What wattage practice amp needed to drive 4 x 12 cab?

[caspercody]

I have a 60 watt all tube Peavey head, and it is very hard to dial it down to a low volume and not wake up anyone. What I want to build is a low wattage (that runs off 9 to 18 volts) practice amp, but what wattage should I be looking at to drive a 4 x 12 cabinet? The cabinet is 16 ohms. I would like to build something that does not have any tone control.

I have looked at the Ruby, Little Gem, Noisy Cricket, Smokey tone amp, and Tube Cricket schematics but would any of these work on a 4 x 12 cabinet? If not, does anyone have a schematic for a practice amp that would drive a 4 x 12 cabinet?

Thanks
Rob

[Jdansti]

>I have looked at the Ruby, Little Gem, Noisy Cricket, Smokey tone amp, and Tube Cricket schematics but would any of these work on a 4 x 12 cabinet? If not, does anyone have a schematic for a practice amp that would drive a 4 x 12 cabinet?

I've used the Noisy Cricket on a 2x12 and it sounds great. I've read that others have had good experience with 4x12s.   I think the other amps you listed would be fine.

If you want a low wattage tube amp, check out:
http://www.diystompboxes.com/smfforum/index.php?topic=96952.0, and the Murder One: http://www.diystompboxes.com/smfforum/index.php?topic=73222.0. Rick (frequencycentral) sells the Murder One PCB on his website.

Which ever amp you choose, you can use a switch or switched jack to allow the use of headphones. When I do this, I use a 100R resistor of the appropriate wattage in series with the headphone jack to make sure I don't blast my ears.

[caspercody]

Thanks for the reply!

I actually have (2) 12AU7A/ECC82 EH tubes laying around with nothing to do. Not sure how compatible they are to ECC86? Or if anyone has a practice amp based around these?

[Jdansti]

The first tube in Markeebee's amp in the first link above is probably a 12AU7 since he mentions that he is using the Valvecaster as a preamp. You'd probably need something other than another 12AU7 for the power amp section.

One option would be to do a hybrid. Use the 12AU7 for the preamp and a solid state amp for the power amp. You could use any of the TDA amps by following their application schematics on their data sheets (for example TDA2009). You wouldn't have to use an output transformer with the TDA amps.

[Mustachio]

Only amp I've built so far is the Superfly and its a cool amp I'd defiantly give it a looking at if I where you. Its a variant of the Firefly. take a look over at AX84 website its got great tube amp projects big and small!

Also I can't say I know this for sure but I believe in certain amps that use a 12au7 in the power section (firefly maybe) I believe you can use a 12au7 in the preamp as well but it may be a little tamer then a 12ax7 , Ive heard people liking 12AT7's as well.

I want to make the firefly next, and then maybe move on to something bigger like the P1 over at ax84.

Have you looked at getting an attenuater for your bigger Peavey amp ? Might be an option. Its hard to get clean sounds at low watts for the most part(but its still clean enough). So If you like dirty tube amp sound then a submini tube amp might be what you want!

I think I recorded a few clips of my superfly ill try to post em soon.

[PRR]

> 4 x 12 cabinet?
> ....and not wake up anyone.

A four-12 can be VERY efficient.

And of course it will "work". Work pretty dang well. "Too well" for your purposes.

Even a part-Watt LM386 into a four-12 will annoy most sleepers.

The real blunt-hammer approach would be to save the Four-12 for shows, use one 4" car-speaker for your late-night work. That's like 10 times less sound for the same watts.

But you also can't rip a 60-Watt into a small car speaker or it will shred.

And no way will a One-4 sound remotely like a four-12. The "ideal" guitar speaker is about the size of a guitar (acoustic). A 10, a 12. We use amps for a big sound, and a four-12 is a BIG GUITAR. OTOH one 4 is smaller than a toy ukulele. Your ear can tell the size of a source.

If you are in-love with the four-12 you should be thinking well under a Watt.

Tube amps below a Watt are tricky. If you have enough voltage to make a tube happy, and enough impedance to get the power down below a Watt, the transformer design becomes a real problem. Gross mis-loading can get you something in the 0.01 Watt zone, but that may not be enuff to hear over the naked strings even with a four-12.

One Watt in a happy four-12 could be 95dB SPL in the room, and easily 70dB SPL in other rooms. If I am trying to get to sleep, that would be annoying.

Don't try for a Complete Solution right away. Get an LM386 and 9V, try it, it will play. 16 ohms on 9V supply is about a half watt. If that wakes the baby, you need to be thinking incredibly small.

[Jdansti]

Maybe not what you're looking for, but the iRig/iRig-DIY clones make for very quiet practice. You could use the effects available in the smart phone apps or you could use your own effects, run the output of the last effect in the chain to your iRig, and choose a clean setting in the app. If you don't want to use headphones, you could run the output from the iRig to one or more amplified computer speakers.

BTW, I've used regular earbud headphones for practice and for troubleshooting pedals, and they sound just fine.

[caspercody]

Thanks! I will try one of the 386 amps. Is any one of them better at not changing any of the guitar tone going thru it? I want to use this to try my distortion build's with, and want to try to get as much of the pedal's true tone.

Thanks
Rob

[FiveseveN]

Just remember that it has a minimum gain of 20, so it will distort with a pretty low signal (say 0.5 V p-p).
If you're driving it into distortion the 386 can get pretty loud, especially with a 4x12 and efficient guitar speakers. You can use a rheostat like the original Little Gem to attenuate the output or (better yet) vary the supply voltage with a LM317.

[brett]

Hi
Re-wire your 4x12 so that you can run either 1x12 or 4x12?
Or just buy an 8" ?
cheers

[chptunes]

You could use any of the TDA amps by following their application schematics on their data sheets (for example TDA2009). You wouldn't have to use an output transformer with the TDA amps.

..or the TDA7052, like tca's 1w Punch Amp.  Thread:  http://www.diystompboxes.com/smfforum/index.php?topic=99271.0

[caspercody]

Thanks for the thread chptunes! I stopped at Radio Shack and they have the 3 watt kit for 50% off. It has the TDA 7267 chip for $9.99. I hope to find time this weekend to build it. It is the K8066RS kit from Velleman. Just thought I would let you know it is at a great price, at least here.

[caspercody]

I made both the 3 watt Radio Shack kit, and the Ruby amp and I would say the 3 watt kit has a cleaner sound. It also sounds like it sounds more like it lets thru more of the original tone. I added a 50K pot at the input side (like they mentioned in the instructions), but it sounds like it might have cut out some of the high tone. Does that sound right?? Can anyone tell me if I need a buffer at the beginning of this?? I am planning on putting my 7 band eq between the guitar and amp and this is a buffered effect (Danelectro Fish and Chips). Should I try yo convert this to a bypass pedal? Or will the buffer help me??

Thanks
Rob

[Jdansti]

Do you have a copy if the Radio Shack schematic that you can post?  That would help with figuring out what to put on the front end.

[FiveseveN]

Can anyone tell me if I need a buffer at the beginning of this??

Yes.

Or will the buffer help me??

Yes, that should do it.

[caspercody]

On reply #10 there is a link to the building instructions.

Thanks
Rob

[caspercody]

oops, that is a link to another tread that has the building instructions link. Look at reply #5 from JOK3RX. Schematic is on page 11, and the volume pot reference is on page 7.

Thanks
Rob

[chptunes]

Here is the Velleman 8066 assembly manual:  http://www.vellemanusa.com/downloads/0/illustrated/illustrated_assembly_manual_k8066.pdf

-Corey

[Jdansti]

Thanks for the build doc. It seems to me that what you need is a pre-amp section like that of the Tiny Giant amp which also uses a TDA chip. If if we me, I'd copy the front of the TG. See: http://musicpcb.com/wp-content/uploads/2011/02/Tiny-Giant-Build-PDF-rev2.pdf

[caspercody]

Thanks, I will give that a try.

So is that a non-inverting gain stage, with a gain of 3.2? I want to let through as much of the tone as I can, will that low pass filter (value of C1) be a good value? That is one thing I have not understood, what frequencies do we let through or not? I know the math equations for calculating this, but never understood how many have figured out where to cut the frequencies off at?


Thanks
Rob