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

[scott2000]

That's great! Darn traces.....

I've got some pieces with little colorful worms crawling around on the boards for sure.....

I even have an old  converter that has scratched out traces and jumpers in quite a few spots....Guess the builder was figuring it out as he went...lol.....Or it's a crazy repair from previous owner.......



Anxious to hear your impressions of that beast!

Thanks for pushing through....

 

[Phrazemaster]

Well happiness short-lived. Still have an intermittent output issue. Audio just cuts out for a few seconds at a time, randomly. Meter still goes during the silence. Weird. But other than that unit is working. Trying to figure out what would cause this. I suppose cold solder joints, but I've touched up almost every joint and can't seem to figure this one.

I may still redo the main board and the other two boards. Sigh. I'm basically going to rebuild the whole thing dammit. Expensive. I'd love to figure this out, but I'm not sure I'm up to the task.

How does one figure out an intermittent issue like this? The unit seems to work properly other than randomly cutting out every 10-15 seconds or so. More cut outs when it's been on for awhile. Any thoughts? Again, meter is moving during the cut outs (silence). So I know audio is routing around the board...

 

[Spencerleehorton]

Check your xlr or do you have it in a patch bay?
When testing some of my stuff my patch bay was fault!
Hope you find the fault dude.

 

[Phrazemaster]

Check your xlr or do you have it in a patch bay?
When testing some of my stuff my patch bay was fault!
Hope you find the fault dude.

Good suggestion, thanks Spencer. I'll check it. Frustrating as heck! I'm so close with it! But I can't have an intermittent unit; otherwise it's worthless!! I'll get this figured...thx for support brother.

 

[scott2000]

All your trimmers are fine too?

 

[Phrazemaster]

In a million turns those little dudes kept chugging along fine. I noticed I was using Vishal trimmers; maybe Bourne but no problems. I suppose any component could be the culprit.

I’ll keep at it.

Thx

 

[Phrazemaster]

Rebuilding my unit, as promised.

Question: if using carbon comps, will it matter a at all if ratio/meter PCBs use metal film? From the schematic it doesn't look like these are directly in the signal path, but I don't understand the schematic well enough to know if this matters.

I had used some carbon comps on the previous ratio board which I'm now rebuilding; wondering if it's worth it to try to salvage them or just go with MF there?

Thanks gang.

Mike

 

[scott2000]

https://web.archive.org/web/20110219152646/http://www.diyfactory.com/data/mbresistors.htm



I haven't read this yet....... I'd think tolerance is the main importance.....Each type has it's own thing about it.....I have plenty of carbon in gear with no issues.... yet...

Always heard mf is the standard for reliability.... and I have plenty of them in use for ages too....

But I haven't read that link yet....lol

Merry Christmas Mike!


edit...just read through....saw this....


It also doesn't matter if you use different makes or compositions of resistor in a circuit. If the parts list does not specifically say that certain parts need to be physically or electrically identical, then a mixture of types can be used without worry.

edit edit....decisions decisions........  http://www.aikenamps.com/index.php/resistor-types-does-it-matter

 

[Phrazemaster]

Thank-you Scott.

I’m really wanting to stay all carbon Comp for signal path. So to rephrase my question: will any musical signal be flowing throughout ratio or meter resistors?

It does not appear so to me, but I don’t understand the schematic well enough to know.

Anyone can advise?

Thanks

Mike

 

[scott2000]

I'm in the same boat when trying to figure out what a schematic does. From what I understand in this, these parts of the circuit basically take a piece of the signal to use as the control voltage for  different functions in that section..(biasing,etc....) and aren't actually the "signal path" that you may be referring to.  Usually manuals will have pretty good documentation in the "theory of operation" sections. I've learned most of the limited stuff I know from spending most of my time reading those sections.  But it's mostly older tube stuff. Still, probably similar....it's all the same to some degree....

But I also know that VU meters in general can affect the quality of the sound in some designs. I've brought this up before somewhere and don't remember why it happens. I think PRR said that in some gear there are actually meter bypass functions for this reason.

But, I'm not sure how resistor noise in general affects the overall picture even if they aren't in the actual signal path??? I'm sure there is some correlation to everything to some degree?

If you have some salt, go take a grain out while you read what I've written.....lol

Good Luck!!!!

Merry Christmas!!!

Interesting to hear more about this.

 

[Phrazemaster]

Hey Scott, your thoughts are most welcome thanks.

I’m interested in knowing more too...

Merry Christmas to you too!

 

[Chrome Heart]

What would cause voltage to ramp up and down during the null adjust? It seems to cycle from 0 to .060 and back when the measurement is taken from TP10 and TP11. This is an MNATS V 1.2 board. Both 2N3707's are 435hfe.

 

[Phrazemaster]

I always found that null adjust a bit wonky - sometimes the value would get really close to 0, say, 0.07. Then I would turn and turn the adjustment knob with no change. Then suddenly it would hit -0.13 with no interval at all in between.

It took me a lot of patience to get this right. But now I'm rebuilding my board per above posts, so I'll have to do this all over again lol.

Best,

Mike

 

[Chrome Heart]

Sonically, I dont detect any issues. I was just wondering if this amount of drift is normal. I notice on the new Hairball boards that these two transistors are face to face, and in contact for thermal coupling. Perhaps this is the reason for the variation on my unit.

 

[diylan]

I’m posting with an issue about drift, but this is different than a mild sway in the meter...

I’ve been using my Rev A for years now and it’s always had an issue with output level sway (but it seems more pronounced at my current location). I’m finally fed up with it to the point where I can’t use it anymore (maybe my standards have just gotten higher).

When in gain reduction mode (with compression off, or on with no input), the meter will drift from around -5 to +3. However, this is not just a metering issue, it affects the output of the unit - with gain reduction switched off, the output level still drifts. Not wild swings or continuous movement, it’ll just move a new spot and say there for a bit.

I have noticed that changes in the incoming mains voltage correlate. My mains voltage is not steady (swings from 114v - 128v), and the meter moves with the changes in the mains voltage. Maybe this is to be expected with that mains voltage variability, but my Rev D doesn’t behave like this, nor does any of my other gear.

In my mind this all points to the power supply. Any ideas out there?

 

[scott2000]

In my mind this all points to the power supply. Any ideas out there?

That's a pretty swing ....But I'm a couple of miles from our power plant and I have a separate feed from the service to my room....so maybe it's normal????
I know regulators like to have a few volts extra to operate correctly. Wonder what it's doing when your power is getting goofy....especially when dropping....

Interesting....... Hope you get it sorted.....Weird that it's been a problem since the start. You think it would be easy to see if it were something wrong with the supply....Maybe a bad part in there............

Have you checked any voltages anywhere when it happens to see if something isn't right????

Maybe the mains isn't the issue.....

Good Luck!

 

[diylan]

Thanks, Scott.

I've got a pretty steady +30vdc, but my -10vdc seems to drift. In general though, the DC voltages all measure within the ballpark of what's noted on the mnats schematic with voltage notes.

I applied a 1k sine wave with (measured) steady AC voltage to the input, to see where the drift first starts happening to audio in the circuit - which would be at the drain of Q1.  Maybe my 5457s are damaged or off spec?

 

[scott2000]

Hard to say.  I'd think it was something else.....

You say all the voltages are normal everywhere more or less.....???




Mike is pretty active on the other thread....

https://groupdiy.com/index.php?topic=63600.0

I know it's not the same build but, he would maybe have some direction..... So many threads on these it's easy to get lost...

Bump for you.....

Good Luck

 

[Echo North]

Thanks, Scott.

I've got a pretty steady +30vdc, but my -10vdc seems to drift. In general though, the DC voltages all measure within the ballpark of what's noted on the mnats schematic with voltage notes.

I applied a 1k sine wave with (measured) steady AC voltage to the input, to see where the drift first starts happening to audio in the circuit - which would be at the drain of Q1.  Maybe my 5457s are damaged or off spec?

Drift like that is usually a bad cap or diode. A bad CR2/CR3 can really mess with your negative rail.

You been through this?
http://www.hairballaudio.com/blog/resources/post/fetrack-troubleshooting-guide

Mike

 

[diylan]

Thanks Mike! (and sorry for the slow reply, I don't have a ton of time to put into troubleshooting).

As per the Troubleshooting Guide, I measured TP18 and got bad voltages, so I replaced CR2 and CR3. Unfortunately that did not fix things.

Right now, at TP18 I measure -2.874vdc and -0.002vdc, at the extremes of Qbias trimmer R59.