hello, i have an old rotel rb 930ax and looking for what i can do to it for upgrades if someone has already done a few. looking to get more depth and richness out of it
That's not easy... they are cold-ish-sounding amps... very flat as well.
I had good results (RA-820BX4) when I replaced the voltage rail filter caps with Nichicons; I also replaced the bridge rectifier with discrete fast-switching soft recovery diodes.
You could use Elna Silmic II... the biggest caps you can fit.
.... you could go completely nutzzzz...if you do not have better things to do... lift the input signal tracks off the PCB (cut them at either end), and use silver ribbons, annealed instead... that would bring a big difference.
I also re-wired the primary transformer winding... I cheated.... but I also placed the driver transitions on the little heatsink! ... and was getting 90W at 6 ohms at the onset of clipping, from that little amp 🙂. I demoed it to a few of my friends... and had to resist the onslaught of offers to sell it...
HOWEVER, even moded, it can not come even remotely close to the sound of a two-gain stage, single-ended pure class A amp... like a few you can get the parts for in Pass forums/DIY Store (FW clones)....
I had good results (RA-820BX4) when I replaced the voltage rail filter caps with Nichicons; I also replaced the bridge rectifier with discrete fast-switching soft recovery diodes.
You could use Elna Silmic II... the biggest caps you can fit.
.... you could go completely nutzzzz...if you do not have better things to do... lift the input signal tracks off the PCB (cut them at either end), and use silver ribbons, annealed instead... that would bring a big difference.
I also re-wired the primary transformer winding... I cheated.... but I also placed the driver transitions on the little heatsink! ... and was getting 90W at 6 ohms at the onset of clipping, from that little amp 🙂. I demoed it to a few of my friends... and had to resist the onslaught of offers to sell it...
HOWEVER, even moded, it can not come even remotely close to the sound of a two-gain stage, single-ended pure class A amp... like a few you can get the parts for in Pass forums/DIY Store (FW clones)....
Having started with a Rotel 60w integrated I can vouch for this. And he's being quite specific for good reason.
Hi,
Check out my diyAudio thread "Improve a Rotel amp THD by 20dB!". The RB-930ax topology is exactly the same as the RA-820ax (and RA-931, etc.) and I do sell the modules for easy 'pop-in' upgrading to an amp with current mirrors, EF-VAS stage, etc. - giving a faster, lower distortion, precise and defined soundstage... These are the upgrades that gives most 'bang for the buck'. (And putting in beefier reservoir capacitors if space allow)
Email me at AngelP@angelhorns. co.uk if you are interested.
Best,
Per
basically:
- Replace all solder joints: desolder and re-solder. With minimal solder: you must be able to look through the board holes!
psu:
amps:
Something to start, to test;-)
https://elektrotanya.com/rotel_rb-930ax_sm.pdf/download.html#dl
- Replace all solder joints: desolder and re-solder. With minimal solder: you must be able to look through the board holes!
psu:
- Remove C905 - C912
- Connect the channel separate psus: NO "double mono" psus!
amps:
- Replace C611 and C612 by > 1 uF.
- The bases of Q683 and Q684 could get a cap (to ground) > 10 uF.
- Remove the 2SB817 and 2SD1847. These sound ernormously gray, flat, slow, tired. Replace only one pair each - almost all other types sound better - and increase the corresponding emitter resistors to > 0.39 Ohm . By means of the value of these resistors you can adjust the sound well. The higher, the more "musical" and also more "depth". Simply adjust the bias (VR601 and VR602).
Something to start, to test;-)
https://elektrotanya.com/rotel_rb-930ax_sm.pdf/download.html#dl
Also known as dual monoblock,"double mono" or "dual mono", it usually translates to 2 separate amplifiers in one box, each with their separate power supplies but only one common signal grounding point at the source device. The plan being to maximise the stereo channel separation - visually at the very least, electrically where feasible and also minimise any other form of stereo degradation. Whether that's strictly necessary, or just a philosophical POV, is down to your own experience and preference. Some audiophiles won't even listen to music without this type feature in place though. This video also discusses some of the differences for non-techs. The only problem being the confused and abused terminology in so many similar videos.
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You could use two thin wires to connect + and + as well - and - of the separate psus.
"The plan being to maximise the stereo channel separation." They should move the speakers further apart;-)
"Some audiophiles won't even listen to music without this type feature in place though." They are not audiophiles;-)
"The plan being to maximise the stereo channel separation." They should move the speakers further apart;-)
"Some audiophiles won't even listen to music without this type feature in place though." They are not audiophiles;-)
The service manual shows the power transformer has one centre-tapped output winding, common to both channels. It does have separate rectifiers and caps for each channel but that doesn't make a lot of difference. Both channels can be configured as one more powerful channel in bridged mono mode but that's not what you are looking for either. It suggests to me that for a dual mono amplifier, you need a second amplifier rather than mess up this one, where you may have difficulty even cutting the copper foil tracks or squeezing in the second power supply with its transformer.
FWIW, The PCB pattern is not the usual type with narrow tracks which could easily be cut to modify its circuit. It appears to be mostly copper with narrow gaps between the very wide tracks and large pads. That makes it difficult to mod. without requiring a few messy wire bridges
Then you still need to consider where the 2nd matching power supply with its transformer will be located. 'Sorry but I don't think this project will be easy or cheap, let alone result in a worthy dual mono amp.
well, i put mur1560 diode bridges and nichicon vz 50v 10,000uf caps in it. adds a bit of snap to it. it is running bridged to a sub currently in my home theater. its driving 1 8+ dvc (4ohm + 4ohm) as an 8 ohm load to the bridged amp. it doesnt clip as much now but would like to get a lil more out of it. gonna go through the audio path and change out the caps as well. then figure out how to get more "bias". what other amps might have a higher capacity transformer i could swap into the little beast? or where could i find a toroidal transformer that would fit in it with double the potential current?
whats a better output transistor pair to put in? im not good at figuring out by data sheets
As you may find out, you can't increase power without the higher supply voltage and current to do it. Bigger transistors alone will do no more than the original type. This amplifier is a toy compared to what you need for a subwoofer which needs lots more power (P=V²R) than from a basic audio amplifier. In bridged mode mono, you could be able to quadruple the power into a lower impedance (4R?) speaker which may be enough but you only have a small transformer which will probably cause distortion when its output voltage sags on peak currents.
I think you should get a cheap class D amp of at least 60W for bass. That's the type HT systems and professionals mostly use now - cheap if used with a switched-mode power supply (SMPS) but plenty good enough for bass and powerful.
I think you should get a cheap class D amp of at least 60W for bass. That's the type HT systems and professionals mostly use now - cheap if used with a switched-mode power supply (SMPS) but plenty good enough for bass and powerful.
just looking for equivalent transistors that are close to drop ins. this amp is a toy, but its enough for my tiny apartment as it is for now to drive a sub. i do have rotel rb-1090, but not the space to use it. so getting the most out of the smaller equipment is just a fun challenge. when my house is built ill be running either tube amps or class a se amps for all channels of the system
well to report, upgrading of diode bridges from stock to mur1560's, rail caps to nichicon 10kuf high temps, the audio path caps from stock to metalized poly caps has made the amp snappier and way tighter in response. played batman the dark knight and response was excellent. still looking for some drop in output device part numbers though. other step is a toroidal transformer with more current capacity
I suppose you were looking for (even) tighter sound with that Rotel??
I always found Rotels cold and sterile... but that's me.
If you decide that too much coldness is not suitable for you, try some friendly and relaxed capacitors... they should be 85 deg C types - not 105.
I always found Rotels cold and sterile... but that's me.
If you decide that too much coldness is not suitable for you, try some friendly and relaxed capacitors... they should be 85 deg C types - not 105.
I would bid adieu to TO-247, TO-3P and larger designs. The best in this size I heard was NJW3182. But almost all TO-220 were clearly more focused, cleaner, more fluid, more accurate: more elaborated.
I would currently recommend proving the TIP transistors in 220 guise;-)
I would currently recommend proving the TIP transistors in 220 guise;-)