Are you being serious? LM741 is a joke albeit one for insiders that do this hobby for quite some years. It is one of the first opamps and sounds very bad. AD711 were already in that device. Why not think simple and buy OPA604? Performs OK and is cheaper than OPA627. If you want the device to be really good then don't bother further and find original OPA627 from a reputable distributor.
I think you will be very satisfied with OPA604.
I think you will be very satisfied with OPA604.
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Also, when working on equipment, the most valuable piece of it is the pcb. If you cannot remove/change devices without damaging it then you need to rethink your plan of attack and have someone qualified do the work.
Hi ! still using the preamp ? could you sum up the mods you performed and provide some opinions on the final sound ?
thanks 🙂
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Still using it, the only change I made was installing sockets for the line inputs. I use the OPA 627's. I am sure there are other mods, do a search. It's been a while since I did this, but I think someone mentioned removing caps next to the line input opamps. But I did not do that. Mine has Black Gate caps, which are pretty hard to improve on.
I have been using several different phono preamplifiers, I listen to mostly vinyl and the phono preamp in the Rotel is a bit harsh sounding. I have a few Musical Fidelity phono pre's and a VTA PH16 which are a major improvement over the Rotel phono input.
Thomas
I have been using several different phono preamplifiers, I listen to mostly vinyl and the phono preamp in the Rotel is a bit harsh sounding. I have a few Musical Fidelity phono pre's and a VTA PH16 which are a major improvement over the Rotel phono input.
Thomas
I just wanted to recommend your excellent web page to all here. You also appear to have an unusally well equipped bench at home.
Hi ! thank you very much for your kind and very helpful reply.
I would look at the power supply.
i am not a big fan of toroidal transformers in low level units ... especially if standard regulators are used.
They have usually poor rejection of higher HZ mains noise
I prefer EI type or better R-core
Then i guess it uses a alps blue
I and a friend compared some years ago a alps blue with an attenuator made with Holco resistors ... the attenuator had a razor sharp soundstage that was impressive. Like the difference between a standard knife and a scalpel 🙄
The sounds exploded in the air ... since then i have become a believer in attenuators for volume control.
This is simply incorrect. Having Black Gate caps in the PSU lines is good. In the signal path no cap is the best cap one can find. OPA627 is a JFET input opamp and it has very low offset. One can use excellent film caps at the inputs and use jumpers in the outputs as 99.99% of power amps also have an input cap. This needs to be verified in each case.
If one leaves the RC-980BX like it is in many cases there are 2 electrolytic caps in series. Carefully review the power amp. When it has input caps the output caps in RC-980BX can be replaced for wire bridges. I can only state this when using OPA627 and have modded at least 3 pieces RC-980BX that all work perfectly till today. If the power amp is DC coupled one can replace the output caps for Wima MKS2-XL in 10 µF 50V film caps. Please NEVER make the complete chain DC coupled as it will always result in costly failure with the slightest error.
RC-980BX also amplifies too much. One can improve that by changing 1 resistor in each channel.
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Hi sorry to jump in ... i guess you refer to the feedback resistor ?
do you think that the quality of the feedback resistor can have an impact on sound ? and in case ... which brand/model can be trusted ?
imho it has an impact ... and i like Holco for instance 😱
Thanks and regards,
gino 🙂
Hi I would not focus on brand names but on trusted industrial quality stuff preferably with tinned copper lead wires. Type/quality before brand names so to speak. Many things have impact but in audio the slightest things are exaggerated which may lead to a device not performing like it can. It really is better to first determine the complete situation and later on care about details.
Please review your setup and verify all available sources for DC coupling/output cap and review your power amp. If you have just 1 source with DC offset you should keep input (film!) caps in your RC-980BX. If your power amp is DC coupled you must keep using output caps in your RC-980BX (again, preferably film types). Then think out the best setup for your RC-980BX and make a list what you need to buy. Also verify if the RC-980BX amplifies too much in your setup. Now after all this you can decide if you want the feedback network to be changed and which type resistor you will be using. Add those 2 to the list, order the stuff and solder in these mods and the RC-980BX is ready with better results than before. The brand and type of resistor will have a small role on the whole. Industrial metal film types will perform fine.
Example: I once had a CD player that had almost 0V offset when playing but when muted it had nearly 2V DC at the output. In such a case one must use input caps in the preamp.
Please note that a fully DC coupled chain will amplify DC which eats your woofers. Although we detest caps at least at one spot you better use coupling caps to make the risk lower when something goes wrong. IMHO the best spot is between preamp and power amp and this can either be in the preamp or in the power amp. Not in both as often found.
Please review your setup and verify all available sources for DC coupling/output cap and review your power amp. If you have just 1 source with DC offset you should keep input (film!) caps in your RC-980BX. If your power amp is DC coupled you must keep using output caps in your RC-980BX (again, preferably film types). Then think out the best setup for your RC-980BX and make a list what you need to buy. Also verify if the RC-980BX amplifies too much in your setup. Now after all this you can decide if you want the feedback network to be changed and which type resistor you will be using. Add those 2 to the list, order the stuff and solder in these mods and the RC-980BX is ready with better results than before. The brand and type of resistor will have a small role on the whole. Industrial metal film types will perform fine.
Example: I once had a CD player that had almost 0V offset when playing but when muted it had nearly 2V DC at the output. In such a case one must use input caps in the preamp.
Please note that a fully DC coupled chain will amplify DC which eats your woofers. Although we detest caps at least at one spot you better use coupling caps to make the risk lower when something goes wrong. IMHO the best spot is between preamp and power amp and this can either be in the preamp or in the power amp. Not in both as often found.
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hi i beg to differ here. I think that feedback resistor (that i still see as a critical component) like any other passive parts in the signal path can have an impact on sound. Like the caps you mention for instance.
It can add noise and non linearity in a negative way. I agree of course the overall design must be sane ... that is not in discussion.
I am asking because i have a similar line stage from Bryston and i was thinking to replace the feedback resistor with a higher quality one.
Moreover i will do what you recommend in order to check if i can bypass the output caps it also has.
Thanks again.
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I think we agree on the same. Please note that when replacing that one resistor for something with nuclear properties you better also replace the other ones in the feedback loop.
Hi ! thanks a lot. I will keep that in mind for sure. I am not using bulk foil type for sure even if they appear to be the very best around ... just honest metal film from Welwyn.
Checked and yes OPA637BP would be excellent for the NE5534. Not so sure about the TL071, it could be that OPA627BP or OPA134 are a better choice for that one. As said I never bothered about the phono part. With either choice please first measure the supply voltages. They are highish around 17V but make sure that they don't exceed +/- 18V. If they are too high you can replace Zener diodes D904/D905 for a slightly lower voltage like 17V. R901/R902 could be upped a little then.
It also may be good to measure DC voltages and then probably choose the 240V tap on the primaries of the transformer (definitely in the EU).
It also may be good to measure DC voltages and then probably choose the 240V tap on the primaries of the transformer (definitely in the EU).
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