Ramsa WR-T820B Recap Question

[phishman13]

Hey there everybody.

I found one of these consoles for a steal since it was in very rough aesthetic condition.  Internally, it's still in decent shape.  It's relatively quiet and free of hum considering the hell it looks like its been through.  However, it does have some definite improvements to be made that I think a recap can take care of.  Also, there is an odd "build up" in the low mid freq. range.  It pushes that part of the spectrum forward a bit making the low half of the spectrum sound a bit off.  Not sure if that is b/c of the overall design and/or the now-mackie-famous opamps.

Now its time for me to whip this thing into shape for some serious recording and mixing use.  I would like to basically give it the treatment that a guy (Nick Peck) gave to his Soundcraft Ghost.

Here is the specific page of his wiki describing his improvements that relates to the recap.

http://www.underthebigtree.com/wiki/tiki-index.php?page=Recapping

I was wondering if anyone who has owned or worked on the Ramsa WR-T820B would have insight on choosing a few capacitor values to replace all the caps.  The ramsa has over 15 different values in its circuitry and ordering Panasonic FMs in many small quantities is expensive.  I was hoping to find the least amount of different values like Nick did for the purpose of saving money by buying quantity, and also increasing values to help the low end of the console improve overall.

If no one knows off hand any good ideas, would it be helpful to upload a schematic of whatever section I'm working on and let people gander at it to see what they can see?  I just don't know enough about changing cap values in circuits and predicting what all might happen.  Can it be narrowed down to something like, all decoupling caps can be value x, coupling caps in audio path can be value y, etc...

I have the service manual with all schematics, so let me know if I need to let you see them to guide my choices.  I'd appreciate any insight, and thanks to Nick for documenting his process so well.  I would have no idea how to express this question without his straight forward layout.

 

[toobdood]

  Stoopid question: Are the mic input caps ALREADY Elna Cerafine?  The caps in my Ramsa are!  Peace, C

 

[shabtek]

altering the cap values may lead to loss of the Ramsa magic.

seriously, do 1 or 2channels and compare to a stock channel.
if that is an improvement you can consider the others...also altering/updating the summing/mixbus may have a bigger impact

find/deduce a schematic. what are the caps doing. ac coupling (dc blocking) can usually be upsized in uF a little. local power caps can be changed a little either way.
If it eq then yer gonna need the same.
electro caps are usually like 10-20% tolerance, don't reduce voltage rating.

ramsa;does it sound bad? for live reinforcement? bypass everything.

 

[phishman13]

  Stoopid question: Are the mic input caps ALREADY Elna Cerafine?  The caps in my Ramsa are!  Peace, C

You know, I had the thing open, looked around, recognized that there were caps in there, haha, but not what kind they were.  Not sure what I was thinking.



Thanks for the responses so far.  It's not that it sounds bad, its just that it doesn't extend very low beyond 40hz.  I've fed some deep stuff into it and then directly into my monitors, the low end is quite less through the console.  And it seems like there is too much of an emphasis on the low mid range.  This results in a "warmer" sound by shifting the spectral balance away from the high end, but I feel like it is too much of a shift.  I suppose this could be more an opamp thing.  I intended on starting with the PSU, then the master section: monitor section, master bus, and then the 8 buses.  Then once I got that knocked out, I'd move onto the channels.  I'd probably start out with the whole master section and a pair of channels to give me an idea as to what it is doing.

I have the service manual, so I can figure out what each cap's role is.  From what I've seen, people are talking about doubling (or more) the value of a lot of these ac coupling caps.  The rationale being that the low frequency cutoff is too high which introduces a phase shift into the audible spectrum.  By increasing the value, it pushes that cutoff lower so that the phase shifts occur below the audible spectrum which in turn cleans and tightens up the low to low mid range.  This is what I am trying to accomplish, in tandem with an overall recap for normal recap purposes. 

I'm not worried about a change in the overall character of the console.  It sounds fine (wouldn't call what it does magic exactly ), but I don't feel married to its sound.  As long as it doesn't sound WORSE when I'm done, I will be happy (which I'm not too worried about).  I know these consoles aren't really worth that much these days, and I have no intention of ever reselling it.  This is my first console, got it for a steal, so I want to experiment and hot rod this thing over time to make it the best it can be.  If that drastically changes its sonic imprint from what it is now, whatever!  Does this help clarify my intent, and what I seek?

...bypass everything.

What exactly do you mean?  Like throwing a small poly cap on the flip side of the board to bypass all the electrolytics?  I've seen that approach, its to help out the high end correct?  That sounds like a possible future upgrade.  Or do you mean to bypass something else?

Thanks again! ;D

 

[abbey road d enfer]

Unfortunately, there's so much BS flying around it doesn't help having a clear vision of the subject.
It is quite evident that the drifting (decrease) of caps values with age leads to a progressive loss of LF response. The notion of phase shift is irrelevant because phase-shift in itself is inaudible (some artefacts created by phase-shift may be audible when they result in overshoot, but not in this case). Most designers take this into account, and use much larger than needed values. And in an effort of rationalisation of purchases, they tend to use a very limited number of different types. In the 70's and 80's, Soundcraft used only four types of caps, one for mic inputs, one for mic gain, one for interstage coupling and one for power rails decoupling. As a result, the LF response of the different stages was not the same, and very often most of the stages have a very low Fc, like 3Hz for the post-fader amp, and some others have significantly higher Fc, like 15Hz for the Aux sends. The same drift in capacitor value will produce negligible effects on the former, but will be audible on the latter. It looks like Ramsa have not chosen to follow the same route. I don't know what is their reasoning, maybe they want all their stages have the same Fc, or they want one stage to define the dominant frequency response. A careful study of the schematics may help in understanding.
One definite factor in favour of careful replacement of caps is the possibility to reduce capacitor nonlinearities, not only by changing for a "better" type (here the difficulty is defining which is "better") but also by increasing the value. The articles by Ciryl Bateman prove without a doubt that increasing the value of coupling caps reduces the amount of THD/IMD they introduce. The continuous development and improvements in caps have led to an significant increase of volumic capacitance that makes possible the doubling of values in the same format using a modern cap, compared to a 10 year old.
Decoupling caps maybe increased too; however, instability problems may appear. This is because the grounding arrangement may not be as solid as it should. The problem is you find out only when you have replaced all the caps! If VLF instability appears (woofy sound, even motor-boating), then you must stiffen the ground rails.
You must be particularly cautious with caps used in an NFB loop, and with the mic gain cap; it is generally a high value low-volt cap (typically 1000-4700u, 6 or 10V). Changing it may produce VLF oscillations.

 

[shabtek]

by bypass i was being an ass: put a jumper from the input to the output, is what I meant.  sorry

if you post a schematic(s) you may get more opinions.

 

[phishman13]

by bypass i was being an ass: put a jumper from the input to the output, is what I meant.  sorry

if you post a schematic(s) you may get more opinions.

Haha.  That would save me a shit load of money and time/stress/troubles!

As for abbey road.
Awesome.  That clears up a lot of my uncertainty in this endeavor.  So I noticed that, like you mentioned, there are only a few roles the caps play, so maybe it would make sense to determine a single value for each role.  It looks like the audio coupling caps are mainly 33uf but vary from 10uf to a few 220uf right before the main outs.  From this info would 220uf be a good value to sub all of them with or might this be too big for the smaller values?  Lets assume physical size is no issue.  This is the value that Nick settled on if you look at his page I showed in the first post.  It looks like the decoupling caps are mainly 220uf as well.  That seems to work out for buying values in quantity.  The mic input caps are 10uf 63V and the phantom power cap is 47uf 63V.  Could I make them all 47uf 63V?  The mic gain cap is 47uf 6.3V.  Unless someone can give me a reason that it should change, it will remain the same .  So far it seems like I order a bunch of 220uf caps of the proper voltage, and then the PSU caps, and then the specialty caps like the high voltage mic input caps and the mic gain caps, and peak detection etc....  That should hopefully save me money since there will only be a few values.

 

[abbey road d enfer]

Ther is no reason why it shouldn't work. Start with a pair of channels and compare to the old ones. Check the mic pre; increasing the input caps may (or may not) increase the leakage current and offset the preamp's operating point. I don't expect it really, but I don't want you to be pissed at me  . I have warned you!
If you're satisfied, just go ahead. Can you post a schemo of the mic amp. I'm surprised at the lowish value of the gain cap.

 

[phishman13]

Can you post a schemo of the mic amp. I'm surprised at the lowish value of the gain cap.

Will do.  Let me scan it into my computer from the service manual and I will post it later tonight.

 

[phishman13]

Here is a link to the channel card schematics.

Check out the preamp, and let me know your thoughts on that gain cap.  What exactly does this cap do in this situation?  Why would it be bigger in other situations?

And this can give you an idea of the other types of cap values that might get their values tweaked.

http://twin-x.com/groupdiy/thumbnails.php?album=363

 

[abbey road d enfer]

The following values should not be altered:
C34 is part of the LF EQ frequency control
C69 defines the hold time of the peak indicator
C51 & 52 define the ramp-up timing of phantom power.
Regarding gain cap. It is in series with the gain pot, which is in fact the shunt element of the feedback loop. The gain of the mic pre is  = R9 + R10/ R11 + VR1
When VR1 is at its max (min gain) G = 36k/50k =>3dB
When VR1 is at its min (max gain) G = 36k/200 => 45dB
So the gain range is not very impressive, as is max available gain.
On many mixers using this type of mic pre, the max gain is 55-60dB. This imposes two important constraints: in order to achieve this gain, the padding resistor (R11) must be made much smaller (4.7R-22R). Increasing R9/R10 is not an option, because the higher impedance would be detrimental to the noise figure. As a consequence, the capacitor (C11) must be increased accordingly (if not LF cutoff frequency becomes too high at higher gain settings - LF cut off frequency is defined by C11 and the sum of R11 and VR1 - its set value, not the nominal value). That's why you'll commonly see 470-6800uF caps in this position. This cap is there to avoid scratchy noises caused by DC in the pot. Larger caps have more leakage than smaller ones, so a low-leakage type must be used, overall bigger and more expensive.
Another problem is that, when squeezing as much as 55dB gain range on a single-turn pot makes more demands on the accuracy and linearity of its law. A standard RevLog pot with 10% of its nominal value at mid-rotation is good for a 40dB range, but awful for 55 or 60dB range. You'll find the 40 to 60dB range crammed in the last 15° of rotation of the pot. So, if you want 55-60dB of gain with a nice regular gain progression, you need a custom-made pot. If you order 10 000 quantity, no problem (except for the 18 month delivery time), if you're in pro-audio, you try to do the best out of the standard product. Soundcraft gained access to custom-made pots from Alps only when they launched their Folio range, which sold in quantities only previously seen in consumer electronics. Ramsa, even though they are part of the Matsushita group, couldn't justify a custom pot.

 

[phishman13]

Ok great! I knew to leave the peak detection one alone, but thanks for giving me a heads up on the others.

Great info about the pre by the way! That helps me to understand it that much better.  I think they spent too much money on the concentric pots for the 3 eq bands so they opted out of the mic gain custom. I'm having a hell of a time finding out what kind they are to find a replacement for the few that have bent shafts. They work, but I'm just being particular. 

So after your review, would you think 220uf would be a fine value for the coupling and decoupling caps?  I feel like if I figure out the new standard value, I can follow suit on all sections of the console for those 2 types of caps.

 

[abbey road d enfer]

As I said earlier, do the mods on one or two channels, and then, if you're satisfied, do the rest.

 

[drpat]

...

 

[phishman13]

Hey drpat!

Thanks for the response.  Its good to hear from a Ramsa user!

That's interesting news about your frequency response.  It sounds like I should look at the PSU first instead of buying a bunch of caps.  I wanted to eventually move it outboard, but I figured I'd recap it and leave it inside for now until the whole thing got recapped.  I have built PSU's for other projects talked about on here, low current stuff.  Is building a high current PSU just using the proper schematic and picking a transformer and components that can deliver/handle that kind of current?  Do you have any insight or specifics on building an external PSU for this console?  Really just the +/- power for the IC's since phantom and led/relays etc can be kept on the old one.

As for the caps, I think I have talked myself into shopping around instead of using Panasonic FMs.  I use those for every project I build, but I think its time to try something new.  Its just that they are so much cheaper than others.  What I have come up with so far is to try the elna's from digikey for as many values as I can use, then the dubiliers from Audio Maintenance for the higher voltage caps and whatever other values I need.  I like the comments/descriptions i have read about those 2 brands.  If I used the Muse ES in just the master section and maybe the groups, it wouldn't be that expensive.  Did you replace every cap in the master section with the bipolar or just the signal coupling caps (not counting stuff like the led indicator ciruits and stuff like that)?  There are caps that are between the - input of an opamp and ground (while the input is into the +, C407 and 416 in the master bus if that helps).  Can those be swapped with bipolars or would those be considered decoupling caps, and need polarized caps?

I'd love to get some info on those redundant ground wires.  I did notice that on each channel bank, they connect the ground on the connector card to the ground bus bar, and then the panel of each bank is also connected to the ground bar.  Is that them?  wild guess...  There's not that many so it doesn't seem like it would be too hard to find.  What should I be looking for?

BTW, I posted some questions over at the analog console forum in response to a thread about this console that sounds a lot like what you did.

http://forum.analogconsole.com/viewtopic.php?f=12&t=838

You answered some of the questions that I asked over there, so not sure if you read that already or just read my mind! 

Either way, THANKS SO MUCH!

 

[CJ]

you could jumper in a cap across the pwr supply cap and listen for bass.
this would instantly tell you if the pwr supply is the problem.

a symptom of dried out caps is bad bass.


this is because as the cap dries, the uF drops, and when the uF drops,

well,

what happens?

we have 1/    2 pi f c

as c = farads (go figure) drops, the equation goes up, the equation is for ac resistance, the more ac resistance, the less signal, but wait,

this would drop all audio by an even amount?

no, as that f = frequency also comes into plat, the lower the f, the higher the ohms again, this means that the first bandwidth to suffer the most from a dry cap will be the bottom end.

i am hungry, howabout lingucia and wagffles for dinner, any objections if i throw in one of those cool engineered over easy eggs that sell for 3.99 a dozen and come with a red sticker on each egg to let you know you are better than everybody else?

 

[phishman13]

Well, after further investigation, I found little puddles around the 2 huge caps in the PSU for the +/- audio rails (EDIT: which turned out to be glue! Why would anybody glue down components?! ha. they still needed replaced pretty bad though!).  So CJ, you think that might have something to do with what you're talking about?  

I put in an order to do a full recap.  I made some decisions based on drpat's input, since he works on this console regularly and has done some comparisons and settled on good results.  I chose to recap the entire console using the stock values.  And then, in the 8 groups, master and monitor section, the 2 track return, and headphone amp, I chose Nichicon Muse ES bipolars for all coupling caps.  Thanks for the advice!  For the rest on those boards and every value I could cover on the input channels, I got the Dubiliers from Audio Maintenance (thanks!).  Whatever values I couldn't cover with those, I snagged Nichicon PWs from digikey.  And for the fat PSU caps, I got Cornell-Dubilier SLP series caps from digikey.

Im gonna attack this a step at a time.  PSU caps first.  Just to see if, like CJ mentioned, that is the main cause for my low end oddness.  And then on to the control room monitor section to create a reference for the rest of my recapping.  Then the master section, then groups, then channels.

I'll post my results as it happens.  Don't wait on the edge of your seat.  I move slowly.   ;D

 

[riggler]

Hey there,
I have this console as well! Would you mind posting your parts lists?
Only if it's convenient, thanks!!

 

[PRR]

> it sounds as if you have a problem if you're not getting much below 40Hz.

Agree.

The board has a LOT of caps. Someone was afraid of DC. Also older PA systems (these were primarily PA boards) were cleaner if subsonics were stiffly rejected. You have the 80Hz cut, but that's brutal. Instead they cascaded simple low-cuts for very small attenuation at 20Hz and considerable drop at 1Hz.

I -estimate- about 0.2dB loss at 20Hz, assuming all is per-plan. Drpat says similar. And despite all the cascade, phase shift is slight.

Therefore, either your other board has bass-rise, or this board has a problem. And with all the different values, probably ONE problem. Like they got a batch of 22u that don't age well.

Learn to use signal generator and voltmeter. Sweep from 1Hz to 100Hz. Verify that it really has a droop before 20Hz. If so, divide and conquer. Measure from one stage to the next to see which ones are flat far-far below 20Hz, and which ones aint. Fix the sick. Don't spray the whole city.

 

[phishman13]

PRR

Thanks for that info and the picture.  I did some calculations before and was getting a lot of numbers in the same range, but just didn't think I was doing it right!  I also just stumbled on this site:

http://www.tangible-technology.com/audiobasics/upgrades/upgrade1_opamp_cap.htm

That's the kind of scoping I need to be doing here then eh?

I will start checking it out when my studio isn't a mess from wiring patchbays.......(never? haha)

Hey there,
I have this console as well! Would you mind posting your parts lists?
Only if it's convenient, thanks!!

Here ya go!

Order list text file
http://www.twin-x.com/groupdiy/displayimage.php?album=363&pos=1

Excel Sheet of full cap list by card.  Sorry if you can't understand the organization of it all.  Just ask me whatever you need.
http://www.twin-x.com/groupdiy/displayimage.php?album=363&pos=0