New Amplifier Design - "Murder One" - Submini Pentode, Low Voltage

[patrickbrose]

I still have not seen an answer to the Power supply question...
Has anyone used a switching power supply for this? Getting a 12v 500ma regulated (or unregulated for that matter) linear supply here in the US is proving to be very difficult. I can get a 12v regulated 1A Switching supply quick and cheap at Rat Shack. But there are no Linear (transformer based) PS anywhere anymore.
-P

[fpaul]

I haven't tried a switching ps but getting a regulated 12 500ma wallwart shouldn't be any problem at all.  Both my local electronics stores have them.  Altex has one you can buy online but it's pricey.  The other store has them cheap but they don't sell online.  Look around, maybe try evilbay.

[derevaun]

It won't break anything to try the Switchmode PS; apparently you'll just hear some interference between it and the voltage multiplier.

If you can find a transformer-based wall wart that puts out 13 - 15 volts, you could put a 12v regulator on its output. Just make sure the voltage difference above 12v is higher than the regulator's dropout. Low Drop Out (LDO) regulators are handy for this.

[TNblueshawk]

Hey Patrick. Just read all 20 pages of this thread  

My build is working. I've got the V7 standard build. Didn't do any pre-amp/power tube thingy.

First on the PS, in the states I had a bitch of a time finding the right PS. First finding a negative ctr made me lose the rest of my hair which I really can't afford to lose so I got a pos ctr, cut it, soldered and back together. The next problem was finding a non switchable one. NEVER did find one so I'm using a switchable one. Results? No oscillation at all, no whine. I got a small hum but very small and no big deal.

My only "issue" I guess is the lack of volume, but then maybe that is the design. I have no way of knowing I suppose. If I put both pots to say 50% I can barely get a sound. Have to crank to 100% max, which doesn't bother me. i just wish I knew for a fact that this is all the volume this circuit puts out. In the back of my mind I keep wondering would a non switchable PS matter or not? Have no idea. I'll still try to find one though and report back any differences if I ever do.

[iccaros]

this puts out less than .4 watts. So the speaker will have a great impact on how loud it is. With my 103db at 1 watt speaker, I can talk over the amp, but its fun to play. At night it is still a little loud but sound carries in my house.

So try a  more efficient speaker and see how that works for you. Nice build by the way

[TNblueshawk]

Thanks Steve.

I'm runnig it into a brand new 10" Weber DT-10. I have to admit I don't know much about speakers technically. Of course brand new is not the best sound coming from any speaker but from an effeciency standpoint I'm thinking this speaker is fine, or is it a more scientific reasoning as to whether this speaker is or isn't efficient? I guess I'm judging the speaker by it being new and it rocks in my Champ amp I built but I know that may not be accurate for this little puppy amp.

[zambo]

speakers have an efficiency rating in db's. I wont pretend i know much about it but i do know this. With a 5 watt amp and an efficient speaker I can play a gig. with an inefficient speaker, the same amp will sound similar but not nearly loud enough. 3 db is a huge difference in loudness. some speaks are 97db and some are 103db. Im sure one of the smart people on here can explain it more gooder but thats the basic idea. 

[iccaros]

I will try the more gooder explanation 

inorder to raise 3db in volume you must double your power. Speakers move the cone by use of charging a coil and either being pulled or pushed by the magnet. The efficiency of a speaking is the rating on how much power it takes to push the speaker. so say you have a 5 watt amp and a speaker that is made to have an efficiency of 96db at 1 watt at 1 foot. So putting in 1 watt the meter would read 96db when standing 1 foot away.  So say you change the speaker to 103 db efficient speaker and now measure, the meter at the same distance with the amp putting out the same 1 watt would read 103db, or the same as if you were putting out 4 watts into the old speaker. So without adding any power we made the amp sound louder.

did that make since?
Also the DT-10's according to the website are purposely inefficient. the goal is to get speaker distortion at lower volumes.

[zambo]

Yeah that!   

[TNblueshawk]

I will try the more gooder explanation 

inorder to raise 3db in volume you must double your power. Speakers move the cone by use of charging a coil and either being pulled or pushed by the magnet. The efficiency of a speaking is the rating on how much power it takes to push the speaker. so say you have a 5 watt amp and a speaker that is made to have an efficiency of 96db at 1 watt at 1 foot. So putting in 1 watt the meter would read 96db when standing 1 foot away.  So say you change the speaker to 103 db efficient speaker and now measure, the meter at the same distance with the amp putting out the same 1 watt would read 103db, or the same as if you were putting out 4 watts into the old speaker. So without adding any power we made the amp sound louder.

did that make since?
Also the DT-10's according to the website are purposely inefficient. the goal is to get speaker distortion at lower volumes.

Makes sense Steve and thanks.

Yeah, I got that speaker on purpose for a little distortion  Maybe that is not such a good idea for this little amp 

Oh well, I intend to build many more cabs with speakers. I think I'll try this amp in my Fender HRD actually when it comes back from the shop. It is a Weber Thames 12" ceramic. Can't get that thing to break up to save my life!

[zambo]

I have used a few stock fender speakers and they always seem to be louder than normal. My blues jr speaker was like twice as loud as anything else i had.

[robot797]

hey guys i am kind of new here
but i have a question
can i use this output transformer?
http://www.conrad.nl/ce/nl/product/516104/Duplex-spoel-voor-100-V-luidsprekersysteem-0625-125-25-50-10-V/0219400&ref=list

it would be nice
(kind of cheap)

[frequencycentral]

I've tried amps with similar transformers - give it a try - nice and cheap!

[karter2000]

Hi all,

I just finished my MO using a kit bought from Rick.  It sounds awesome, even as a bass amp!  I have one question, and I'm not sure it it's stupid or covered before.  If I wanted to use the MO as a preamp or drive another amp, do I need a dummy load similar to a Herzog?

[iccaros]

Hi all,

I just finished my MO using a kit bought from Rick.  It sounds awesome, even as a bass amp!  I have one question, and I'm not sure it it's stupid or covered before.  If I wanted to use the MO as a preamp or drive another amp, do I need a dummy load similar to a Herzog?

its in ricks drawing on page 17, see the alternative switch added to power out section
http://www.diystompboxes.com/smfforum/index.php?topic=73222.320

[frequencycentral]

Added switch to select preamp or power amp at output socket:



What's happening in the above layout is that the preamp out is taken from lug 2 of the volume control. One half of the DPDT selects either the preamp or the power amp to the output socket. The other half of the DPDT cuts HV to the pentode and the output transformer when the DPDT is in preamp mode - as it's bad for the pentode and transformer to see high voltage without a speaker attached. I'd really stress that caution needs to be taken with this switch, as you don't want to send the power amp output into anything other than a speaker. It's a cool mod though - in preamp mode you've got a massive warm tube overdrive 'pedal' type effect.

[karter2000]

Thanks for the replies guys.  I was thinking it would be cool to tap the output from the transformer, to get the tone of the power section.  Would using a fixed load like the Firezog work?
http://www.aronnelson.com/gallery/main.php/v/DougH/amp/Firezog.gif.html?g2_imageViewsIndex=1

[robot797]

hey
can i replace the 6111 with a pair of 5676 tubes?

pleas i need an fast awnser

[iccaros]

hey
can i replace the 6111 with a pair of 5676 tubes?

pleas i need an fast awnser

I guess you could, it would take a redesign, like 1.2v heaters on those and direct heaters, which means .... well there would be a lot of work

[robot797]

could you pleas try
(i have nine 5676 tubes and nine 5672 tubes)

so i need a use for them