bellari question with caps and chips

[versuviusx]

ok so i called the ballari guys up and talked to them about changing out the caps and the chips in the RP583. and they said that i wouldn't be able to hear a change by changing the chips to burr brown and i wouldn't hear a change in changing the caps. the reason being is that there is already military grade caps in it and the guy there said that the op amps would not be worth the time to change out. he also said that there is a possibility that i could put a chip in it and actually have worst performance because they would be more unstable even though the have better specs. can anyone verify this? he said the only thing that would really change the sound would be changing the tubes.

 

[soundguy]

[quote author="versuviusx"]he also said that there is a possibility that i could put a chip in it and actually have worst performance because they would be more unstable even though the have better specs. [/quote]

that is infact true and applies to rechipping anything.

the part about the caps though is utter nonsense so far as Im concerned. I have never tried on that box to tell you definitively, but I have never changed caps in any box and not had it drastically inffluence the quality of the sound in either a good or bad direction. This assumes you are talking about electrolytic caps. You can change the *brand* of caps in the power supply section ONLY and sometimes hear a difference in the audio of the amplifier without even changing the audio coupling caps in the circuit. The fact that they use mil caps is entirely irrelevant to the quesiton you asked. "improve" is relative anyway, there are caps that many like that I dont, your idea of "improve" is largely based on what you like personally not what some guy on a telephone or the internet says is good.

dave

 

[bcarso]

quote: "the reason being is that there is already military grade caps in it "

Maybe it sounds best in combat action.

The military did used to get some pretty nice parts, at least from a reliability standpoint. I found a professor at UCLA who was a gov't excess property packrat. He used the somewhat flimsy excuse of needing parts for his nocturnal animal experiments, which were grant-funded, to get huge lots of everything under the sun. I managed to persuade him that I was actually making stuff and not just transferring his inventory to mine.

The result was that the very elaborate detector system I built had extremely high MTBF, despite the predictions of my enemies. The only component that failed was a ceramic cap that was from a standard grade source. It began to leak and boy was it hard to find, as it caused an indirect but fatal effect which looked for all the world like something else would have caused it. The Monday-morning quarterbacks, who had said I would never finish the system, now said that of course it should have had self-diagnostics built in. There is no pleasing PhD's, especially if they have managed to get tenure.

 

[SonsOfThunder]

[quote author="versuviusx"]ok so i called the ballari guys up and talked to them about changing out the caps and the chips in the RP583.[/quote]Why?

Why don't you just change them and see for yourself? I think those already have IC sockets in them, right? Are you willing to take someone elses word rather than just pop some stuff around and see for yourself? Maybe it will, maybe it won't.

For me, experimentation IS the fun of DIY. Go for it!

Maybe it sounds best in combat action.

That's CLASSIC!!! Gotta remember that one. :green:

 

[pucho812]

There is no pleasing PhD's, especially if they have managed to get tenure.

YOU KNOW WHAT PHD STANDS FOR? phd = Piled High and Deep :grin:

 

[versuviusx]

hi ok so i'm looking for a replacement for my ROHM BA4560 and i don't know which one to go with.

i went to this web site
http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?templateId=5275&paramTable=yes&familyId=585

and i'm thinking about getting the OPA637 as it has a slew rate of 135 which may be better than the typ: 4.0 which is what the BA4560 has.

Is it good to have a really high slew rate or a very low slew rate? i have no idea.

also in the specs it says TYP does this mean typical?
i'm thinking it does. let me know.

 

[bcarso]

High slew rate is better---as long as not much else is sacrificed to get it. If it is sufficient, it basically means that large signals will be reproduced/amplified like small signals. When the slew rate is inadequate sine waves tend to be turned into triangle waves.

To find out how important slew rate might be in a given application, figure out what the largest signal swing will be at the op amp output at the highest frequency of interest. The required minimum slew rate for a sinusoidal waveform is given by 2 x Pi x frequency x peak voltage, and occurs at the zero crossings.

So suppose I am expecting a 20kHz 18V peak (12.73V rms) sine wave at the output of my op amp. At the zero crossings I'm going to need to move at 2.26V per microsecond. Probably I'll want a little margin of safety on that, even though such a signal is likely pretty rare.

Now---if I have a bunch of way-out-of-band crap that's gotten into my system, or if I'm trying to please people who claim to hear well above 20kHz, I may want to have a much higher slew rate. For when that rate is exceeded some fairly intense harmonic and intermodulation distortion, and serious level-shifting (for asymmetrical slew rate limiting especially) may cause some very audible in-band garbage. Otala made a career out of this stuff when he coined the term transient intermodulation distortion (TIM), although some mention of the effect can be found in much earlier references (e.g. remarks in an appendix of the Radiotron Designer's Handbook 4th Ed., if memory serves). Otala focused on internal overloads in amps with lots of feedback where small signals riding on big ones were essentially erased momentarily.

So--it doesn't hurt to have a higher-than-required slew rate capability. Interestingly, the cheap FET amps like the TL072 have quite a bit better slew behavior than the cheap bipolars like the 4560. There are some old bipolars that use input stage emitter degeneration to allow for frequency compensation tailored to higher slew rate (LM318 for example) but they have higher noise in consequence.

Yes, typ means typical.

 

[Kev]

Maybe it sounds best in combat action.
That's CLASSIC!!! Gotta remember that one. :green:

yeah funny

honest ... it is funny :wink:

BUT
... may I be grumpy for a second or two ?
Might not sound better BUT it might be the difference between working and not working when the going gets TUFF

You may not record audio in a combat situation BUT I have a couple of friends that do.
If I can put more reliability into their gear, then the sooner they get the shot or get the audio snippet ... the sooner they get back under cover and the more chance my mates get back here, where it is safe.

The serious NEWS boys are nuts.
You will never catch me doing things like that !
:shock:

 

[kiira]

[quote author="versuviusx"]ok so i called the ballari guys up and talked to them about changing out the caps and the chips in the RP583. and they said that i wouldn't be able to hear a change by changing the chips to burr brown and i wouldn't hear a change in changing the caps. the reason being is that there is already military grade caps in it and the guy there said that the op amps would not be worth the time to change out. he also said that there is a possibility that i could put a chip in it and actually have worst performance because they would be more unstable even though the have better specs. can anyone verify this? he said the only thing that would really change the sound would be changing the tubes.[/quote]

LOL.

"Oh no you can't possibly improve anything on a Bellari preamp we have spared no expense to make it the finest mic preamplifier that money can buy, bar none. That's why we selll it for $400 you fool."

I've redone an Rp220 with the following changes. The same genearl things could be done to the 583 I imagine - not familier with the insides a that one tho.

I replaced the Ba4560s with Burr-Brown 2604s, all the electrolytics with Nichicon, Elna,or BC or Black Gate, any other sketchy mylar caps with polypro, the input transformer with a Jensn je115 or equivalent OEP, Cinemag, UTC, Thordarson, Stancor,Triad etc. And the cheeseball 12ax7s I'd replace with NOS RCAs or the Tesla/JJ Telefunken copies that Uncle Ned sells for $7 or so.

Bypass R15 & R41 with 120uF caps to stop possible oscillation an I think you will be able to leave out C8,C9,C18 and C37. Double the coupling cap size too.

This removed the wolliness from the preamp and made it pretty aceptable.

Kiira

 

[Flatpicker]

[quote author="pucho812"]YOU KNOW WHAT PHD STANDS FOR? phd = Piled High and Deep...[/quote]I always thought it was "Post Hole Digger".

 

[Flatpicker]

[quote author="versuviusx"]and i'm thinking about getting the OPA637 as it has a slew rate of 135 which may be better than the typ: 4.0 which is what the BA4560 has.[/quote]From what I've read, the OPA637 is a good sounding op amp, but a faster slew rate doesn't always mean it's going to sound better. IIRC, a 2520's slew rate is pretty slow, but we all know how it sounds.

 

[SonsOfThunder]

[quote author="kiira"]"Oh no you can't possibly improve anything on a Bellari preamp we have spared no expense to make it the finest...."[/quote]
This is exactly the kind of response that I would expect if I were to call a manuf. and ask their "opinion" of any modification.

They are not going to be so hip on you making changes to their "baby" if for no other reason to keep you from voiding the warranty. Or at least to keep an inexperienced "solder poker" from possibly making a mess of their equips and then trying to blame them or asking to send it for free repairs or bugging them for troubleshooting tips.

2604 should be a drop in that would work well if the surrounding components will allow it to. I have the schem for this thing somewhere. I'll see if I can dig it up.

HTH!
Charlie

 

[SonsOfThunder]

[quote author="Kev"]You may not record audio in a combat situation BUT I have a couple of friends that do.[/quote]
Nothing funny about that, Kev. Good point!