Beginner: Slone Preamp

scott_jcp · 6th February 2005, 08:35 AM

I am new to DIY audio, but have been working with pro-audio for quite some time now. As my first project, I decided to construct the first pre-amplifier design in Slone's 80 audiophile projects book. However, as I got into the construction of it, I got confused. The design obviously calls for a power supply, but the schematic does not show where it should be brought into the circuit. I thought it would be the Vcc + and - on the op-amp, but the schematic also details a decoupling circuit for those, so the power cannot be applied there. How is this circuit supposed to work?

Thanks in advance,
Scott

Nuuk · 6th February 2005, 01:28 PM

Scott, it depends on which opamp you are using!

Find the datasheet (Google) for the opamp and that should give you the pinout details. Usually the negative rail goes to -Vcc (or -V) and the positive to +Vcc (or +V). The other + and - pins asre for the signal connections.

When you have made that preamp, you may care to try a very simple discrete circuit. You can find details of one on my web site.

scott_jcp · 6th February 2005, 10:34 PM

I managed to figure out enough to look up the datasheet for my op-amp. The reason I am confused is that the schematic shows a pair of decoupling capacitors for the Vcc+ and - terminals, but doesn't show where the power would be connected to this part of the circuit. I assume power needs to be applied across this, but I don't know how to decouple it AND apply power.

Also, where on your site is the gainClone schematic?

Oh, and one more thing. I am currently reading (though slowly) Douglass Self's book on amplifier design, which is very informative, but doesn't address issues beginners may have, like how to determine what components to use to achieve different output wattages, etc.

Thanks a million, this is a great forum.

scott_jcp · 7th February 2005, 12:56 AM

I finished my circuit, and the volume and loudness controls work. However, all is not well. Instead of getting music, I get a continuous thumping noise (about 5 fairly low thuds a second). When I turn off the input source, the sound still continues. Any idea where I need to check for the problem? Its figure 3.1 in Slone's 80 projects. I did not build the phono section, and for the op-amp I used NTE997 with the positive input on the diagram in invert-input and the negative input on the diagram in non-invert-input (of the IC).

Thanks in advance.

Nuuk · 7th February 2005, 08:11 AM

Quote:

Also, where on your site is the gainClone schematic?

Go to the Gainclone section.

I'm afraid that I have no expereince of the project that you are building so cannot offer advice. I suspect to get any help, you will need to at least post the circuit diagram here.

JojoD818 · 7th February 2005, 10:35 AM

Scott,

I have the same book, but can you be more specific, what page is it? is it the preamp in figure 3.1? I am not too familiar with the opamp you used but is it a single or dual opamp?

Besides that, in the schematic, the "+" in the opamp means you have to connect it in the non-inverting and the "-" in the opamp means it has to be in the inverting pin of the opamp. If I read your post correctly, I belive you have accidentally interchanged the opamp connection.

Jojo

JojoD818 · 7th February 2005, 10:37 AM

Oh, and the decoupling caps in Mr. Slone's diagrams means that you put the caps very near the pins of the opamps.

HTH,
Jojo

pinkmouse · 7th February 2005, 10:38 AM

Sounds like LF oscillation, or "motorboating". From what I have read, this is usually caused by a missing ground reference somewhere.

scott_jcp · 7th February 2005, 11:36 PM

"Motorboating" seems like an accurate description of the noise.

What exactly do you mean by ground reference? Everything on the diagram that is supposed to be grounded I have connected to my power supply ground. Also, I am using RCA jacks, and I have the outside (which I guessed to be ground connected directly to the outside of the jack on the other side of the system. The inside is what I have wired to the preamp. Is this correct?

Another though I had about the problem is that I am using a computer power supply to test the system, but the -12V lead apparently can only output .8A, much less than the amount supplied by the positive lead. Could this cause the motorboating?

Thanks again!

ken.berg · 8th February 2005, 03:43 AM

AS Jojo pointed out, make sure that your feedback resistor (R19) goes (on an NTE 997) from pin3 to pin 1 and pin 4 to pin 6, or pins 12-14 & 10-8. Good practice to short the unused non-inv inputs to ground, and short the unused inverting inputs to the unused outputs.

A feedback network between 2-3, 4-5, 12-13, 9-10 creates positive feedback and builds an oscillator, not an amplifier.

Leaving unused opamps floating is another invitation to instability.

6th February 2005, 08:35 AM	#1
scott_jcp diyAudio Member Join Date: Feb 2005 Location: Richardson, TX	Beginner: Slone Preamp I am new to DIY audio, but have been working with pro-audio for quite some time now. As my first project, I decided to construct the first pre-amplifier design in Slone's 80 audiophile projects book. However, as I got into the construction of it, I got confused. The design obviously calls for a power supply, but the schematic does not show where it should be brought into the circuit. I thought it would be the Vcc + and - on the op-amp, but the schematic also details a decoupling circuit for those, so the power cannot be applied there. How is this circuit supposed to work? Thanks in advance, Scott

6th February 2005, 01:28 PM	#2
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Scott, it depends on which opamp you are using! Find the datasheet (Google) for the opamp and that should give you the pinout details. Usually the negative rail goes to -Vcc (or -V) and the positive to +Vcc (or +V). The other + and - pins asre for the signal connections. When you have made that preamp, you may care to try a very simple discrete circuit. You can find details of one on my web site. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

7th February 2005, 10:38 AM	#8
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Sounds like LF oscillation, or "motorboating". From what I have read, this is usually caused by a missing ground reference somewhere. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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6th February 2005, 10:34 PM	#3
scott_jcp diyAudio Member Join Date: Feb 2005 Location: Richardson, TX	I managed to figure out enough to look up the datasheet for my op-amp. The reason I am confused is that the schematic shows a pair of decoupling capacitors for the Vcc+ and - terminals, but doesn't show where the power would be connected to this part of the circuit. I assume power needs to be applied across this, but I don't know how to decouple it AND apply power. Also, where on your site is the gainClone schematic? Oh, and one more thing. I am currently reading (though slowly) Douglass Self's book on amplifier design, which is very informative, but doesn't address issues beginners may have, like how to determine what components to use to achieve different output wattages, etc. Thanks a million, this is a great forum.

7th February 2005, 12:56 AM	#4
scott_jcp diyAudio Member Join Date: Feb 2005 Location: Richardson, TX	I finished my circuit, and the volume and loudness controls work. However, all is not well. Instead of getting music, I get a continuous thumping noise (about 5 fairly low thuds a second). When I turn off the input source, the sound still continues. Any idea where I need to check for the problem? Its figure 3.1 in Slone's 80 projects. I did not build the phono section, and for the op-amp I used NTE997 with the positive input on the diagram in invert-input and the negative input on the diagram in non-invert-input (of the IC). Thanks in advance.

7th February 2005, 10:35 AM	#6
JojoD818 diyAudio Moderator Join Date: Mar 2003 Location: diyAudio Special Operations Center	Scott, I have the same book, but can you be more specific, what page is it? is it the preamp in figure 3.1? I am not too familiar with the opamp you used but is it a single or dual opamp? Besides that, in the schematic, the "+" in the opamp means you have to connect it in the non-inverting and the "-" in the opamp means it has to be in the inverting pin of the opamp. If I read your post correctly, I belive you have accidentally interchanged the opamp connection. Jojo

7th February 2005, 10:37 AM	#7
JojoD818 diyAudio Moderator Join Date: Mar 2003 Location: diyAudio Special Operations Center	Oh, and the decoupling caps in Mr. Slone's diagrams means that you put the caps very near the pins of the opamps. HTH, Jojo

7th February 2005, 11:36 PM	#9
scott_jcp diyAudio Member Join Date: Feb 2005 Location: Richardson, TX	"Motorboating" seems like an accurate description of the noise. What exactly do you mean by ground reference? Everything on the diagram that is supposed to be grounded I have connected to my power supply ground. Also, I am using RCA jacks, and I have the outside (which I guessed to be ground connected directly to the outside of the jack on the other side of the system. The inside is what I have wired to the preamp. Is this correct? Another though I had about the problem is that I am using a computer power supply to test the system, but the -12V lead apparently can only output .8A, much less than the amount supplied by the positive lead. Could this cause the motorboating? Thanks again!

8th February 2005, 03:43 AM	#10
ken.berg diyAudio Member Join Date: Nov 2003 Location: Tempe, AZ	AS Jojo pointed out, make sure that your feedback resistor (R19) goes (on an NTE 997) from pin3 to pin 1 and pin 4 to pin 6, or pins 12-14 & 10-8. Good practice to short the unused non-inv inputs to ground, and short the unused inverting inputs to the unused outputs. A feedback network between 2-3, 4-5, 12-13, 9-10 creates positive feedback and builds an oscillator, not an amplifier. Leaving unused opamps floating is another invitation to instability.

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