JLM AUDIO

maybe it is the damaged board. there must be either a lost connection somewhere or my jumpers are causing the oscillation.

weird that its the same on both boards though, if it is the boards.

i replaced the input 47pF with 100pF - no change.

greenmanhumming wrote:maybe it is the damaged board. there must be either a lost connection somewhere or my jumpers are causing the oscillation.

weird that its the same on both boards though, if it is the boards.

i replaced the input 47pF with 100pF - no change.

It is not the input 47pF that will need to be increased if it is to do with the front end gain stage. The 2 x 47pF on each side of the first opamp stage would be the ones to increase to bandwidth limit that stage.

Like I said before with out photo's of the wiring layout and PCB it is hard to help. Also need the frequency and ac volts of the oscillation at all the opamp output pins of each stage to see where the oscillation is being generated.

what are the dimensions of this board?

same size as the ba?

weroflu wrote:what are the dimensions of this board?

BAN PCB is 1.4" (35.5mm) x 5.15" (130.8mm).

same size as the ba?

BA PCB is 1.4" (35.5mm) x 4.85" (123mm)

So BAN PCB is just slightly longer.

on the worse affected side theres an oscillation at pin 2 of the first chip of 3mv and pin 2 of the second chip of about 2.5mv, and about 5.5mv at the output. thats measured with the x10 on the scope probe so the actual readings were 10x that.

wavelength looks on my scope like about 1.2uS - about 800khz!?? well above the audible range, but at some gain settings you can hear whistling that changes in frequency, i can't see that on the scope though and it comes and goes, but the high frequency oscillation on the scope is steady at pin 2 of the first chip, and changes a little up and down with the gain on the later points, but only by about 2x over the whole gain range.

I've already increased the 47pF caps on the first chip to 100pF

i should add it reads about 10mv on pin 1 of the first chip, and 5mv on pin 1 of the second chip.

the other side of each chip is something similar but lower level.

Ok that sounds more like power supply rail oscillation due to the small 10mV size of the 800khz and would explain why both pres have the same problem.

What do you see on the 48v feeding the BAN?

Are you using a linear or SMPS 48v rail?

I might have done the 10x the wrong way around I think I divided by 10 when I should have multiplied so tru figures much larger.

I'm using the smaller Jlm switching power supply. With some extra filtering too.

Actually I suspect the audible whistles and the steady supersonic oscillation may be unrelated.

Both channels are subjectively similar to listen to with whistles at some gain settings, but the frequency I can see on the scope goes away at higher gains on one preamp but is much the same regardless of gain on the other though it lowers in frequency a bit at highest gain.

There's no obvious audible click or anything at the point where the hf oscillation disappears on the one where that happens.

I'll check the power supply with the scope tomorrow, tho I think I have done that before and not found anything.

greenmanhumming wrote:Actually I suspect the audible whistles and the steady supersonic oscillation may be unrelated.

Both channels are subjectively similar to listen to with whistles at some gain settings, but the frequency I can see on the scope goes away at higher gains on one preamp but is much the same regardless of gain on the other though it lowers in frequency a bit at highest gain.

There's no obvious audible click or anything at the point where the hf oscillation disappears on the one where that happens.

OK the whistles is what we want to measure the frequency and volts of. If you can adjust the gain to get the whistle to happen and measure that it will the info I need. Also if it is happening at the highest gain setting make sure your input and output wiring is spaced apart and either shielded or tight twisted.

I couldn't get the whistles to show up on the scope well enough to see a voltage or frequency.

I have bought new boards and rebuilt the BANs using some new parts and some retrieved from the old boards and all works fine now!

I used low temp lead/tin/silver solder and socketed the input transistors and the gain pot leads.

I have learned:

* socket the input transistors!
* don't use lead free solder on these boards it makes it near impossible to get components out again without taking the through plating with the component lead.

anyway it now all works great.

I also recently built a pair of preamps using the THAT 1512 and 1646 chips. these also sound great! possibly even better than the BAN - hard to say. Though they do require +/- 15v. How about a JLM pcb implementing the schematics from the THAT datasheets, with a go between type set of phase/pad/phantom switches etc?

boring I know, but would be really useful, I'd buy a bunch of them.

greenmanhumming wrote:I couldn't get the whistles to show up on the scope well enough to see a voltage or frequency.

I have bought new boards and rebuilt the BANs using some new parts and some retrieved from the old boards and all works fine now!

I used low temp lead/tin/silver solder and socketed the input transistors and the gain pot leads.

I have learned:

* socket the input transistors!
* don't use lead free solder on these boards it makes it near impossible to get components out again without taking the through plating with the component lead.

anyway it now all works great.

I also recently built a pair of preamps using the THAT 1512 and 1646 chips. these also sound great! possibly even better than the BAN - hard to say. Though they do require +/- 15v. How about a JLM pcb implementing the schematics from the THAT datasheets, with a go between type set of phase/pad/phantom switches etc?

boring I know, but would be really useful, I'd buy a bunch of them.

Cool good to hear the BAN are all working.
The THAT chips are simple to use but my list of projects I am trying to finish at the moment for JLM and other companies is way to long to add another project.

What performance difference does the V8 opamp yield in the BAN pre? Using, say, 4 2604's as opposed to just one. For that matter, using 4 of any opamp instead of one. What difference does the increase produce?

cosmodos wrote:What performance difference does the V8 opamp yield in the BAN pre? Using, say, 4 2604's as opposed to just one. For that matter, using 4 of any opamp instead of one. What difference does the increase produce?

V8 is great for driving very long cable runs or step up output transformers. Other wise I would in most cases use for the normal pure BAN a OPA2604AP as the output opamp. As it give electronic balanced output with great headroom.

Joe, I'm looking at a pair of BANs as a pre for stereo miking. I have a little PCB design to do mid-side decoding that I can switch in and out, but it works on unbalanced signals. Is there any unbalanced take off point on the BAN PCB just prior to the outputs? Will TP3 and ground do it for me? I could then return the signal the 51R and 10K resistors. If I read the thing right, this signal point would be -3db, but I can live with that. And I'd have to be careful about noise ....