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One-Way
Bronze Member
New Zealand
104 Posts |
 Posted - 03/23/2009 : 06:32:13
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Hi there folks,
This is a post I put on the ESP site but havent had much feedback yet. I thought some of you techo toilers may be able to help me.
Im fairly new to full electronics schematic work but have done heaps of stuff with building and wiring guitars, cabs and the like.
I have built the chassis for the amp project out of aluminium and have it drilled for all controls and plugs, switches etc. I bought an unfinished amp project cheaply on my local auction which has given me most of the parts I need for this project.
I hav been studying the schematic for a few weeks now and there is few things that Im not quite sure of. http://sound.westhost.com/project27.htm
-On the pre-amp circuit it shows the 15volt power supply in bottom left corner. Does it connect to the right hand end at transistor BC549? I see there is a 15 volt +/- supply to both op amp 1 and from transistor BC549. I assume these are all connected by supply rails?
-With the +/- 35volt end of the above supply, does this connect to the +/- wires that come from the rectifier to the power amp board?
-On the pre-amp TL072 opamps does it only need connection 1,2,3,4,8 on OP amp1 and 5,6,7 on OP amp 2? Are the other terminals left unconnected?
-On the pic of the pre-amp board it shows 6 electrolytic caps but not on the schematic. What the story here?
I have a OPA2134 opamp. Will it replace one of the TL072 ops or both of them?
Sorry to I am asking so many probably stupid questions but Im learning lots as I go.
Thanks in advance,
Derek
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Edited by - One-Way on 03/23/2009 09:45:03 |
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nosi0
Gold Member
Netherlands
511 Posts |
Posted - 03/23/2009 : 10:06:17
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all i know is that the schematic has two TL072 but its should connect to one, so connect all connections to one. thats my opinion anyway i'm sure other people know it would be poinless have 2 TL072 and only connect half to each.
I had quite some  so excuse my language |
Edited by - nosi0 on 03/23/2009 10:07:04 |
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bossarea
Forum Admin
United Kingdom
3652 Posts |
Posted - 03/23/2009 : 13:33:59
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In the lower left corner, where it says +15V, should be connected to collector of Q1 (BC549) where it indicates +15V. The power supply (figure 3) marks the outputs with +35V and -35V. That translates to VCC and VEE in the pre-amp and power amp schematic. On the internal wiring schematic (figure 1A), he calls them +VE and -VE. No points for consistency.
As nosi0 pointed out, the opamp contains two opamps so why are there two on the picture of the PCB? The schematic names the opamp as U1A and U1B, indicating that he only use one but the photo shows two. The answer would be in the PCB layout perhaps?
C3, C8, C12, C13, C14 and C15 are electrolytic. C12 and C13 are marked correctly in the schematic, but the rest aren't.
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nosi0
Gold Member
Netherlands
511 Posts |
Posted - 03/23/2009 : 15:05:39
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| look in my topic about the blues breaker the schematic also has "two" TL072's but in the actual PCB there is only one. On the schematic i have for the blues breaker he smartly calls its 1/2 TL072 |
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One-Way
Bronze Member
New Zealand
104 Posts |
Posted - 03/24/2009 : 05:54:03
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Thanks for the help guys,
I think it should have two separate TL072 opamps to boost the input signal and give more gain. The earlier version of the pre-amp only used one.
The electrolytics are a mystery as they have to have the correct +/-polarity so I cant immediately see how that would work as per the existing schematic? |
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bossarea
Forum Admin
United Kingdom
3652 Posts |
Posted - 03/24/2009 : 09:59:44
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There's a couple of tiny pictures of the PCBs. I can see from those that there's only one opamp on the PCB so you're probably right that an older version had two of them.
It's not that hard to figure out the polarity of the caps.
C3 : - to the side that connects to ground
C8 : - to the side that connects to ground
C15 : - to the side that connects to VR5
C14 : - to the side that connects to emitter of Q1.
If I'm wrong, they'll blow up and you should connect it the other way round when replacing it. 
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One-Way
Bronze Member
New Zealand
104 Posts |
Posted - 03/28/2009 : 01:39:47
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Thanks guys,
Things are making more sense now I have drawn out the circuit on vero-template layout paper. |
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Building 100 watt solid state amp
