gainklone problems, maybe...

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
hey everyone. i jumped on the bandwagon and threw together a gainclone. i used the minimized schematic, or rather the peter daniel schematic. unfortunately, im pretty much an idiot with electronics, and im having trouble with the schematic. i know its dead simple, but there is just a couple things i cant figure out.

i figured out the whole schematic, and put it together really close p2p, and it turned out well. however, i dont get the input part of the schematic. peter has been trying to help me out, but im just such a novice, i hate wasting his time. maybe someone else in here can help me out.

from pin 8, i have a 220K resistor connected to pin 3. then i have 10K, 1W resistor connected. but then what? i know there is supposed to be a 2.2uf (or 4.7uf) non polar cap there, but then where does that go? that whole area of the schematic just doesnt make sense... can someone just simple spell it all out for me? like, part A goes into part B? i looked on numerous websites trying to figure out how the diagrams work, and how to put them together, but no luck.

i hastily tried a few things, and got the amplifier to produce sound, but it was more like noise. you can tell what is playing, but its a bit tinny, but more importantly, buzzy and noisy. (however, this could be due to the fact i was using 2 12V 8AH lead acids for a temporary power supply...) I have yet to find a transformer to use for cheap. however, when it was playing, the sound beneath the "crap" was very nice. i was using a cheap old aiwa speaker to test, and i have NEVER heard such tight and pronounced bass from it, ever. i didnt think it was capable.

thanks to everyone in advance. i would really like to figure this thing out, becuase i think it could be an awesome project! im really trying to learn amplifier/electronics design, but im still such a beginner.
 
This is the schematic you should use. 220K resistor is between pin 3 and 8. From your RCA jack the signal goes to the pot (if not using pot connect the input with 50k resistor to ground), then you connect the cap, the other pin of the cap connects to 10K resistor and the other lead of resistor connects to pin 8. So, pin 8 is connected with 2 resistors: 10k and 220k.
 

Attachments

  • pd.jpg
    pd.jpg
    54.3 KB · Views: 2,524
cowanrg said:
will using that lead acid power supply make the sound really bad, or do you just think its the resistor configuration i had?

No reason the batteries would make it sound bad. Unless they're dead of course. :)

Be aware that with +/- 12 volt supplies, you're not going to get much but about 5 or 6 watts out of it. And unless you're loudspeakers are fairly efficient, don't expect to get much volume.

Be sure you're not driving the amp into clipping by trying to get enough volume out of your speakers.

se
 
cowanrg said:
yeah, im using 2 12 volts for a total of 24VDC, so there is enough voltage, but as far as power, who knows...

Um, that circuit needs to be powered with a bipolar supply. In other words, +V and -V. If you're using two 12 volt batteries in series and running a straight 24 volts to the power supply pins on the chip, it's not going to work properly with that circuit.

You'll need to use the batteries like this:

<center>
<img src="http://www.q-audio.com/images/bipolar.jpg">
</center>

maybe it is clipping... i had the pre-amp running at a level that i would use for my normal speakers. but even at very low volumes, the sound was still crap. oh well, soon enough i will figure out whats wrong...

It sounds like you may have it hooked up to a single 24 volt supply.

The LM-3875 can operate from a single supply, but not using Peter's circuit.

se
 
Steve Eddy said:


Um, that circuit needs to be powered with a bipolar supply. In other words, +V and -V. If you're using two 12 volt batteries in series and running a straight 24 volts to the power supply pins on the chip, it's not going to work properly with that circuit.

You'll need to use the batteries like this:

It sounds like you may have it hooked up to a single 24 volt supply.

The LM-3875 can operate from a single supply, but not using Peter's circuit.

se

ah cool. i can try that... so basically use the point where i connected the positive to negative to make the series, and make that the ground? i can try that. the batteries have plenty of juice i think. they are like 5 pounds each.

i still have a question of if that transformer will work for this application. i just want something to test it out, so i can see how this damn thing sounds.
 
Peter Daniel said:
I tried it with my Aleph X and it definitely influences sonics. With the resistor in place, the amp seems to be cleaner (or smoother) sounding. I don't really know the reason behind it.;)

Could be because it's loading down the output stage of your source component. With that 50k resistor (or using the pot with the volume turned all the way up) your input impedance is about 8.3k.

Shouldn't be a problem for most solid state output stages, but a lot of tube output stages may start to choke on it.

Also, the lower the input impedance, the more significant the effects of cable capacitance, i.e. it will start rolling off the highs at a lower frequency.

That perhaps might also explain why it sounds smoother.

Anyway, as long as you like the result that's all that counts.

se
 
cowanrg said:


ah cool. i can try that... so basically use the point where i connected the positive to negative to make the series, and make that the ground? i can try that. the batteries have plenty of juice i think. they are like 5 pounds each.

Well, the point where you connected the positive and negative battery terminals to wire them in series, yes.

And how much juice the batteries have depends not on their weight but how much juice they have. If they've been discharged, it doesn't matter how heavy they are, they'll be out of juice. :)

i still have a question of if that transformer will work for this application. i just want something to test it out, so i can see how this damn thing sounds.

Sorry, I missed that question. What transformer do you mean?

se
 
well, im listening to it now.

it doesnt have that NASTY noise in the background. however, i put in that 50K resistor like peter said, and there is a nice BUZZ in the speaker. and, its very quiet. i tried without, and its fine.

also, i am not using the 4.7uf cap on pin 8. the idiot at the electronics store forgot to put it into my bag :) maybe that has something to do do with it. i will say this thing has some POWER. im not 100% quality, but that's partly due to the power its getting probably... in the 5 minutes ive been listening to it, its gone from 26.4 volts, down to 25.33 and dropping as we speak.

any ideas as to why adding that resistor adds so much hum? (from the ground, i have a kinda star ground, and from that there is a lead going to the ground on the rca jack, and in between the star ground and the rca ground, im connecting it... i hope thats right...)

oh yeah, is there any way to avoid that nice thump when i connect the positive and negative? will a switch stop that, or do i need a soft start circuit?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.