What Replacement Speaker ?

[tomana]

This is my first post and wanted to say ... "Hi"

I was reading a reply in a thread here at MEF and it was so thorough, I knew I would get the right answer to my question so here goes:

I have a Crate Taxi 30 guitar amp that uses a TDA-1560Q car radio output amplifier chip. Since this Crate is a battery powered street amp, I figured they opted for this chip so the amp could provide a decent volume level and long run time on a sealed lead-acid 12V battery. This it does extremely well. As for sound quality ... meh.

The amp is 14 years old and the original Crate speaker distorts at high volume when I play the low E string (82Hz) so I figured it might be time for a new speaker? This amp was originally intended for use with an electric guitar, not the electric acoustic I am using (Alvarez AD60SC with Yari 600TMk II Pre-Amp; I use the saddle piezo pickup blended with an Alvarez sound hole pickup). There's also an independent dedicated vocals channel on this amp. The cabinet is a sealed particle (pressed) board and has a small port cut out on the front speaker board. There is also a 2" piezo tweeter.

I attached the Crate Taxi 30 schematic for your viewing pleasure {8^D

Crate speaker specs:

Woofer Crate Custom Design 8”, 8 ohm, 50 watt rms 1” voice coil
Tweeter 2” Piezo , 8 ohm, 50 watt rms

It's a small cabinet (approx 14" x 12" x 12"). In that MEF thread I read, it said a HiFi full range speaker "reproduces" sound and a guitar speaker "produces" sound. I'm guessing an acoustic guitar would want a HiFi reproduction, but not sure.

Also, I play drop D tuning a lot (low E lowered to 41Hz)

What reliable replacement speaker would be the best choice for an acoustic guitar with pre-amp and a handheld Shure 57 mic setup?

[Jazz P Bass]

My take on the whole issue is: is the amplifier itself distorting the signal?
You really need to scope the output to see if this is happening.
Or not.
I would thing an 8 inch speaker would have a hard time with 41Hz.
Then again, Peavey made an awesome 8" bass practice amp (model?).
Whether or not it was the cabinet or the speaker or the combination, they pulled it off.

[Chuck H]

First, welcome. And thank you for being clear and linking a schematic. You've obviously read some posts here and determined some protocols before posting.

Second, I agree with JPB. It's probably the amp that is distorting. But it could be the speaker. I'm sure it's not designed for the bottom end of an amplified acoustic guitar. So... Using the same exact settings on the amp and guitar that you normally do when the amp distorts, plug the amps output into a different cabinet. Choose one that is sure to handle any bottom end. Like a PA cabinet or console speaker. Try to match impedances as well. Now, did the distortion go away? If it did then a new speaker could help. If the distortion is still there then it's your amp that's distorting.

It's possible that a different speaker could still help though. If the speaker were of a full range type and had better bottom end you wouldn't need to push the amp as hard for the same amount of bass. And so, likely, the bass on the amp could be turned down a little so it won't distort. This can also be tested by plugging into a different cabinet.

[pdf64]

Drop D bottom string is 73Hz.
What about if the speaker port is loosely filled, then tightly filled with fabrics, eg a sock?
Is the surround of the woofer still serviceable; sometimes the material degrades?
Pete

[soundguruman]

This is my first post and wanted to say ... "Hi"

I was reading a reply in a thread here at MEF and it was so thorough, I knew I would get the right answer to my question so here goes:

I have a Crate Taxi 30 guitar amp that uses a TDA-1560Q car radio output amplifier chip. Since this Crate is a battery powered street amp, I figured they opted for this chip so the amp could provide a decent volume level and long run time on a sealed lead-acid 12V battery. This it does extremely well. As for sound quality ... meh.

The amp is 14 years old and the original Crate speaker distorts at high volume when I play the low E string (82Hz) so I figured it might be time for a new speaker? This amp was originally intended for use with an electric guitar, not the electric acoustic I am using (Alvarez AD60SC with Yari 600TMk II Pre-Amp; I use the saddle piezo pickup blended with an Alvarez sound hole pickup). There's also an independent dedicated vocals channel on this amp. The cabinet is a sealed particle (pressed) board and has a small port cut out on the front speaker board. There is also a 2" piezo tweeter.

I attached the Crate Taxi 30 schematic for your viewing pleasure {8^D

Crate speaker specs:

Woofer Crate Custom Design 8”, 8 ohm, 50 watt rms 1” voice coil
Tweeter 2” Piezo , 8 ohm, 50 watt rms

It's a small cabinet (approx 14" x 12" x 12"). In that MEF thread I read, it said a HiFi full range speaker "reproduces" sound and a guitar speaker "produces" sound. I'm guessing an acoustic guitar would want a HiFi reproduction, but not sure.

Also, I play drop D tuning a lot (low E lowered to 41Hz)

What reliable replacement speaker would be the best choice for an acoustic guitar with pre-amp and a handheld Shure 57 mic setup?

The battery no longer holds a full charge, and although it turns on,
the reduced voltage kills the headroom, and you have too much distortion.
So, it's really the battery that should be replaced.

[J M Fahey]

Agree that it's basically amp distortion; that you should not expect *much* out of an 8" speaker in a minuscule box and an aging battery certainly won't help.
Yes, that amp plugged into an EVM15L into a properly tuned box will have gobs more acoustic output at low frequencies .
Such box will be at least 20"x20"x14" and weigh over 40 lbs.
Not *that* portable.

[Jazz P Bass]

The battery no longer holds a full charge, and although it turns on,
the reduced voltage kills the headroom, and you have too much distortion.
So, it's really the battery that should be replaced.

Uhmm, before flat out recommending that the OP replaces the battery, how about we suggest that the battery voltage be checked.

[tomana]

Uhmm, before flat out recommending that the OP replaces the battery, how about we suggest that the battery voltage be checked.

No problem, I already used my trusty DVM and confirmed +13.24Vdc under load so it's not the battery.

[Steve Conner]

If you want to try a new speaker, I'd suggest the Eminence Beta 8.

[loudthud]

Make sure that pins 7 and 11 of the power amp chip are about 6.5V with no signal.

[olddawg]

Is there room in the cabinet to mount a 10" speaker and then tune the port? Also use aire efficient speaker, will that chip even put out a clean 50 watts of of a 12v rail, or is it a bogus car stereo spec? You might not even need a 50 watt rated speaker.

[J M Fahey]

Yes and no.
It's not a "bogus car stereo spec?" (such as 1200W PMPO ) but not plain RMS either, basically because it can not handle a continuous tone for a long period of time.
Never seen the TDA1560 used there, but the 1562 (the improved version) is roughly equivalent to a 50W RMS amp, under "normal" conditions.
Basic problem is that rails "float" to almost twice the 12V supplied by the battery, but then you are getting your juice from a 4700uF capacitor which is *not* getting power from anywhere (because it was disconnected from the battery and put in series with it) so you will have "24V" ... for the time it takes to discharge a 4700uF cap with, say, a 2 or 3 Amp current: milliseconds !!!
Nice trick to reproduce loud *transients* when listening to recorded music in your car; probably not that useful in a typically overdriven guitar amp.

[rjb]

Basic problem is that rails "float" to almost twice the 12V supplied by the battery, but then you are getting your juice from a 4700uF capacitor which is *not* getting power from anywhere (because it was disconnected from the battery and put in series with it) so you will have "24V" ... for the time it takes to discharge a 4700uF cap with, say, a 2 or 3 Amp current: milliseconds !!!
Nice trick to reproduce loud *transients* when listening to recorded music in your car; probably not that useful in a typically overdriven guitar amp.

Just free-associating here....
Might this trick be useful for reproducing the transient string attack for a clean acoustic guitar amp?

[J M Fahey]

Weeellll, if you make 12V battery powered portable guitar amp, you will have a 15W RMS which can handle peaks and short transients just like a "real" 50 or 60W amp; that's the logic behind this chip.
And, say, a 100 W ampwith 400W peak capability?
It has been done commercially, Marshall had a series of Bass amps which offered "1000 W peaks easy handling" with, say, a 200 or 400W RMS amp.
Nice idea, those must have been discrete amps (about 10/15 years ago), maybe actual result was not as expected because they quietly disappeared a couple years later.

[J M Fahey]

..repeat post..