Gelf Electronic-any info

[rotation]

Hi!

Someone from Croatia/Europe contacted me about Gelf Electronic 24/8 (split??he call it like this) mixer. He says it was done in mid 70s, probably custom. He didn't get manual with it and i can't find any info about this company on the internet. There is only one place where Gelf is listed as a company, nothing else.
I haven't got photos from the mixer for now. I asked this guy to get some.

So, anyone ever heard of Gelf Electronic or maybe had some of their gear? Where should i search for manuals?
Guy says it's preamps and specially EQs are good, but there is not enough headroom. Someone suggested him to recap summing module. I think it should be done, but he should first start with input modules, from beginning. Can you give me some advices about what to do with mixer first?

Thanks!

Miha

 

[gyraf]

Best thing in such case is to try to trace down a list of earlier owners, users and servicemen - one of them must have the original manual, or know who to contact about repair issues.

 

[rotation]

I contacted a shop that sels similar mixer. That was the only thing i could find except for info on custom preamp made by Gelf for The Who's bass player.

As i said, the owner of mixer already started to recap summing module ,even if he don't really know why. He claims that if he changes electrolyts on summing module he could rise the headroom. Is this really correct way to do it? I'm sure it won't hurt, but i thnk he should start with input modules first.
There are some tantals too. What are they doing there? Can he change them for electrolyts or he should use tantals?
I got some photos of input modules (only some parts of it). There are line and mic inputs into transformer, Tl074 (CN, Motorola's sign, T8712) and MCI458P (Motorola's sign, 7838). The EQ seems to be based on inductors, but i'm not sure as i don't regonise them.
So what could tantals be doing in this circuit? Is it opssible to replace them with something else?
Is anyone willing to help if i get the schem and better photos?

Thanks!

Miha

P.S.: Somebody else contacted me about the same problem with A&H console MOD3 from 70's. We have good pictures, user manual and some schematics. Why are vintage mixers lacking headroom? Is it because of bad caps, design or something else? Btw, A&H sounds good or better compared to sound card he is using to record and mix.

 

[SSLtech]

Headroom... capacitors...

Complete bullcrap.

There's so much misinformation and 'wishful' implication in the posts thus far that I don't want to even bother.

Here's one brief effort:
Tants have their good points and their bad points. There is no simple answer to the question you posted about replacing them with other electrolytics.

As for recapping increasing headroom, whoever said that has such a tenuous grasp on reality, I suggest that you cease taking advice from them.

<<...consoles from the '70's having poor headroom...>>
Bollocks.

headroom is -above all other single factors- a function of the power rail voltage.

I think you might be confusing 'bad gain staging' and 'marginal operator ability' with 'poor headroom'.

Keith

 

[rotation]

[quote author="SSLtech"]Headroom... capacitors...

Complete bullcrap.

There's so much misinformation and 'wishful' implication in the posts thus far that I don't want to even bother.

Here's one brief effort:
Tants have their good points and their bad points. There is no simple answer to the question you posted about replacing them with other electrolytics.

As for recapping increasing headroom, whoever said that has such a tenuous grasp on reality, I suggest that you cease taking advice from them.

<<...consoles from the '70's having poor headroom...>>
Bollocks.

headroom is -above all other single factors- a function of the power rail voltage.

I think you might be confusing 'bad gain staging' and 'marginal operator ability' with 'poor headroom'.

Keith[/quote]

Look, all this claims in my post are from Roginator, guy who sels old transformers and stuff. He told that guy to change all tantals with Panasonic "double capacitor" to increase the headroom. He didn't mention finding schematic first or start with input modules...
He "suggested" some other things too...
When i said that old mixers don't have enough headroom i was thinking about this two. I know some of them are excellent.


What should we do first except for not listening advices from everyone?
For now i told that guy to stop recaping until we have schematics and more info from experienced people.

Thanks Keith!

Miha

 

[SSLtech]

Hey, -Sorry if I sounded like I was getting at you... Just fed up with the misinformation that gets circulated.

But if that's what Roginator said, then he's COMPLETELY wrong.

I'm completely fed up with the utter nonsense that is being spread about what Re-capping will achieve.

It Doesn't improve noise (hiss/hash). I hear people expecting it to magically make noise go away on a daily basis, and I'm sick of it.

It doesn't improve headroom. That's just wrong. I'll say it to Roginator directly. I would dearly love to know on what he bases this claim.

Replacing old caps CAN bring-back low-end, when the old caps have gone low-value, but if they still read full value, (as they often do) then don't expect even this.

Old power suply caps can improve 120Hz/100Hz power hum rejection, and improve PSU rail stiffness, but again... -if the old caps still read fukll value, don't expect this improvement either.

MEASURE the old caps that come out. If they measure above-value, then you may get no benefit from replacing them. You wouldn't replace tires on a car if they were still perfectly good, so why replace caps that measure perfectly good?

Keith

 

[rotation]

[quote author="SSLtech"]Hey, -Sorry if I sounded like I was getting at you... Just fed up with the misinformation that gets circulated.
Keith[/quote]

No problem, i knew you get lots of questions like this all the time.. Yes, tell to Roginator about it. He had other strange claims too.

Ok Keith, i will do as you said and see what's up.

Thanks a lot for taking time.

Miha

 

[JohnRoberts]

Just to expand on Keith's comments about recapping, if he thinks he's irritated he needs to design consoles and then listen to new owners ask how much benefit to expect from sundry component replacements. :evil:

I suspect the lore surrounding beneficial recapping has to do with old tube gear. Old caps really did lose their electrolyte and actually fail open circuit, plus the extra heat from all those bottles just increased losses.

Modern capacitors are much improved, and while I can't speak for all, many designers are conservative so a given cap could degrade to a fraction of the initial value without significantly impacting the audio passband.

In a several decades old console I'd be more suspicious about switches, faders, pots, and jacks degrading than ICs or capacitors. If the desk is really old some more modern ICs might help, but this is not a given as the IC technology for audio bandwidths has been quite respectable for decades, so a decent design should still make good sounds.

JR

 

[NewYorkDave]

Everyone's looking for a magic bullet. ****, look at me: I installed extra RAM in my PC to whip the latency and buffer overload problems I was having when programming drums in Reason, only to discover that a good part of my difficulty was really due to the fact that I can't play to a click worth a sh*t! :wink:

So John, I read on the Internet that I can make an AMR console into a Total Sonic Orgasm Machine TM if I change all the caps and bias the op-amps into class-A... :razz:

 

[JohnRoberts]

don't poke the bear... :guinness:

JR

 

[rotation]

[quote author="NewYorkDave"]Everyone's looking for a magic bullet. ****, look at me: I installed extra RAM in my PC to whip the latency and buffer overload problems I was having when programming drums in Reason, only to discover that a good part of my difficulty was really due to the fact that I can't play to a click worth a sh*t! :wink:

So John, I read on the Internet that I can make an AMR console into a Total Sonic Orgasm Machine TM if I change all the caps and bias the op-amps into class-A... :razz:[/quote]

I read i could transform Gelf console into high end console with lots of headroom by changing 130 tantals to 130 Panasonic 47uF (35 V) and replacing 4 unknown (to me) caps from, i guess, PSU to 4 RIFA 1000uF (25 V)...

Keith and John Roberts:

I asked for detailed photos of one input module, PSU and summing module, and alyready got LOTS of photos of console's interiors.
I think i will start to write schematic of input module and continue with summing and PSU.
Is it ok like this? Should i do something else first? Problem is, that console is far from me. I will go there, but first i need a good reason.

Miha

 

[JohnRoberts]

Perhaps a good starting point is to run some measurements on the audio path and see if there are any issues that need to be addressed.

It may not need fixing. If it does, measurements will suggest what to look for.

JR

 

[SSLtech]

[quote author="JohnRoberts"] measurements will suggest what to look for.[/quote]
Ah, there you go again John... -Getting all "proper" and "Engineer-ey" on me/us.

Can't you give us all a break and just share the brand name of the various PCB coatings that you used to use to reduce noise, improve distortion, add headroom, cure cancer and reduce the trade deficit?

-I KNOW you're keeping it close to your chest, but we've been civil or long enough... -Don't make thing get ugly! :wink:

Keef

 

[JohnRoberts]

One thing I discovered early on, is that finesse matters in circuit design. There is such a thing as an optimal value as well as type of components. The hot rod, recap mind set is IMO over invested in how a "type" of cap acts, instead of how a given "value" cap acts in a specific circuit.

To wit, bigger and/or higher voltage is not always better, but may be. Newer is not always better but may be. I like to joke that consoles are the most complicated simple circuit to design, power amps come in a close second. Some would argue the opposite order. I guess it depends what you're working on at the time. Simple in concept, difficult in execution.

Sorry no magic potions, just attention to detail and the experience of having already made most of the common mistakes.

JR

 

[SSLtech]

I dig it.

[quote author="JohnRoberts"]Newer is not always better but may be.[/quote]

You just reminded me that there are two types of fool in the world:

One who says: "This is old and therefore good"

And another who says: "This is new and therefore better".

Keith

 

[SonsOfThunder]

I'll stick my neck out and risk getting whacked by the big guns (keef and JR!) and say that from my experience with a few older/cheaper mixers there is probably something to be gained by simply removing capacitors. My Yamaha MC1602 has a bunch of small value caps around every opamp input and I can only imagine that removing some of these could increase bandwidth and open up the top end on some of these mixers.

Now the problem would be that the mixer might be more susceptible to RF interference, but in many environments, it wouldn't be an issue.

 

[JohnRoberts]

I am not familiar with what's inside that particular mixer but I will offer the general observation that especially in lower cost (value) products, you don't throw in extra parts, especially if these extra parts limit performance. The classic engineering story is about a TV set maker who would force his engineers to justify the need for every component by walking around the lab with a pair of clippers and removing parts until the set stopped working.

I can't answer your hypothetical, but my general observation is that it's better to limit bandwidth in a controlled manner using a filter, than allowing the electronics to run out of gas and be the limitation.

JR

 

[SonsOfThunder]

JR,

I'm not saying that the parts themselves are superfluous, but that their values are sometimes way too conservative. It is probably bad practice to just remove them altogether. I need to drag out that mixer and do some real measurements and prove or put to bed that theory of mine.

I'm sure you've designed more stuff than i ever have/will. But I agree with your view of filtering. Also our Sr. Design Eng says never use a part that's any faster than you really need. Though I've seen some of his audio amp designs that go beyond 100kHz too. :green:

 

[JohnRoberts]

Regarding speed, if you properly bandlimit signals you can design circuitry that is impossible to slew limit, so faster than needed parts are either a waste of money or more likely compromise something else to be very fast. There is no free lunch, while some newer parts are quite nice.

JR

PS: wrt to slew limiting, devices become progressively less linear as they approach slew limit, just like approaching voltage limits, so I prefer a comfortable margin of more speed than needed, just not excessive speed for the application. There are many fairly common parts that are adequately fast.

 

[da_ardvark]

[quote author="NewYorkDave"]Everyone's looking for a magic bullet. ****, look at me: I installed extra RAM in my PC to whip the latency and buffer overload problems I was having when programming drums in Reason, only to discover that a good part of my difficulty was really due to the fact that I can't play to a click worth a sh*t! :wink:

So John, I read on the Internet that I can make an AMR console into a Total Sonic Orgasm Machine TM if I change all the caps and bias the op-amps into class-A... :razz:[/quote]

Dave I'd be interested in hearing some of your programmed drums from REASON. Mine end up sounding like crap :sad: