Bass preamp schematic help needed

[Skywalker83]

I think i'll go with the LM4562. would i use these for all four of my op amps?

 

[audioguru]

I think i'll go with the LM4562. would i use these for all four of my op amps?

The opamps in the circuit, the LM833 and the LM4562 are dual opamps with two opamps in each package. Each package has 8 pins.

 

[Skywalker83]

Ok, i'll go and re-draw my circuit so its laid out better!! Thanks for all your help. I shall return.

 

[Skywalker83]

I realise a mistake i've made in the circuit. If im using 2 dual op amps to give my four op amps (1 dual chip for the input, Bass and treble section. And the other chip for the Mid and output), then i've made a mistake with the 3rd and 4th op amps . If you look, they are both set up with pins 5, 6, and 7. If i now correct that and put the the op amp with pins 1, 2, 3, 4 & 8 at the Mid section , how does that effect the set up??

 

[audioguru]

You can use either of the twp opamps with pins 1, 2, 3, 4 & 8.

 

[Skywalker83]

Ok , here the new version of the active, a bit cleaner and different layout. i haven't added the values and part ID's yet. If you need reference just look at my last diagram

I've taken a connection from the input path of V+ to the first set of op amps along to the pin 8 on the second set (it runs across the top og the scematic). Would this work?

**broken link removed**

 

[audioguru]

The power supply is feeding both opamps on their pin 8 and is fine.

 

[Skywalker83]

Great ,Thanks!!

 

[Skywalker83]

I have a question about the circuit. Someone on another forum said the following

Are you sure you want the mid controls to come straight off the input? Why not on the output of the first buffer stage?

Why does The MID and FREQ come straight from the input and not from the output of the first op amp like the BASS and TREB??

I'm just wondering.

 

[audioguru]

Why does The MID and FREQ come straight from the input and not from the output of the first op amp like the BASS and TREB??

Where?
Mid and Freq are fed from the output of IC1b which is the Bass and Treble opamp.
R16 connects to "half the supply voltage" (C1) which is DC and biases IC2a.

 

[Skywalker83]

I kind of thought the same thing, but i just wanted to check! Thanks again guru!

 

[Skywalker83]

Ok, a couple of questions about the construction of the board now as far as parts go.

I'm going to go for parts rated at 25v + (incase i want to try the circuit at 18 volts at some point)

The trim pot will be 100K varaible resistor trimmer.

Resistors will be 0.25W carbon film 5% tolerence

Capacitors will be ceramic

There are currently 2 tant capacitors in the circuit, and the other polarised capacitors would just be electrolytic capacitors. As party of my circuit was more or less copied from an already existing circuit, should i just keep the 2 tant caps as they are , or switch them to electrolytic,or switch all the polarised caps to tant ones OR keep the whole circuit as it is?

Also, the polarised caps that go from IC1 and IC2 pin 8 to ground. Are they the correct way round. i though i read somewhere at somepoint that the plus side should be towards ground. Is this correct or are they fine the way they are?


I may change tha value of some of the pots that i have in the diagram.

the bass and treble and goin to be a 100K stacked concentric pot

the Mid frequency sweep will be a 50K log pot.

The Mid pot on original circuit was a 5K linear pot, but im not sure if this may be to low, and should be increased to 25K??

And the volume pot will be a 10K linear pot.

 

[audioguru]

Ceramic and tantalum capacitors produce distortion when they are used for audio coupling. Use metalized plastic film capacitors with a 5% tolerance instead.
The power supply polarized capacitors should have their positive wire connected to a positive voltage and the negative wire connected to a less positive voltage.

Dual concentric pots are a special order. Single pots are common. The tone control pots should be linear and the volume control should be an audio-taper.

 

[Skywalker83]

How do electrolytics go as far as this kind of circuit is concerend. I have see high quality preamps that use them. If i was to use a mixture of Met.plastic film and non-polar electrolytics would that work? I'm just concerned about board size. I'm trying to keep it as small as possible.

 

[audioguru]

My cheap clock radios and telephone answering machines use cheap small non-polar electrolytic coupling capacitors. The same for cheap PA amplifiers.

High quality amplifiers (and audio things that I design) use inexpensive, small, accurate, extremely low distortion metalized plastic film coupling capacitors. One of my projects uses two 1uF 5% 63V metalized plastic film capacitors that are small but cost about $1.00 each. I try to keep the impedance of a circuit high enough so that a 0.33uF capacitor produces enough bass frequencies.

 

[Skywalker83]

What suppliers and or makes of parts do you recommend? I know that ALPS come recommended but i can only see the option of bulk buying from them (qnty of 100+). RS certainly have all thae parts i would need, but i have heard numerous stories about product poor quality.

 

[audioguru]

RS might be RadioCrap. They sell "seconds" parts from China. They are gone from Canada.
Digikey and Newark sell good quality electronic parts.

 

[anextday]

bass preamp schematic

Hey just joined this forum and saw a guy asking about bass preamps and i was wondering if i can get the full, correct schematic diagram for it. thanks very much.

 

[audioguru]

I don't know what instrument you want to preamp. Is it an electric bass guitar? Is it a bassoon? Is it a string bass? Is it a tuba?

 

[anextday]

bass preamp schematic

Hey sorry for not being specific...I'll like to build a preamp for my electric bass guitar, however i also want to have the option of choosing active or passive like the guy you helped out named skywalker83. Its just an experiment i'd like to do just like skywalker83. Thank you...