc to go wrong to begin with, and measures better without an unnecessary pre-amp stage- which overall are the things I wanted.
To begin with I'll probably just look at replacing any old electrolytic capacitors and leave it as is. Maybe add a pair of balanced inputs, but could make an external converter instead. That seems like a level of DIY that I've got time for at the moment, with a fair chance of success, and in total it really shouldn't cost very much at all. I hope to pick it up later in the week 🙂
Why would you add additional components to the signal path? Because other Rotel models have these and they look "high end"?
Well, Rotel RMB-1905 has just added an opamp in front of its line input to provide the balanced input - are you convinced that it will bring any benefit with your equipment? Perhaps the balanced output of your active crossovers is also created by an opamp after the line output?
Bottom line is - why complicate things that work?😉
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Mainly because my DAC only has balanced output, and so some kind of conversion is desirable. As such, it might as well be at the power-amp input rather than at the DAC output, since then the (existing) balanced line is maintained for the distance between components. This is simply a practical thing - I don't actually understand why a balanced input might somehow look high-end, it is a perfectly valid method but I don't think of it as unusual or special.
Obviously there are a variety of ways in which the conversion might be done, including simplistic ones like just leaving a pin unhooked. But I've a couple of 'THAT' balanced input boards that could be quite neat, and seem to offer decent quality without the cost of things like transformers.
Obviously there are a variety of ways in which the conversion might be done, including simplistic ones like just leaving a pin unhooked. But I've a couple of 'THAT' balanced input boards that could be quite neat, and seem to offer decent quality without the cost of things like transformers.
It is a Topping DM7. I came into it after my active crossover died, but even then it was more costly than I'd wish. However, it is multi-way so means I can use the source PC instead of needing a physical crossover any more. In the past I've done similar with multi-way sound cards.
I haven't found any technical details of the DM7's outputs, but suspect it'll be like some of their previous products that are known to have rather simplistic output stages (possibly not even truly balanced) that benefit from proper receivers rather than the unhooked-pin method or simple TRS-to-RCA leads.
I haven't found any technical details of the DM7's outputs, but suspect it'll be like some of their previous products that are known to have rather simplistic output stages (possibly not even truly balanced) that benefit from proper receivers rather than the unhooked-pin method or simple TRS-to-RCA leads.
@Kev06
I briefly considered a DM-7 for my system ended up combining my existing MiniDSP SHD via SPDIF/AES with a soon to be modified DCX2496. I am running all balanced connections to my subs and six channels of amplification. The DCX is marginal from a noise standpoint, but livable - your concern about SNR is valid in my experience.
I have a design for a simple balanced to unbalanced converter circuit that might suit your Rotel, if interested I will give you the build information, gerbers, bom, schematic. Send me a PM on the forum if you are interested.
I briefly considered a DM-7 for my system ended up combining my existing MiniDSP SHD via SPDIF/AES with a soon to be modified DCX2496. I am running all balanced connections to my subs and six channels of amplification. The DCX is marginal from a noise standpoint, but livable - your concern about SNR is valid in my experience.
I have a design for a simple balanced to unbalanced converter circuit that might suit your Rotel, if interested I will give you the build information, gerbers, bom, schematic. Send me a PM on the forum if you are interested.
That sounds like a nice setup; your crossover is quite similar to what I had before, and that worked very well. In fact I've still some significant misgivings about changing, it just seemed that as a PC has now become my only source, I might as well make more of its potential and save on extra hardware. Though yes, I have learnt that along with the advantages of an active setup come some challenges, of which noise is one.
The balanced lines you're using also worked well for me. The previous suggestion that they're about looking high-end was quite unexpected; they just seem so mundane. Anyhow, my outputs are now TRS rather than XLR but that doesn't change anything except the connector. I suspect that the DM-7 simply has a balanced topography, as many DACs apparently do (internally speaking), and topping don't add a conversion. But whatever their reasoning, because I want to use this amp with single-ended input, that conversion is down to me instead. I'm quite happy with that because balanced lines to the amp don't seem inappropriate for low noise and a reasonable distance.
Thanks for the offer of the circuit, that is very thoughtful! I shall see how I get on with the THAT boards, since I already have them, but if there is need to build anything I'll be very interested indeed.
Cheers,
Kev
The balanced lines you're using also worked well for me. The previous suggestion that they're about looking high-end was quite unexpected; they just seem so mundane. Anyhow, my outputs are now TRS rather than XLR but that doesn't change anything except the connector. I suspect that the DM-7 simply has a balanced topography, as many DACs apparently do (internally speaking), and topping don't add a conversion. But whatever their reasoning, because I want to use this amp with single-ended input, that conversion is down to me instead. I'm quite happy with that because balanced lines to the amp don't seem inappropriate for low noise and a reasonable distance.
Thanks for the offer of the circuit, that is very thoughtful! I shall see how I get on with the THAT boards, since I already have them, but if there is need to build anything I'll be very interested indeed.
Cheers,
Kev
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Connecting a PC to an audio system can often turn into a noisy nightmare! Ground loops that make you listen to your mouse scroll wheel moving are very common. I think this is why many motherboards are switching back to optical digital out, even though they don't perform as well as wire. In this situation balanced interconnects only makes sense.
THAT1206s work great in this situation, but you need to be very careful how you connect the ground. Pin 1 connects to the chassis of the amp, not audio ground.
THAT1206s work great in this situation, but you need to be very careful how you connect the ground. Pin 1 connects to the chassis of the amp, not audio ground.
It sounds like you are all set... 😀 Meantime my plans have hit a stumbling block. I have a recently purchased 2022 vintage DCX2496 and they shrank the chassis and have done a few other things apparently, my just completed kappaDCX board doesn't physically fit, and with it goes the much needed and planned for upgrade path.
They shrank the 2496? Amazing, it was already pretty cramped. Which way did they shrink? Was 19" thin and pretty shallow depth.
It is either shallower or the DSP board grew, I don't have an older one to compare it to. The box is approximately 19cm (7.5") deep. I have figured out that there is enough room if I mount the DSP board on taller standoffs as there is sufficient clearance height wise.
Yes I've had enormous PC-related noise frustrations in the past, though by far the worst were with an internal sound card (i.e. where the analogue stage was also in the PC). I've also had some trouble with external USB sound-cards and DACs, though a lot comes down to the device itself; some USB DACs and souncards have been massively better than others on exactly the same computer.
The new DM7 seems extremely quiet with a test laptop, so I'm hopeful that it'll remain so when moved to the intended PC. Though there is no certainty; in particular the laptop isn't earthed whilst the PC is, which can make a big difference to some DACs (though it probably shouldn't). The DM7 has no optical input either, presumably because of the multi-channel nature of it, so fingers crossed. But If all else fails I could just use the laptop for music permanently.
Thanks very much for the pointer on the THAT 1206s, they seem like a good method but I've not actually used them before. At least they'll be under my control to implement, so that should help if there are any issues.
Cheers,
Kev
Anyway getting back to the thread, I might also look at improving the amp's speaker protection at some point. I haven't picked up the Rotel as yet so could be wrong, but the schematics suggest it might be quite basic in that respect (and for an active setup there wouldn't even be a passive crossover in the circuit). So some kind of fault/DC blocking seems desirable. Perhaps combined with a delay to block any on/off thumps, if it needs it.
Had this been for a traditional 2-way speaker then it would be easy and cheap to add a protection capacitor to the tweeter at least, for blocking DC and excessively low-frequencies. But here I'm intending a small wideband driver rather than a tweeter, where the crossover point would be quite a lot lower than normal and so require quite a big capacitor, and it wouldn't protect the woofer anyway.
In fact thinking further.. it could also be worth physically attenuating the input level at the amp, such that the source PC/DAC can't push the drivers beyond their mechanical limits (in the event of gremlins etc). I have also found this kind of thing can help with noise, too: turning the amp as low as possible (whilst of course still allowing the source to drive it to the desired SPL & peaks) reduces sensitivity to some kinds of noise from upstream. So, I guess in the absence of a traditional pre-amp, which the power-amp would once have been used with, there could be a few arguments for making a minimal addition to the input (inside or maybe just before the power amp) that might include both the required balanced input/conversion plus a simple attenuator (for use at setup, not as a regular volume control).
Had this been for a traditional 2-way speaker then it would be easy and cheap to add a protection capacitor to the tweeter at least, for blocking DC and excessively low-frequencies. But here I'm intending a small wideband driver rather than a tweeter, where the crossover point would be quite a lot lower than normal and so require quite a big capacitor, and it wouldn't protect the woofer anyway.
In fact thinking further.. it could also be worth physically attenuating the input level at the amp, such that the source PC/DAC can't push the drivers beyond their mechanical limits (in the event of gremlins etc). I have also found this kind of thing can help with noise, too: turning the amp as low as possible (whilst of course still allowing the source to drive it to the desired SPL & peaks) reduces sensitivity to some kinds of noise from upstream. So, I guess in the absence of a traditional pre-amp, which the power-amp would once have been used with, there could be a few arguments for making a minimal addition to the input (inside or maybe just before the power amp) that might include both the required balanced input/conversion plus a simple attenuator (for use at setup, not as a regular volume control).
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Speaker protection relay modules including power on delay are pretty cheap in eBay, Aliexpress etc.
DSP board grew, it appears that this change was made back in 2016, and the simple solution is to use standoffs to raise the DSP PCBA above the edge of the kDCX. We should relinquish the thread back to Kev06 discussion. 😀
Thanks! If they're any good then it would save building something, and likely cost no more. I shall have a look.
Cheers, Kev
I would say that they are pretty useable. You should only check out their schematics - there is probably more than one way to build them.
From my own experience and observations best reliability in most cases you will get with refurbished amp devices older than 40 years, because such of later manufacturing date savings were made more and more (cheap elcaps without screw terminals e. g.).
From the 90s it was quite pronounced, from the 2000s it was extremely pronounced - both in terms of component quality and circuit design quality.
Compare the NAD+Rotel devices from 80s, 90s, 2000s and 2010s, also A+R Cambridge (later TAG-McLarren now Audiolab), Creek, Cambridge Audio, Naim Audio and many more.
Doing the attenuation at source instead at the power amp input isn't a good idea in general - independent of amplifier's age.
A wide range of integrated active crossover networks in active loudspeakers fight with this issue - SNR in low level area isn't good, because the inherent noise of active crossover network (OP-Amp) stages wasn't attenuate with reducing the level at volume control on used preamp. Same situation is to observe in all integrated amplifiers, as long as attenuator resp. volume control potentiometer is located at input of line preamp stage instead at power amp input.