Jazz

1272 trouble, need help with trouble shooting strategy
« on: January 27, 2007, 09:52:10 AM »
Constructed a 1272 Hotrod and it worked very fast.

Now I have built two more this time making my own pcb using JC's design.

I could really use some help with a approach to trouble shooting this. My understand of the circuit is rather limited. I need some strategy, an order or something. I assume testing the output of the input transfomer would be a place to start. Not sure. Need the trouble shooting wizards to give me a hand please.

Thanks, ~R
 :cry:


rodabod

1272 trouble, need help with trouble shooting strategy
« Reply #1 on: January 27, 2007, 11:38:40 AM »
Get a copy of the schematic and follow your board from input to output to make sure that all of the connections/tracks are correct.

Then check that you have stuffed the board correctly!

This will not take long.

If that fails, then you could measure the board at various points using a scope, but the fact that both of your new ones do not work makes me wonder....
Quote from: tv
punchy fat bastard chip

rascalseven

1272 trouble, need help with trouble shooting strategy
« Reply #2 on: January 27, 2007, 11:55:55 AM »
Jazz,

What, exactly, is the problem you're having with the two new ones?  I'll try to help you.

JC
"If you dig the gig, do it. -But listen to the signal, not the person talking."  -Keef

rodabod

1272 trouble, need help with trouble shooting strategy
« Reply #3 on: January 27, 2007, 12:42:16 PM »
Edit: Oops - didn't realise you were using JC's design and not the original Hotrod design.

Still trace through your circuit though as a simple start to make sure it is correct.
Quote from: tv
punchy fat bastard chip

Jazz

1272
« Reply #4 on: January 27, 2007, 01:37:23 PM »
OK, hang tight, I failed to drill a hole in the pcb and therefore did not install R19 - 1K8 on the pre amp section. How the heck I missed that even using a check off sheet I dont understand.

Strange one board even worked for a while then stopped. The other one sucked major current thru the 12ohm 1watt resistor and started a small barbecue.

I'm ready to test soon, gonna take a break. Then Ill let you know what happens. I'm out of 2n3055 transistors and may have blown one.

Thanks, be back asap.
    :shock:

Jazz

1272
« Reply #5 on: January 27, 2007, 02:50:13 PM »
ok, still does not work. Installed the missing resistor, gave it a good visual inspection.  

pre #1 - 12ohm 1 watt resistor gets hotter than hell faAAAst.

pre #2 - zero output when testing with a dynamic mic.

I'll take a break. Not sure what to do next. Verified components, carefully inspected it under a bright lamp with magnifier.

Food time, been up all night.  :cry:

PS - to simplify the circuit a bit I do not have the rotor switch installed on pre #2 just a resistor as seen in JLM simple hotrod schematic.

AnalogPackrat

1272 trouble, need help with trouble shooting strategy
« Reply #6 on: January 27, 2007, 03:48:53 PM »
Turn the bias trimmer on the output stage all the way to the other end.  Turn the thing on for a couple of seconds and check the 12ohm...it should not get hot.  Now do the symmetrical clipping adjustment using the bias pot and you should be in business.

You may have cooked your 12ohm (and the 47ohm also gets toasty when things are maladjusted), so you might want to check it if you left things on for a while...

A P
If it is to be, it is up to me.

Jazz

1272 trouble, need help with trouble shooting strategy
« Reply #7 on: January 29, 2007, 02:23:57 AM »
Quote
Get a copy of the schematic and follow your board from input to output to make sure that all of the connections/tracks are correct.

Then check that you have stuffed the board correctly!


Thank you rodabod, I agree and that much I do know and have done.

Quote
Turn the bias trimmer on the output stage all the way to the other end. Turn the thing on for a couple of seconds and check the 12ohm...it should not get hot. Now do the symmetrical clipping adjustment using the bias pot and you should be in business.

You may have cooked your 12ohm (and the 47ohm also gets toasty when things are maladjusted), so you might want to check it if you left things on for a while...

A P

Thanks AP, I have learned that on the 1st one I built, apprciate your reply.

Jazz,

Quote
What, exactly, is the problem you're having with the two new ones? I'll try to help you.

JC


HI rascalseven, thank your for your support, I will need it and will pm you, I need to take care of some biz first. Again, thank you.

Jazz

Sounds TITS, no noise/hum, audio output from here to Poland
« Reply #8 on: January 30, 2007, 10:06:02 PM »
You will love this mistake.

PCB artwork was upside down so all the bc transistors had been installed 180 degrees off. What a joke I know. Thats why I decided to walk away from it for a couple of days and that always works for me to look at it with a fresh brain.

I think I have a nice idea so I'm not going to show any pics yet until it's all mounted as I plan too. Won't be too long. But in a nut shell, I'm stacking pcbs like bunk beds so I'm gonna put (12) 1272's in one two space rack.  Why (12) ?   for remote work, eight for drums, the other four for remaining rythm section.  I'm using external power so it should work.

 :thumb:

Tekay

1272 trouble, need help with trouble shooting strategy
« Reply #9 on: January 31, 2007, 12:52:38 AM »
If the layout was mirrowed, what about the 2N3055?
Thomas "TK" Kristiansson
----------------------------------
"The Sound Is In The Iron"
www.vintagedesign.se  www.tkaudio.se


Jazz

1272 trouble, need help with trouble shooting strategy
« Reply #10 on: January 31, 2007, 01:39:12 AM »
Dont know what to say there, but it does work now, strange. Makes no sense at this time does it? Well....lets see who can figure out why?

 :thumb:

Love your gear Thomas, 1st class stuff

rascalseven

1272 trouble, need help with trouble shooting strategy
« Reply #11 on: January 31, 2007, 05:34:33 PM »
Did you use MY layout (the file Kevin posted on another thread) or did you make your own layout just using my schematic?  If it's mine I don't see how it is possible to reverse only one type of transistor and not the other.  :?: :?: :!:

I accidentally reversed the entire layout when developing a PCB once myself, but my fix was to reverse ALL the transistors.  I actually put the 3055's on a separate little PCB and wired them over.  It worked great.

When you say it 'works' does that mean it passes audio, or it actually calibrates properly and sounds good?

:?

JC
"If you dig the gig, do it. -But listen to the signal, not the person talking."  -Keef

Jazz

1272 trouble, need help with trouble shooting strategy
« Reply #12 on: January 31, 2007, 11:18:43 PM »
Quote
Did you use MY layout (the file Kevin posted on another thread) or did you make your own layout just using my schematic? If it's mine I don't see how it is possible to reverse only one type of transistor and not the other. Question Question Exclamation


I used your PCB layout.

I'm using the JLM Hot Rod schematic since I prefer the 2x12 switch

Quote
When you say it 'works' does that mean it passes audio, or it actually calibrates properly and sounds good?


It was a very fast test, Aux send from a console playiing music from a CD. I was at the end of my energy therefore did not calibrate nor did I run any tests yet to verify sonic quality and such. Tonight I will continue and I will find out whats going on here.

Maybe we need to get the catholic priest over here and do some room cleaning.

 :green:

Jazz

1272
« Reply #13 on: February 02, 2007, 06:34:06 AM »
Have not got back to that pre yet, waiting for some parts in the mail.  I did however go back on another 1272 and grounded it as JC suggested.

DEAD clean and quiet. Toggle back and forth between rec mode and mute etc, my ears hear no noise. You gotta love that. When I read that JC said "I've tried everything" I could relate....I kept going back and back and tearing these prototypes apart and rewiring certain elements and just about had enough.

But when you nail it, the payoff is worth it. I did an A/B test against other mic pre's in my studio and the home made clone is the winner. I was spinning my wheels on the 1081 and decided to abort mission and Im so glad I did because it was over my head.

Quote
When you say it 'works' does that mean it passes audio, or it actually calibrates properly and sounds good?


You posted your technique for calibrating at one time NO? Are you referring to the adjustment of the varible resistor?

I'm using 31267 trafos and JLM trafo on the output. Joe told me how to tweek that voltage but I lost the info in a computer crash and I'm trying to search my notes and find it again.

Jazz

Mirror
« Reply #14 on: February 03, 2007, 10:29:09 AM »
Quote
If the layout was mirrowed, what about the 2N3055?
_________________
Thomas "Tekay" Kristiansson

The 2n3055  was also backwards. It did work,not just pass audio but I actually took the output and recorded it.... playing music from a CD. Thin lifeless audio sound of course.

Quote
When you say it 'works' does that mean it passes audio, or it actually calibrates properly and sounds good?  JC


Just passes audio. I just drilled a couple of new holes and was able to mount it. I messed around a bit calibrating but was having trouble. Probably a break is all that is needed.

Can anyone recommend a good quality 5k pot ? I bought some greyhill rotar switches.

babyhead

Re: Mirror
« Reply #15 on: February 03, 2007, 01:44:32 PM »
Quote from: "Jazz"

Can anyone recommend a good quality 5k pot ?


I <3 PEC brand pots... Digikey. Too bad they are too big for my Fenders.


BTW, do you know any body with a panel stretcher?


 :?


 

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