[danlaix]

Has anyone include a bass boost in their amp?
I dont mean the PPA, but just merely try and include
a resistor, caps and also a switch?

I'm building an amp with a bass boost but apparently i dont hear any difference in sound by switching on and off by the switch.

Here's how i set it up, the switch, the resistor and the caps are all in parallel, thats according to the PPA schematic.

Anyone with the same problem? Anyone there to help me solve this problem?

Thanks.

 

[eyevancsu]

I added a bass boost switch on a pimeta and two cmoys, but that was a while back. I really dont remember how i did it, but the boost was there, it was subtle (actually, more apparent than subtle), and it boosted the bass alot nicer than without.

-ivan

 

[PeterR]

What values did you use?

 

[danlaix]

Quote:

What values did you use?

caps = 0.1 uF
resistor = 100 K

I could hear the difference with and without adding the resistor and caps. But the switch just doesnt change anything in sound.
I've double check on the switch, it worked perfectly fine.

 

[tangent]

Quote:

the switch just doesnt change anything in sound.

The switch has to short the cap and resistor. Measure the resistance across them while toggling the switch. (With the amp turned off.)

 

[danlaix]

Quote:

The switch has to short the cap and resistor. Measure the resistance across them while toggling the switch. (With the amp turned off.)

Yup, i followed what is exactly on the PPA sch. Switch short the cap and resistor, or in other words, the switch, resistor and caps are all connected in parallel. I meansured across the them using my cheap multimeter, i can only set the x1 ohm, thats the lowest i can go. And it measured 0 ohm.

Is there something wrong?

 

[tangent]

What's the feedback resistor value?

 

[danlaix]

feedback resistors:

R3 = 220 ohm
R4 = 2.2 K
R5 = 3.3 K
R6 = 1M

 

[danlaix]

Ok. That was according my schematic.

Based on the labeling on the PPA, that should be:

R6 = 220 ohm
R5 = 2.2K
R3 = 3.3K
R4 = 1M

 

[PeterR]

With those values there'd be almost no global feedback at all, so the bass boost won't do much either.
Edit:
The values in your first post would make much more sense, can you recheck what you've actually used?

 

[tangent]

Also, if R4 is indeed 2.2K, the bass boost resistor value of 100K is way too high. The bass boost resistor and the feedback resistor (R4) add when bass boost is engaged, so the two should be within an order of magnitude of each other. Personally, I like to keep them equal or close to it, which gives a ~2x maximum boost.

 

[danlaix]

Quote:

Also, if R4 is indeed 2.2K, the bass boost resistor value of 100K is way too high. The bass boost resistor and the feedback resistor (R4) add when bass boost is engaged, so the two should be within an order of magnitude of each other. Personally, I like to keep them equal or close to it, which gives a ~2x maximum boost.

So i should lower the bass boost resistor?

Anyway, check out the sch.

Please correct the error as i've been troubleshooting this for a few days already.

 

[ITZBITZ]

I just finished an amp with the bass boost circuit and it is quite noticable.

Values used were 33.2k and .27uF. The stock PPA values were used for the feedback resistors.

Very nice improvement on the bottom end, more of a compensation than a boost.

 

[PeterR]

Ok. R3 (your schematic) is several orders of magnitude too low. The opamp is running in little more than unity gain so there's nothing left for global feedback. Make R3 220k(!)ohms or larger. Now you have a global feedback loop controlling the gain (1+R6/R5). So R6 is by far too large. Try R6=6.8k for a gain of about 3. Then R8=10k, C1=220nF.

 

[iWeasel410]

Could someone make a tutorial on how to add bass boost to a cmoy?