[BUILD] 1176LN Rev D DIY

[offthewallstudio]

40V is much too high for you positive rail. 

Something is wrong with your build.  You'll have to go through and and figure out what's wrong.  You may have your voltage regulator in backwards.

ah thanks mike. I did see this in the thread but took for ever for me to find. Weird. ... thanks

 

[offthewallstudio]

40V is much too high for you positive rail. 

Something is wrong with your build.  You'll have to go through and and figure out what's wrong.  You may have your voltage regulator in backwards.

ah thanks mike. I did see this in the thread but took for ever for me to find. Weird. ... thanks

im also trying to post photos of the build. Omg i never have this tough of time lol

 

[Echo North]

40V is much too high for you positive rail. 

Something is wrong with your build.  You'll have to go through and and figure out what's wrong.  You may have your voltage regulator in backwards.

ah thanks mike. I did see this in the thread but took for ever for me to find. Weird. ... thanks

im also trying to post photos of the build. Omg i never have this tough of time lol

Regulator looks ok.

Are you sure you're measuring in the right place?  The one side of the 1.1K 1/W resistor?

Make sure all of the power supply parts are rented correctly and your resistor values are right including R89.

 

[patxiplg]

Hey Mike:

I think I'm going to replace all the transistors and see if that solves the problem of the huge gain and noise. Could you tell me which ones have no relation with audio signal so I don't change those?

Thanks!

I'd probably just start with Q6.  You could do all the transistors in the boxes labeled "signal" and "Line" amp.  Possibly one of those is weird.  Make sure you don't have any 470Ω, 47K, 470K resistors swapped.

Hi Mike:

Today I changed the Q6 as you told me with a new Motorola one (that's ok, right?) and the noise and huge boost are slightly lower, but the problem is still there. I'm still waiting to receive the other transistors models (all) I ordered to change them too. In the meanwhile I'd like to know which elements are responsible of boosting the output signal. I guess the ONLY one that BOOSTS output is the "SIGNAL LINE AMP" area, right? I understand that the output transformer has a fixed step-up ratio too, right? Do you think it could be faulty too?

I'm assuming that the problem is not in the input preamp section, that's why I'm asking you again for the parts of the circuit that boost the output signal.

Thanks in advance!

 

[patxiplg]

Hey Mike:

I think I'm going to replace all the transistors and see if that solves the problem of the huge gain and noise. Could you tell me which ones have no relation with audio signal so I don't change those?

Thanks!

I'd probably just start with Q6.  You could do all the transistors in the boxes labeled "signal" and "Line" amp.  Possibly one of those is weird.  Make sure you don't have any 470Ω, 47K, 470K resistors swapped.

Hi Mike:

Today I changed the Q6 as you told me with a new Motorola one (that's ok, right?) and the noise and huge boost are slightly lower, but the problem is still there. I'm still waiting to receive the other transistors models (all) I ordered to change them too. In the meanwhile I'd like to know which elements are responsible of boosting the output signal. I guess the ONLY one that BOOSTS output is the "SIGNAL LINE AMP" area, right? I understand that the output transformer has a fixed step-up ratio too, right? Do you think it could be faulty?

I'm assuming that the problem is not in the input preamp section, that's why I'm asking you again for the parts of the circuit that boost the output signal.

Thanks in advance!

 

[offthewallstudio]

40V is much too high for you positive rail. 

Something is wrong with your build.  You'll have to go through and and figure out what's wrong.  You may have your voltage regulator in backwards.

ah thanks mike. I did see this in the thread but took for ever for me to find. Weird. ... thanks

im also trying to post photos of the build. Omg i never have this tough of time lol

Regulator looks ok.

Are you sure you're measuring in the right place?  The one side of the 1.1K 1/W resistor?

Make sure all of the power supply parts are rented correctly and your resistor values are right including R89.

ill look today. Again with this thread i was not notified on the reply and it took me for ever to locate this post again... is anyone else haveingtroubles with hitting the next page button and it brings you too a whole different spot on thos thread?

 

[Echo North]

"Next" is next thread.  You need to click the page numbers to move forward.  There is a notify link at the top of every thread you can use.

 

[offthewallstudio]

"Next" is next thread.  You need to click the page numbers to move forward.  There is a notify link at the top of every thread you can use.

ah lol. Well i. Proud and embarrassed to say I FIXED IT!!!!!!! im a dope i didnt put in ths 220 resistor in r48 :/ lol. Its perfact now! Thanks!

 

[bxershrts]

Good afternoon.
Thanks again for your replies and advice mnats and mike.

ok....my apologies - my dyslexia did put the decimal point in the wrong location.

Throughout the day the voltage changes. Between morning and at dinner time. Not by huge amounts but there is a measurable difference.

Quote from: mnats

    Is your negative 10 volt supply (-10V) working? If so, what is the voltage at the junction of R66, R76 and R72?

Yes my negative -10v is working. I have given 2 different measurements. one at -9.73 and -9.98 this is due to different times of the day.

At the junction of R66, R 76 and R 72 the voltage this afternoon reads -9.75

Quote from: bxershrts on March 04, 2015, 03:15:47 PM

    I have measure the pcb : here are my finidings.

    28.65 R87
    -0.973 CR6 <------ This is a decimal place error. -9.73 vdc

Quote from: bxershrts on March 06, 2015, 04:48:21 PM

    The power supply is working and 29.8 and - 9.98.


There is a big difference between -0.973 and -9.98. If it is in fact -9.98 what is the answer to the second question I asked?

Other measurements appear to vary from post to post. Example:

Quote from: bxershrts on March 04, 2015, 11:18:43 AM

    I have just checked the voltages at Q11S and Q12B and they are both identical at 3.843 volts dc.

Quote from: bxershrts on March 04, 2015, 03:15:47 PM

    Q12 
    B 0.248 - My mistake , I missed adding the "3" in 3.248. But as I said the differences are also due to changing R59 and R44 affects the Base Voltage at Q12.


Be sure you apply enough pressure to the test probe to get a stable reading. It's not possible to help you in a methodical way unless the data you present is accurate.

Mnats, the differences in voltages I have presented are due to R44 being variable. R44 affects the voltage reading of Q11 S. As I am trying to find out why i am not getting any volts to my output and VU meter, I have rotated each variable trim pot on the board looking to see where there is no voltage swing. I inadvertently do not return the variable trim pot to its exact position it was in..

 

[bxershrts]

Assuming your negative rail is near -10V and not -0.1V (see MNATS post above) you need to examine your QBias voltage.

My negative rail is near -10v @ -9.74

The QBias voltage is a negative DC voltage supplied from the -10V DC rail to the gate of the FET.  If there is near 0 VDC at the gate, your FET will have very low resistance (source-drain) and much of your signal will be dumped to ground.  Further explanation can be found on the "Introduction" page of the build guide on my site (trap door analogy).  Seems like that is your issue.  By removing the FET you've removed that low resistance to ground and you've got your gain back.

So why is that?

First issue could be that you're neg rail is too low.  If it's really -0.973 that's you're problem.
Negative Voltage rail and power supply work as expected
If you have the right rail, then something is wrong between the rail and the gate bias.  Typically a gate voltage would be -0.70 to -1.50 after setting the QBias.  The range varies because the transfer curve of the FETs vary.

Open the D schematic. In the lower right you'll see two resistors. R35 and R60.  These form a simple voltage divider and their purpose is just to knock the -10V DC rail to a lower voltage for the trimmer R59 which sets that Bias voltage (-0.7 0 to -1.50). One end of R35 is connected to the neg rail and one end of R60 is connected to ground. Where they meet is the divided voltage.  That voltage is roughly -2.75 volts.  R59 sits between that voltage and ground (0V).  The wiper of R59 trims that range down to what ever you need for QBias. Before setting the QBias you need to start with that trimmer at max resistance to make sure you bias is as close to that full negative voltage.  If you're still losing signal test that circuit.

What is your DC at either side of those two resistors. R35 should be your neg rail voltage and roughly -2.75.  R60 should be roughly -2.75 and 0V.

my voltage at R35 is -2.80
my voltage at R60 is -2.80
my vltage at the oposite side of R60 is 0vdc

What is your DC V at pad 18 (wiper of R59). It should roughly -2.75 with trimmer all the way in one direction (also where you should start QBias calibration) and closer to 0V in the other direction.  All that checking out?

My DCV at R59 and Pad 18 are the same -2.8v and 0v with the trim pot all the way clockwise

From there that neg voltage travels from pad 18 through the attack/release side chain (check all of that wiring as well as R and C on the attack and release and is wired over tho pad 7 which connects to the gate of Q1 and the meter FET.  Pad 7 has a pretty high impedance so it's hard to measure it with a common DMM but you can try and see what you have there.

I measure 11.82 vdc @ pad 7

0V could indicate and issue with wiring from pad 18 to pad 7.

Finally if all of that checks out, you may have a bad FET.

Go through all of this carefully and report back.

Mike

 

[studiostuff]

I don't mean to offend anyone. But is OFFTHEWALLSTUDIO for real, or is this a pal of Mike's trying to find out how far he can go before Mike figures out the joke???

If he's for real, put me down for participating in a fund raising drive which would refund  OFFTHEWALLSTUDIO the cost of his kit, plus $50 for the effort.

I'm down for $10 and mean not to offend anyone. OFFTHEWALLSTUDIO seems like he could hurt himself with his kit... and my motive is selfish; I want to be able to buy Hairball kits in the future.

 

[Echo North]

I measure 11.82 vdc @ pad 7

There's your problem.  That should be similar to your Pad 18 voltage (smaller neg voltage).

You sure you have that section of wiring correct?  What is your DC at PAD 7 if you remove the wire from it?

Mike

 

[Echo North]

Or a solder bridge on your Q11 FET?

 

[bxershrts]

Thanks for all your ideas Mike, I really appreciated the breakdown in the last few posts.

I checked pad 7 with the cable removed and it is 0 volts.  The CW lug on the pot reads 11 and some volts.

I also want to note I have removed Q1 out of circuit - this is for all the measurements I have taken. ( chasing the idea that it is a bad fet)

 

[Echo North]

Thanks for all your ideas Mike, I really appreciated the breakdown in the last few posts.

I checked pad 7 with the cable removed and it is 0 volts.  The CW lug on the pot reads 11 and some volts.

I also want to note I have removed Q1 out of circuit - this is for all the measurements I have taken. ( chasing the idea that it is a bad fet)

So weird.  Where is all of that positive voltage coming from...are you feeding it a signal?  Don't for now.

That wire should just have a low negative voltage. 

 

[bxershrts]

Mike - I am not feeding it signal.
I am going to look at the wiring again. And check for solder bridging between the pot lugs . I have a checklist and diagram that I check 20x times before I sign off on it. Just my own personal system to have absolution on wiring.  But, you never know when solder drips and goes askew.

I do check the solder pads on everything with a zoom magnifying glass after I have soldered. Then i check for continuity on the traces , as I have seen many a soldered joint in my life just acting as glue and not having any continuity with the trace. 

Your replies along with mnats have been wonderfully exciting and informative as I am piecing together electrically how this works in my mind.  I appreciate the electronic descriptive approach more than "put the thingy on the pad and see what it does"

Mnats and Mike @ Hairball are great minds in the world of DIY,  and I thank you for it.

Stephen

 

[Echo North]

Check the MNATS rev D page and double check the PCB files to make sure you're testing the right pads if the labels are covered up by the terminal blocks.

Your pad 18 has -2.8V DC  which is reasonable.  It leaves pad 18, is wired to one lug of the release, travels through the release and two one lug of the attack before connecting over to pad 7.  It should still be around -2.8 but yours is 11V so it's picking up a shit ton of positive DC somewhere and it should't be.

Do you have a negative DC voltage at Pad 21?  What it is in 20:1 ratio?

Check all of that Pad 20/21/19/18 wiring.

We're getting close...

Mike

Mike - I am not feeding it signal.
I am going to look at the wiring again. And check for solder bridging between the pot lugs . I have a checklist and diagram that I check 20x times before I sign off on it. Just my own personal system to have absolution on wiring.  But, you never know when solder drips and goes askew.

I do check the solder pads on everything with a zoom magnifying glass after I have soldered. Then i check for continuity on the traces , as I have seen many a soldered joint in my life just acting as glue and not having any continuity with the trace. 

Your replies along with mnats have been wonderfully exciting and informative as I am piecing together electrically how this works in my mind.  I appreciate the electronic descriptive approach more than "put the thingy on the pad and see what it does"

Mnats and Mike @ Hairball are great minds in the world of DIY,  and I thank you for it.

Stephen

 

[Echo North]

I checked pad 7 with the cable removed and it is 0 volts.  The CW lug on the pot reads 11 and some volts.

Which pot do you mean here.  Attack or Release?

Also check that pad 21 voltage and report back.

 

[mnats]

I have a checklist and diagram that I check 20x times before I sign off on it. Just my own personal system to have absolution on wiring.  But, you never know when solder drips and goes askew.

I do check the solder pads on everything with a zoom magnifying glass after I have soldered. Then i check for continuity on the traces , as I have seen many a soldered joint in my life just acting as glue and not having any continuity with the trace. 

I've spent some time thinking about the mindset you need to troubleshoot. There are two situations you'll find yourself in - one where the piece of equipment worked at one time and now does not and another where the thing has never worked. For the latter it is often unproductive to think that there is nothing you've done wrong and expeditious to simply try to find the issue.

My DCV at R59 and Pad 18 are the same -2.8v and 0v with the trim pot all the way clockwise

Is this measurement with the wire connected to the pad or not? If not, what is the voltage coming from R58 of the switch bank?

I also want to note I have removed Q1 out of circuit - this is for all the measurements I have taken. ( chasing the idea that it is a bad fet)

If you read the explanation of how the circuit works on Hairball's site you would know that a positive voltage on the gate of the FET will shunt most of your signal to ground before it even hits the amplification stages. Mike typed it all out in this post. So drop the idea of bad components or replacing output transformers and fix what is clearly wrong - the positive voltage creeping into the gate of the FET that must be coming from somewhere.

 

[bxershrts]

Check the MNATS rev D page and double check the PCB files to make sure you're testing the right pads if the labels are covered up by the terminal blocks.

Your pad 18 has -2.8V DC  which is reasonable.  It leaves pad 18, is wired to one lug of the release, travels through the release and two one lug of the attack before connecting over to pad 7.  It should still be around -2.8 but yours is 11V so it's picking up a sh*t ton of positive DC somewhere and it should't be.

Do you have a negative DC voltage at Pad 21?  What it is in 20:1 ratio?

Pad 21 @ 20:1 Ratio = -6.84
Pad 21 @ 12:1 Ratio = -4.37
Pad 21 @  8:1  Ratio = -3.52
Pad 21 @  4:1  Ratio = -2.84

Check all of that Pad 20/21/19/18 wiring.

We're getting close...

Mike

There's your problem.  That should be similar to your Pad 18 voltage (smaller neg voltage).

You sure you have that section of wiring correct?  What is your DC at PAD 7 if you remove the wire from it?

Mike


I checked pad 7 with the cable removed and it is 0 volts.  The CW lug on the pot reads 11 and some volts.


Which pot do you mean here.  Attack or Release?

sorry Mike, I was referring to the attack pot cw lug wired to pad 7.

Also check that pad 21 voltage and report back.

I read -6.84 vdc

Mnats : Is this measurement with the wire connected to the pad or not? If not, what is the voltage coming from R58 of the switch bank?
With Pad 7 connected to the cw lug of the attack pot the voltage at r58 is -2.8 vdc

I also want to note I have removed Q1 out of circuit - this is for all the measurements I have taken. ( chasing the idea that it is a bad fet)


If you read the explanation of how the circuit works on Hairball's site you would know that a positive voltage on the gate of the FET will shunt most of your signal to ground before it even hits the amplification stages. Mike typed it all out in this post. So drop the idea of bad components or replacing output transformers and fix what is clearly wrong - the positive voltage creeping into the gate of the FET that must be coming from somewhere.

Mnats : Earlier Mike had asked me to remove the fet from Q1 to see if there would be a gain increase at the output.  I have removed the fet.  It has not been resoldered in - I have been taking measurements with the fet removed, I have simply indicated this is the case. Having matched pairs of 2n5457's are not easy to come by. I also do not have sockets for easy removal and installation, yet. I ordered sockets for the fets and will put these in when they arrive. Until then the fet will stay out of circuit as I do not want to damage the trace on the board or have any excessive heat drift the fet from being matched.

I have read Mikes posts and the documentation, they are wonderfully descriptive.