GSSL HELP THREAD!!!

[djob]

Cheers Jakob,

Yeah seems you're right on. It's nice to get an understanding of why that was occurring. On taking DIMM current readings across the meter it would seem the meter is not linear. Of course it's all about the sound in the end, but after all that work and with everything else about the GSSL now so wonderful it would be nice for the meter to follow suit - yes anal and proud If anyone can recommend a well priced and accurate/linear 1ma meter plz let me know!

 

[jameslangtry]

Hi guys,

New to the forums and first time poster so I hope this post is in the right place. I have a problem with my GSSL. This is the third one I've built so I'm quite familiar with the PCB layout. I'm also quite pedantic and careful when it comes to soldering so I've already checked the board with a magnifying glass looking for shorted pads and blobby soldering. So far, everything looks fine.

Earlier today I power up for the first time. Power LED came on and I breathed a sigh of relief. However when I moved the unit across the room to my computer to start putting sound through it I noticed that the LED had gone out. I imagine that the unit only stayed power up for about 10 seconds before dying.

The first thing I decided to measure with my volt meter was the +15v and -15v links that go from the regulators to the two VCAs. When  measuring between the two I get around 15v, which doesn't seem right because surely +15 +-15V = 30v? Between the +15v trace and ground I get -0.34v and between the -15v link and ground I get -15v. This would suggest that the +15v link is not getting the power it needs which leads me to think that there is a problem with my 7815, 7915 or 7812. I don't think it's the 7812 because it isn't particular warm to touch, but the 7815 and 7915 are quite warm when power is applied.

It's all very well saying that the 7815 and 7915 could have gone wrong but why? Were the ones shipped to me faulty or is it something else further down the line?

I have a list of test nodes from a previous points which I will carry out shortly and post here if any of you have any suggestions based on what I've said so far. Any help would be greatly appreciated.

Thanks guys.

 

[dipfrik]

I'am not an expert but what happens when you switch the unit on-off-on again?
Is it stable? If so i would recommend to change all regulators.
I replaced all by TI regulators here and since then everything is fine.

This thread has several messages to a topic called "latching regulator".
Maybe this is one way to start and not so expensive?

Cheers, Sven

 

[jameslangtry]

The unit is definitely stable. On and off makes no difference.

I did some tests with all the ICs removed (but left the regulators in of course) and applied power. The power LED lit up with power connected and no ICs inserted.

Following the advice of this man:
"Check all of the voltages i.e. with the negative test lead on 0v. check the op-amp socket pins  for +and- 15v.  Dual op-amps pin 8 for +15v, single op-amps pin 7 for +15v. Pin 4 for -15v.
Except in the case of the op amps in the control circuitry which should be at +and- 12v. Also the quad op-amp.
Check also the pins where the VCA chips go - always with ref. to the schematic of course.
Doing this is always a good move so you can make sure no damage will occur before you put the IC's in their sockets.
Having a scope is always useful because if you're not getting any signal you can probe about to see where it stops and that usually pinpoints the fault."

All voltages seemed to be stable and healthy for each IC socket. Re-inserting the ICs didn't help. The thing still won't power up.

I've ordered new regulators and that's the only thing I can do for now unless anyone else has any suggestions. I've removed the existing regulators and tried testing them by consulting their individual data sheets for pin information. I then applied voltage and measured the output. Two seemed fine but the L7915 started to smoke so I think that one is toast (either due to my mistake or it was broken anyway).

 

[Harpo]

...I noticed that the LED had gone out. I imagine that the unit only stayed power up for about 10 seconds before dying.

The LED only shows the low current +12V rail from 78L12 operating. There are 4 other supply rails in this build.

Between the +15v trace and ground I get -0.34v

7815 is latching.

but the 7815 and 7915 are quite warm when power is applied.

The differential between unregulated DC input voltage and regulated DC output voltage times current drawn by the connected circuit is transfered to heat by the voltage regulators. What is your mains transformers secondary AC voltages ?

It's all very well saying that the 7815 and 7915 could have gone wrong but why? Were the ones shipped to me faulty or is it something else further down the line?

That's what multimeters are good for. Measure the voltages and you know it for sure. From your previous wording both positive regulators at the bipolar supply rails are probably only hanging on startup. Some pages back (pg.301/302 IIRC) I posted a latchup fix that seems to work quite well. Could have other reasons as well, FI ICs or caps fitted with wrong orientation, shorts, broken or wrong parts, ....

The unit is definitely stable. On and off makes no difference.

Not the definition of 'stable', it's the definition of 'broken'.

I then applied voltage and measured the output. Two seemed fine but the L7915 started to smoke so I think that one is toast.

The unidentified applied voltage to the regulators from whatever source would have a magnitude and should be a DC voltage with the correct sign in respect to 0V reference voltage. Be more exact with identifying your parts. Your "L7915" will be broken, but there is no L7915 in this build, so this will be a typo (might be a LM7915 or a 79L15 or whatever typo permutation). You fitted the correct type of rectifier ? Some close up pics of your build might help as well.

 

[Che_Guitarra]

Hi guys.  Looking to jump on this project.

I'm just wondering if there's a consolidated shopping list for this project?  A BOM for parts (large and small), or even a Mouser project cart link?  At 308 pages this thread is getting hefty, and i've not spotted a consolidated/itemised list.  I can kinda see what I need by going to PCBgrinder.com, but I want to avoid an extended period of buying random/overlooked finishing parts... I live in Perth, Australia - nothing is cheap to get here, and nothing is fast to get here.  Postage is always my biggest cost when undertaking a project.

 

[jameslangtry]

Hi Harpo,

Thanks very much for your input. Every piece of information you offer is a great help. Forgive my lack of understanding (i've been fascinated by electronics my entire life but never received any formal training).

7815 is latching.

Does this mean that the 7815 is broken? How can latching be prevented.

As I made some mistakes when trying to test my regulators, I have bought new ones and am waiting for them to arrive.

What is your mains transformers secondary AC voltages ?

My toroid is 18x2 so i get 36v from end to end when both cores are connected in series. The centre tap is connected to the middle pad on the power input section on my board - is this the correct way to do it? I thought that the centre pad was ground and therefore should be 0v?

That's what multimeters are good for. Measure the voltages and you know it for sure. From your previous wording both positive regulators at the bipolar supply rails are probably only hanging on startup. Some pages back (pg.301/302 IIRC) I posted a latchup fix that seems to work quite well. Could have other reasons as well, FI ICs or caps fitted with wrong orientation, shorts, broken or wrong parts,

I will report back here once my new regulators are fitted. I'm always nervous when probing the board when powered up in case i accidentally short something out. Also this was before I had the good idea of checking the datasheet to see which pin served what function so I had no idea what pin was responsible for and therefore didn't want to start probing the board in case i wreck the device (too late). How can I prevent them latching and hanging on startup? Also how is the voltage reference (output voltage) decided for the regulator? Is it an inbuilt reference or is it decided by passive components on the board?

I know i'm not very good with regulators but if there is one thing I take a lot of time over is component orientation. I have double and triple checked all pole sensitive caps/ICs/packages. I will take a look at your latchup fix. Thanks again

The unidentified applied voltage to the regulators from whatever source would have a magnitude and should be a DC voltage with the correct sign in respect to 0V reference voltage. Be more exact with identifying your parts. Your "L7915" will be broken, but there is no L7915 in this build, so this will be a typo (might be a LM7915 or a 79L15 or whatever typo permutation). You fitted the correct type of rectifier ? Some close up pics of your build might help as well.

I consulted the datasheet for the LM7915 so i knew which pins were input, output and ground. I then applied 12v (which i believe was within the tolerance specifications for this device) to the input but obviously i did something wrong as it started to smoke. I will make sure to be more specific in future but please remember i'm an amateur and am struggling with troubleshooting this build. I apologise for the typos. I fitted the rectifier that was supplied with the kit from PCBGrinder. I assume it is the right one and I'm fairly sure it is in the correct orientation.

Like is said previously I'm still waiting for fresh regulators to arrive so there are currently none visible in the picture attached.

 

[gyraf]

..remember the wire link at the *HPF, or it won't compress..

 

[dipfrik]

…good point! I can't see it on the photo.

 

[frereyvan]

Hi guys.
I have just finished to assembly my GSSL (PCB Grinder) with true bypass , CRC and Expat turbo (Turbo not plugged for the moment...)
Without AOP and VCA and board, no problem.
When i plug the AOP, problem : the -12 V and - 15 V are good every time,  but the + 12 V and the +15 V are good only one time on five about.
I must switch on/ off 5 or 6 times to have the good voltages.
The regulators aren't hot.

Any idea ? Change the regulators ?
Thanx.

 

[jameslangtry]

..remember the wire link at the *HPF, or it won't compress..

Is that HPF link on the secondary board which contains the Attack, Ratio and Release controls? If so, I know the one you're talking about and it is there (but not visible in the photo)

 

[dipfrik]

…sorry but it's not there

 

[Harpo]

7815 is latching.

Does this mean that the 7815 is broken? How can latching be prevented.

>'Some pages back (pg.301/302 IIRC) I posted a latchup fix ...

My toroid is 18x2 so i get 36v from end to end when both cores are connected in series.

...on paper. You've got a multimeter to measure the real world -probably higher- AC voltage that gets rectified to more than 50V raw/unregulated DC or bipolar raw +/-25V with 0V reference voltage in between. The >10V differential between >25V in and 15V out times current drawn by the connected load is transfered to heat by the voltage regulator. A dual 18VAC secondary will generate a lot more heat than a dual 15VAC transformer.

Also how is the voltage reference (output voltage) decided for the regulator? Is it an inbuilt reference

inbuilt reference for 78xx/78Lxx/79xx/79Lxx fixed voltage regulators. You can change output voltage by external components, but not needed or done on this circuit.

I consulted the datasheet for the LM7915 so i knew which pins were input, output and ground. I then applied 12v (which i believe was within the tolerance specifications for this device) to the input but obviously i did something wrong as it started to smoke.

As previously said, 'and should be a DC voltage with the correct sign in respect to 0V reference voltage'. You overlooked the LM7915 being a negative voltage regulator. You applied +12V (being at least 12V outside parts tolerances) to the regulators input that expects a negative input voltage, hereby killing the device. You'd need more than -15V in (lookup datasheet for dropout voltage) for the 7915, so the regulator can regulate down to -15V.

Is that HPF link on the secondary board which contains the Attack, Ratio and Release controls?

It is next to the TL074 on main board, labled '*HPF' and missing in your pic.

 

[gyraf]

I know I've said it before, but thanks Harpo!

Jakob E.

 

[jicama]

Some help needed please!

I ordered the turbo mode and the CRC for the GSSL 11 which use THAT2181b, but the manual for the turbo mode is from 2008 and has THAT2150, I assume I need to use in the turbo pcb the same IC as my main board, but do I need to change the other components as well? Resistors value, capacitors??

Thanks

 

[gyraf]

just make turbo board a replica of main board - they like to be symmetric

 

[jicama]

Ok then I'll wait to buy the components until the turbo pcb arrives,

Thanks Gyraf

 

[jameslangtry]

…sorry but it's not there

Thanks Dipfrik! Just put it in now

Harpo, thanks for the advice. All three new regulators arrived today, they are installed and now the device powers on! There is however a remaining issue. There is a significant amount of noise on the output at quite high levels, extending from around 50hz up to around 800hz. I suspect a possible ground loop but I have double checked my grounding for the device and it all seems ok. Something is very wrong with the output. I don't know whether I can pass signals from input to output yet as I have not tried.

Do you have any ideas as to what could be typically responsible for a ridiculous and unpleasant amount of noise on the output when the unit is powered up?

Any ideas are greatly appreciated.,
Thanks.

 

[Harpo]

Do you have any ideas as to what could be typically responsible for a ridiculous and unpleasant amount of noise on the output when the unit is powered up?

1st.suspect is missing standoffs or insulating material between pcb and the conducting case ground to prevent shorting out pins to your case ?

 

[jameslangtry]

1st.suspect is missing standoffs or insulating material between pcb and the conducting case ground to prevent shorting out pins to your case ?

Standoffs are now installed. Noise still persisting. The noise is much more than 'hiss'. It's a full bodied aggressive sound. Could the VCAs have suffered due to my blundering with the old regulators? I've measured the +15v and -15v traces to the VCAs and they are fine. I will remove all the ICs again and re-check all the voltages and post results here when done. I'm also re-checking every single solder joint in case the issue lies there.