JLM Baby Animal

[usekgb]

Just get the JLM14. You won't be dissapointed! The OEP may give you more gain, but I have found that my BA's with the JLM14, 99v, and JLM1:1: have more than enough gain for most everything that I do. This combo really sounds excellent.

Cheers,
Zach

 

[z15]

Well, this was my first build and seems to work very nicely and sound good! 1 channel of BA with JLM14 + 99v and DI, in a light mobile case. The only thing I screwed up during construction was wiring the gain pot wrong way round at first, but it was pretty obvious what was wrong when testing the first time :grin:

I could post a picture of two but I don't have a digicam handy and there isn't anything much special anyway - the wiring is a bit messy due to the small box and my newbiness and the box is a pretty standard little Hammond extruded aluminium case. I'm planning to ask a friend do me some stencil artwork on top plate of the case though, if any standard spray paint will stick on anodized aluminium... After that it might be worth showing for fun!

Big thanks to Joe & Matt... and to people who had already posted questions here that came to my mind when building!

 

[JimiH]

Well, here goes my third post...

Just finished a BA channel using JLM14/John Hardy 990/JLM111 combo. Sounds bloody fantastic!! And to top it off, I got it right the first time! Worked straight away it did. I'm so proud of myself. This is my first real forray into DIY as far as studio/recording gear goes... well, first that I actually followed through with and actually works!

I am currently usig a presonus firebox which, unfortunately, has -10dB line level inputs. What I am wanting to do is pad down the output of my BA so I don't get are correct, and the preamp sounds right, b so much hiss. It's not too bad, but it's deffinitely there, and I would like to get rid of it. Would I be going about it the right way by attenuating the output by 14dB or roughly 5:1... I think..? How would one go about doing this?

So yeah, I'm mega happy with the sound I'm getting out of this baby, but should the 990 really be getting so hot? All the voltages measure all good but the opamp gets almost too hot to touch. Could I be getting some kind of really high frequency oscillation?

Just gotta say, this forum is awesome! Especially this BA thread. There is such a wealth of information I refered to while building that I hardly had to ask Joe any questions at all. I'm looking forward to making the second channel out of the parts I ordered that are just laying about idly. I'm thinking of getting a quad mic pre rack enclosure off Purusha and in that I guess I had better get another 2 channels worth of BA parts. Oh dear. And so it starts...

 

[JLM Audio]

Just get the JLM14. You won't be disappointed! The OEP may give you more gain, but I have found that my BA's with the JLM14, 99v, and JLM1:1: have more than enough gain for most everything that I do. This combo really sounds excellent.

:grin: Yes if it is your first BA this is the benchmark setup to start with.

Well, this was my first build and seems to work very nicely and sound good! 1 channel of BA with JLM14 + 99v and DI, in a light mobile case. The only thing I screwed up during construction was wiring the gain pot wrong way round at first, but it was pretty obvious what was wrong when testing the first time.

Big thanks to Joe & Matt... and to people who had already posted questions here that came to my mind when building!

Thanks everyone for posting up here and helping out other BA builders :grin:

I am currently using a presonus firebox which, unfortunately, has -10dB line level inputs. What I am wanting to do is pad down the output of my BA so I don't get are correct, and the preamp sounds right, b so much hiss. It's not too bad, but it's deffinitely there, and I would like to get rid of it. Would I be going about it the right way by attenuating the output by 14dB or roughly 5:1... I think..? How would one go about doing this?

This is the right idea as it will get the BA working at the right signal level. If you are doing it on the output of the BA unbalanced then a 820R in series with a 180R to 0v will give you a 14dB pad. But the place this pad should be is on the input to the firebox and so all your gear can run at pro level into it. But so all your equipment can drive into the pad it would be best to scale the resistors up to make a 10k load so use 8.2k in series with 1.8k to 0v. If the firebox is balanced in then make a U pad using 2 x 3.9k and a 1.8k.

So yeah, I'm mega happy with the sound I'm getting out of this baby, but should the 990 really be getting so hot? All the voltages measure all good but the opamp gets almost too hot to touch. Could I be getting some kind of really high frequency oscillation?

You can usually hear if the opamp goes into oscillation at high gain settings as the gain pot will make a pop as it hits the point where the oscillation starts. But an oscilloscope is the easiest way to check if you have access to one. You can make the 47pF as large as 220pF if needed which will limit the bandwidth a bit more and may help if there is oscillation.

 

[MegaMutt]

Hi Joe and all here.

I recently picked up the baby animals that therecordingart sold here a few weeks back. He had prestuffed the boards and it seemed like a good way for me to get my hands around all of this and see a project already started through to completion. Thanks to Art for his fine work on stuffing the boards.

With all that said, I'm finally getting around to wiring these things up and need some help.

Sorry if it seems so basic, but this is the first DIY project that I will complete. So please bear with me...

I'm using the 48v JLM BA power supply. The boards are configured with the JLM 14 and OPA 2604.

I'm a bit confused by the wiring overlay diagram on the JLM site.

EDIT:

therecordingart was helpful to send me this info via email and I think I've got it down:

Connect + from the plug to one of the contacts on your on/off switch then wire from the other contact on the on/off switch to the first PCB in the chain.

+ from the plug (or on/off switch) goes to 48V on the PCB
- from the plug goes to 0v on the PCB
Output + on the PCB goes to pin 2 on the XLR
Output - on the PCB goes to pin 3 on the XLR
0V on the PCB goes to Pin 1 on the XLR
Input + on the PCB goes to pin 2 on the XLR
Input - on the PCB goes to pin 3 on the XLR
0v on the PCB goes to pin 1 on the XLR

You'll have to "daisy chain" the PCBs 48v and 0v. The 0v on the last PCB in the chain you can wire that to the pin 1 on one of the XLRs and then daisy chain all of the pin1s together.
The same goes for the gain swith. I know I had to daisy chain those to 0v as well.

You'll end up with a spaghetti mess of wiring, but it makes sense when you think that 0v is ground. Every last XLR, PCB, and gain pot needs to be connected to 0v.

For the gain pots, 2 of the pins on the pot get tied together and go to 0V.

Ok, here some addtional questions:

Joe mentions that his connector grounds to the case when connected. Do I need to connect an additional ground off of the connector or off of the pcbs to the case?

Any addtional direction, comments or help is appreciated. I'm really looking forward to getting these up and running.

Thanks,

-rich

 

[JLM Audio]

Joe mentions that his connector grounds to the case when connected. Do I need to connect an additional ground off of the connector or off of the pcbs to the case?

The DC connector we use does connect the case to 0v when the DC plug is inserted. So nothing else needs to be done. If you want a better connection to the case you can take a wire from the 0v at the DC connector and run it to the 4 chassis pins on the XLR's so there mounting screws also connect the 0v to the case.

Also when using power coated rack cases it is worth using a ohmmeter when the case is screwed together to check all panels are electrically connected as the powder coating can stop the connection. All that is needed usually is to use a drill bit in the countersunk holes to take some paint off under were the screw head sits into the top and bottom panel to fix this. If you touch a toggle on the front panel and an audio buzz comes out of the mic pre output this will usually be the problem.

 

[Hammond]

Hi All

I'm building two BA with OEP + 99V and two DI.
I've a stupid question, the two 100uf 50V caps in the DI does have a polarity or not? i'm a bit confused cause there's not a + or - sign on the cap or pcb but one leg is longer than the other.
Thanks

 

[JLM Audio]

I'm building two BA with OEP + 99V and two DI.
I've a stupid question, the two 100uf 50V caps in the DI does have a polarity or not? i'm a bit confused cause there's not a + or - sign on the cap or pcb but one leg is longer than the other.

The JLM DI kit comes with 1 x 100uF 50v Green EXR cap which is polarized and must go in as marked and 2 x 100uF 50v black Non polarized caps. The Non or Bi polar (BP) caps can go in either way around which is why there is no positive marked.

 

[Schmilsson]

[quote author="JimiH"]
I am currently usig a presonus firebox which, unfortunately, has -10dB line level inputs.[/quote]

I'm pretty sure they're +4dB if you use TRS.

 

[JimiH]

I'm pretty sure they aren't. I was getting mega hiss (well, substantial) when I was going straight from my baby animal in and now that I have padded it down it's all good.

 

[Purusha]

I have a question regarding the variable Z. I am using the 60k + 200k log pot in my LL1578 in high ratio combo but
can't hear much difference. I wonder why. I was expecting more impact just like with my all JLM iron combo...

I am also trying to get the info on what R+pot should I use for variable Z with OEPs A3C in high gain. Anyone knows this?

 

[mattmoogus]

Ive tried variable Z with the 1578 and it doesnt sound any good to me. I have the pot there but I always leave it open (250k) as ive never heard a useful sound come out of it set any lower.


M@

 

[Purusha]

Good to know :thumb:

What about with OEPs, worth to have the variable Z on these?

 

[mattmoogus]

The one we use (I can never remember the number, the higher ration one) works well with variable Z - you get a big tonal change and it still sounds good/useful at all settings.
From memory, we use the same 100k log pot as we do with the 1:4 but with a 15k stop resistor. I think if you try to deload it too much it gets really bright and you need a big dampening cap to stop it oscilating.


M@

 

[Purusha]

Can you give me more info about this big cap? How big and where it goes?

 

[mattmoogus]

[quote author="Purusha"]Can you give me more info about this big cap? How big and where it goes?[/quote]


Its CL.


M@

 

[Purusha]

Thanks Matt, now I just need to find out the increased value of that cap :thumb:

 

[mattmoogus]

You can try different values and see what happens if you want. Id just stick with the 100k pot though, then you can use the standard value for CL listed on the website. You get heaps of tonal change that way anyway.

BTW, as a general rule, the variable Z idea doesnt work with high ratio transformers as their sec load resistor is already so high you cant really de-load them any more, and if you overload them often the freq response becomes unusable, ie bad sounding.



M@

 

[Purusha]

BTW, as a general rule, the variable Z idea doesnt work with high ratio transformers as their sec load resistor is already so high you cant really de-load them any more, and if you overload them often the freq response becomes unusable, ie bad sounding.

I see, so my high ratio is wrong for this. Low ratio will give me a little less gain, yes?

 

[JimiH]

What's going on? Has everyone become bored with their baby animals?? I wanna see some BA bragging and more show off photos! I just finished a second channel with a JLM14/Hardy 990/JLM111 combo. Magnificent little preamp. I can't believe how "uncrap" I can get a 57 to sound through these Babies. I am very much in love with these preamps.