stereo pre amp pcb

[nazirdigi]

how is this pre amp pcb.

what is the sound quality of this board?

[Tekko]

Eww UA741, this useless opamp shouldent be used to anything but DC applications such as temperature regulation.

Replace with NE5532 or OPA2153 or LM4562.

[Mr. Triatic]

toss it.

this would be a way better choice if you need treble and bass controls:
NE5532 volume control board kit 10 times pre-amp A51 - eBay (item 120656537393 end time Feb-03-11 07:44:36 PST)

[nazirdigi]

anybody have high quality stereo preamp pcb ls post

[nazirdigi]

how is this sch

[indianajo]

I don't know what input you have that will need a gain of 2. CD players, FM tuners, PC's have enough voltage to run a power amp, they just need to be switched or mixed. You don't need quite +-15 to run to a power amp, I am getting more voltage out than I need with +-7.2 derived from an 18 VDC wall transformer, regulated with 2 each 1n5344 zener diodes. See this thread diy dj mixer about a 4 input mixer. You may not need the high gain stage for condenser microphones. See this thread about the power supply with the zeners. Improving a "Disco mixer" to mid-fi performance. I like the pinout of the op amps in this schematic, it is the common 8 pin dip pinout of many op amps. I'm using ST33078's op amps for low noise, Peavey uses JRC4560, NJC2068's have an equivalent datasheet. 7815 and 7915 have been hard to find recently and have way more current than you need for a few 5 ma apiece op amps. If you have access to used band equipment, used disco mixers and band mixers make good basis for upgrading as in the disco mixer upgrade above. Stay away from numark disco mixers, the slider pots are **** and the op amps are in line package, rare except in 4558 ( another noisy beast but better than the 741). I find on my upgraded disco mixer, having all three inputs turned up at the same time (FM radio, CD player, Magnetic phono cartridge) doesn't make more noise than turning two down, if I switch off the radio when not used. The CD player and phono turntable switch themselves off at the end.

[BobEllis]

I agree that you probably do not need gain, unless you are running from a low output source like an i-pod.

Take a look at Pavel Macura's (PMA) Audio Buffer in english Most sources will be able to handle a 50K pot as a load, just feed that into the buffer and you're set. For 12 Euros it's a steal, and can be configured with gain if you really need it. There's an update thread in this forum. Pavel also has a nice Jfet discrete preamp, DISPRE2.

A Pass B-1 would also be a good option if you don't need gain, with boards and JFets available from Pass Laboratories simple and clean.

Consider a more elegant power supply than 7x15 regulators. Preamp/buffer performance is improved with better supplies. LM317/337 would be a step up. You could also go to a shunt regulator. There are several shunt regulator threads in the power supply forum, some with boards available. www.twistedpear.com also has a shunt regulated PSU kit available.

Just to be a little contrarian, I'd stay with 15V rails for the headroom it provides. True, you probably don't need it, but there is an extremely small price to be paid for it.

Whoever did the schematic in post 5 is really afraid of DC. There isn't a need for all those NP caps. Just the input and maybe the output would be fine.

[indianajo]

The link above "twistedpear.com" is for sale. About output voltage headroom and required input voltage: most audio amps require at most 2VAC peak to peak to max out. The datasheet on JRC4562 shows the output voltage with +-5 v power supplies at +-4 at 25 deg C. A 20 VAC CT transformer is $7 from mouser.com, a switch $2, a fuse holder $3, a Fuse $1. Then you need to buy a steel box to put the transformer in separate from the box you put the op amp circuit in, to avoid the hum war I went through on the disco mixer detailed above. Connector, $1. or you can buy a wall transformer at 10 VDC or above at the charity resale shop, $1. Sorting through a grocery cart of hundreds of surplus wall plug transformers, I found several at 9 VDC, one at 12 VDC, one at 14 VDC, one at 18 VDC, none above that until you reach 30 VDC. My RA-88a disco mixer as purchased ($15) was actually operating the 33078 op amps at +-3.2 VDC with the OEM installed 300 V rail resistors from the rectified 17 VCT transformer. (had a little more voltage with the hissy 4558 OEM op amps) This was adequate for the magnetic phono at 20 mvAC in and the CD player at 1 VAC in, but the FM radio volume pot was dropping out when I had the volume low enough not to clip (produce harmonic distortion). So I got more headroom at +-7.2 V with a couple of $.75 1N5344 zener diodes running off the 18VDC wall transformer, which transformer was outside the mixer box. Much less hum, sounds great. The 4 33078's draw 20 ma, so no strain on the zener voltage regulators, but buy two LM317's if you want to be more conventional and burn more power. This thread really belongs under analog line level forum.
Have fun.

[BobEllis]

Oops - Twisted Pear Audio

Most, but not all amps need less than 2VAC to reach maximum output. The Pass F5 is but one example that needs more. But the real reason for me is that most circuits are cleaner with the signal swing a small portion of that available. Since we are only talking about something under 100 mA for the preamp, increasing the rails from 5V to 15V only increases power dissipation at most 2W. Worth it in my book, but if you'd rather not go there, that's fine.

Wow, you had a tough time getting rid of hum. I've not had that kind of problem with line level gear. In my active crossover there is only 1.5" between the power transformer and regulators and in a different direction two of the crossover boards. I have no hum issues. Then again, I didn't have a hum issue with the crossover on a slab of MDF without paying any attention to where the power cord was. Just lucky I guess.

Normally a preamp in a 12" x 16" box with as much distance as possible between line level signals and the PSU should be sufficient to avoid hum. A nice thick divider between line level and PSU wouldn't hurt, but is probably unnecessary with proper grounding