Has anyone (besides me) thought to remove or bypass the dolby and DSP pre-amplifiers in a surround sound receiver and instead use the power amplifiers with active crossovers? I’ve noticed that I can buy good quality dolby digital surround sound 5.1 and 7.1 receivers for really cheap, … really . cheap. Currently I only use them for stereo, ignoring 3-5 100W channels, it would be nice to put the robust power supplies and amplifiers of significant output to good use.
So before I get to buying a stack of Sony receivers, are there receivers that would be easier to modify? I have a Sony STR-DG510 that seems perfect for modifying because it’s easy to see where the computers control everything and where they can be removed from the circuitry.
I realize this is starting with mid-fi at best, but it can be quite good if the noisy digital parts are removed and the power supply is modded.
So before I get to buying a stack of Sony receivers, are there receivers that would be easier to modify? I have a Sony STR-DG510 that seems perfect for modifying because it’s easy to see where the computers control everything and where they can be removed from the circuitry.
I realize this is starting with mid-fi at best, but it can be quite good if the noisy digital parts are removed and the power supply is modded.
If you notice carefully, the receiver has >100W with low THD only when driven 2ch. Putting in a decent headroom, that gives you about 70W stereo. In other words, all 5 channels are not really 100W if low THD is a requirement. The power supply is not that great either.
However, this is true of most AVRs irrespective of brand.
https://www.diyaudio.com/community/threads/beetlejuice-speakers.409269/post-7603091
Yes, check the picture above 😊,
I have Rotel rsx-1055 (paid 20euro) and Sony str-dg700 (paid 10euro for it 😂).
Rotel is much easier, has dedicated power Amp board and fully discrete amps made of very fine parts. These are fine high gain- feedback amps on their own.
Sony Amp board is however mixed on main board, amps are UPC xxxx chip drivers and outputs are darlingtons. Difficult to segregate power amps from rest, and then amps are much lesser than in rotel case.
Yes, check the picture above 😊,
I have Rotel rsx-1055 (paid 20euro) and Sony str-dg700 (paid 10euro for it 😂).
Rotel is much easier, has dedicated power Amp board and fully discrete amps made of very fine parts. These are fine high gain- feedback amps on their own.
Sony Amp board is however mixed on main board, amps are UPC xxxx chip drivers and outputs are darlingtons. Difficult to segregate power amps from rest, and then amps are much lesser than in rotel case.
For the purpose of listening to music, most avrs are pretty junk. They will certainly play music but won't do well compared to any decent stereo amp.
I like to take a different approach and get cheap and or faulty avrs for anything I can salvage.
Rectifiers, transistors, caps, resistors, heatsinks, power transformers etc.
Even chassis.
Chassis + heatsink + transformer is the bulk of the cost of a build. Get that for next to nothing and your build costs a heck of a lot less.
I like to take a different approach and get cheap and or faulty avrs for anything I can salvage.
Rectifiers, transistors, caps, resistors, heatsinks, power transformers etc.
Even chassis.
Chassis + heatsink + transformer is the bulk of the cost of a build. Get that for next to nothing and your build costs a heck of a lot less.
I am currently doing such a repurpose of my Yamaha RXV1700 and would advice against starting this kind of conversion. I got my AVR for free so thought it would be a nice use of 6 of the 7 channels for my active speaker setup. As I have no interest in home theather I startet dissecting the thing. One of the problems is you quickly strip away all protection and control circuits, so I had to make all that from scratch, including new speaker output relays with delay, DC-protection, over-current protection etc. Next issue is input stage, wich tends to be a part of other circuits wich also was stripped away. Power amp board might not be suitable to directly accept input from a external preamp or DAC, so you might need a custom made input stage as well. This is where I am at now, about to start making 6 channel balanced input board to complete this build.
All this work for a (as pointed out by others) kind of mediocre sounding amplifier. I am concidering if I should finish this franken-amp or just reuse whatever parts usable and build a DIY amp with PCB's from some proven design
All this work for a (as pointed out by others) kind of mediocre sounding amplifier. I am concidering if I should finish this franken-amp or just reuse whatever parts usable and build a DIY amp with PCB's from some proven design
Hi,
I agree very much with previous 2 posts, but with reservation. Indeed most of old AVR are not worth spending time. I also opened quickly few models from Denon, Yamaha and Onkyo, all power amps were STK hybrids or worse. Even chassis + heat sink + PS were so poor that it does not make any sense to spend 5 minutes on them.
Comparing to those, Sony model I have and mentioned above is very good, but still not worth any effort I think.
All these AVR's costed new in 200 to 300 euro range!
But where is reservation, models like Rotel rsx-1055 costed new 1,200 Euros, this is still mid- class and there are much better models to look for, still could be cheap.
Below is circuit diagram and PCB of that Rotel; full of very good transistors that are often not obtainable for us as DIY-ers. PCB is completely dedicated to power amps and easily disconnected together with decent heat sink. It also has only one protection connection that needs to be enabled to bypass protection circuit that's on another board, easy enough.
The amp schematic is four stage; LTP + LTP+ VAS + Output, probably one stage too much for our liking, but than again it is good built, good transistors, good PS and chassis, worth 20 euro I paid for it for sure if you keep amp PCB or just cannibalize it.
So my bottom line would be not to look at budget range of old AVR's but in higher (when new) price range, and than check service manual for details before buying.
If you look for units marketed "no remote" , " not working" or "for parts and repair", im sure shipping costs will be more expensive than unit itself.
Cheers,
Drazen
I agree very much with previous 2 posts, but with reservation. Indeed most of old AVR are not worth spending time. I also opened quickly few models from Denon, Yamaha and Onkyo, all power amps were STK hybrids or worse. Even chassis + heat sink + PS were so poor that it does not make any sense to spend 5 minutes on them.
Comparing to those, Sony model I have and mentioned above is very good, but still not worth any effort I think.
All these AVR's costed new in 200 to 300 euro range!
But where is reservation, models like Rotel rsx-1055 costed new 1,200 Euros, this is still mid- class and there are much better models to look for, still could be cheap.
Below is circuit diagram and PCB of that Rotel; full of very good transistors that are often not obtainable for us as DIY-ers. PCB is completely dedicated to power amps and easily disconnected together with decent heat sink. It also has only one protection connection that needs to be enabled to bypass protection circuit that's on another board, easy enough.
The amp schematic is four stage; LTP + LTP+ VAS + Output, probably one stage too much for our liking, but than again it is good built, good transistors, good PS and chassis, worth 20 euro I paid for it for sure if you keep amp PCB or just cannibalize it.
So my bottom line would be not to look at budget range of old AVR's but in higher (when new) price range, and than check service manual for details before buying.
If you look for units marketed "no remote" , " not working" or "for parts and repair", im sure shipping costs will be more expensive than unit itself.
Cheers,
Drazen
Off course there are some AVR's more worth considering than others. The Yamaha RXV has similar design as the example above, with dedicated PA-pcb built with discrete devices. I think it was in the 1000-1200€ category around 2011. I also have a cheap Denon AVR which is absolutely not worth any work. Darlington OP devices and typical low-end mass production solutions.
I still believe it's better advice to build something from scratch than to modify existing products. It is a really good learning experience though. Being a very time consuming project, I've almost finished reading Doug Self's Amplifier book parallell to this, and that's been a great help looking more realistic on these things
Here's Yamaha RXV schematic
I still believe it's better advice to build something from scratch than to modify existing products. It is a really good learning experience though. Being a very time consuming project, I've almost finished reading Doug Self's Amplifier book parallell to this, and that's been a great help looking more realistic on these things
Here's Yamaha RXV schematic
Attachments
Hi,
Here I wrote one line about rebuilding existing (not build from scratch) 6 channel pro PA amp to something more hifi. https://www.diyaudio.com/community/threads/beetlejuice-speakers.409269/post-7635793
Schematics of this amp is very good, and reproduction is more than fine, but not negligible cost and a lot of working hours.
What Arthur is thinking off is faster and much cheaper way of getting to the goodies of active speakers and start enjoying, there is a lot of the time afterwards to replace one stereo amp pair after another, with perfect amps of choice.
A friend of mine (not DIY-er) is freak on Naim - Linn vintage equipment, he wants to convert Linn Isobarik's to full active but only with Naim amps, he has active Linn XO, but it has been over one year and he still did not buy another 2 Naim stereo amps, neither he cut and open speakers to accept 6 wires.
Going for perfection sometimes lets you just wait with nothing, and we don't live forever 🙂
Here I wrote one line about rebuilding existing (not build from scratch) 6 channel pro PA amp to something more hifi. https://www.diyaudio.com/community/threads/beetlejuice-speakers.409269/post-7635793
Schematics of this amp is very good, and reproduction is more than fine, but not negligible cost and a lot of working hours.
What Arthur is thinking off is faster and much cheaper way of getting to the goodies of active speakers and start enjoying, there is a lot of the time afterwards to replace one stereo amp pair after another, with perfect amps of choice.
A friend of mine (not DIY-er) is freak on Naim - Linn vintage equipment, he wants to convert Linn Isobarik's to full active but only with Naim amps, he has active Linn XO, but it has been over one year and he still did not buy another 2 Naim stereo amps, neither he cut and open speakers to accept 6 wires.
Going for perfection sometimes lets you just wait with nothing, and we don't live forever 🙂
Words to live by right there🙂 On that note, I used my Yamaha amp for some time as a normal AVR with SE inputs in direct mode, bypassing internal DSP and such. Then i got myself a 8 channel DAC with balanced outputs so ideas started to take form. Somethimes (or often) some hind-sight or what it's called tells you something was perhaps not worth investment in time, and also what seems like a cheap and easy way to something good becomes quite expensive.
Indeed this RXV1700 is actually not that bad, and is the reason for trying to convert it. My THD and noise measurements are not all bad. But there is some room for improvement, and some issues that is not so easy to fix. One thing worth knowing is grounding and earthing. These amps often are class 2 compliant, and when gutting all that extra stuff from the chassis it seems more sensible as a DIY'er to convert to class 1. That is not as easy as one would think, in regards to hum and buzz. Grounding scheme in these units are mostly quite complex. Amplifier decoupling and PSSR is not designed for a easy convertsion.
I agree to this, and whole post, that PA amp that I rebuilt is is Class1 and is now better than Rotel (Class2 safety).
What I think is reasonable to do, if unit specific design is allowing it, is:
Disconnect line audio input of power amps
Cut out 7.1 (or whatever) aux input RCA jacks from the rest of the world
Now connect those 2 (aux inputs with power amp input) by small coax cables
Check if it works?
If yes, check if there is amplifier-speaker protection circuit on any another PC board, and if yes or bypass it or figure out how to keep it. This is circuit dependent, on my Rotel example, there is just one pin that needs to be enabled (bias pin)
Now one can start removing unwanted components, first disconnect PS from boards you to not need, cheek if amp works, and if yes, out with that board, one by one.
Must emphasize this again, the donor unit must be ok for this, and if all ok and thought through by checking guts an service manual over coffee, in one afternoon we have decent multi channel PA 🙂
Like this we did not touch safety schematics of the unit, it can stay as is, Class2. Of course I agree it would be better to redo PS , but I'm talking quickest way to result.
Looks like you had good success with your PA project there, but I also see you commented in the end that it's not recommended 🙂
I think your "check-list" approach in last post is the right way to do it. I went the other route, just ripping all the boards other than power amp and psu.
This was after spending much time studying service manual, and concluded there was too many dependent and intertvined circuits to keep any of it.
I can totally understand OP's question though, as there is not many multichannel power amps available which is not either expensive or has poor performance. Second hand market is not full of alternatives either
Multichannel AV amps? No, thanks, not for me. Some time ago I needed 2* 5 channels of Audio in order to testwise set up a stereo pair of 5-way dipole Horbach-Keele arrays. At first I indeed was intutively tempted to resort to two of these multichannel AV amps, one for each channel. Digging more deeply into the specs, the schematics and the physical layouts of some of these consumer multichannel boxes, I quickly discarded this idea. Look e.g. at the mostly underrated or at best strict-minimum-rated power supplies and heatsinks, the crowded layout and the like. Yuck! I instead went for six similar Yamaha stereo amplifiers. Second-hand and over some few weeks I found 2xAX590, 1xAX592, 2xAX870 and 1xAX890 amps which gracefully did the job straight away, without any further mods needed.
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I do that a lot. Unfortunately, many manufacturers of inexpensive equipment are going the way of the laptop computer and using plastic with conductive paint for shielding. I generally buy 20 year old mid-fi equipment that has mostly soldered parts, good cases, and robust power supplies. I‘m putting a Le Monstre in my old Oppo‘s case.
This is what I was thinking of doing, plus upgrading some parts, and hopefully not end up polishing a turd.
I frequent Goodwill looking for parts and tools and occasionally come across a nice amp. A few of them actually have good specs, granted not up to modern hi-fi but good enough for listening and experimenting and they are much better than the average over hyped Panasonic.
The key is, as you stated, separating the digital from the analog. The Sony I have has everything on separate boards, which has me thinking it won’t be too difficult to turn it into a four channel amp.
It just kills me to see all of that technology headed to the landfill. It all started when stereo replaced mono and two channel came out, then quadrophonic, then back to stereo, then Dolby, Dolby 5.1, 7.1, 9.2, …
Also, guys this is diyaudio not superduperhifithatImadeallbymyselfaudio.
Good point. I’ve thought about beefing up the power supply, but maybe it would need several! If two or more are needed it’s probably best to make several amplifiers instead.
I think a lot of the distortion and noise can be eliminated by bypassing or removing the digital components. In the receiver I have there are two power supplies, one big 80V one for the power amps and one small 20V one for the preamp/computers.
One thing I discovered in every one of my surround amps is the bypass for pure stereo doesn’t really bypass anything. The analog signal still goes through an A-D conversion then D-A before the power amps.
This comment probably killed my experiment dead. 😢
I like the link, that’s a nice system you have!
Also, it’s cheaper and faster to buy three AV receivers. Heck, I don’t think I’d spend $150.
About the specs showing low distortion with two channels but not all, I don't necessarily see the issue if the plan is to drive say a 3-way active speaker. Channels feeding tweeters and maybe small mids will not be as power-hungry and total power needed probably won't be any more than two channels driving "normal" speakers.In some cases even less if complex load with passive xo is hard on amp. There is a calculated frequency where power needs are split 50/50 high and low, and I think it is around 300Hz for traditional systems
HiFi world magazine did a group test of some integrated amps, but threw in a multi channel AV amp (Onkyo I think), and the AV amp held it's own. I presume that an AV amp would be useless without the remote, so they could be a bargain - even if they couldn't be used, it would be worth it just for all of the sockets and speaker terminal posts around the Back. One advantage would be the same amp used for all frequencies, so there's be consistency.