Author Topic: New low voltage tube amp project. Runs on 12v walwart 62v inside. not to scary.  (Read 39578 times)

amptramp

There is an interesting page here:

http://diyaudioprojects.com/mirror/members.aol.com/sbench/50c5.html

on using cheap power toroids as audio output and input transformers.  Most toroids have the equivalent of a very limited gap so push-pull is where they are best but some have significant binder thickness that translates into a larger gap and these are suitable for single-ended use.  The 50C5 has a relatively low output impedance and will take a 2500 ohm output transformer, but a triode output should be lower.  BTW the Steve Bench site is awesome for tube stuff.  the Tubecad site is another good one.

sajy_ho

Hi guys, here's mine:

I did a few changes, raised B+ to 100V, added a simple headphone out:http://www.sophtamps.ca/images/headphonebox/headphonebox1.4.jpg
As I could find only a pp OPT, I'm using only a half of the primaris; so I used a dpdt to swith between Greg's amp and a pp class A Firefly type amp.
The sound is cool in SE mode, rich with harmonics and totally awsome, In the pp mod at high volume it sounds like a jtm45 fully cranked.
Maybe not the loudest but definitely the best sound of my gear! Thank you Greg

Sajad
Life is too short for being regretful about it.

zambo

Sweet! Thats a good looking amp! Would you mind posting a quick schematic for your amp switching between se and pp? thats very cool!
I wonder what happens if I .......

sajy_ho

Sweet! Thats a good looking amp! Would you mind posting a quick schematic for your amp switching between se and pp? thats very cool!

Hey Greg, glad you liked it:
Life is too short for being regretful about it.

thomasha

Awesome! ;D

Soundclips please!


sajy_ho

Awesome! ;D

Soundclips please!


Thanks, I wish I  was a good player. :icon_rolleyes: I'll post a clip as soon as I find someone to play.
Life is too short for being regretful about it.

Scruffie

Sweet! Thats a good looking amp! Would you mind posting a quick schematic for your amp switching between se and pp? thats very cool!

Hey Greg, glad you liked it:

Very clever idea! Been humming and haring over building another AU7 power amp build but I think this might make a project very much worth it.

Might be a good idea to make it an internal DIP to make sure it's not flicked when the powers on... seems like it might not be good for the tube/transformer.

DefiantAudio

I have a ton of 12au7s laying around, like 200 ish 100V 10uf caps, and around 100 diodes. I think this amp is definitely going to happen. Just waiting  on an order of maxx1044 to get here. I'm sure I will have plenty of questions regarding this build when it finally gets started as I am new to diy amps and high-er voltage stuff.
Think for yourself, question authority.

DefiantAudio

For instance, can I split the 12V from a wallwort to power the tubes as well as the maxx, or do I need separate 12V sources?
Think for yourself, question authority.

sajy_ho

For instance, can I split the 12V from a wallwort to power the tubes as well as the maxx, or do I need separate 12V sources?
Of course you can, but that wall wart needs to be at least 1A.
I'm using a 12V-1A switching adaptor.
Life is too short for being regretful about it.

JustinFun

I built this over the weekend - my first amp build! Sounds good but I've got a couple of issues.



Yes, i did put too many turrets in!

There's a high pitched whine which is fine at about half volume but gets intrusive when it's cranked. Is this the charge pump? I'm using a 7660s. Anything I can do to reduce it? I've got an indicator LED and two 'tube glow' LEDs hooked up to the 12v supply as well (with 4.5k limiting resistors) - would this be an issue?

The amp seems to rely on a guitar with grounded strings to work properly - it's fine with my strat (as long as I'm holding the strings) but it buzzes like crazy with my Les Paul. Have I missed something obvious with the grounding? I've checked continuity of ground between input jack, output, power and board and all seems OK.

Any help/advice gratefully received - it's so close to being right it's frustrating!

sajy_ho

I built this over the weekend - my first amp build! Sounds good but I've got a couple of issues.



Yes, i did put too many turrets in!

There's a high pitched whine which is fine at about half volume but gets intrusive when it's cranked. Is this the charge pump? I'm using a 7660s. Anything I can do to reduce it? I've got an indicator LED and two 'tube glow' LEDs hooked up to the 12v supply as well (with 4.5k limiting resistors) - would this be an issue?

The amp seems to rely on a guitar with grounded strings to work properly - it's fine with my strat (as long as I'm holding the strings) but it buzzes like crazy with my Les Paul. Have I missed something obvious with the grounding? I've checked continuity of ground between input jack, output, power and board and all seems OK.

Any help/advice gratefully received - it's so close to being right it's frustrating!
I wish someone more knowledgeable like Greg would answer your question, but I think that whining you said is related with the chip you're using, replacing it with another chip that could handle more power(like LT1054) will help.
As for the background noise, using shielded wire in grid paths will help a bit. if you can't use shielded wire, adding a 10-68k grid stopper resistor before the first grid would help too.

Life is too short for being regretful about it.

samhay

^There's a high pitched whine which is fine at about half volume but gets intrusive when it's cranked. Is this the charge pump? I'm using a 7660s.

If the noise is coming from the charge pump (which it may or may not be):
Are you sure it is the 7660S and not the 7660?
If it is the 'S' model, do you have pin 1 connected to pin 8?
I'm a refugee of the great dropbox purge of '17.
Project details (schematics, layouts, etc) are slowly being added here: http://samdump.wordpress.com

JustinFun

Thanks both.

Samhay: It's definitely a 7660s (unless it's an ebay fake - can't remember where i got these from, they've been in my stash for a while). Pins 1 & 8 are connected (I've just checked continuity).

Sajhy - are these the wires I would need to replace with shielded ones (highlighted in purple)?



Not sure if this will solve my problem though, it feels like something is up with the grounding - when I'm using the Les Paul the buzz goes away if i touch the enclosure.

sajy_ho

Sajhy - are these the wires I would need to replace with shielded ones (highlighted in purple)?
Yes exactly those wires, plus the one comming from input jack (green) and those two green wires connected to tone and volume. Don't forget to connect ONLY ONE SIDE of the wire's shield to ground.
Not sure if this will solve my problem though, it feels like something is up with the grounding - when I'm using the Les Paul the buzz goes away if i touch the enclosure.
If your problem is only with les paul and doesn't get away even with touching the strings, you probably need to make sure that guitar's bridge is tighed to ground.
Life is too short for being regretful about it.

JustinFun

Yes exactly those wires, plus the one comming from input jack (green) and those two green wires connected to tone and volume. Don't forget to connect ONLY ONE SIDE of the wire's shield to ground.
Not sure if this will solve my problem though, it feels like something is up with the grounding - when I'm using the Les Paul the buzz goes away if i touch the enclosure.
If your problem is only with les paul and doesn't get away even with touching the strings, you probably need to make sure that guitar's bridge is tighed to ground.

Thanks, will give that a try.

My Les Paul (a 90s Standard) emphatically does *not* have its bridge tied to ground - lots of gibsons from that period (and earlier) do not. It's not an issue on any other amp.

zambo

It looks good, is the chassis grounded? The chassis is a big sheild for the amp innnards. I use a jack that is grounded to the chassis. I have had smps whine when they arnt loaded down enough. The lt1054 hasnt been an issue like this so i dont know what tro say other than sheided wire from input to the first cap and sheilded wire from the cap and grid leak resistor ( 1m 2nd turret over ) to the tube socket. If your wires are running kinda funky they can pick up noise. Using a chopstick ( something non conductive ) to move them arouind while its on and whining helps. You have to be REALLY CAREFUL!! The voltages may not kill you but they cant be good for you so one hand in back pocket while chopsting so the shock doesnt make it across your chest cavity. Im not kidding it can F@#$ you up bad! I will see if I can get one to start whining. I suspect the chip though.
I wonder what happens if I .......

zambo

After looking at it some more, check your lead dressw and see if shortening up the wires to the tubes does it. They will pick up stuff being that close to eachother. sheilded wire helps but is not a replacement for good lead dress. I suck at it, i should know  :icon_redface: sorry i havent been on much, doing a bathroom remodel in a hurry for a client. went from tubes to tubs overnight. dont like the change  :icon_wink:
I wonder what happens if I .......

Jayallen

Just built this and it sound good. . I wondering if it is possible to get this to push 1 watt? I read if you bypass the 380r resistor you would get more output and distortion but I don't need more distortion. My power is smps I can get up to a 190v but it starts sputtering so 100v max for me. Just wondering what I could do. Thanks

thomasha

Hi,
this is a nice amplifier!
If you are using a higher voltage you need to change 380r to a lower value.
When you say bypass the 380r resistor you're talking about the bypass capacitor or you shorted the tube cathode to ground with a wire?
If you shorted the cathode to ground the sputtering could be a cause of current draw.
If you change the 380r to a lower value maybe it would work without the SMPS suffering from too much current draw.
I would start with 190r and see how it sounds.

Which SMPS are you using? Has the mosfet a heatsink? is the noise coming from the inductor? How big is the transistor? can it handle current enough to run the amp?
 I would expect at least 25mA with a higher voltage. (two tubes in parallel)

Good luck!