Carolina SongBird amp

[10thTx]

This amp has nice sustain, & smooth overdrive. The mosfet CF prior to the passive effects helps with Boss digital delay. The overdrive is reasonably clear and not muddy with chords or lead work. Harmonics are decent too. With the digital delay, it sound really big for a 3 watt SE amp.

I am getting some of the "blooming" effect that I get on the Tweed BluezMeister and Tweed Overdrive amps that I've built.

It will work with a 6V6 or 6K6. I like the 6K6 better and it gives a very nice smooth tone, IMO.

With respect, 10thtx

[Andy Le Blanc]

Is V1 really a 12av7? whats the plate v , the rating is low 150v for the type.
good to see lower voltage types being used

[10thTx]

Yes, the V1 is a 12AV7 which I like there. I've tried a 12AY7, 12AT7, 5751 & 12AX7 also in both positions with various combinations.

I don't remember the voltage right off but I think it's around 150-160v?

All sounded good to me but I prefer a clearer sounding overdrive tone.
The sustain even with the 12AV7 is quite good.

With respect, 10thtx

[David Root]

12AV7 design center is 300V. Typical shown in the datasheet is 150V. Interesting design, how much tweaking did it take and what does the 12AV7 bring to the table other than lots of current?

Edit, I take that back after running V1A thru TubeCAD, you're only running about 1mA or so, assuming your B+ is about 200V. Nicely centered Q point too. PSRR is awesome--minus 26 dB!! Gain probably around 40 or so?

[10thTx]

David,

Your knowledge of electronics and amps is waaayy beyond mine so I am unable to answer some of your questions.

There is an editable ExpressSCH version of the schematic and layout here: http://www.el34world.com/Forum/index.php?topic=11889.0

I probably have spent more time tweaking this simple amp then any I have built including the Tweed BluezMeister and Tweed Overdrive Special (which borrow from D-type amps). The TBM and TOS are my other two amps.

The 12AV7 still provides enough overdrive to have sort of a clear sounding overdrive. Not a clean OD but a clear tone. The notes aren't muddy at all and the notes articulate well in chording.

My understanding is the 12AV7 lies somewhere between a 12AY7 and 12AU7 but closer to the 12AY7. Having compared all those in the same position in a V1, I'd say that's a reasonable description.

My goal was to have an amp that had a clear smooth sustain/OD with some of the blooming effect & nice harmonics with touch sensitivity. I feel like this amp does that reasonably well with just 3 tubes. I'm honestly surprised it turned out this good.


My personal opinion is the mosfet CF helps with the digital delay tone and perhaps makes it a smoother sounding amp? BTW, the amp is amazingly quiet at idle but quite loud for 3 watts or so.

With respect, 10thtx

[David Root]

I don't know much about MOSFETS except that they seem to be the closest solid state device to a tube tonewise, so I guess it should complement the rest of the circuit.

You've actually tweaked it the right way, with your ears. It's nice to have the numbers, and it can speed up the process, but the ultimate arbiter is still your ears.

[Cliff Schecht]

The idea behind the MOSFET source follower is to give you a completely transparent current boost to drive long cables without loss. It provides a low impedance output to drive high impedance inputs without any signal attenuation. It's literally a buffer and won't distort or really impact the audio at all.

The IRF820 is overkill for driving external effects, it's good for AMPS when all you need is a few mA in most situations. It's a vertical trench MOSFET that's designed for switching applications (i.e. it's optimized for linear region operation) but at the same time, it's a super linear source follower and if you have the room it never hurts to overrate components.. I've used them in a similar manner (just as a tonestack buffer, not an effects driver) and can say that they are transparent "tone" wise other than the effects that naturally happen when you swap out a high impedance source for a low one (better bandwidth, less distortion).

[10thTx]

I tried another version of this ............

The front end is more Marshallish topology but with different values and a Dumblish tone stack .......... going into a OD section.

I tried recording something that shows a contrast between the clean and the OD in the amp. The difference in the clean and the OD is simply I moved both the volume and OD drive from "5" to "6.5" and picked a little harder when I played. In other words, I find it to be fairly touch sensitive and it cleans up well when picked more lightly. There is not a DPDT switching between the clean and OD .......... the preamp & OD are connected with no switching.

http://www.soundclick.com/player/single ... i&newref=1

Another soundclip but to a backing track. Please excuse the glitch in the recording mixdown.

http://www.soundclick.com/player/single ... i&newref=1

With respect, 10thtx

[SoundPerf]

Sounds really nice. Cool slide work on the second clip.

I have the schematics of your other amps along with this one now and want to explore these builds sometime.