sorry for not completing that thought in my last reply. I meant to write: “Suggestions for alternative 63V PS caps smaller than 10KuF. Like Paulus I’d like a little more filtering capacitance using 4 or, if size & space allows, 6 caps per channel. I’d be satisfied w/ 12K/channel; I believe 15KuF total per channel might max the transformer and/or bridge rectifiers (BRs).Hi there Tony,
Why would you go lower then the stock 10KuF
I’m fully aware that 4 or 6 smaller caps of total equal value will recharge faster than 2, thus improving performance.”
I know more caps of an equal total value can and often do have greater in-rush issues. Increasing total capacitance makes it worse. The 980 series amps have a 1+ second delay upon power up. That may allow the transformer time to recover.
I suppose if the in-rush is too high even briefly, the line fuse would blow. Should that happen, I know Rod Elliot sells a kit that slows the cap charging upon power up though perhaps that type circuitry is on board just requiring a tweak.
Suggestions on how to lengthen the power up delay if necessary?
Yeah the increased in-rush could cook the BRs. No harm upgrading to higher current models as preventative measure. I don’t know the transformer’s VA rating as I have yet to look under the hood to take notes of such.
thanks for caring enough to discuss it at length.If they are able to produce a large amount of power and handle enough current then there should be no problem.
Don't know if I made anything clear here but I tried
sorry for the fat fingering and poor proofing before posting.
Behringer DEQ 2496. The 2496 is a pro device that has a BUNCH of processors including a built in RTA and Pink Noise generator - useful for tweaking sound systems.
Behringer | Product | DEQ2496
Thanks again.
Hi Tony and Paulus,
But they do take up more space and you should take great care in ensuring the lowest possible resistance between the caps, or you could easily lose all 'advantage'.
The RA-980's 1 sec 'on' delay is purely anti-thump protection, it does not restrict the reservoir cap charging (nor should it, or you'd never get the blessed thing started).
There are 'soft start' solutions using a Mosfet with a R-C filter to the gate - or even the crude old series thermistor rod used in early TV sets (but then your amp would of course only play in black and white).
As I have said before, with a Rotel's quality PSU components - I wouldn't worry about increasing up to 20,000uF, although I must admit that I have only tried up to 15,000uF.
And gone back to 10,000uF because I found the actual audible difference at domestic listening levels to be very marginal.
What is important is that you replace the old caps with high quality low ESR types and where possible decrease any resistance between the caps and trafo.
Even a broad 35um copper pcb track does need some help, see what I always do on the GND tracks in RA-820 and 931's.
Best,
Per
That is because, f.ex. four 2700uF in parallel has a lower total internal or Equivalent Series Resistance (ESR) than a single big 10,000uF can.
But they do take up more space and you should take great care in ensuring the lowest possible resistance between the caps, or you could easily lose all 'advantage'.
The RA-980's 1 sec 'on' delay is purely anti-thump protection, it does not restrict the reservoir cap charging (nor should it, or you'd never get the blessed thing started).
There are 'soft start' solutions using a Mosfet with a R-C filter to the gate - or even the crude old series thermistor rod used in early TV sets (but then your amp would of course only play in black and white).
As I have said before, with a Rotel's quality PSU components - I wouldn't worry about increasing up to 20,000uF, although I must admit that I have only tried up to 15,000uF.
And gone back to 10,000uF because I found the actual audible difference at domestic listening levels to be very marginal.
What is important is that you replace the old caps with high quality low ESR types and where possible decrease any resistance between the caps and trafo.
Even a broad 35um copper pcb track does need some help, see what I always do on the GND tracks in RA-820 and 931's.
Best,
Per
Attachments
Another “I’m sorry” for taxing your expertise and patience. BTW: where I wrote “…980 series amps…” above, I referred only to RB 980/981 amps, not RA as I’m unfamiliar w/them.
1. Back to an earlier question: What brand (PS) cap to use in place what Paulus suggested? I know I’m shopping for low ESR aiming for equal or slightly higher 12-13K uF total capacitance. Space permitting, still considering 4 caps per channel as the new caps manage to pack higher values of capacitance in smaller containers - 4 6800uF. In case no one has noticed, like the 991, the 98X amps transformers provide separate secondary windings along w/dedicated BRs, & capacitor banks.
2. Per: totally w/you on maxing PS component conductivity*. That dogma has served me well for amp/speaker/driver connectivity.
*using heaviest that fits or, as you (Per) have demonstrated, tricks to improve an existing connection path.
3. Paulus: where did you find that aluminum plate to mount your PS components?
4. Per: do you use a Variac for first-time power-ups either post mod or for something that was in storage for a while?
Many thanks while I shop for the test equipment you recommended to begin my upgrade/restoration journey.
Tony
1. Back to an earlier question: What brand (PS) cap to use in place what Paulus suggested? I know I’m shopping for low ESR aiming for equal or slightly higher 12-13K uF total capacitance. Space permitting, still considering 4 caps per channel as the new caps manage to pack higher values of capacitance in smaller containers - 4 6800uF. In case no one has noticed, like the 991, the 98X amps transformers provide separate secondary windings along w/dedicated BRs, & capacitor banks.
2. Per: totally w/you on maxing PS component conductivity*. That dogma has served me well for amp/speaker/driver connectivity.
*using heaviest that fits or, as you (Per) have demonstrated, tricks to improve an existing connection path.
3. Paulus: where did you find that aluminum plate to mount your PS components?
4. Per: do you use a Variac for first-time power-ups either post mod or for something that was in storage for a while?
Many thanks while I shop for the test equipment you recommended to begin my upgrade/restoration journey.
Tony
Hi Tony,
Ok, I did a RB-980 repair and upgrade for an retired music critic called Dave here in the UK and he was totally over the moon with the result.
All that really was done was putting in a couple of emitter followers and changing a few components to adjust various voltages and currents, see schematic.
Although I must warn that this is quite fiddly work (drilling and cutting tracks, etc.) and you really need to keep your concentration throughout (I am sure that Paulus would agree with that).
The new modules should make this a simple de-solder/replace procedure - I hope.
1&3) I think that I'll let Paulus chip in on this from his 991 experiences.
4) No, I don't use a Variac - but I cry a lot.
Whenever I get into strange territory like amps that I am not familiar with or that has been sitting in a damp attic since the Korean war, I do use a special mains outlet with an incandescent lamp in series with the live wire.
Normally, the lamp will light up briefly and then dim down - if not.... it's time to call the fire brigade.
For the upgrade experimentation I use a double 30V lab supply with current limiters which will immediately flag up any mistakes or disasters without causing any meltdown.
Per
Ok, I did a RB-980 repair and upgrade for an retired music critic called Dave here in the UK and he was totally over the moon with the result.
All that really was done was putting in a couple of emitter followers and changing a few components to adjust various voltages and currents, see schematic.
Although I must warn that this is quite fiddly work (drilling and cutting tracks, etc.) and you really need to keep your concentration throughout (I am sure that Paulus would agree with that).
The new modules should make this a simple de-solder/replace procedure - I hope.
1&3) I think that I'll let Paulus chip in on this from his 991 experiences.
4) No, I don't use a Variac - but I cry a lot.
Whenever I get into strange territory like amps that I am not familiar with or that has been sitting in a damp attic since the Korean war, I do use a special mains outlet with an incandescent lamp in series with the live wire.
Normally, the lamp will light up briefly and then dim down - if not.... it's time to call the fire brigade.
For the upgrade experimentation I use a double 30V lab supply with current limiters which will immediately flag up any mistakes or disasters without causing any meltdown.
Per
Attachments
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Hi there Per & Tony,
I"ll try and answer question number:1
I was planning to buy stock Rotel units but the brand BHC doesn't exist anymore so they (Rotel service) went for Kemet units at 50 euro's per piece.
This would set me back about 400 euro's for both amps
Then I noticed a patent number on the sides of the cap, via Google I read that it was about "Slit Foil" invented by Dennis Neal Morecroft.
His company, I mentioned a few posts earlier, still sell these caps today although they use the term "guided current" instead of "Slit foil".
I asked around to some friends with knowledge and years of expertise what to do and they said that I should stick with the specs used by Rotel, the rest is history.
About the aluminium, I bought that at a local shop.
I"ll try and answer question number:1
I was planning to buy stock Rotel units but the brand BHC doesn't exist anymore so they (Rotel service) went for Kemet units at 50 euro's per piece.
This would set me back about 400 euro's for both amps
Then I noticed a patent number on the sides of the cap, via Google I read that it was about "Slit Foil" invented by Dennis Neal Morecroft.
His company, I mentioned a few posts earlier, still sell these caps today although they use the term "guided current" instead of "Slit foil".
I asked around to some friends with knowledge and years of expertise what to do and they said that I should stick with the specs used by Rotel, the rest is history.
About the aluminium, I bought that at a local shop.
Paulus et al:
Thought you’d find this interesting
Listening #16 | Stereophile.com
Irrelevant side note: where is Velswijk and is that your country’s flag next to your screen name?
Thanks for your help. Tony
Thought you’d find this interesting
Listening #16 | Stereophile.com
Irrelevant side note: where is Velswijk and is that your country’s flag next to your screen name?
Thanks for your help. Tony
Hi there Tony,
Thanks for the read, much appreciated
Yes, the flag besides my screen name is of my country, The Netherlands
And Velswijk is the very small village I live in.
It Is in the east of our country, that specific area is called De Achterhoek
Just visited Hificollective on the www and I read that Supertech caps are no longer available with slitfoil. They now suggest KEMET and explain why;
Kemet Slit Foil Electrolytics | HIFICollective
Paulus
Thanks for the read, much appreciated
Yes, the flag besides my screen name is of my country, The Netherlands
And Velswijk is the very small village I live in.
It Is in the east of our country, that specific area is called De Achterhoek
Just visited Hificollective on the www and I read that Supertech caps are no longer available with slitfoil. They now suggest KEMET and explain why;
Kemet Slit Foil Electrolytics | HIFICollective
PaulusOUCH! I recall pricing the DNM caps. IIRC it came out to $113* plus shipping for 8 caps netting 40K uf/Ch but as Per advised, in his experience 20K/ch will do.“…they (Rotel service) went for Kemet units at 50 euro's per piece.
This would set me back about 400 euro's for both amps
MAN, I wish he sold those in a 6800K uf or the next size down. You have space for four 10K caps per channel. I’m confident I have space for four much smaller size/channel. I recall reading in a TNT article, everything else being equal, multiple smaller caps of equal value will recharge faster
So I should stick to the DNM caps to refresh my PSs for their quality and specs matching. I should forget about other brands of slit foils even if they exist
What sort of shop did you find the plate aluminum? Perhaps my welder/neighbor can hook me up.About the aluminium, I bought that at a local shop.
Many thanks. Tony
Hi there Tony,
With the original/stock spec I mean that you stick with "Slit Foil" caps (if they where used in your amp btw)
The brand, i don't know. I'm happy with mine, sold by DNM but manufactured by Supertech to DNM's specs.
About the sheet metal, ask your neighbour, I'm sure he can hook you up
Best, Paulus
With the original/stock spec I mean that you stick with "Slit Foil" caps (if they where used in your amp btw)
The brand, i don't know. I'm happy with mine, sold by DNM but manufactured by Supertech to DNM's specs.
About the sheet metal, ask your neighbour, I'm sure he can hook you up
Best, Paulus
Great thread just found it and analyzing. Did you had chance to think about RB-976?
Just comparing schematics and tring to pick what parts of 820 stage 3 can be passed to that one.
Actualy I have MK2 version which has slightly different power output stage.
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Hi,
The RB-976 is a basically a box with three RA-820/RA-931 power stages inside. All the upgrades that I described for these would work well.
You'll need three full sets of CM1 and VAS3 modules, ie. 12 in total - and I have currently run out of these, awaiting a new production (actually CM2 and VAS4) from PCBWay.
I have found that if you manage to properly match the LTP and balance their dc loads, there is little to be gained from the input stage rail filters. The resulting vastly increased PSRR takes care of any 50/100Hz ripple.
What speakers do you have that manages 105 dB/W?
Best,
Per
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Klipsch LaScala, but active way, without passive networks (that's why I need so many amp channels, I may even buy second 976 mk2 cause I need at least 2 additional channels for experimenting).
Ok so probably I'll be interested with those modules when they will be available.
Actually light humm can be heard but only if you are really close to the speaker.
Previously I was using Rotel RB-956AX and with it it was much worse.
RB-976 MK II has two transistors more, but of course input part is more or less similar.
Ok so probably I'll be interested with those modules when they will be available.
Actually light humm can be heard but only if you are really close to the speaker.
Previously I was using Rotel RB-956AX and with it it was much worse.
RB-976 MK II has two transistors more, but of course input part is more or less similar.
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Found interesting article with really similar amp layout. It describes some of discussed here approaches and their impact on distortion.
Distortion In Power Amplifiers
Distortion In Power Amplifiers
Great insight Per! Gotta love a guy that simplifies the complicated!
Unrelated question: per your advice, shopping for an external PS (+/- 30V). What minimum current* rating do you suggest? I found one rated at 5A. Assuming RMS is that high enough?
*continuous and/or peak?
Thnx. Stay healthy Tony
Hi guys,
Sorry about the hiatus - other things suddenly took priority.
I will try (belatedly) to give answers.
Tony, yes that would work fine. Make sure that the dimensions will fit.
Per