Welcome to Solid State Guitar Amp Forum | DIY Guitar Amplifiers. Please login or sign up.

March 28, 2024, 06:54:48 PM

Login with username, password and session length

Recent Posts

 

TDA2003 - Reducing Voltage Gain

Started by blackcorvo, March 06, 2013, 12:14:51 AM

Previous topic - Next topic

blackcorvo

#30
Quote from: Roly on July 07, 2013, 12:06:34 PM
There are a pile of freeware signal generators, but to test your loudspeaker an audio sweep generator is more useful than just a spot signal generator.  I've downloaded this one and a) it works, and b) didn't seem to virus or crash my system.  Your computer sound card may well have enough grunt to drive the speaker directly for this test.

I did the test but I'm not sure if my results are correct.

It seems that this speaker reproduces the frequencies of 130Hz and 3,5kHz a little louder than the rest, and it drops at about 17kHz (I can hear up to about 18kHz on my headphones, so I'm pretty sure it's not my ears).

---

Just for fun, I made this sample recording the same riff twice (even tho I kinda mess up in the rhythm because of soundcard delay), only changing the tone from Maximum to Minimum. I've used the Philips speaker for all the tracks I recorded so far.

https://soundcloud.com/corvolino03/stereo-test

It may not be a guitar speaker, but it's pretty damn good IMO.

J M Fahey

#31
1) nice test, gostei ;)

2)
QuoteIt seems that this speaker reproduces the frequencies of 130Hz and 3,5kHz a little louder than the rest,

Well, to be more precise: it probably resonates at 130 Hz , so it has a peak there, and most (all?) guitar speakers have a strong peak between 2500 and 4500 Hz, so what you heard is accurate.

EDIT: here you have the frequency response curve from a Jensen 8" guitar speaker.

Peaks at 130 and 3500Hz.

Any similarity is not a coincidence:

blackcorvo

That's really neat! I accidentally a Jensen :lmao:

This makes me consider buying that pair from the photos, and taking them to be re-coned the same way they did to mine. They're reasonably priced IMO: 60,00$ BRL for the pair, which is about 30,00$ USD.
There's even another pair of Alnico Philips speakers going for 50,00$ BRL... Hmm.

I even happen to have a 10" woofer here, but it sounds like crap with the guitar. It sounds really mid-range-y and dead. Maybe it's because I don't have a box for it, but still, it shouldn't sound like that for the size. I might do the sweep test with it tomorrow and post my results.

J M Fahey

Regular woofers are useless for guitar, their typical thick cones kill all attack and definition.
Muddy sound.

You *will* hear "something" even at high frequencies, because human ear is very sensitive, but as soon as you play close to othermusicians or a drummer, you get swamped.

blackcorvo

#34
Quote from: J M Fahey on July 08, 2013, 10:34:54 PM
Regular woofers are useless for guitar, their typical thick cones kill all attack and definition.
Muddy sound.

You *will* hear "something" even at high frequencies, because human ear is very sensitive, but as soon as you play close to othermusicians or a drummer, you get swamped.

I see. Well, I can still keep it for a future project, maybe a 5.1 system (since I have a set of 2x 4" and 2x 6" speakers I got from my brother-in-law I could use for it), or I could get a friend to re-cone it for me with a real guitar speaker cone... Who knows.

For now, I'm quite happy with I've accomplished so far.

Very soon I might try it out with a 32v c.t. Transformer I have laying around.

[UPDATE]

I think I blew my TDA2050 :(

I had about 46vDC from that transformer. It played as normal for some minutes but then, complete silence. I even tried touching the chip's input pin, but no signal of life. I suspected it was the output capacitor so I changed it, and again nothing. I then tried it with my 12v battery and still nothing. Then I suspected it had somehow blown my speaker, so I tried with another. Dead silent.

I guess I'll just buy a bunch of these chips next time I go downtown, so in case I blow another one I can just change it. Oh boy.

[UPDATE 2]

I went to get the chips yesterday, but they only had 2 in stock and I didn't have time to look around other component shops for more...
Kinda feels like when you're running out of lives in a videogame, and you can't find any nearby, and all that while the time for that level is running out.

Anyways, 2 of them should be enough for a month worth of playing around.
I tested the circuit with my V100GT (Goldtop copy with P90s), and this time everything worked OK at 46vDC, but... it doesn't sound that great. Too much mids.
This made me consider simply copying some combo schematic instead of fiddling with a circuit until it sounds good, since I won't have much free time for that once I start on my new job in a couple of weeks.


[UPDATE 3]
Nevermind that last part. I had the wrong speaker plugged in and took me some time to figure it out.  :duh AND I fried another TDA :( damn, these things are dying easier on my hands than MOSFETS!
I also changed the gain resistors on the TDA2050 (which are now the same values from the datasheet), and I added 2x 1N4148 clipping diodes on it's input.

stormbringer

Using the clipping diodes on the output makes the amount of clipping volume dependant, you might get a better result using a separate gain for that and a gain stage after that amplifies the 0.7 or so volt you got after clipping to the wanted max level. Otherwise, once they start clipping the volume knob wont increase the volume, just add distorsion.

arin

#36
So I've read the complete discussion ranging from limiting the output of a power amplifier (couldn't stress power enough) to feeding it less signal, the simple answer to the solution is to just add a filter in case a lesser signal causes any glitches. Also, you can mess around with the 2R2 as shown earlier by a respected member but I really doubt that you'll be able to find the resolution you want.

http://www.7pcb.com/

Roly

Quote from: blackcorvoAND I fried another TDA :( damn, these things are dying easier on my hands than MOSFETS!

I'm a bit concerned about this because these chip amps are generally pretty robust and internally protected against most things that you can throw at them, so I'm wondering how you are managing to get through so many.
If you say theory and practice don't agree you haven't applied enough theory.