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

[iccaros]

Plat resistors worked, not sure why, are we not increasing gain with 100K?.. any case, I think I will bring them down to 68K and try that, they are a little farty.. I think 68K is what I used before.. hope to have sound samples soon.

[Jdansti]

Clean Mod

I know this is an old thread, but I thought people would want to know about this.

I've had an M1 board sitting around for a couple of years and finally got some time between honey-do projects to build the amp. It sounds good, but needs some tweaking. I don't know if this is the same thing that others have experienced, but it's kinda farty when the volume is close to max. I've done the resistor mods and it's helped, but maybe I need to increase the resistor values more.

The other thing I've read is that it doesn't get very clean. I've discovered an easy clean mod by accident. When I first fired it up, all I could get was clean, and when I turned up the gain, the volume decreased down to nothing at full gain. After trouble shooting, I found a solder bridge between R1 and R2 where they connect to the 6111 anodes. After fixing that, the amp behaved normally. As a test, I shorted the two resistors with a clip, and I got the nice clean sound again. The only thing is you have to turn the gain down or you'll lose volume. I placed my DIY Landgraff Dynamic Overdrive in front if it with the resistors shorted, and the volume went way up and sounded great. I plan to install a SPST across the resistors to act as a clean/dirt switch.  Sorry if this is already common knowledge.

Photos:
http://www.diystompboxes.com/smfforum/index.php?topic=36392.msg937986#msg937986

[thomasha]

that sounds like local negative feedback, and gain controls the amount of signal been amplified that produces the feedback.
Maybe that's why the gain needs to be at low settings.
Merlin has something about it: http://www.valvewizard.co.uk/localfeedback.html
I used NFB from OT to cathode and it works too.
About the farty sound, I reduced the coupling caps to 4.7 nF , and put a 470 pF cap across the grid stopper. That made things sound better IMO.
Nice build btw 

[Jdansti]

Thanks, Thomasha. I might try that cap mod if I can get to them. I hot glued the pentode tube to a few components to keep it from moving around (it doesn't get hot like the 6111). I'll see if I can safely remove the hot glue.  Either way, I can at least place a cap across the grid stopper as you suggest.

BTW, I just did a little research on grid stoppers and ran across this article that you might find interesting and informative:  http://www.aikenamps.com/InputRes.htm

Thanks for the tip and welcome to the forum!

[AJDbass]

Hi,

Thanks for sharing this great design. Really great project for starting with the build of tube amps. Sorry, I know this is a old thread, but I have a few question regards the PSU.

I build this design, but was wondering about the PSU ampere rating. I read a 500mA regulated AC-DC wallwart is commonly used. I tried my design with a cheap 12V AC-DC wallwart wich is probably non-regulated, and the amp didn't work too well. When the volume/gain knobs are at 3 o'clock, the amp has this weird tremolo effect (it is called motorboating right?). I also have a tiny computer cooler van paralel on the power jack wich consumes 0,08 mA.

So I assumed the circuit didn't get enough amperes to work right. I found another 12v regulated PSU but this one delivers 2,5 A. I tried this one, and it immediately worked and soundend better, but that lasted for about 10 seconds before the amp didn't work anymore. I found out the 17660S IC crashed (got really hot and smelled a bit). So I guess it's not a great idea to use a 2,5 A PSU? I always thought the circuit only gets the amount of amperes it uses and I know the IC is rated for at least 13v.

Thanks

[bluebunny]

You're right: PSUs don't push out amps; circuits draw what they need.  So a 2.5A PSU won't hurt the circuit.  However, if your PSU is unregulated, then it could be putting out way more than 12V - enough to upset the 7660.

Check out one of my own queries further back in the thread concerning the motorboating phenomenom.  There's an easy fix for it (you just sub a couple of parts).

[AJDbass]

You're right: PSUs don't push out amps; circuits draw what they need.  So a 2.5A PSU won't hurt the circuit.  However, if your PSU is unregulated, then it could be putting out way more than 12V - enough to upset the 7660.

Thanks, I can safely use this PSU then. It's regulated and quit, stays nice at 12.0 volts at my voltmeter.

Check out one of my own queries further back in the thread concerning the motorboating phenomenom.  There's an easy fix for it (you just sub a couple of parts).

I did read about fixing the motorboating phenomenom, but the motorboating disappeared after using the 2.5A PSU in stead of the cheap unregulated 500ma PSU I used. Unfortunatelyt short after using the new PSU the 7660 died on me. I've got a couple of 7660 IC's on my way, can't wait to try it again.

[tonyharker]

Unfortunately some 7660s esp the ICL ones crap out at 10.5v so running them on 12v will destroy them.

[bluebunny]

Unfortunately some 7660s esp the ICL ones crap out at 10.5v so running them on 12v will destroy them.

Isn't that the MAX1044 you're thinking of?  Datasheets for both Harris and Intersil 7660s suggest a nominal 1.5V - 12V working range, with 13V quoted as the absolute upper limit.

[derevaun]

It could have hit it with more than 13v. If it's rated for 12v at 2.5A, it would push more than 12v when the current load is lower.

I'd make a regulated supply by using a 15v supply with a 12v regulator.

[AJDbass]

I just noticed I used a ICL7660CPA, not the 7660s. The ICL7660CPA is rated at max 10v  :

The IC's I just ordered are the intersil ICL7660S CPAZ, with a working rate between 1.5 - 12V, so I think those should be fine.

It could have hit it with more than 13v. If it's rated for 12v at 2.5A, it would push more than 12v when the current load is lower.

Thanks for the input. I've used a voltmeter to measure the voltage with and without load; it stays at 12.0v most of the time and the max voltage I read was 12.4v. I think I can safely use this PSU. I will find out when the new IC's arrive. It could take 2 - 3 weeks so I have to be patient   

[Jdansti]

The voltage might be different with no load vs a load. Maybe the multiplier chip causes the PS to behave differently than it would with a purely resistive load.

Or maybe I don't know what I'm talking about! Just throwing it out there that these PSs sometimes behave differently when disconnected from the device you're powering.

[AJDbass]

Hi there,

A few days back the ICL7660S IC's finally arrived. I replaced the bad ICL7660CPA and noticed that this new IC doesn't even get warm, even after more than an hour. So that's a good thing. The bad thing is that I still had the motorboat thing going on. I tried the resistor mods and the motorboating now starts a little later when turning up the volume and gain, but it's still there. I could place a small resistor at the pots so they act like they can't be turned up all the way, but I will lose some volume.

I do get the feeling that there's a little more going on. I think the amp is a little quiet compared to some clips I saw on youtube, but of course it's hard to be sure. I am using a speaker with a decent efficiency. I implemented the preamp switch, and in preamp mode there is no motorboating whatsoever. Works great as a cleanish boost/overdrive.

Anyway, It is a really fun little amp. I really like the overdriven sound with single coils. Here are some foto's of my build. I used an old analog amperemeter. Enjoy!

[Magnus]

Hello,
it took some time but now it is finished,
my "Murder One" in an Type-B-Enclosure.

Data:
-------
Enclosure: Hammond 1590-B
Output-Transformer: Fender Reverb-OT
Voltage-Converter: MAX1044
Tubes: NOS VALVO 5672 (Pentode) / NOS THOMSON 6111 (Triode)
PCB: etched pertinax
Resistors: Vishay Dale CMF55 (0,1% tolerance ),
standard metal-film-resistors (1% tolerance)
Capacitors: Selected NOS Tropical Fish, Panasonic FC-Electrolytics
Diodes: 1N4148, 1 x 1N4007
Power: ~ 1 Watts (?)

I used this layout: "Murder One" - V7

...this is how it started (19 holes ):


...the pcb before installing:


...guts:


...Tube-sockets (Inline-sockets), glued to the pcb with epoxy:


...the Tubes, ready for installing with their sockets:


...Murder One, Size-comparison:


...Murder One, Front-view:


...Murder One, left:


...Murder One, right:


...Murder One, activated:


...6111-tube-detail-picture:


Sounds really nice

At full power you can hear it in the next room
and its possible to play clean (quiter of course but still ok)...

I made the wood-plate from an old piece of wood,
hammered letters into it, sanded it and applied some thick coats of clear-coat...

Tips for other builders:

1) Take a look at the datasheet of your 6111-tube to make shure how to wire it up correctly,
I did it wrong the first time, because I installed the pcb with its solderside towards the inner enclosure  

2) The 18 Ohm-resistor caused some really huge heat (flowing into the parts beneath),
I installed a cement-resistor outside of the enclosure - problem solved   (Thank you for this tip, bluebunny!)

Thank you for this great circuit, Rick      


Greetings from Germany
Magnus

[mth5044]

That is beautiful! Great job!

[Magnus]

Thank you 


Greetings
Magnus

[Perrow]

...this is how it started (19 holes ):

Nice work there (and not just the drilling). That's how my 1590A looked like before installing my Superfly, didn't have room for tube guards so only 15 holes, but then again, on a A size enclosure.

[Brymus]

Beautiful Magnus !!!!
I love it looks like Rick built it himself.
Soundclip please?

[Magnus]

Hello,

@Perrow:
Thank you  
I know your project - great looking build and really small  

@Brymus:
Thank you for your kind words  
I can not record sound clips because I don't have an interface and a microphone, sorry...


Greetings
Magnus

[kalegood]

Wondering if I could get some trouble-shooting help here. This is my first electronics project, so, ya know. Learnin' a bit.

I built my Murder One and had a high-pitched hum that I thought was a grounding issue on the pot. Everything else was working well, though. I put it in the enclosure and now it has stopped working. No amplification at all (well, some, but no output).

I've borrow my friend's oscilloscope; the preamp stage is working fine from what I can tell (the signal is amplified 2x). On the preamp, here is what my readings are (same results with 2 different tubes):

Pin 1: no signal, no voltage
Pin 2: 70 volts, signal about 1/2 of the input (from the 1/4 inch jack).
Pin 3: a bit more than 1 volt
Pin 4: same as the output from the preamp
Pin 5: the ground is good.

It may be good to note that I crossed B+ and the other power line, frying my ICL7660. That has been replaced, obviously.

Any help would be appreciated.

Thanks,
kale