Electronics > Beginners

Building a sound mixer within my guitar amp with line IN & mic input

<< < (9/20) > >>

dazz:
I believe I need much more than 40dB of gain if I want to take full advantage of the power that the amp can deliver. The power amp has a gain of 20dB, so x10 voltage gain. At 24V the voltage swing at the output of the power amp is 48V peak to peak, so at 20bB that's 4.8V at the output of the mic preamp. I read somewhere that the typical output of a dynamic microphone is 1mV, so that's 20log(4.8/.001)=73.6dB. Quite a lot of gain indeed. I understand the voltage output of the mic will depend on many factors, but does that work as a rough approximation?

The plan is to design the preamp to be used with a good mic like a shure sm58 or something like that. I guess there's no point in designing for crappy equipment.

So I couldn't find any pnp transistors, but there's a local store I can resort to. Bit of an inconvenience to drive there, but anyway. They have BC557C's in stock so I should be able to start breadboarding Yansi's preamp shortly

BTW, I'm guessing it's probably a good idea to roll a proper pcb for this to minimize noise issues, right? short & thin traces with proper separation and all that.
Oh, and I need to modify the schematic so that it works with a single dc power supply, I'll do that now

schmitt trigger:

--- Quote from: dazz on June 04, 2019, 04:31:14 pm ---
BTW, I'm guessing it's probably a good idea to roll a proper pcb for this to minimize noise issues, right? short & thin traces with proper separation and all that.
Oh, and I need to modify the schematic so that it works with a single dc power supply, I'll do that now

--- End quote ---

And a proper ground plane, too.

Zero999:
Regarding modifying the schematic for a single supply. Awhile ago, Audioguru posted some schematics showing single and dual supply configurations for inverting an non-inverting amplifiers. here's my version, which includes the differential configuration.


The circuit Yansi posted can also be converted to single supply, fairly easily.



The -17V supply becomes 0V and +17V, 24V. R6 and R7 can be replaced with potential dividers consisting of 10k resistors going to +24V and 0V, with the tap connected to the bases of Q1 and Q2. I can upload a schematic if that's not clear, but don't have time at the moment.

dazz:

--- Quote from: schmitt trigger on June 04, 2019, 07:49:49 pm ---
--- Quote from: dazz on June 04, 2019, 04:31:14 pm ---
BTW, I'm guessing it's probably a good idea to roll a proper pcb for this to minimize noise issues, right? short & thin traces with proper separation and all that.
Oh, and I need to modify the schematic so that it works with a single dc power supply, I'll do that now

--- End quote ---

And a proper ground plane, too.

--- End quote ---

Yeah, I always try to have a large ground plane taking up as much area as posible.


--- Quote from: Zero999 on June 04, 2019, 08:26:57 pm ---The -17V supply becomes 0V and +17V, 24V. R6 and R7 can be replaced with potential dividers consisting of 10k resistors going to +24V and 0V, with the tap connected to the bases of Q1 and Q2. I can upload a schematic if that's not clear, but don't have time at the moment.

--- End quote ---

Thanks Hero, this one was super straightforward. I'll keep those pics for future reference too

I have the preamp modeled in spice and working fine. Trying to figure out the best way to increase the gain. I get some 20dB with a 20V dc supply.
Can I change the values of the resistors in the differential opamp to achieve more gain? I can significantly increase the gain by increasing R8 but will that mess up the CMRR?

Zero999:
You need to increase the value R9, so it's the same as R8, to keep the CMRR high.

You will probably need to add another stage of amplification afterwards.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod