Langevin Am16.. has it been DIYed ????

[emrr]

Again, I think Manley/Langevin would be bulding them if the price point made sense. There are just too many good used ones on the market at too low a price from the manufacturing point of view.

 

[Tillmann]

I'd like some feedback on people who have used the originals and others that DIY'ed them. I've got a set of four of the Chae DIY's. I've been having some problems with them overloading using a Schoeps capsule. I'm just curious how these should handle hot output levels from mics. Someone told me that the original AM16's should be "bullet-proof" as far as distortion and input overloading. I've not had problems with these in the past, but I can't get mine on the bench for a bit since I'm using them for a location project, so I'm not sure if this is just an issue with that mic in particular or if these are prone to rather nasty distortion from hot mics. Perhaps mine just need some servicing?

Cheers,

T

 

[jensenmann]

My AM-16s are racked with input pads à la JLMaudio. I never expierienced the problems you have. But it may origin in the fact that I mostly use dynamic mikes with it.

 

[Tillmann]

Thanks Jens. I've mainly used dynamics with them in the past as well. That's a major reason why I'm asking.

 

[Rob Flinn]

I have 2 original AM16's. I have to admit that I don't actually use them a great deal. However, when I have used them I have never experienced any problems of the type you are describing

 

[emrr]

look at the specs for max output, subtract the gain amount, there's the overload point. Any condenser will easily overload a fixed gain preamp like this when used without a pad. Most vintage stuff like this overloads by -22 dbm, some won't even take -30 dbm. A 57 on a guitar amp will put out -15 dbm easily.

 

[emrr]

From:

http://www.groupdiy.com/index.php?topic=6620&start=30

[quote author="emrr"][quote author="Rob Flinn"]Donny Sparks

With regards to my post:

and Rob,
"Just a small point but if you have these mic amps set for +24dBm operation the harmonic generation is greater by 0.25% than if you have them set for +18dBm."

is that desireable harmonic generation as in even harmonics?

Probably the best thing to do is try it both & see if you notice a difference. Then you have the option of hardwiring one way or being able to select the harmonic generation with a switch.[/quote]

I'd think the distortion would be primarily 3rd harmonic, being a balanced circuit.

I think this power/distortion issue needs to be looked at another way. WITH 6 DB MORE LEVEL GOING THROUGH THE UNIT, you get another 1/4% distortion. This is true of most any gear at some point approaching the maximum headroom. I bet it's at least the same (if not lower) distortion when set for high power with identical levels (say, +16 dBm) passing. Is it the transformers approaching saturation at the higher power level? Is it the transistors? Is it both? Anyone really know?

Another thing; this is a fixed gain preamp. When you go high power for more output capability, the maximum input point also moves. So, there is a magic point in the headroom shift where the lower power setting will crap out and have more distortion than the higher power setting. If the specs are to be trusted, then -27dBm is maximum input for the low power setting, and -21dBm is max for the high power setting, so -24dBm would be a problem for the lower power setting and yield more distortion than the higher power setting. If you extend that thought to 20 db input pads, you still end up in a zone where the output of many modern condensers could cause problems with the low setting. Hell, with the high settting too. At any rate, I'm not convinced there's a great reason to run at the lower power setting, at least not with any type of loud input signals and hot mics. If you're always putting a 77DX into it then it could be another story.

There may be some noise issues with the power shift that I can't address from experience yet. I believe Soundguy had some commentary about greater noise in the AM-17 with the higher power strapping, but that is actually a shift from 1W (high line level) to 8W power amp level, with power transistors as outputs. They may behave differently.

Put in a power shift switch if you really want to nerd out......[/quote]

 

[cannikin]

[quote author="Tillmann"]I'd like some feedback on people who have used the originals and others that DIY'ed them. I've got a set of four of the Chae DIY's. I've been having some problems with them overloading using a Schoeps capsule. I'm just curious how these should handle hot output levels from mics. Someone told me that the original AM16's should be "bullet-proof" as far as distortion and input overloading. I've not had problems with these in the past, but I can't get mine on the bench for a bit since I'm using them for a location project, so I'm not sure if this is just an issue with that mic in particular or if these are prone to rather nasty distortion from hot mics. Perhaps mine just need some servicing?

Cheers,

T[/quote]

Hi Tillmann,

I don't have "hot mic" issues with mine, you have the impedance switch, right? that should give you some control.... If you hard-wired the switch for just one impedance that might be your problem. I use mostly ribbons with mine, never ever had any distortion problems. I'm sorry I can't help any more than that .... all the transistors have heat sinks Correct? ... I knew Chae was very clear that they need to be sinked well because of heat issues. Maybe one burned up?

let me know

 

[emrr]

Neglected to mention, but a very low Z load could affect the overload point of the Schoeps electronics. I don't know those mics output characteristics, but I seriously doubt that's the issue.

The high power strap bit in the quoted post should considered.

I'm 95% certain this is a normal overload issue, and any attempts towards repair are wasted effort, at least until you put some tones in, measure some levels, and get a grip on the headroom issues inherent. Everyone posting with no problems is also using dynamic mics and ribbons. I've never seen a ribbon overload a preamp like this. I see 57's overload them with no pads up front. Condensers have even higher output, right? Even with an input pad, a 57 on a snare will come close to overloading a pre like this at times. It's not uncommon to put a 414 on a bass amp, pad the mic 10 db, then use a 20 db input pad before an AM-16. Yes, that's only 10-15 db gain out of a fixed gain 40-45 db preamp,with 30 thrown away.

 

[Tillmann]

Thanks folks, for all the feedback. Doug, thanks for highlighting your previous post. I saw it before during my search and was gonna go there when I could. I can't get at the thing to open it up right now since it's in a rack on a truck traveling from location to location. Cannikin, as to you using it with ribbons, well there you go. There's not a ribbon that I know of that has anywhere near the output of a Schoeps transistor series. I've never had problems with this before, but I've never used them with this mic doing hot vocals either. I've pretty much used them with dynamics and room mics. The impedance switch did nothing for me.

I'm kinda doubting that a transistor burned up, just by how it's responding. It's overloading, but sounds fine on normal level sources. I actually bought the rack that Chae did himself, so I feel like his work would be solid, and have no reason to believe otherwise yet. I contacted Chae and just found out that the "gain" knob is actually an output attenuator (could have found that out myself if the original build link had not disappeared from the site- likely was always in the Black Market and never got moved to the Lab and was therefore deleted- DOH!), and I read here (thank you search function!) that with this circuit, attenuating the input is a much better idea unless you want to push the circuit. My guess is that what I need to do is to modify this to have a variable input pad that can work at not only 20, but also 30 and maybe even 40dB. That way, in cases like this, I can run the outputs virtually wide open and not get any "bottlenecking". The 20dB pad was not enough in some instances where the singers were right up on the grill of the mic screaming "I'M YOUR HOOCHIE COOCHIE MAN...". :grin:

I'm also gonna investigate the "high power mode" a bit more (emailed Joe Malone about it yesterday). Maybe it's running in low power mode and the high power mode would help with some additional headroom.

 

[Tillmann]

[quote author="emrr"] I'm 95% certain this is a normal overload issue, and any attempts towards repair are wasted effort, at least until you put some tones in, measure some levels, and get a grip on the headroom issues inherent... ... ...[/quote]

Thanks again, Doug. I started typing my last reply before you posted this, so there's some overlap there. We're having the same gut feeling without even knowing it, so I think that's a good thing! :thumb:

 

[Whoops]

By the way anyone by chance has a Chae Langevin board in the drawer?

I would buy it from you.

thanks

 

[0dbfs]

Not sure what the AM16 sowters are going for but there is an AM16 for $300 on VintageKing:

http://vintageking.com/Shop-Used-Categories/Mic-Pre_2/Langevin-AM-16-mic-pre-used

Cheers,
j

 

[Whoops]

By the way anyone by chance has a Chae Langevin board in the drawer?

I would buy it from you.

thanks

The AM16 Sowters input and output are going for 55 Pounds each

 

[emrr]

Looks better this month since the pound has fallen so far.  Only thing i would bring up again regarding cloning is transistor matching.  I've not done one of these, but the Altec 9470A can be a real PITA to get correct low end response out of.  Output matching really must be done in circuit, and response measured.  The Altec at least can be down 6 dB at 100 Hz with poor output matching.  So be prepared to possibly delve into that aspect. 

 

[SoundBase]

Cinemag also makes transformers for them. I'd be interested if some one has done pcbs. Not sure what transistors to use as I haven't seen 2n929 at digikey or mouser.
Sometimes its fun just to diy anyway.

 

[Whoops]

Cinemag also makes transformers for them. I'd be interested if some one has done pcbs. Not sure what transistors to use as I haven't seen 2n929 at digikey or mouser.
Sometimes its fun just to diy anyway.

Hi,
I didnt know that Cinemag made langevin am16 type  transformers, I couldnt find it in their website. What transformers are those?

A PCB was made a long time ago, it was a limited run. If you want to buy a board the only option is finding someone that bought one but never completed the project. You could post in the Black Market

Cheers,
T

 

[CJ]

did some boards a while back, never stuffed them,

need the C cores to make the transformers, AM 16 sound is in the iron,

waved soldered these and the guy left a solder bridge, wtf, over?  ???

you can get bolt on heat sinks for this project,

these boards are double sided, hard to DIY, traces run over each other which forms mini capacitors to kill RF and other gremlins,

 

[Whoops]

did some boards a while back, never stuffed them,

need the C cores to make the transformers, AM 16 sound is in the iron,

waved soldered these and the guy left a solder bridge, wtf, over?  ???

you can get bolt on heat sinks for this project,

these boards are double sided, hard to DIY, traces run over each other which forms mini capacitors to kill RF and other gremlins,

Cool boards CJ,

are you doing the transformers yourself?

thanks

 

[Whoops]

I found a picture of Chae's Board that was offered a long time ago.
in the picture the transformers are Sowter.

The project at the time was called Bellerophon.

It makes sense that people are interested at the moment in DYing the Am16, prices of original units are quite high nowadays in the second hand market, I've been following the sales of AM16 on ebay and people are paying 400/500 dollars for 1 channel. I know it was not the same some years ago but things changed.

I have some AM16 documents and schematics if anyone needs them for research.

Thanks