My new MiniAmp 2.0 (incl. soundsamples and schematic)

[FcKw]

I was told in another THREAD (about my first mini amp), that my new mini guitar amplifier would be worthy its own thread, so I will show you the amp in this thread in some more detail.
It is an approximately 1.5W-2W guitar amplifier with two 12AX7s in the preamp and one ECC99 in the poweramp. It provides a full tone stack with controls for treble, middle and bass and one volume control. The poweramp is an ECC99 in a push-pull configuration fed from a cathodyne phase inverter. The preamp is inspired by the Vox Night Train (which seems to be inspired by designs like the Blues Express Version of the Trainwreck Express for example). For the output-transformer I used a Hammond 125B and for the power-transformer I used a toroidal transformer with secondary: 200V 0.1A and 6.3V 1.5A...

Enough of that geek-talk, how does it sound? Well, here are some soundsamples :
http://www.youtube.com/watch?v=lOb-RVET8So

Here are some pictures:





And here is the schematic:



greets
Patrick

[defaced]

I really dig this amp.  What prompted you to add the NFB around the first two triodes?  That's something you don't see in every preamp circuit.  And what kind of pot did you use for the power tube cathode bias to be able to hold up to the power/DC current? 

[John Lyons]

Nice work!
Can you post a larger version of the schematic?
I'd like to see what you did there.

thanks

John

[jrod]

Well done! The clips sound great!

How did you lay it out? Point-to-point?

[~arph]

Very nice!  I wouldn't dare touching it with the mains going in though 

[John Lyons]

Hmmm, ok...couldn't click on the thumbnail before...odd...

[FcKw]

I really dig this amp.  What prompted you to add the NFB around the first two triodes?  That's something you don't see in every preamp circuit.  And what kind of pot did you use for the power tube cathode bias to be able to hold up to the power/DC current?  

Thanks, The NFB is taken from the Vox Night Trains "Bright Mode" and it should attenuate the lower mid frequencies, I still have to test it without it. If my notes of my calculations are right, there should be a power dissipation around 1/2 W and a current of 60mA, so you should use a potentiometer that fits that needs. I settled with a fixed resistor of 150Ohm 0.6W if I remember correctly.

Nice work!
Can you post a larger version of the schematic?
I'd like to see what you did there.
...

Thanks, ooops sorry, I forgot to link the "real size" pictures, it should be working now, just click the small image to get the bigger one.

Well done! The clips sound great!

How did you lay it out? Point-to-point?

Thank you, yes it is wired point-to-point except the power supply. The power supply is done on a small turret-board.

Very nice!  I wouldn't dare touching it with the mains going in though  

also thank you, but why? it's not different then any other amp out there, the dangerous voltages are all inside the enclosure and the enclosure is properly grounded?

Patrick

[Kitarist]

Does it take pedals well?

How much did it cost you to make one?

What kind of transformer did you use?

Thanks!!!

[electrosonic]

Really nice. How does it sound with humbuckers?

Andrew.

[FcKw]

Does it take pedals well?

How much did it cost you to make one?

What kind of transformer did you use?

Thanks!!!

I didn't use any pedals with the amp yet, but I can try it this weekend. Are you refering to any specific type of pedal?

It cost me something around 100€ (~133$) to build this one.

As I wrote in the first post the OT is a Hammond 125B and the PT is a toroidal transformer with secondary: 200V 0.1A and 6.3V 1.5A, THIS ONE to be exactly

Really nice. How does it sound with humbuckers?

Andrew.

It sound really nice, too. What really impressed me with my Epi LP was the really nice sparkly chime I got with this amp. I'm not sure if I can manage to do some soundsamples with the HB equipped Epi LP as I'm in the process to sell it to get a Gibson LP with P90s right now...

Patrick

[Der Groovemeister]

Wow! Looks and sounds absolutely great. Some gut-shots please!

[Kitarist]

Can you please post some inside shots

[Top Top]

It does sound really good. If it weren't for my fear of AC wall current, I would love to build something like this (and I think this is what the other person who said they "wouldn't touch it" was getting at).

[gtudoran]

Nice work. You could have a little more power if you make you amp more B class (you hold the tubes in cutoff). The solution i've made is to take the 6.3v from heaters, rectify and filter it and then feed it on the grids. This is my version of the amp - it use 6n6p russian double triode as a power tube (is more or less the same thing with ecc99; ecc99 has 5w maximum anode disipation so you could have 3-4w of clean sound in PP configuration).

A little picture of my head


Here is the schematic that i've made - it's tested and work like a charm.


and this is a sound clip (added just a little reverb at mix)
http://soundcloud.com/analog-sound/micpreampmp3


Best regards,
Gabriel Tudoran
Analog Sound

[merlinb]

Here is the schematic that i've made - it's tested and work like a charm.

V4 seems to be missing a bias resistor. Drawing error?

[gtudoran]

Hmmm nop... as far as i remember this is the way i did it...
And according to this is ok.... i didn't use the diode thow.

Best regards,
Gabriel Tudoran
Analog Sound

PS: Are you merlin the valve-wizard? if yes thank you a lot for all the usefull information from your site.

[FcKw]

Wow! Looks and sounds absolutely great. Some gut-shots please!

Thanks, inside pics will be following this weekend.

It does sound really good. If it weren't for my fear of AC wall current, I would love to build something like this (and I think this is what the other person who said they "wouldn't touch it" was getting at).

Thank you, yes this should always be handled with care of course, but if you follow some rules (poperly grounding the chassis, taking the plug of the wall, discharging the caps etc.) you can minimise the risk to zero.

Nice work. You could have a little more power if you make you amp more B class (you hold the tubes in cutoff). The solution i've made is to take the 6.3v from heaters, rectify and filter it and then feed it on the grids. This is my version of the amp - it use 6n6p russian double triode as a power tube (is more or less the same thing with ecc99; ecc99 has 5w maximum anode disipation so you could have 3-4w of clean sound in PP configuration).
...

Thanks, your amp sounds nice too, how does it sound breaking up? What is your OTs primary resistance on the output-triodes? My amp is more biased for a better sound than for the highest output, so I chose to go more in the class A direction than class B.

@MerlinB
Hey MerlinB, you're book is my favorite at the moment. With the help of your book I cured some really bad distortion artifacts from the cathodyne PI on this amp, THANKS!!!

Patrick

[gtudoran]

My OPT has 8k to 4 and 8ohm output impedance. The maximum distorsion that you can get is for classic rock/blues rock but with a boost pedal in front or with a OD pedal you can get a lot of gain for lead and heavy rock... i love it. I think that is like more then a power amp with el84 in SE configuration. If i remember well i have 20-22mA idle current @ 170V anode voltage and @ full blast i get that power tube compression (very nice for studio recording or for small gigs if you use a mike to go in a PA).

Best regards,
Gabriel Tudoran
Analog Sound

PS: I will try to make a video clip with it tonight (if my cam is working) and postit on you tube.... i'm not very skilfull but ....

[merlinb]

Hmmm nop... as far as i remember this is the way i did it...
And according to this is ok.... i didn't use the diode thow.

Ah, the difference is that the diagram on my website is for a DC coupled stage. Your circuits shows an AC coupled stage (preceded by the tone stack caps), so that triode has no bias. However, if you like the sound then who am I to argue! 

[DougH]

Fckw- sounds and looks great! 

Any chance of a clip with it turned up more?