JLM Baby Animal

[mattmoogus]

Can you measure 48v between pins 1 and 2 of the input XLR when phantom is on? If the led is coming on there aint much else in the way other than wiring. Take some hi res close up pics of the PCB and wiring (with macro mode on) and email to Joe or me and we should be able to spot the problem.


M@

 

[Schmilsson]

[quote author="mattmoogus"]Sounds like you have your soundcard/mixer set to -10 instead of +4?...

The pots will make a little noise especially when the circuit is still stabilising but it shouldnt be very loud unless youre running it into a -10 input.

M@[/quote]

I've got a firebox, same as whoever it was having problems with that combo earlier in this thread. The firebox is balanced, perhaps not set to +4? Who knows, I'll send them a mail.
I've tried it in other setups too(balanced +4) but it's pretty much the same, distorts way too easy. DI's bass for instance distorts with the pad in and the gain at zero. I mean, should you even get a signal?

 

[bluezplaya]

Hey guys, I was wondering how to hook up a 5mm LED for the power switch. What resistors do I use?

Thanks,
Adam
:sam:

 

[Schmilsson]

[quote author="mattmoogus"][quote author="JLM Audio"]For the power LED you can use 4k7 to 10k in series with a LED across the switched 48v rail.
[/quote]


10k is the official JLM brightness value for 48V :wink:
:razz:



M@[/quote]

 

[yodermr]

[quote author="mattmoogus"]Can you measure 48v between pins 1 and 2 of the input XLR when phantom is on? If the led is coming on there aint much else in the way other than wiring. Take some hi res close up pics of the PCB and wiring (with macro mode on) and email to Joe or me and we should be able to spot the problem.
M@[/quote]

Matt, I emailed some pics to Joe.
Checked for 48v between pin 1and pin 2 - nothing. Trying to think through this, I noticed that I never grounded pin 1 or the (-) to the case, so I did. It didn't give me 48 between 1 and 2 and now I have a worse(?) problem. After that experiment, the 48V light won't come on and I can't even get a dynamic mic to work. Crank the gain and it will crackle through.

Also, not sure what it means but i have 48v going into the board but any other test point your schematic specs out at i get at most 1.6v


M

 

[mattmoogus]

Are your 10ohm resistors ok? Do they measure 10ohms in circuit?

You definitely need to connect pin1 to 0V on the BA PCB, as well as 0V from the DC power input socket.


M@

 

[yodermr]

[quote author="mattmoogus"]Are your 10ohm resistors ok? Do they measure 10ohms in circuit?

You definitely need to connect pin1 to 0V on the BA PCB, as well as 0V from the DC power input socket.


M@[/quote]

the 10ohm is not ok. reading about 800k now. i'll replace, rewire and report back. i can steal a replace out of the other ba kit i have.

anything special about the green resistors :?: thought i read somewhere they were carbon instead of metal film. any reason i can't replace with metal film :?:

 

[yosh]

I'm a huge fan of the JLM stuff since I built the dual 99v. Amazing. Now I'm thinking about putting together a few of these and I have a question about the Hybrid opamp. It seems to me that it would be useful to add a switch on the front panel wired to the two pads which change the opamp from class A to class A/B. Is there anything about this idea which would not work? Would it be bad to switch the opamp while the unit is powered up?

Thanks in advance.

-Josh

 

[yodermr]

[quote author="mattmoogus"]Are your 10ohm resistors ok? Do they measure 10ohms in circuit?

You definitely need to connect pin1 to 0V on the BA PCB, as well as 0V from the DC power input socket.
M@[/quote]

replaced the 10ohm, rewired the connections and grounding scheme, fired her up and...perfect :green: no noticible noise. sounds very nice so far, gotta play more with it

that noise when you have the pad on and crank the gain is still there...but...what i found is that i really don't need to go there. lots o gain flexibility

i'm excited, three more to go....
m

 

[mattmoogus]

Ok cool!
:thumb:
Weve found that the normal metal film 10ohm resistors have been failing on bootup, thats why we now put carbon 10ohms in instead. If you can find them locally you should replace the metal film 10ohm as one day they will probably fail. If you cant drop Joe an email and well send you some carbon ones.

Do you only get the noise with the pad in or does it occur whenever you have the gain up at full? I would suggest sorting that issue out before building the others in case you do the same thing to all of them.


M@

 

[yodermr]

The noise occurs with the pad on and only when you get to the last few detents on the gain (all the way up)

On the 10ohm resistor, I have a 1/2 watt carbon one. Is this Ok?

 

[mattmoogus]

That resistor should be fine. I havnt seen the pics of your wiring so I cant say why its still oscilating at high gain...might have to wait for Joe on that one.


M@

 

[yodermr]

[quote author="mattmoogus"]That resistor should be fine. I havnt seen the pics of your wiring so I cant say why its still oscilating at high gain...might have to wait for Joe on that one.
M@[/quote]

yea, well, uhmm, it seems i didn't get rl installed [27k or 100k] :shock:
could that be the problem :?: sounds so nice now, should it even be able to work without it :?:

 

[Purusha]

Matt, please check your PMs :wink:

 

[yodermr]

[quote author="mattmoogus"]That resistor should be fine. I havnt seen the pics of your wiring so I cant say why its still oscilating at high gain...might have to wait for Joe on that one.
M@[/quote]

Ok, I put in the missing RL resistor and the problem went away. Everything sounds great now.

Sorry, for the trouble, going too fast and not thinking

M

 

[mattmoogus]

Yup that makes sense. Without RL the OEP gives a big top end boost and extra gain, hence the oscilation at high gain settings. Glad to hear its all working now!


M@

 

[Purusha]

I have a question regarding the JLM 1:4 + 99V + JLM 1:1:1 vs OEP + 99V. What is the actual difference in the sound of these two? I would make a second pre of one of the two mentioned for some stereo coloring. I might also use such pair for mastering as well. I heard some people go through such pres to get some nice analog color. Would any of these two be great for this? One could also use such stereo pre for gain stage of the passive Pultec.
I have one empty space left in my Quad pre case but I don't know which one of these two make any sense to go stereo. Anyone wants to comment?

BTW, I wish someone would make a few BA PCB layouts in PDF with all changes required (zener, resistors, jumpers...) for most of the combos used around here. I am still struggling to grasp it from the JLM site. It could be done in a more simple visual way.

 

[Schmilsson]

[quote author="Purusha"]
BTW, I wish someone would make a few BA PCB layouts in PDF with all changes required (zener, resistors, jumpers...) for most of the combos used around here. I am still struggling to grasp it from the JLM site. It could be done in a more simple visual way.[/quote]

When I saw the charts on the website I was kinda confused but as soon as I got my package from jlm and had the pcb's in my hand it was really easy to comprehend.

 

[Purusha]

OK, I got it now. The first table is understood. The second also.

The only thing I don't dig is when should one go for high and when for low ratio setting (OEP262A3C and LL1538) ?

 

[matta]

The only thing I don't dig is when should one go for high and when for low ratio setting (OEP262A3C and LL1538)

Totally up to you, only major difference is that one has more gain. So do you need +70db of Gain with the OEP, you might if you have some Ribbon mics, but you may choose to not need that much and go for the LOW ratio.

All about options Bro, I like options

Cheers

Matt