[BUILD] 1176 Rev A - Back to the beginning...

[Andy Meyer]

I am getting 0v from the secondary measuring at the terminal strip.  The primaries are both reading 58v at the "off" switch.  Here are some photos.  Pardon that bad quality as all I have is an iphone.

 

[ChrioN]

In the original schematic, Q1 and Q11 is the same type transistor as Q2 and Q4. So they can all be 2N5457?

 

[MicDaddy]

Andy Meyer, which toroidal are you using?

If you're using the Avel-Lindberg, looks to me that your pairs of blue/purple & brown/grey on the primary side, are swip-swapped at the switch.

See attached photo from Mnats wiring guide

I cannot remember which wire was what on the primary side of that transformer or if swapping these pairs would cause an issue?  But definitely a place to start.

 

[Andy Meyer]

Mic Daddy,

I am using the Avel-Lindberg transformer. I originally had it connected to the switch as it's pictured in Mnats' wiring guide and had the sam results as I have right now.  After reading through his wiring guide for non A.L. transformers it seemed like it was opposite?

Here is the link to Avel- Lindberg. Can anyone confirm the correct wiring for the primary?

Thanks so much,
Andy

 

[MicDaddy]

From my experience with the Avel-Lindberg, I wired two Rev A units exactly like Mnats wiring guide and they both work flawlessly.

Have you removed the 4 primary wires from the switch and measured voltages at the terminals on the switch?  What did they measure?

Just follow the ac up to those terminals and if it is correct then wire the primaries according to Mnats guide.  If you still have nothing on the secondaries the transformer is suspect.

Edit: Have you checked your fuse? 

 

[Andy Meyer]

Mic Daddy,

You were right.  Bad fuse.  I feel silly for not checking that right off the bat.  I am going to pick up a new one tomorrow and see if that gets me further.

 

[MicDaddy]

Mic Daddy,

You were right.  Bad fuse.  I feel silly for not checking that right off the bat.  I am going to pick up a new one tomorrow and see if that gets me further.

Hey don't feel bad, I was roughly 12hours into my first unit, had it power on successfully, I then shut it down and moved it (to snap a quick 'success photo'), and it wouldn't power back on.  I don't want to offer how long it took me to realize the fuse (upon inspection it looked fine and even chimed with the DMM).

You may think of jumping up to a 500mA slowblow.  I could not get 250mA to work worth a darn without popping and bumped both my units to 500mA.

 

[ChrioN]

How was it concluded that Q2 and Q4 should be J309, and what do they substitute?

 

[Andy Meyer]

It works!  Just a bad fuse.  Time to calibrate.

Thanks again for the help.

-Andy

 

[0dbfs]

Hey Guys,

I just got my dual Rev A out of storage and powered up to find out I had never sorted out an issue I was having with the 30V rail.

This unit uses mnats PSU board to power two RevA (1.1) PCB's..

The problem I am seeing is that when I connect the 30V line to both main PCB's the 30V will drop consistently until it get's to about 14,15,16V then it "thumps"... Oscillates between say 14V-to-maybe 16V... This causes low freq oscillating sound at the output of the channels. The 30V LED on the psu-board also pulses with the voltage drop.

Powering one main board (either one) is fine. No voltage drop, no oscillation. the -10V rail stays solid at like -9.28V or so even with both main-boards connected...

I initially thought this was a problem with the avel-lindberg being underrated but I went with a higher rated psu trafo from AL and it behaves the same.

Any ideas? I can disconnect all of the switches/etc with the same result. Maybe it's the 30V regulator instead of an issue on either of the main-boards? Do I need decoupling on the mainboards to decouple the 30V from eachother?

I just connected/jumpered 30V from the PSU to each of the mainboard 30V points and bypassed the mainboard "internal" psu. Problem only happens with 30V connected to both mainboards.

Seems like when I connect up 30V to both mainboards the PSU can't supply enough current and starts dropping voltage after maybe 15 seconds then settles around half of the 30V and oscillates.

Any ideas would be appreciated. I can poke and probe later tonight.

Best,
jonathan

 

[MicDaddy]

Are the PSU regulators getting warmer when attempting to power the two boards?

How warm do they get when powering one?

How are they heat-sinkd?

Shooting in the dark, are those regulators ESD sensitive?

Perhaps check the regulators with a DMM?

 

[0dbfs]

No heatsinks on either the 317 or 337.... And yes they are pretty toasty. I have not taken a temp at the moment but I think a couple of my meters have temp-probes that I can test.

Let me hacksaw a bit of aluminum today at work if I can find the time and drill it to mount on the devices. Pretty sure I have some extra 317's and 337's in my shop...

Any pointers on how to meter them to confirm they are ok or not? I mean I can swap em out and see what happens but i'm all about finding the smoking gun and positively identifying the fault through diligent testing and observation.

I guess I could put an appropriate load on the 30V rail and leave the mainboards bypassed to see if the PSU starts wheezing and gasping (or rather see when it starts).

I guess I could meter current consumption of a single mainboard to approximate the "live load". Then just make the PSU draw that much current with some appropriately rated resistance/rheostat to see if I can make it fall over without any main-board.

Cheers,
jb

 

[MicDaddy]

From the thumping/oscillation you described wants to make me think thermal shutdown.

Try a heat-sink on both regulators and see what happens, if you sink it to a chassis be sure it's insulated.

 

[0dbfs]

Hey MicDaddy, thanks! I cut a couple pieces of aluminum angle bracket and drilled them to mount directly to the tab for air cooling fins. Didn't have any proper heat sinks. These appear to work.

My meter shows about 150F at the tab of the 30V /317 with the sink. The device is spec'd for about 250F so within range.

The 30V rail now measures a steady 29.82V and the oscillation has stopped with both mainboards connected.

I'll let them burn in for a while to see if they fall over. Might try to bring the temp down a bit more. They are still pretty toasty.

Cheers,
jb

 

[MicDaddy]

Awesome!!  Glad to hear it was a simple fix.

Let us know how they sound.  I like the sound of mine a lot  ;D

 

[0dbfs]

hmmm... PSU issues now appear to be good to go. Left it powered-on overnight and it was still stable in the AM... I'll check her stats after work today to see if it's the same.

The units have some significant distortion. Seems uncharacteristically sensitive to level. I have used 1176 black/silver face units before and seems input/output is normally in the 10-2 o'clock range depending on the source. This unit(s) are more like 8-9 o'clock range for input/output... Leads me to think of potential issue with the IP-Tx or Attenuator connections.

Anyone know if the hairball attenuator uses linear/log/rev-log curve?

Got through the null-adjust-cal and moved to tracking adjust when my 0-set-adj and tracking-adj trimmers both affected the GR meter exactly the same. Also, had to go back and adjust for 1/2 db overbias/q-bias to get the desired ip/op settings for 10db compression (output level) and 0 with GR bypassed. Those steps are with 20:1 selected and switching between gr active/bypassed tweaking I/O until you consistently read -10/0 on the meter.

my 20:1 control voltage reads as -6.13 V and I have good signal/continuity from output pot into the gr-ctrl amp (ie; no resistance). That tells me that the 20:1 setting is wired correctly. It is very distorted while other ratio's are better until pushed harder that is...

When it compresses, it is distorted. More distortion than compression. Cool sound but should surely be cleaner for typical compression duties. Pretty easy to use it as an overdrive-box with GR bypassed as well..

Measurements look as expected when compared w/schematic so far.

Pretty tight in there for a dual unit in 2RU. Makes it slightly painful to service. I will probably redo all the wiring in an attempt to clean it up a bit and make it easier to connect/disconnect all of the boards. I have a feeling that these 1.0 boards need a couple mods. I will do regular 2RU single units in future builds of these or D versions.

These are version 1.0 boards. ANyone know of a list of changes between 1.0 and the current RevA boards?

Anyway, not too sure if some of this may be PCB rev1.0 issues, other, or combination. Anyone see anything similar or have other issues specifically with rev1.0 PCB's?

Thx,
jb

 

[Biasrocks]

The REV A's have a lot more gain than later versions, hence the lower input level. On my build I used a trimmer to adjust the threshold to react more like later versions. I think the distortion you're getting is another separate issue.

Mark

 

[phantomas]

I just finished some minor troubleshooting and calibration of my two Rev A comps. A big thank you to all on the forum that made the project possible. The troubleshooting part I did to myself by adding stepped input attenuators, side chain insert and stereo link.

I managed to buy the wrong attack pot with a dpst switch instead of a spdt, meaning I can just break the pad 22 to ratio board circuit without grounding it. So for testing I just soldered in a separate toggle switch for taking pad 22 to ground. Now I find that for all practical purposes this switch does nothing. What side effects would leaving the side chain input floating instead of grounded have.

I'm more of a sound person so excuse my patchy understanding of electronics.

Cheers,
Tomas

 

[MicDaddy]

Hi Tomas Congrats and Welcome!!

Care to share how you implemented the side-chain?

Your inquiry is a tad above my pay grade so I'll sit back and let someone else tackle that one  ;D

 

[phantomas]

Thanks MicDaddy!

I bought the Hairball stereo link boards that are based on the MC77 circuit, but since I wanted an external side chain insert I borrowed some more from the MC77 and made my own PCB.
Very simple just an extra TL072 a couple of caps and resistors for the side chain input buffer and instead of the op-amp output buffer I used an old Lundahl tranny. Two 9V relays using the -10V rail are used for switching link and side chain.

Cheers,
Tomas