JLM AUDIO

Hi CC Interesting project idea. How many channels are you thinking? I've built a summing box using transformers rathers than DINGO's so I've done the virtual earth summing thing - its easy enough and works well. My initial though is that you should, for each input channel, stick with the full parts ...

The four most significant differences between the DInGo and the PUP are that the PUP - (1) has no VCA (2) has no capacity for the 99V/Hybrid/550c type discrete opamps (3) has no onboard relay for hard-bypass of the external signal loop and (4) uses the opamps to electrically balance and isolate the ...

Anything is possible. It would be a bit of kludge, though. You would need to mount the 99V off board and run connections for the in+, in-, 0V and out pins, using the 24V supply for the DINGO and a separate 34V supply just for the 99V. You'd also need to upgrade the electro caps across the output to ...

Thanks Joe - good to hear that.

Oh man Discobeet I'm really sorry, but guess what I ditched in my Christmas clean up of my computer? It was getting a bit out of date with PCB versions,my BA's are now getting 4 years old or so, so it was starting to be more of a hinderance than a help. The BA is just not that hard to build, either....

I have a gorgeous looking 50mA DC meter - its NOS from the USSR Nuclear Submarine program, so its built ruggedly.

I understand that you can use a 1mA meter is the MAC, but what is the best way to get the range to 50mA? A voltage multiplier? Maybe around the opamp feeding the meter?

Output impedance is 10K looking at the schemo. While the LL5402 is specified for a different opamp design, there's no reason why it couldn't work well - how did you wire it all up?

Brightness is a mostly question of current and colour. Any standard (as distinct from superbright) red 3mm LED is likely to within the right sort of brightness, so you shouldn't need to sweat this too much. Sticking with red? Good idea - red light is far better at helping you retain night vision (or...

The 48V indicator? Its a bog standard 3mm round red LED, you can buy a bag of 'em at your local bits'n'pieces store for a few bucks. If you're anywhere near NW Sydney I can give you a handful of 'em. But you could always go for a different colour if you'd like .... just to customise your gear a bit....

Second half of OPA2604AP is used as the inverted -out adding 6dB gain like a 1:2 output transformer would normally do. I'd like to make sure I understand this. R11 and R12 are both 10K, so the opamp is simply unity inverting, yes? BUT, when you apply this inverted signal as the -ve in a balanced li...

the opa2604 is a dual opamp, correct? so using this opamp you have two gain stages? Yes, and maybe. The 2604 is certainly a dual opamp, but opamps have many uses apart from amplifiers. In the basic BA, for example, you can use a 2604 instead of a 99V - the circuit uses 1 of the opamps as the gain s...

Joe can answer the rest of this, but I can help out with the gain question. The gain of the circuit is the sum of the gains from the input transformer, the amp circuit and the output transformer. The first and last of these depend on the transformer windings: the JLM 1:4 has a gain of 12db, the OEP2...

any idea why the sk170 fets didn't work right? I've just looked at the datasheet for the 2SK170 and from what I can see, the terminals are mirror image to the BC550C. You would need to rotate each of the transistors 180º compared to my diagram if this is in fact the case. Let me know if that works.

GreenManHumming wrote:how do I double the input transistors?

I've updated my chart to show the combinations - JLM will correct if I'm off beam.

Have I got this right? BAN TRANSISTORS.jpg If you use one of the matched pairs like the LM,2Sk or MAT or, do you need the trim circuit (2 x 2K2, 1K pot and 470u cap) or could this be omitted? Also, with L1 and L2 (just behind the DI connector), you ignore the centre hole of the three on the PCB when...