JLM AUDIO

OK Joe,

I'll just make sure the right power supply goes with the right mic pre.

Thanks again.

Sylvain

Finished up my BA4 with Jensen transformers & 990s, Sound great.
Channels 1&2 = JT-MB-CA, Channels 3&4 = JT-11K8-APC. Outputs = JT-11-BMQ.
+/- 0.5 dB 20-20khz - +1 dB boost @ 30khz with the 11k8
noise floor @ -107 with gain up.
0.0019 THD


DSC_0003 by rhythminmind, on Flickr

DSC_0005 by rhythminmind, on Flickr

DSC_0014 by rhythminmind, on Flickr

DSC_0020 by rhythminmind, on Flickr

DSC_0029 by rhythminmind, on Flickr

DSC_0031 by rhythminmind, on Flickr

DSC_0034 by rhythminmind, on Flickr

DSC_0037 by rhythminmind, on Flickr

DSC_0047 by rhythminmind, on Flickr

DSC_0056 by rhythminmind, on Flickr

DSC_0054 by rhythminmind, on Flickr

DSC_0060 by rhythminmind, on Flickr

Nice looking BA4 build and some cool photos

So can anyone shed some light on my low output distorted BA circuit? My other channels are working fine except for one and I have tried everything. This circuit in question is an OEP/99v/1.1.1 combination.

Circuit was working fine before, but suddenly now I have this medium range output, - well I mean that my my VU input meters only move to about half way where as on my other BA circuits they almost blow full on and go into clipping. Also the output when turning the BA's gain control past about 3 o'clock on this BA circuit is distorted.

For the sake of it:

1) all voltages check in the same with that on the BA outlay diagram
2) I tried swapping 99v's but the problem remains
3) tried to get rid of the 1.1.1 output transformer and wire the output xlr directly but problem remains
4) Tried a different SMPS 48V power supply but still the same problem.

I just don't get it. I am stumped. The only thing I can think of is the OEP input transformer has thrown in the towel?

Any advice greatly appreciated.

deuce42 wrote:So can anyone shed some light on my low output distorted BA circuit? My other channels are working fine except for one and I have tried everything. This circuit in question is an OEP/99v/1.1.1 combination.

Circuit was working fine before, but suddenly now I have this medium range output, - well I mean that my my VU input meters only move to about half way where as on my other BA circuits they almost blow full on and go into clipping. Also the output when turning the BA's gain control past about 3 o'clock on this BA circuit is distorted.

For the sake of it:

1) all voltages check in the same with that on the BA outlay diagram
2) I tried swapping 99v's but the problem remains
3) tried to get rid of the 1.1.1 output transformer and wire the output xlr directly but problem remains
4) Tried a different SMPS 48V power supply but still the same problem.

I just don't get it. I am stumped. The only thing I can think of is the OEP input transformer has thrown in the towel?

Any advice greatly appreciated.

Does the output hiss turn up with the gain pot turning up?
What ratio is set high / low?
What ohms do you get between pin 2 & 3 of the input XLR with the pad off?
What ohms do you get across Rload?

Thanks for your help Joe

1) 21.3 ohms between pins 2 and 3 of xlr input
2) RL = 10k resistor and 100k pot
3) Ratio is set low or middle position of the pins
4) Not a huge amount of hiss, but at about the last 20% of the gain knob's maximum hiss starts and does increase until the gain is maxed. The distortions is very rough - like if you plug a bass guitar into the DI it sounds like an overdrive pedals been added from about 3/4 of the gain control till the max gain.

Thanks

deuce42 wrote:Thanks for your help Joe

1) 21.3 ohms between pins 2 and 3 of xlr input
2) RL = 10k resistor and 100k pot
3) Ratio is set low or middle position of the pins
4) Not a huge amount of hiss, but at about the last 20% of the gain knob's maximum hiss starts and does increase until the gain is maxed. The distortions is very rough - like if you plug a bass guitar into the DI it sounds like an overdrive pedals been added from about 3/4 of the gain control till the max gain.

Thanks

Ok the opamp seems to working if the hiss can be heard at full gain. And the wiring to the primary of the input transformer is correct. Is the votlage at the out pin of the 99v around 24v?

But I needed you to measure ohms with a meter across the RLoad position with variable impedance set as high as possible which should be about 1k to check the secondary of the input transformer is intact ?

Also would be good to check the JLM111DC 3 windings still measure 15ohms each?

With impedance fully clockwise I measure 1.2k across RL

Am getting 25.3v at Op amp +Out

My output transformer seems to read:

53.7ohms between +1 and +2
38.2ohms between +1 and +3
16.9ohms between +2 and +3
23.1ohms between -1 and -2
7.8 ohms between -1 and -3
16.9ohms between -2 and -3

Maybe this output transformer is part of circuit is the culprit? But the thing is, without an output transformer I still get low gain and distortion, and using another JLM1.1.1. I also get the same.

Still confused.

Thanks again

deuce42 wrote:With impedance fully clockwise I measure 1.2k across RL

Am getting 25.3v at Op amp +Out

My output transformer seems to read:

53.7ohms between +1 and +2
38.2ohms between +1 and +3
16.9ohms between +2 and +3
23.1ohms between -1 and -2
7.8 ohms between -1 and -3
16.9ohms between -2 and -3

Maybe this output transformer is part of circuit is the culprit? But the thing is, without an output transformer I still get low gain and distortion, and using another JLM1.1.1. I also get the same.

Still confused.

Thanks again

Ok you need to test the output transformer per winding +1 to -1 , +2 to -2 , +3 to -3 each should be 15R. But doesn't seem to be the problem if swapping the transformer didn't change anything.

Is the output transformer wired +out to 0v on the output of the BA?

Remove the +out wire and measure between +out and 0v on the BA terminals to see if you measure 10k or a short?

Check the 51R next to the opamp output pin measures 51R?

Do any of the 470uF 50v cap have puffed up tops?

Ha, so that pesky 51R at the output was measuring like 6k or thereabouts. Strange, replaced it and now I have full output! Thanks Joe.

I just have one final question, the circuit does seem to have a bit bit of distortion, at least compared to my other BA's- although my other BA's have jlm1.4 and cinemag input xformers and this one's an oep. Am wondering if the slight distortion is a function of the input transformer or some other part of the circuit needs a bit of my attention?

Thanks once again

deuce42 wrote:Ha, so that pesky 51R at the output was measuring like 6k or thereabouts. Strange, replaced it and now I have full output! Thanks Joe.

ok cool.Usually means short happened across the BA output while it was outputting high level audio or the output was driven into a extreme clipping output level.

I just have one final question, the circuit does seem to have a bit bit of distortion, at least compared to my other BA's- although my other BA's have jlm1.4 and cinemag input xformers and this one's an oep. Am wondering if the slight distortion is a function of the input transformer or some other part of the circuit needs a bit of my attention?

Thanks once again

The OEP does sound different and some describe it as Neve sounding distortion. Swap that 99v with another 99v in a different channel and see if the distortion follows the opamp or stays with that BA PCB?

Hi,

I have a BA2 "everything kit" with 99V and VTX trany.
It worked fine for the first few weeks and then one channel stopped working and fried the 99V. (I thought the problem was caused by a faulty power supply at first). The 99V was replaced and it worked for about a year. Now, it seems to have done the same thing again (also frying the 99V).

My voltages seem correct everywhere. I can't find a short after visual inspection with a magnifying glass.
I am at a loss for ideas. I don't want to put another 99V in there until I find what's up with this BA.
Does anyone have any thoughts on this one.

BTW, I've built about twelve BA so far and this is the first and only one that has givien me a problem.

Any suggestions are appreciated.

Sylvain

Sylvain wrote:Hi,

I have a BA2 "everything kit" with 99V and VTX trany.
It worked fine for the first few weeks and then one channel stopped working and fried the 99V. (I thought the problem was caused by a faulty power supply at first). The 99V was replaced and it worked for about a year. Now, it seems to have done the same thing again (also frying the 99V).

My voltages seem correct everywhere. I can't find a short after visual inspection with a magnifying glass.
I am at a loss for ideas. I don't want to put another 99V in there until I find what's up with this BA.
Does anyone have any thoughts on this one.

BTW, I've built about twelve BA so far and this is the first and only one that has given me a problem.

Any suggestions are appreciated.

Sylvain

Hi Sylvain

Is the 51R next to the output pin of the 99v opamp ok or open circuit or burnt?

The only thing that can blow a 99v in a BA is a short on the 99v opamp output pin or -in pin to 0v or 48v either direct before the 51R resistor or after the 51R. Can be worth changing the 470uF output cap in series with the 51R encase it is faulty but usually will have a puff up top of the cap and burn or open circuit the 51R and/or 10R.

This can also be a short applied on the primary or secondary of the output transformer while the pre is swinging high level output signal but this will usually burn or open circuit the 51R resistor.

Hi Joe,
Thanks for your response.

The 51R next to output pin of 99V is looking burnt(brownish tint) but still measures 51ohm(in circuit).

I also noticed that +OUT an 0V on the BA are shorted... That seems wrong to me, wright?

Sylvain wrote:Hi Joe,
Thanks for your response.

The 51R next to output pin of 99V is looking burnt(brownish tint) but still measures 51ohm(in circuit).

Ok there there is either a occasional short after the 51R or the BA out or transformer output was shorted while high audio level was on the output.

I also noticed that +OUT an 0V on the BA are shorted... That seems wrong to me, wright?

You should be able to measure the 15R of the transformer primary? Best to check this is 15R and also to check you have 30R between pin 2 and 4 of the output XLR?