JENSAMP-51X (Germanium Mic-Pre by Darius Kubarth)

[[silent:arts]]

... I was really hoping to hear from [silent arts] on this point because it is your board and looking at your build it appears you did exactly this. Just want to be sure on this because of the importance of wiring the power correctly. Thanks so much for you're time.

I can't tell you more, nashkato already said everything.
like said, paralleling the secondaries in phase is the way to go.
while the color scheme you pasted says nothing, look at writing at the transformer.
sometimes there is a little schematic on it, with the colors written next to it.
most times there will be a dot at one end of a winding.
the two with the dots are going together, the others are going together.

Just curious, what did you have in mind for the on board relays and fixed voltage when designing this?

are you referring to the FP48 PSU or the Jensamp?
the FP48 PSU is an older PSU design. I want to have switching power etc separated from the audio power.
for the Jensamp the same, plus why use the +24V for switching if the -24V isn't used?
some sort of power balancing the different voltages too.

hope this helps

 

[Blackout]

Thanks. It seems I am not expressing myself clearly enough here. Its all good though. Im pretty sure I have it wired right and the rest will become clear in due time when I test it. I appreciate you taking the time to help me. Have a good one.

 

[Sansodor]

I've finished a pair of these and all functions are working as they should. However, one of the modules is slightly noisier than the other. Just tested
with generating some 1khz sine through a speaker and recording it with a SM58. When gains are maxed, there's about -6dbfs difference in the noise floor.
Would you think this is normal or should I look into it?

Sami

 

[[silent:arts]]

Sami,

might be tolerances in the transistors.
6 dB is not trivial, but nothing wrong.
try a trim pot for R6.

 

[Blackout]

Hello all. I have my 2 ch rack finished and unit powered up, but have run into a few problems.  :-\  To make this simple I think I will just make a list of whats is good and where the problems have popped up.
Good:
Both channels pass audio with dynamic or condenser mics (with  some problems), pilot light works, phantom pwr LED works on Ch.1, Voltages at the regulators and at the card connector are correct for +24v & +48v.
Bad:
Even with the gain all the way down signal still passes ( I dont really care too much but thought I should mention it), Ch.1 volume drops out at 7 on the dial, Ch.2 drops at 8 on the dial. It doesn't go 100% but get very quiet.  None of the LED's work except the +48v on Ch.1. There is also an unnatural sounding lack of clean headroom and mild backround noise.

I have tried wiring LED's 2,3,4 reversed as per the pdf and the regular way with no avail. used different LED's every time. The 19" rack pdf calls for those last three LED's to be wired reverse; does the load resistor stay on the anode or does this change because of the reversal? I have gone through and double checked all wiring and solder points and can't seem to solve these issues. I would greatly appreciate any help that you guys could offer. Many Jensamp's have been built as of now and a good few also done in a 19" rack format. I was hoping everyone could share their knowledge and help a builder thats run out of ideas and is weary from three days of trouble shooting. Phew. Rant Over. Much thanks. 
                                                                                                                                                                        -------Blackout                                                                                     

 

[[silent:arts]]

Hi Mr. Blackout,

some good news: not everything is a problem 

Even with the gain all the way down signal still passes

yes, it is a MicPre, not a guitar amp

Ch.1 volume drops out at 7 on the dial, Ch.2 drops at 8 on the dial. It doesn't go 100% but get very quiet

either wrong resistor values at that steps, or cold solder joints

There is also an unnatural sounding lack of clean headroom and mild backround noise

could be normal, depending on definition. the Jensamp doesn't have much headroom. if it would be clean with 0,0001% distortion nobody would like it.

for the LEDs: did you check if the relays are working? I have a feeling there is some missing power.

please post a pic of your PSU and the wiring to the card edge connector.

 

[Blackout]

for the LEDs: did you check if the relays are working? I have a feeling there is some missing power.

please post a pic of your PSU and the wiring to the card edge connector.
[/quote]

Well, there we go. I haven't wired the fixed +24v regulator to the last pin on the card connector. This is where the relays get power correct? If so, is there anything I need to know about wiring it? The diagram you made for us rack builders included this point in the "reverse polarity" color legend. How do I reverse the polarity of a single wire? If I am missing anything do tell. A little side note...I am getting power for the 12v power "on" lamp from this point and just using the appropriate resistor in series. Will this prove to be a poor choice? If so where to move it to?  Thanks.  By the way, what are the relays controlling in the circuit? Forgive me if its a painfully obvious question. Between school, work, music and everything else, teaching myself about electronics theory is slow.

 

[[silent:arts]]

... I haven't wired the fixed +24v regulator to the last pin on the card connector. This is where the relays get power correct?

yes (and LEDs 2/3/4)

If so, is there anything I need to know about wiring it? The diagram you made for us rack builders included this point in the "reverse polarity" color legend. How do I reverse the polarity of a single wire?

make sure you changed the polarity of C/D/LED components in that path, nothing more to do.

By the way, what are the relays controlling in the circuit?

Phase reverse / Input transformer impedance

 

[Blackout]

... I haven't wired the fixed +24v regulator to the last pin on the card connector. This is where the relays get power correct?

yes (and LEDs 2/3/4)

If so, is there anything I need to know about wiring it? The diagram you made for us rack builders included this point in the "reverse polarity" color legend. How do I reverse the polarity of a single wire?

make sure you changed the polarity of C/D/LED components in that path, nothing more to do.

By the way, what are the relays controlling in the circuit?

Phase reverse / Input transformer impedance

All Done. Relays, switches, and their respective LED's are working ( except for one). When rewiring the LED's one through hole on the top was damaged and seems to no longer connect  . It is the "K" (cathode) inlet for LED4 (these are reverse polarity so the anode will actually go there, but for the sake of continuity I am describing like the layout. The cathode is connected just fine so is there an alternate location I can connect the anode? I tried a few different points but no luck. Not sure what to try next, any ideas? I am still getting those weird volume cuts on dial at 7 and 8 respectively from ch.1 to 2. Re flowed all solder points on resistors and capacitors, checked for correct values on every part etc.  Please. This is all thats stands between me and a working Jensamp. Thanks so much.    -------Blackout.

PS- Thank you to everyone that has helped me thus far.

 

[[silent:arts]]

... When rewiring the LED's one through hole on the top was damaged and seems to no longer connect  . It is the "K" (cathode) inlet for LED4 (these are reverse polarity so the anode will actually go there, but for the sake of continuity I am describing like the layout. The cathode is connected just fine so is there an alternate location I can connect the anode? ...

LED4 (speaking in silcscreen language):
K is connected to RLED4 (but bottom copper, a broken through hole on top shouldn't be a problem)
A is connected to the ground plane (which is the top copper layer)

 

[Blackout]

... When rewiring the LED's one through hole on the top was damaged and seems to no longer connect  . It is the "K" (cathode) inlet for LED4 (these are reverse polarity so the anode will actually go there, but for the sake of continuity I am describing like the layout. The cathode is connected just fine so is there an alternate location I can connect the anode? ...

LED4 (speaking in silcscreen language):
K is connected to RLED4 (but bottom copper, a broken through hole on top shouldn't be a problem)
A is connected to the ground plane (which is the top copper layer)

And what to do if both sides are damaged? After removing the board from the case and inspecting the bottom it was clear the entire hole was void of a contact  :'(.                                                                                                                                                                                                                                                                                                                                                                                                This is a first for me. The iron wasn't too hot and only one change was made. The anode next to it recieved the same exposure and is fine  ??? Oh well...so be it. I guess these things happen every once in a blue moon. Anyway, If this is the case what would you suggest as an alternative to wiring this particular LED (4) to work with the Hi-Z-DI switch? Also, the volume is still cutting out at 7 on the dial on BOTH channels.  I triple checked both resistor and cap values and flowed all solder joints. All is correct; so why on earth is it STILL cutting out? I've tried rewiring the switch to the board with different wire, checked for continuity with meter between resistor and cap for each gain step and between switch inputs and their corresponding resistor and cap set. Everything checks out. ( The only one that does NOT is the very last pair - R5, C13, but these are not part of the switch.) Has anyone run into a similar problem on this or any other build with a rotary switch? I would appreciate any help Thanks.

 

[[silent:arts]]

we do one after the other, first the LED:

... And what to do if both sides are damaged? After removing the board from the case and inspecting the bottom it was clear the entire hole was void of a contact  :'(.                                                                                                                                                                                                                                                                                                                                                                                                This is a first for me. The iron wasn't too hot and only one change was made. The anode next to it recieved the same exposure and is fine  ??? Oh well...so be it. I guess these things happen every once in a blue moon. Anyway, If this is the case what would you suggest as an alternative to wiring this particular LED (4) to work with the Hi-Z-DI switch?...

good desoldering needs practice, good equipment, and still with all of this **** can happen.
solder the LED directly to the LED resistor leg next to it.

 

[Blackout]

we do one after the other, first the LED:

... And what to do if both sides are damaged? After removing the board from the case and inspecting the bottom it was clear the entire hole was void of a contact  :'(.                                                                                                                                                                                                                                                                                                                                                                                                This is a first for me. The iron wasn't too hot and only one change was made. The anode next to it recieved the same exposure and is fine  ??? Oh well...so be it. I guess these things happen every once in a blue moon. Anyway, If this is the case what would you suggest as an alternative to wiring this particular LED (4) to work with the Hi-Z-DI switch?...

good desoldering needs practice, good equipment, and still with all of this sh*t can happen.
solder the LED directly to the LED resistor leg next to it.

Great. All LED's work. Now I have to fix my other problem which is of much greater importance. Volume is cutting at 7 on the dial on both channels. When 7 is reached the volume drops to near zero. Moving up to twelve the volume ends up lower than the first position. Its really baffling and i'm stumped. Sorry for asking so many questions. This is the first project that I cant figure out the quirks no matter how many things I try. Its really vexing. I'd love to hear anyones thoughts on why the volume is dropping at 7-12.  I only used one pin stop on the rotary switch ( I believe thats right), because this is a rack is used short flying leads from left to right and than the common. Am I missing something? What can cause this on both channels? I also tried disconnecting one module at a time, every variation and its always the same.  Thanks for listening and for any help I may get. Will post pics soon.
                                                                                                                                                                                                            ---- Blackout

 

[Blackout]

Here's a pic of how the Grayhill was wired to the board. If any other pics are needed to gather info please let me know.

 

[Blackout]

Well, all problems have been solved . It turns out that the stop pin was in the wrong position. It gave me the twelve point rotation I needed, but not the correct gain staging; hence no sound after 7 on the dial. In case anyone was wondering or having problems, the pin goes in top dead center. Box is dead silent, has a much more appropriate starting point in volume and the clean to sweet distortion is much more gradual. Wonderful circuit you guys have created. Really, its one of my favorites now. Thanks for all your hard work!
Until next time............                                                                                                                                                                                                                                                                                                                                                                             

 

[Blackout]

Not so pro looking finished Jensamp and VP25........

 

[Blackout]

another

 

[3nity]

Hey!
Does any body here has the front panel measures for a custom panel?
Id like to desing my own panel but id like to get it right!
Thanks

 

[shabtek]

: see reply #72 1 page back

 

[3nity]

obviously not fpd please!!! ???