Group Buy Interest?

[vicenzajay]

Yes...

there aren't any good

or even adquate fixes yet

but there are two things

that will definitely be

in the ultimate list of fixes

1) rotate the power transformer

2) swap out the q4 and q5 transistors

on the eq boards


read this thread for more detail:

http://www.prodigy-pro.com/diy/index.php?topic=27791.100



i'm sure at some point

it will all be put into

a more cogent/cookbook form

but there's still a ways to go

Even I understand this much trying to follow the different threads....but my question is specific as to what MSHilarious, Dgatwood, and others are discussing concerning components not being able (or very close to not being able) to handle operating voltages.....the posts from the last 1.5 pages, really.

Perfectly willing to wait for the cogent cookbook format for modding - but the latest posts seem to indicate a latent possibility of outright component failure in perhaps a fairly catastrophic fashion.

This is what I'm asking clarification for - the 24 vs 35 vs however many volts discussion.

Jay

 

[Booda]

Well my 73s and 84s (2 each) have been working pretty well so far. I feel pretty lucky about it & I think there's quite a few others that are working too... there were 600 of these units sold and 300 of the 81. The only time I get any noise issues is when I have the input up to 12 o'clock (or I should say just past the 9 o'clock popping spot) But haven't needed to go that high. My Senn 441 needs the most gain out of my Mics and It still doesn't require me to go past the Pop spot. (BTW- I'm sure most know this but if you just click the Mic/Line button when going past the Pop... it's a quick remedy and you don't have to tell clients to take off their Headphones for a quick second.)

I feel bad for those with totally unusable units. I think the 81 camp should get replacements myself... and not at Chance and TnC cost but the Manufacture. It may have been said already but I'd bet the group of 100 pre's that got held up were the 81s.

 

[mshilarious]

Look, I have no affiliation with the group buy at all, I'm only helping because it's on this board and I like kicking things around. And if several of us need to brainstorm, I don't know of another place to do it that it isn't already being done. Prodigy-Pro has many more qualified people, but it seems clear to me that some of the most capable people there aren't interested (probably they built their own Neve clones from scratch, which work), so that thread doesn't get the attention that you might hope for.

So if you want me to shut up, lemme know; that will be the end of my assistance (which is limited anyway, because I don't have one of these units).

Back to the caps: the answer is none of us know right now. A cap manufacturer will tell you the DC + AC ripple voltage seen by a cap should never exceed its rating. But they are conservative, because they want to avoid exploding caps. crazydoc measured +33VDC at the first cap after the rectifier. That means that peak AC voltage will in all likelihood exceed 35V, but I don't know if the cap manufacturers mean ripple before or after the cap is applied. Usually, a design would leave enough cushion that nobody would worry about that. For comparison, the +/-15V rails on an ART MPA use 35V caps.

If you have a transformer secondary that measures 27VAC unloaded, that means peak voltage is 27 * (2^1/2) = 38V. Once you smooth the rectified AC, you have DC with an AC ripple--several mV of remaining AC on top of the DC voltage. You then knock down the ripple with resistors, caps, and regulators until your DC is clean enough for your purpose.

So what will fail, when, and will it fail? I would guess the most likely candidate for failure is that first cap after the rectifier. But I can only guess the consequences--it depends on voltage, temperature, time, and the quality of the cap. The most likely scenario is that cap will degrade over time, losing capacitance and increase leakage current. That could cause more noise in the circuit, or it could cause the power supply to eventually fail. It could explode destructively (electro caps have a vent on top to release excess pressure), but I don't think that is the most likely result. I rather think it is likely the units might need recapping in five years or less, whereas a good quality, properly rated cap should last 20 years or more. But these caps could also survive just fine, who knows?

If you want to be completely safe, replace the power supply caps with 50V rated Nichicon PW series, which are really excellent caps for this application.

 

[cannabis]

Even I understand this much trying to follow the different threads....but my question is specific as to what MSHilarious, Dgatwood, and others are discussing concerning components not being able (or very close to not being able) to handle operating voltages.....the posts from the last 1.5 pages, really.

Perfectly willing to wait for the cogent cookbook format for modding - but the latest posts seem to indicate a latent possibility of outright component failure in perhaps a fairly catastrophic fashion.

This is what I'm asking clarification for - the 24 vs 35 vs however many volts discussion.

Jay

there's not a simple answer to your concerns


i'm no expert, but on my projects

that i've designed or built

(some of which even worked )

i always use a capacitor

with a working voltage

of about 20% or more above its rating



in theory, using a cap

at it's rated voltage and temperature

should be ok

but manufacturing differences

and quality control issues

might cause early failure



i believe dgatwood mentioned

a capacitor failure in one of

his supply filter caps earlier

and these are made in china (?)

so i don't know that

i'd have a lot of confidence in them



but i'm not going to change mine

 

[pohaku]

By all means, please continue. I'm relatively handy with a soldering iron, but fairly clueless about what to do with it. I appreciate the discussion and education. Maybe some of it will even sink in

Look, I have no affiliation with the group buy at all, I'm only helping because it's on this board and I like kicking things around. And if several of us need to brainstorm, I don't know of another place to do it that it isn't already being done. Prodigy-Pro has many more qualified people, but it seems clear to me that some of the most capable people there aren't interested (probably they built their own Neve clones from scratch, which work), so that thread doesn't get the attention that you might hope for.

So if you want me to shut up, lemme know; that will be the end of my assistance (which is limited anyway, because I don't have one of these units).

Back to the caps: the answer is none of us know right now. A cap manufacturer will tell you the DC + AC ripple voltage seen by a cap should never exceed its rating. But they are conservative, because they want to avoid exploding caps. crazydoc measured +33VDC at the first cap after the rectifier. That means that peak AC voltage will in all likelihood exceed 35V, but I don't know if the cap manufacturers mean ripple before or after the cap is applied. Usually, a design would leave enough cushion that nobody would worry about that. For comparison, the +/-15V rails on an ART MPA use 35V caps.

If you have a transformer secondary that measures 27VAC unloaded, that means peak voltage is 27 * (2^1/2) = 38V. Once you smooth the rectified AC, you have DC with an AC ripple--several mV of remaining AC on top of the DC voltage. You then knock down the ripple with resistors, caps, and regulators until your DC is clean enough for your purpose.

So what will fail, when, and will it fail? I would guess the most likely candidate for failure is that first cap after the rectifier. But I can only guess the consequences--it depends on voltage, temperature, time, and the quality of the cap. The most likely scenario is that cap will degrade over time, losing capacitance and increase leakage current. That could cause more noise in the circuit, or it could cause the power supply to eventually fail. It could explode destructively (electro caps have a vent on top to release excess pressure), but I don't think that is the most likely result. I rather think it is likely the units might need recapping in five years or less, whereas a good quality, properly rated cap should last 20 years or more. But these caps could also survive just fine, who knows?

If you want to be completely safe, replace the power supply caps with 50V rated Nichicon PW series, which are really excellent caps for this application.

 

[cannabis]

If you want to be completely safe, replace the power supply caps with 50V rated Nichicon PW series, which are really excellent caps for this application.

just make sure whatever you swap

that it's going to fit, physically



in general, for every increase

in capacitance or voltage

there is a corresponding increase

in physical size



as it is, the 4700uF filter caps

are on long leads

because they have to be

lain on their sides -

otherwise, they'd stick up too far

to put the cover on

 

[WhiteStrat]

So if you want me to shut up, lemme know; that will be the end of my assistance (which is limited anyway, because I don't have one of these units).

DO NOT SHUT UP! We thoroughly appreciate the input. I'm like pohaku--handy and confident enough to whip out the soldering iron and do the grunt work, but lacking the head knowledge to know just what to do without some serious guidance.

I've got 2 of the 73's with two more coming from another BBS member. Mine seem to work fine (in general the 73's seem to be the least problematic), but if you're interested in getting under the hood and poking around, let me know. I'll send you a couple--or just have the extra 2 sent your way when I buy them.

 

[drBill]

i'd agree these are

very poorly designed

to last very long

(or even work out of the box )

I'm holding off dong anything until the experimenting is done, there's a consensus, and someone puts together a mod "howto" for us that aren't that adapt.

Yea. How about some sort of official declaration/tutorial of TnC approved repairs/mods?

Cool.

In

the meantime

I'll just

use mine

every

day

and smile...

 

[tarnationsauce2]

i believe dgatwood mentioned

a capacitor failure in one of

his supply filter caps earlier

Keep in mind dgatwood's unit had a modified power supply regulator.

 

[thajeremy]

So if you want me to shut up, lemme know; that will be the end of my assistance (which is limited anyway, because I don't have one of these units).

Ill send you one of mine to check out if you want....

I almost hitched a ride with my wife last month when she had to drive up to Cape Fear, NC....I was gonna contact you and see if you would be interrested in taking a look at one in person...as you can see...i didnt do it....

 

[mshilarious]

I almost hitched a ride with my wife last month when she had to drive up to Cape Fear, NC....I was gonna contact you and see if you would be interrested in taking a look at one in person...as you can see...i didnt do it....

That's still two capes south of me, and over a five hour drive . . .

 

[antichef]

pop fix

I ghetto-ized instructions posted by 0dbfs over at prodigy pro:

by moving that R43 lead from where it is over to to the R44 lead, position 7 on the gain switch becomes an "off" position, but the nasty pop is gone -- I even measured that 7R8 resistor that cooked on Jason's unit, and it stayed at a steady 2 volts throughout the entire gain range! I did this on both of my 81s and both 73s, too (I think the resistor number may be different on the 73, but it's in the same place - 4 over from the left).

0dbfs recommended replacing R43 with a 1.5k resistor and putting it in that position, but I decided to try it with just moving the existing 680k one because I'm lazy and ignorant, and I didn't even have to pull the board to do it (just pried up the lead with a little screwdriver and the touch of the soldering iron, then soldered it to the other lead).

Losing position 7 is kind of a bummer, but I heard that the original N*ves were like that too (and I guess we know why).

Disclaimer: I'm not 100% sure I know what 0dbfs did, because his pictures were even blurrier than mine - I asked some clarifying questions over there and am waiting for a response. I got impatient and tried this anyway, and it seems to work. But if 0dbfs clarifies the circuit mod to be different from what I did (other than the 1.5k resistor thing), I'm going to do what he says. (edit: 0dbfs didn't puke all over what I did, so I'm going with it - he did mention that he strategically used a piece of shrink wrap to reduce the risk of undesired connectivity between the moved lead and the old pad -- good idea)

DO NOT SHUT UP! We thoroughly appreciate the input. I'm like pohaku--handy and confident enough to whip out the soldering iron and do the grunt work, but lacking the head knowledge to know just what to do without some serious guidance.

total concurrence from me. I'm like WhiteStrat and Pohaku, but less patient.

 

[vicenzajay]

Exactly...

DO NOT SHUT UP! We thoroughly appreciate the input. I'm like pohaku--handy and confident enough to whip out the soldering iron and do the grunt work, but lacking the head knowledge to know just what to do without some serious guidance.

I've got 2 of the 73's with two more coming from another BBS member. Mine seem to work fine (in general the 73's seem to be the least problematic), but if you're interested in getting under the hood and poking around, let me know. I'll send you a couple--or just have the extra 2 sent your way when I buy them.

My question was certainly NOT intended to close down discussion - rather it seemed that some sort of consensus had been reached, and I didn't understand it. Thus the question.

Jay

 

[WhiteStrat]

My question was certainly NOT intended to close down discussion - rather it seemed that some sort of consensus had been reached, and I didn't understand it. Thus the question.

Jay

No sweat, Jay--I wasn't responding to you at all. I was simply encouraging mshilarious to keep sharing his insights with us! I'm with you--I'm looking forward to a consensus!

 

[dgatwood]

Keep in mind dgatwood's unit had a modified power supply regulator.

Yeah. And it was one of those ceramic caps, which probably means I bumped it too hard and the thing broke internally and arced. I'm really a little baffled by the amount of output hum on the unloaded supply, though. Oh, well. I don't see the hum once the supply is loaded down (now), so I'm not going to worry about it.

 

[dgatwood]

So I've been hacking on it a little more tonight, working on the grounding problems. The grounds really suck on the 81. Really suck. I shouldn't see a >6mVDC difference in grounds between the boards and the power supply. Really, really, really suck.

I've replaced some of the little 100uF caps with a mixture of 1,000uF and 2,200uF caps and I'm in the process of star grounding all of the minus sides of those caps. The ground is greatly diminished. It isn't gone completely, but I'm definitely making progress at reducing the weird popping, crackling, scratchy noises when I turn the pots and the hum associated with it. I've only reworked some of the boards and I haven't fully connected the star points together yet, either, so there's a fair amount of basic hacking before I even start into things like reducing trace resistance on critical ground traces to various parts of the boards.

I also noticed that if I swap board 5 (the rightmost of the two boards with the inductors on them) and board 3 (the board two boards to the left that does not contain any inductors), the hum drops significantly. I did this before I did any of the grounding mods, so I'm wondering if that would knock the hum down further.

I also noticed that the outer metal of the inductors isn't grounded. Grounding that with a ground wire seemed to help a little, but I don't have a good way of doing that permanently, so I'm going to assume that's a red herring and move on.

 

[P. Glaser]

Thanks to all of you techy guys for the diligence in finding a cure for the ACMP's. I look forward to the final Mod-Manual.

 

[bigtom]

Thanks to all of you techy guys for the diligence in finding a cure for the ACMP's. I look forward to the final Mod-Manual.

I second that. I do hope someone will be kind enough to put all these fixes together in one place(with pictures).

Thanks Guys and keep up the good work!

P.S. If you ever need something hit with a hammer, I'll gladly return the favor!

 

[buckyball]

Anyone else on here live in Nashville? I have a couple of ACMP-84s that seem to be functioning pretty well and I'd love to compare them to some of the other TnC pres.

 

[wmtunate]

Anyone else on here live in Nashville? I have a couple of ACMP-84s that seem to be functioning pretty well and I'd love to compare them to some of the other TnC pres.

I'm in Nashville. Still waiting on my 81s though.