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

[c3tester]

Quick shout out to TNBluesHawk (and others that have provided patient guidance).  I finished my first M1 build (prototype)  a month or so ago.  Learned tons, and I've got some fixes to incorporate into the finished product.  Distorted sound is great, clean sound is kind of muffled and maxing both gain and volume produces a kind of tremolo effect.  Got some investigating to do.  Thanks for all your help.  I'll try to post a pic.


...just tried.  Can't figure out how to attach a picture.  Sorry.

[bluebunny]

Check out this piece of advice given to me by sadcakes (which Rick had previously mentioned earlier in the thread).  I also had "tremolo", but this small mod got rid of it.

[c3tester]

Thanx BlueBunny.  Sounds like what I might need ...I'll give it a try.  Had some hum, but switched power supplies and things are quiet as can be.  Seemed to help a little with oscillation too (has a little lower avg output).  Great little amp.

[Ibanezsr500]

Hey guys,

Alright, I've got one of these built and wired up, but I'm having a few problems.

Problem no.1: I'm not getting the full 80V at B+, it's currently reading 46V, nowhere near close. The power supply is reading 12V, and the voltage increases are happening in a consistent fashion (ie. all stages are increasing the voltage by x, I haven't got the exact numbers in front of me at the moment, but all the stages seem to be working as intended). Also, the Maxx1044 is getting hot, I can't keep my finger on there for more than a few seconds. And, the caps that are handling the higher voltages are getting warm, but not so much that I can't touch them. Te actual PCB surrounding these caps is getting hot also, but I'm assuming that the heat is transferring from the caps onto the board. And yes, the caps are rated for 100V.

Second problem, which may be related to problem no.1, I'm getting a fuzz factory-esqe occilation when the gain is cranked, but the volumes backed off to about 3/4. I'm also getting the motor-boating people were having issues with earlier in the thread when both the gain and volume are dimed. I haven't yet deviated from the layout, so all values are exactly the same as Ricks V7 layout.

Now, I'm currently using a switchmode regulated power supply. I can't find a non-switchmode one for a reasonable price here in Aus, let alone a place that sells one.

Any help would be appreciated. I've checked the board for shorts, dry solder joints etc, but I can't find anything that would be causing me to have these problems. Except the power supply, would it be the reason that I'm not getting full voltage?

[bluebunny]

I was never getting the full 80V in mine either (more like 68V?).  Different diodes might help - Schottkys with lower drop.  I didn't try this 'cause I couldn't be ar5ed with swapping 'em all out.

I also found my 7660 getting hot.  (BTW, the max. input voltage for the 1044 is only 10.5V.)  But I think it was more to do with the voltage dropping resistor sitting close by.  This was reaching boiling point and heating up everything in the vicinity!  I "fixed" this by bolting a 10W resistor to the outside of the case!

Check out the motorboating fix - mentioned in my post about three entries back.

[Ibanezsr500]

Ok cool. Thanks. I ruled out the power supply, as I was able to run the amp off a 12v battery I had laying around.

Yeah, I figured that the max1044 was getting hot from the 12V, I didn't realize that it would get that hot though! I'm getting a reading of 90 degrees Celsius! And that's not even the hottest part of the board, the 2W resistor is getting up to about 120 degrees Celsius. The diodes and caps are around 80 degrees as well. Are these normal temperatures? That's pretty freaking hot for something mounted in an unventilated metal box...

[bluebunny]

That's pretty freaking hot for something mounted in an unventilated metal box...

Uh huh.  I'd ventilate the box.   

[Thecomedian]

heat sinks are pretty nice too 

[iccaros]

My latest Incarnation of the murder one..  Still need to stain and polyurethane, and then final test once put back together..

[frequencycentral]

Still enough intetest in this project for me to have a run of fabbed, screenprinted and soldermasked PCBs made?

[wgc]

I'd be interested in a pcb

[Maik]

me too

[iccaros]

Rick, what would the cost on those be?

[frequencycentral]

Rick, what would the cost on those be?

Same as the etched ones I've been doing, around £12 GBP.

[iccaros]

I would be in for at least 2.. these are popular gifts for friends.. my next one will be covered in Shag Carpet..

[Scruffie]

How would the PCB be designed? Board mounted jack, switches and pots? Just the same as the original layout? etc.

[frequencycentral]

How would the PCB be designed? Board mounted jack, switches and pots? Just the same as the original layout? etc.

I'd just thought same layout as my original etched PCBs, but fabbed, silkscreened and soldermasked. That way it would fit 1590B as in my production numbers, as well as being friendly to those who wanna go with other form factors. Open to ideas though. I guess PCB mounted 9mm alphas would work well. Though going the whole way and having everything PCb mounted would make it impossible to build in a 1590B.

[iccaros]

IT would, but after building 3 of them, I like more space. It cool to do it small, but I find that the 1 watt and 2 watt are really close to other parts, if you made a version that had mounted pots, it would be nice to open up the layout, maybe add a second pentode.. or at least space.. but its your design, either way I can make work.

In my current build I am getting a tremolo effect when all pots are dimed out..  its hard to get probes in between some parts to trouble shoot..


Note, the above is just my opinion, not meant to give advice or fool people into believe I have any real knowledge.

[bluebunny]

@iccaros: check this out for a tremolo fix:

Check out this piece of advice given to me by sadcakes (which Rick had previously mentioned earlier in the thread).  I also had "tremolo", but this small mod got rid of it.

[iccaros]

thank, I am on that route, I replace all the tubes, and tried a bigger grid stopper, but not the load resistors, I was going to rebias, I know its oscillation from high gain, I can see it on the oscope, so next I will go with load resistors, I Am also may change c14 to a  .022 as this time its sounding a little dark