Swapping OP27s into CMOY

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I just recently got access to a bunch of parts and tools, unfortunately, the only op amps I at my disposal without going out and buying anything are op27s.

After a lot of googling, I haven't found too much on their use beyond the datasheet (which, if all else fails, I just might make two cassette amps and kludge them together with a pot...) and the fact that they have been used in one or two diy projects (http://www.head-fi.org/forum/thread/383129/cheap-amp-for-akg-240-df apparently based on this project: http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=gilmore3_prj.htm )

I realize that these are singles, but it looks like browndogs can be used to make doubles. With that knowledge, and the fact that I am the cheapest person in my own little world who doesn't want to put any money into this at this particular point in time,

I think I can probably just dead-bug them together, skipping the trim and null pins and, shorting the 4s and 7s to get a 8 pin dual op-amp.

With this, I'll probably be building and attempting to debug on a breadboard, and then soldering them together dead bug style in the end.

My question is thus:

Is there anything wrong with following the tangentsoft walkthrough (http://tangentsoft.net/audio/cmoy-tutorial/) with this replacement?

Circuit building background:

I have little experience with circuit building, but read and dabble a lot. I can follow a diagram, but probably improvise too much to get consistently working results.

I did try to rig up the cmoy from the tangentsoft walkthrough, for one side using a function generator for input and a wallwart for power. the power looked like it was ok, but when I tried it out, the output was quieter than the input and wasn't responding to changes in the pot or capacitor (not sure I had the polarity and value right and whatnot so even shorting it out didn't have an effect on volume). as there are only seven components to the amplifier section, I'm not sure what could have been wrong which led me to doubting the op-amp. That said, I could be fully in the wrong and have messed up some aspect of the circuit or grounds, or completely overlooked something else.

So to sum up the ramblings above:

Will a doubled pair of OP27s work with the CMOY pocket amp?

Will I get any interesting effects beyond 'louder?' Warmer, and Fatter would be nice, anything at all would at the very least be interesting.

Long shot: Is there anything that stands out about an output that is quieter than the input and does not respond to the trim pot?

Hi Soymilk, Thanks for your input,

I'm thinking that it was probably me that wired something wrong... I just wanted to make sure there wasn't anything inherently wrong with my process at the very base level.

No harm in just skipping the trim and other pins of the single chips when combining them?

with gain being (r4/r3)+1, I directly followed the schematic with regards to the resistors ((10k/1k) +1), which should give me a gain of 11.

with respect to gain, is it possible to swap out one of the resistors for a trim pot for on the fly gain changing?

does gain affect anything other than volume (and noise)?

Efficiency aside, another note that might be of use, but doesn't seem to be something at the same level of my current problem: I had rigged the system up to a function generator and a tv speaker for testing so I wasn't risking my mp3 player or headphones, But I don't think that they should have resulted in being quiet if directly hooking the function generator to the speaker got me a decent volume of sound. Maybe the function generator was set at too high of a volume (vpp)?

Now that I think about it, I don't think I was adjusting the pot since it was one of the screwdriver adjustment types and just wanted to test if the thing was working. left halfway, if I remember correctly.

that might resolve that issue.

...That's probably way worse than a noob mistake.

I guess I was just way too hung up on maybe messing up polarity and using the 'wrong' amp that something so simple didn't occur to me.

Pars:

I could still have messed up the wiring, but i don't think the m jumpers apply so much since I was just working off the schematic on a temporary protoboard (solderless breadboard?) to test things out before I soldered things together.

The thing that really seemed weird while troubleshooting was that i was using a ceramic input disc capacitor (are they polarized?). flipping it around and shorting it out and all that didn't seem to have an effect on the output volume, then again, maybe I should have been listening for frequency (my ear isn't the greatest for that, I don't think)

Another thing I had read about was stray capacitance as a result of using a protoboard, would something like that apply in a notable way on a circuit like this?

nikongod:

Thanks for the datasheet, that was the one that I found the cassette amp on to test the amp if this didn't work. That said, beyond the pinouts and the example schematics, I didn't really get any information out of that sheet. My level of understanding is a little limited at this point and I'm trying to find a balance between following directions and using what I have.

With regards to the op27 itself, are there any special characteristics that are noteworthy? or is a lot of the sound alteration due to the other components in the circuit (resistors, capacitors...)

soymilk:

I was thinking that adding a 10k pot to the gain loop would give me the chance to work with a r4/r3 between 0 and 10 with a gain of anything from 1 to 11, which seems to be within the range of possibilities. that said, changing one gain while leaving the other alone would probably be screwy with the ultimate sound output, right? Adjusting two gains to be perfectly equal seems like it'd be the hardest part when working with two individual ~270 deg potentiometers.

I'm still a little lost on what exactly gain does for me... is it clipping? would clipping ever be desirable?

edit: proper name (probably) for the solderless breadboard

Zigis:

that did occur to me, I'm not sure why I wanted a browndog if my footprint wasn't going to change as a result anyways, maybe I was thinking that somehow a double behaved differently from a single and wanted to match pinouts of the double (which probably makes things confusing more than anything else). the trim pins confused me as to why you might need them in a single, but wouldn't need them on a double.

so, it sounds like there's no problem with using op27 in a cmoy then?

Well, I solved my first issue!

I hadn't connected the power ground to the amp ground!

Joy! An easy fix! This solved my prototyping issues, it turns out that I can almost read a circuit diagram, because I got an output!

So, I tore down my build and redid it with both channels on a breadboard, wire-wrapping the points before I soldered them, and it works!

Almost.

The right channel works, and it's an acceptable first build, I'd say. but the left is silent.

I can't think of any reason why it might be, the schematic is identical, it's not the amps, because swapping either of the singles doesn't change the result I get, Checking things with a ohm meter is only marginally useful since the circuit changes the effective resistances between points.

That said, I think that the two channels are essentially identical in just about any possible means of checking between two points.

Should I be checking with a voltmeter? what are the points I should troubleshoot?

could the headphone jack I pulled from an old cd player be of effect? I'm having a hard time seeing any differences between the l and r as far as the circuit goes, and the only points not common to them is the input and output

I'll give the connections leading to and away from both jacks a try.

qusp:

so far, I've been just checking resistances, though, I suppose that even values that are *off* would still give an output, so I'll keep looking for a short.

I'm not sure that pictures will help much, for the same issues that make trouble shooting difficult: my work is a bit of a mess.

I'm using a lot of wire wrapping using the leads, and solder bridging, and some random added wire, so I'll add an annotated picture.

some comments: the top half is really messy, so I would think that the problem is in there, but all it does is provide power, and if the right side is working, it means the power is being routed correctly, the left is connected in the same way, but the only difference in the two is where the two connect to their respective jacks. I'll keep playing around with a multimeter

the cable in is just some cat5, I completely ignored pins 1,5,8

I'll try checking that there is a connection between the opamp socket and the back side of the board