Ok I have the amp playing music through my creative aurvana lives and it all sounds good.
It seems make things sound better by reducing some of the 'muddyness' in the bass and making things clearer sounding (had my headphones plugged into the lineout of my X-FI before).
I guess this is due to better output impedance.
Just one last question with the amp at 1x gain it still amplifies the sound by about 20% with the pot turned all the way up, is this normal?
It seems make things sound better by reducing some of the 'muddyness' in the bass and making things clearer sounding (had my headphones plugged into the lineout of my X-FI before).
I guess this is due to better output impedance.
Just one last question with the amp at 1x gain it still amplifies the sound by about 20% with the pot turned all the way up, is this normal?
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If none of the resistors R17,19,21 and 23 are in circuit then you have gain of actually slightly under 1
If you have any resistors from pins 2 and 6 of U1 to ground then you have gain.
Look at the circuit
The output stage is unity gain (1) because there is 100% feedback wrapped around the opamps. The input stage has unity gain as long as there is no resistance from pins 2 and 6 to ground. The 1.5k feedback resistor doesn't have any effect in that situation, its still unity gain.
The 100 to 274 ohm inout resistor and the 10k form an attenuator but the effect is negligible.
So no gain set resistors and you have unity gain. Any resistance present and you have gain depending on the value of those resistors.
Even if you have no test equipment other than a meter you can "prove" the gain by setting up a small DC voltage on the input (with a preset pot) and seeing how much that voltage gets amplified.
If you have any resistors from pins 2 and 6 of U1 to ground then you have gain.
Look at the circuit
The output stage is unity gain (1) because there is 100% feedback wrapped around the opamps. The input stage has unity gain as long as there is no resistance from pins 2 and 6 to ground. The 1.5k feedback resistor doesn't have any effect in that situation, its still unity gain. The 100 to 274 ohm inout resistor and the 10k form an attenuator but the effect is negligible.
So no gain set resistors and you have unity gain. Any resistance present and you have gain depending on the value of those resistors.
Even if you have no test equipment other than a meter you can "prove" the gain by setting up a small DC voltage on the input (with a preset pot) and seeing how much that voltage gets amplified.
Try this and it will make sense,
Op Amp Gain Calculator
You want the second example, non inverting.
Edit... how are you calculating or determining that the gain is "20%" etc. One effect you might be encountering is the "loading" of the O2 vs whatever you are comparing against. The O2 presents as a 10k load to the source. If your source impedance is "high" then the O2 may be loading it less than whatever else you are comparing against and thus seem as though it is "amplifying" when in fact it is not.
Op Amp Gain Calculator
You want the second example, non inverting.
Edit... how are you calculating or determining that the gain is "20%" etc. One effect you might be encountering is the "loading" of the O2 vs whatever you are comparing against. The O2 presents as a 10k load to the source. If your source impedance is "high" then the O2 may be loading it less than whatever else you are comparing against and thus seem as though it is "amplifying" when in fact it is not.
I want to get better quality 3.5 jacks for my amp. I tried searching for objective2 and jacks on the site and the result pointed to this thread, all 370 pages of it.
I recently built my first O2 and there was only one thing damaged that I had to fix. I'm really enjoying the amp, as long as it is stationary. As soon as I try to take it with me, I get annoying scratching noises when the input cable is moved. I tried 2 different 3.5-3.5 cables, but they all fit loosely.
Is there a high quality direct-fit replacement for these jacks? Maybe something with higher spring tension and gold plated contacts?
I recently built my first O2 and there was only one thing damaged that I had to fix. I'm really enjoying the amp, as long as it is stationary. As soon as I try to take it with me, I get annoying scratching noises when the input cable is moved. I tried 2 different 3.5-3.5 cables, but they all fit loosely.
Is there a high quality direct-fit replacement for these jacks? Maybe something with higher spring tension and gold plated contacts?
I just finished building an O2 for myself. This is the second one. I went through the tests and finally ran it with headphones. Every thing seemed fine. I had it plugged into my pc and was listening to iTunes when the volume more than doubled without touching anything. It appears to happen to both channels. It doesn't matter which setting the gain switch is in. The O2 turns on and works for 30 secs to several minutes and then suddenly more than doubles the volume. I'm going to try swapping the 2068 opamp between the two units to see if the problem follows the opamp.
I have access to an oscope and a cheap generator. I'll try getting some measurements in case the problem does not follow the 2068.
Any suggestions for other troubleshooting steps?
I have access to an oscope and a cheap generator. I'll try getting some measurements in case the problem does not follow the 2068.
Any suggestions for other troubleshooting steps?
Other info. I did not populate R17 and R21 for a gain of 1 with the switch in the "out" position. R19 and R23 are populated with 1K resistors for a gain of 2.5 in the "in" position. The gain switch gives a very noticeable change in volume between the two positions. This is true either with the normal volume or the much boosted volume. I tried a DVD player as a source with the same results (sudden large change in volume without touching the O2). The gain switch casing is not touching the "via". The solder joints are bright and shiny with a good meniscus. I am a loss to figure out where the effective lower gain resistance in the two channels is coming from. Well, measurements tomorrow.
Only the feedback factor affects the gain of the opamps. The fact both channels were doing this points to a common issue athough without first hand seeing it all, its hard to imagine what.
For no other reason than you mentioned a PC... try a normal line source such as a CD player. Floating ground/cracked print to the earthy end of the volume control ? Does it still sound "normal" when the gain increases, correct channel separation and so on, not "phasey" ?
Or you might have fixed it
For no other reason than you mentioned a PC... try a normal line source such as a CD player. Floating ground/cracked print to the earthy end of the volume control ? Does it still sound "normal" when the gain increases, correct channel separation and so on, not "phasey" ?
Or you might have fixed it
Even though I couldn't see any shorts, I got a fairly stiff brush and cleaned the bottom of the O2 with denatured alcohol. Since doing that, there has not been any recurrence of the issue. A little solder whisker that I could not see even under a magnifying loop??? I don't know but the O2 has been rock solid for several hours now. Fixed? I don't know but I hope so.
I remember working on TI's ASC (Advanced Scientific Computer) in 1972. I could measure a short between two traces which came close to each other on only one place on the board. I could see nothing under the inspection microscope. Anyway, I took an Xacto knife and dragged the blade between the two traces at that point and the short went away and after replacing the board, it then worked normally.
I remember working on TI's ASC (Advanced Scientific Computer) in 1972. I could measure a short between two traces which came close to each other on only one place on the board. I could see nothing under the inspection microscope. Anyway, I took an Xacto knife and dragged the blade between the two traces at that point and the short went away and after replacing the board, it then worked normally.
I have very limited experience soldering and testing electrical components, but I've followed the instructions for testing as closely as possible, and have run into some problems.
I have built it without the batteries, and have not installed D2, D6, R1, R2 or battery terminals.
LED turns on, and fades slowly (maybe 10-20 s) after power is removed.
With U2 installed (but not U1, U3 or U4) I get a very low reading (0.5 - 2.3 VDC) over ground and the U3 and U4 pins. Only the "correct" pins are showing any voltage, though. Initially there was a 11.5ish voltage on one pin, and the same across C8 and C9 together, which I assume was half of what it should have been, but now that have dropped to almost nothing as well.
My best guess would be I have either damaged something when I was trying to fix some solder joints, or I have a solder bridge somewhere. Any ideas to where I should start looking?
Will upload pics when I find my camera.
I have built it without the batteries, and have not installed D2, D6, R1, R2 or battery terminals.
LED turns on, and fades slowly (maybe 10-20 s) after power is removed.
With U2 installed (but not U1, U3 or U4) I get a very low reading (0.5 - 2.3 VDC) over ground and the U3 and U4 pins. Only the "correct" pins are showing any voltage, though. Initially there was a 11.5ish voltage on one pin, and the same across C8 and C9 together, which I assume was half of what it should have been, but now that have dropped to almost nothing as well.
My best guess would be I have either damaged something when I was trying to fix some solder joints, or I have a solder bridge somewhere. Any ideas to where I should start looking?
Will upload pics when I find my camera.
It looks like the negative rail is OK and the positive rail missing. If you remove D1 (or just lift one end) does the voltage come up to plus 12 volts on the regulator output ? If it does then there could be a problem (short somewhere) but do the checks first. If it doesn't then leave D1 disconnected and check the voltage on pin 1 (input) to the regulator. There should be over plus 16 volts here. If that's no good then D3 could be open circuit or there is a physical problem somewhere (break in continuity).