Author Topic: Giant hogweed needs volume help  (Read 2050 times)

TGP39

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Giant hogweed needs volume help
« on: March 19, 2015, 04:13:06 AM »
Hi guys. I just spent half an hour writing up a nice build report / tech help problem that suddenly disappeared. So this one will be shorter.
Just finished the giant hogweed by David. Has some really cool sounds, but I'm having a problem with the volume levels. When the octaves switch is off, I barely reach unity. When I turn the octaves switch on, I get a big jump in volume.  The only snafu I had building this was with T7. I used a BC549, but I had it soldered in the wrong direction. So I attempted to desolder it (huge disaster) and I eventually wound up resoldering a new BC549 via point to point using the schematic (see pics).



Here are the voltages I took.
t1 e-156mv, b-737mv, c-2.1v
T2 e-1.51v, b-2.1v, c-7.9v
T3 d-5.8v, g-2.53v, s-730mv
T4 e-440mv, b-355mv, c-9.4v
T5 e-0, b-348mv, c-350mv
T6 e-0, b-335mv, c-350mv
T7 e-1.13v, b-1.63v, c-6.9v

U1 1    2    3    4    5    6     7    8 (in volts)
    8.8 6.6 6.5  0    0  .175  9.5  6.6

U2   1     2     3      4      5      6      7      8 (in volts)
      4.7  4.7  4.7    0    4.3    1.4   4.7   9.5

U1 is LM308n, U2 is TL072

supply voltage is 9.66 volts



I will post more pictures. Any help is greatly appreciated. I have the build on my workbench so I can take any other readings if needed. Thanks guys.

Steve.
     
« Last Edit: March 19, 2015, 08:37:19 PM by TGP39 »
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TGP39

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Re: Giant hogweed is killing my rose garden.
« Reply #1 on: March 19, 2015, 04:16:26 AM »
solder side pics.....





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drolo

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Re: Giant hogweed needs volume help
« Reply #2 on: March 20, 2015, 03:43:18 AM »
The voltage for the collector of T7 looks weird.

Not sue for e and b but c should be around 5V for T7

pin 6 on the Tl072 looks too low.
It should be at half supply normally but I will need to check the voltages this evening when I get home.

I suspect that there is something weird around T7. can you try to audio probe your signal after T7? It should be a bit over unity, maybe twice as loud, in any case not less than unity.


drolo

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Re: Giant hogweed needs volume help
« Reply #3 on: March 20, 2015, 03:49:29 AM »
If nothing helps, I will send you another board. It's my fault you soldered the transistor in reverse in the first place ...

TGP39

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Re: Giant hogweed needs volume help
« Reply #4 on: March 20, 2015, 04:00:16 AM »
Hi David. I will audio probe around T7 when I get a chance today. Thank you for the help.  Honestly, it's not your fault. I should have looked at the schematic before soldering all the transistors. I really appreciate it though. Does my T7 point to point job look correct?  I double checked the schematic and I thought that would do the trick. Thanks again.

Steve.
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drolo

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Re: Giant hogweed needs volume help
« Reply #5 on: March 20, 2015, 05:07:47 AM »
It's not easy to see but it seems like you soldered the collector to the junction of R13/R32/C18 instead of the junction of R32/R29.

the best spot would be here :


TGP39

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Re: Giant hogweed needs volume help
« Reply #6 on: March 20, 2015, 03:27:40 PM »
I'll try that. Should I solder it so that R29 and r32 have a solder bridge between them?

Steve.
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drolo

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Re: Giant hogweed needs volume help
« Reply #7 on: March 21, 2015, 12:55:00 AM »
they are already connected together. You can connect the collector to either resistor on the spot shown above

TGP39

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Re: Giant hogweed needs volume help
« Reply #8 on: March 21, 2015, 05:20:39 AM »
Ok. I understand now. Will give it a try.

Steve.
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TGP39

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Re: Giant hogweed needs volume help
« Reply #9 on: March 21, 2015, 06:27:11 PM »
Hi David. I repositioned the collector as you mentioned above. My new voltages for T7 are c=5.55 , b=1.35 and e=0.84. I'm going to test and see if this did the trick.

Thank you for your help. Steve.
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TGP39

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Re: Giant hogweed needs volume help
« Reply #10 on: March 22, 2015, 05:04:06 AM »
Well David,  your suggestion about re-routing T7 worked!  After looking at the schematic again, I have no freakin clue why it worked.  Lol, but it worked. I am going to test everything later today, but I think this did the trick. Thank you for your help David.

Steve.
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drolo

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Re: Giant hogweed needs volume help
« Reply #11 on: March 22, 2015, 05:12:43 AM »
glad you were able to sort it out