need simple preamp

JoeBob · 1st January 2002, 10:11 PM

I'm working on my LM3886 based amp and was thinking that after I should make a preamp for it. I'm almost done my amp modules and have to wait for my transformers so maybe now would be a good time to work on a preamp, the thing is what design to use. I'd like to keep it simple and use a single IC based idea (as is my amp) whlie not trading sound quality. Any ideas would be apreciated. Since my amp boards are almost done I'd like to start the preamp in a week or two...

paulb · 1st January 2002, 10:25 PM

I'd recommend something very simple with an audio grade op-amp like the TI OPA2134. Selector switch, volume control, op-amp with gain of 5 or so. Do you want/need tone controls? Balance control? Remote control (!)?
You can use a stepped attenuator instead of a potentiometer for volume if you wish.
There are many DIYers at headwize.com that have done evaluations of different op-amps, you may want to browse around there for a while. Use an IC socket and you can plug in different types to see if you can hear the difference.
You may be able to get away with no opamp at all if your source is, say, a CD player.

JoeBob · 1st January 2002, 10:34 PM

No, I don't need tone controls, or balance controls, just selection and volume. I'll probably use mainly a CD or PC soundcard, so I know I could probably not even use a preamp (which is what I was originally planning), but I'd like to build one and use an opamp so that if ever I wanted to expand and use different devices I could.

I was looking at the LM358, would that workout fine?

paulb · 1st January 2002, 11:13 PM

LM358 is an older design that is probably very poor for audio, at least by today's standards. LM833 would be better.
But I think both are duals. Build it with a 358, get it working, then plug in an 833 (or OPA2134) and see if you can tell the difference.
Pick an op-amp that is unity gain stable; while you're not using it at unity gain it will give you more stability at small gains as well.

JoeBob · 1st January 2002, 11:15 PM

Ok, I'll try the 833, I like nationals service, took only a day to get my 3886's, and I like to be consistent. But if TI's opamp is of noticable better quality, I'll go for it...

JoeBob · 1st January 2002, 11:29 PM

Well, after looking them both over, the OPA2134 looks better. Especially since an older post said that the LM833 caused softer bid-bass (although that poster said replacing with an LF353 solved his problems).

AudioFreak · 2nd January 2002, 01:41 AM

JoeBob,

The LM3886 based amps usually need around 750mV RMS to acheive rated output .... most equipment should be able to supply this so you probably wont need any gain in the preamp.

AudioFreak · 2nd January 2002, 01:43 AM

JoeBob,

How did you get your 3886's from National in a day?

JoeBob · 2nd January 2002, 02:12 AM

24hr overnight ups shipping, from noth dakota to here in quebec canada.

Since I based my amp on Rods LM3875 amp, could I use the OPA2134 in Rods "Simple High Quality Hi-Fi Preamp" project 02 I do believe? Instead of the NE5532s?

And sure I porbably won't NEED gain, but it's fun, sho why not?

AudioFreak · 2nd January 2002, 02:17 AM

which supplier did you purchase the parts from?

1st January 2002, 10:11 PM	#1
JoeBob diyAudio Member Join Date: Nov 2001 Location: Montreal, Canada	need simple preamp I'm working on my LM3886 based amp and was thinking that after I should make a preamp for it. I'm almost done my amp modules and have to wait for my transformers so maybe now would be a good time to work on a preamp, the thing is what design to use. I'd like to keep it simple and use a single IC based idea (as is my amp) whlie not trading sound quality. Any ideas would be apreciated. Since my amp boards are almost done I'd like to start the preamp in a week or two...

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Old fashioned simple preamp	PMA	Analogue Source	19	14th August 2007 09:12 AM
PCB for simple OP-preamp	kmj	Chip Amps	8	8th August 2005 09:10 PM
simple preamp	pxr5	Solid State	9	20th November 2004 07:29 PM
Simple discrete preamp	OliverD	Solid State	69	22nd July 2004 10:14 PM
Very Simple Preamp	Christian	Solid State	1	21st March 2002 09:50 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

1st January 2002, 10:25 PM	#2
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	I'd recommend something very simple with an audio grade op-amp like the TI OPA2134. Selector switch, volume control, op-amp with gain of 5 or so. Do you want/need tone controls? Balance control? Remote control (!)? You can use a stepped attenuator instead of a potentiometer for volume if you wish. There are many DIYers at headwize.com that have done evaluations of different op-amps, you may want to browse around there for a while. Use an IC socket and you can plug in different types to see if you can hear the difference. You may be able to get away with no opamp at all if your source is, say, a CD player.

1st January 2002, 10:34 PM	#3
JoeBob diyAudio Member Join Date: Nov 2001 Location: Montreal, Canada	No, I don't need tone controls, or balance controls, just selection and volume. I'll probably use mainly a CD or PC soundcard, so I know I could probably not even use a preamp (which is what I was originally planning), but I'd like to build one and use an opamp so that if ever I wanted to expand and use different devices I could. I was looking at the LM358, would that workout fine?

1st January 2002, 11:13 PM	#4
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	LM358 is an older design that is probably very poor for audio, at least by today's standards. LM833 would be better. But I think both are duals. Build it with a 358, get it working, then plug in an 833 (or OPA2134) and see if you can tell the difference. Pick an op-amp that is unity gain stable; while you're not using it at unity gain it will give you more stability at small gains as well.

1st January 2002, 11:15 PM	#5
JoeBob diyAudio Member Join Date: Nov 2001 Location: Montreal, Canada	Ok, I'll try the 833, I like nationals service, took only a day to get my 3886's, and I like to be consistent. But if TI's opamp is of noticable better quality, I'll go for it...

1st January 2002, 11:29 PM	#6
JoeBob diyAudio Member Join Date: Nov 2001 Location: Montreal, Canada	Well, after looking them both over, the OPA2134 looks better. Especially since an older post said that the LM833 caused softer bid-bass (although that poster said replacing with an LF353 solved his problems).

2nd January 2002, 01:41 AM	#7
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	JoeBob, The LM3886 based amps usually need around 750mV RMS to acheive rated output .... most equipment should be able to supply this so you probably wont need any gain in the preamp.

2nd January 2002, 01:43 AM	#8
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	JoeBob, How did you get your 3886's from National in a day?

2nd January 2002, 02:12 AM	#9
JoeBob diyAudio Member Join Date: Nov 2001 Location: Montreal, Canada	24hr overnight ups shipping, from noth dakota to here in quebec canada. Since I based my amp on Rods LM3875 amp, could I use the OPA2134 in Rods "Simple High Quality Hi-Fi Preamp" project 02 I do believe? Instead of the NE5532s? And sure I porbably won't NEED gain, but it's fun, sho why not?

2nd January 2002, 02:17 AM	#10
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	which supplier did you purchase the parts from?