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

[iccaros]

@BlueBunny
This voltage multiplier doubles voltage Charging the first capacitor and at another point causing it to discharge, charging the next capacitor.  This is added in stages so that the starting voltage is higher, which results in a doubling.

We have a few point of loss in this design, one is the diodes, as you mentioned, but also the rate at which the capacitors discharge. If C1 discharges faster than c2 can charge, and with standard parts this could happen, up to 20% faster, and C2 is always conducting to the next stage, then you could have a situation where C1 is not fully charging C2 in comparison to draw. Since some of this is caused by how long the cycle of discharge, caused by the switching frequency of the IC, there is some fudge range, and 9v does not sound too bad, but not the best and "should" not make a lot of different in volume, but some, as this design is already "quite"

In a design I have been working on, using the same basic supply http://www.diystompboxes.com/smfforum/index.php?topic=94778.0 you can see my voltages starting at 9v, at third stage with load I saw 25v.


Looking up your speaker, it looks to be a very inefficient speaker as it is rated for 116db at 150 watts @ .5 meters. Do you have a speaker you can test with? another guitar amp you can just unhook the speaker for a second and test?
The Murder one is putting out less than .4 watts.  (65mw max for that tube and your not going to get half that If I remember correctly)
This is one of those Just Loud enough amps, I love them, great for practice and for recording.

I am on travel till Friday, and I just got my transformers in, just need a voltage drop resistor for the heaters and I will have mine completed. I will measure my voltages and let you know how it comes out. I have an SPL meter and will measure with my efficient Red Coat speaker and my speaker from a Mic stand monitor to see how much difference I get.

[bluebunny]

Thanks for this further information, iccaros.

The speaker is less than ideal - just what I had lying around for testing purposes.  Something better is in the pipeline, just not here yet!  Will be interested to hear how your build turns out.

[iccaros]

I have a good 68 volts on mine, I just completed today, fried a max 1441.. if you forget to connect the grounds, speaker and transformer, this power supply pushes 15v back to main voltage. . Man that 18R 2watt gets hot.. after 10 min its really hot to touch..

[bluebunny]

if you forget to connect the grounds, speaker and transformer, this power supply pushes 15v back to main voltage.

Are you saying my speaker shouldn't be a "floating" circuit, but that I should ground the speaker?

Man that 18R 2watt gets hot.. after 10 min its really hot to touch..

Careful with that!  I measured mine at well over 90^oC (~200^oF)!   

[iccaros]

yes, I believe the speaker should be grounded..
hmmm, will have to recalculate that resistor.. clip a heat sink to it..

[bluebunny]

Thanks - I shall give that a try...

[bluebunny]

Hmmm...  grounded the speaker, but I can't see it made a whole lot of difference.  Sounded pretty much identical.   

[zambo]

bad speakers will make you rebuild an amp for no reason! Try a different speaker. I have thrown ( given) away about half of my speaker stash cause they just weren't any good.

[iccaros]

Build complete
I measure 69 volts off the OT
Sounds loud enough through my Red Coat Wizard speaker.
Through the 4X12 Marshall is cool
this amp takes pedals well, the tone of the amp stock cranked is OK.. (I understand my speakers will make up 80% of that sound)
After messing with my Wha peddle I think I will do some tone adjust on the next, or maybe not. I say that because with my Govonor pedal this things sounds awesome.. I played it for an hour strait, had to turn off as with that Red Coat it traveled through the house too much at 11pm.

I also hooked it to some very inefficient speakers, and to a EV monitor speaker, its way too under powered to push these inefficient speakers to usable volume. I think this is Blue Bunny's issue.

Will post sound clips tomorrow.

Thanks Rick, fun project.

[bluebunny]

I have a more appropriate speaker in the works, so this sounds encouraging!

[iccaros]

@BB
here are some pictures and some OK sound clips, I did two, the first is with the pre volume @ 5 oclock and master at max. I go back and forth between using pedals and not..
its a wave file so be prepared.. this goes from the stright amp, to using my super-overdrive to the govenor. Wah, Delay and Belton Reverb as needed. 
http://dl.dropbox.com/u/14312589/MOCleanpre%20set%20to%205%20master%20max%20with%20effects.wav
my board


the amp, I put it on one of my other amps to show size


Last clip is me just jamming with pre gain going form 7oclock to max and back to add effects..
http://dl.dropbox.com/u/14312589/MOCleanpre%20set%20to%207%20master%20max%20with%20effects.wav

[bluebunny]

[ WAVs.  It's a wonder Microsoft don't sell hard disks.  ]

Sounds great - thanks for putting these up.

[snarblinge]

Hi Rick, read through all of this finally, and gathering bits together to build one.

what were your reasons for ditching the bias in V7 or reverting back to V5 basically, or am I missing something, I plan to turret this so want to plan it out before I begin.

thanks

[frequencycentral]

V7 is far in advance of V5. V5 had the -ve bias to get cleaner cleans, whereas V7 is set up like a proper tube amp with correct cathode biasing.

I've never experienced the motorboating others have recently noted, but on my next revision of the PCB I'll add the mods mentioned here:

....try cutting the HV trace between C12 and R1/R2 and bridging the cut trace with a 22k resistor. For completeness, also consider adding another 10uF 100v cap between R1/R2 and ground. Basically, cutting the trace, bridging it with the resistor and adding the extra cap is creating a B1 (to the 5672's B+), really you're converting the preamp section to a Superfly preamp.

[snarblinge]

thanks man, with keener eyes i could have spotted that, was just looking at the switch and traces..... i'll stick to 7.

[fpaul]

Is there a "best" way to secure the tubes to the sockets?  I was thinking of either soldering or hot gluing the outside legs and was wondering what others have used.  I had some problems getting it boxed without a tube falling out.  It's finished now but I don't think the tubes could stand up to much bumping.

I used the version 5 board with 6112/100k plate resistors. 

[frequencycentral]

I don't use sockets. I solder them. I've never had one come back yet for re-tubing.

[fpaul]

solder them

Thanks Rick, I'll solder them eventually.  I'm still trying to decide if I want to add cathode resistors/caps on my rev 5 board.  One side looks easy, the other more of a kludge.

I'm liking the little amp.  Put a dirt box in front and it's great for practice without worrying about going deaf or cops showing up.

[Jamirox]

Hi,

Do someone can post a PCB File other than the .gif of the version  7 ? Because when I print it's always upsized or downsized, I could match the IC pin pitch but it's too much effort if someone has the PCB file in real size

Thank You

[frequencycentral]

Hi,

Do someone can post a PCB File other than the .gif of the version  7 ? Because when I print it's always upsized or downsized, I could match the IC pin pitch but it's too much effort if someone has the PCB file in real size

Thank You

Resize to 48%.