I need a council, I'm looking for a very very clean 15-20W amp schematic

[kagliostro]

I'm looking for a very very clean amp in the range of 15W - 20W


better if is a simple amp with layout documentation (a Fender ??)


Many Thanks


K

[DummyLoad]

fender AB763 deluxe. build one channel


--pete

[tubenit]

I agree with Pete.

I'd build the normal channel only with only two gain stages into the LTPI & have reverb and vibrato.

http://el34world.com/charts/Schematics/files/fender/Fender_deluxe_reverb_aa763_schem.pdf

You can use a 12AY7 for V1 and a 12AT7 for the LTPI.

With respect, Tubenit

[Ed_Chambley]

You could build a 6v6 Standel.  If you do not have to have tubes these are very clean and nice.  Maybe find a JBL 10" or 12".

Deluxe is good too, but I don't consider them "clean" amps for some reason.

http://jazzamp.com/product/combos/jazzamp-112/

[MakerDP]

Check out the "Core Building Blocks" projects at AX84.com.

Look at the Clean Preamp and the 20W Push Pull Poweramp. Schematics, layouts, chassis drill plans... all there.

http://ax84.com/buildingblocks.html

I built the Core Simple Preamp with the Core 20W Push Pull (basically a normal-channel-only AB763) using Edcor iron and I am VERY VERY happy with it. It's my stage amp right now for my blues band. It gets pretty clean but can also get pretty mean if you want it to, especially after I added Merlin's LTPI "Scale Control" to it.

[jjasilli]

Ditto to Dummyload, or a Princeton.

[topbrent]

It depends what flavor of clean you prefer to hear.  Some like pristine cleans, others like voxy chime, some like a little hair on the note, ect. 
I am in the camp that prefer to hear the world through Fender blackface/silverface ears...

Super clean, almost break up resistant?  Blackface/Silverface Princeton- non reverb.  AA964


Slightly less clean, but still super clean?  Single channel AB763 non reverb, (w/appropriately placed channel simulation 220k signal dumps. )
- Sluckey has a nice layout.

[Leevi]

Gibson GA50, remove microphone channel i.e. one tube less


http://el34world.com/charts/Schematics/files/gibson/Gibson_GA-50.pdf


Leevi

[kagliostro]

Many thanks Fiends

all the proposal are very interesting, some really intriguing, like a Standel with 6v6, but I think to it like a project that is to be build and refine (improved)

not a build and drive

when I posted the question, in my ignorance as player, I was thinking to a Princeton so ...

AB763 vs AA964 which one you consider more clean ? The AA964 as Topbrent prefers ?

Thanks

Franco

p.s.: Pete, the Standel named by Ed_Chambley remembered me a thing, did you drew a sketch of layout for your good clean fun ... ?
if you have a pencil one I would like to try to draw it using Visio (as now I'm a bit more confident with it) Thanks

[DummyLoad]

p.s.: Pete, the Standel named by Ed_Chambley remembered me a thing, did you drew a sketch of layout for your good clean fun ... ?if you have a pencil one I would like to try to draw it using Visio

sorry franco, i don't have anything yet, not even on paper. i lost interest in the project and shelved it.

--pete

[kagliostro]

OK Pete, anyway thanks

but that is a thing that I want to do one day or one other

Franco

[Ritchie200]

Franco,


What about something completely different like a big tube single ended using a KT120 or KT150 with some voltage.   Loads of headroom with sweet breakup if you ever do drive it hard.  You could put whatever front end you wanted on it?


Jim

[kagliostro]

Ciao Jim

the guy who is interested on this thing now uses a PSE with 2 x 6L6GC as power section and the AX84 clean as preamp

now seems he is interested to the Standel 25L15 (also if I'm pushing for the AB763 or AA964)

As I haven't reached a good know how about the real circuit of the 25L15 preamp my proposal is to use the preamp of the good clean fun ...

by DummyLoad and the Williamson power section (may be with 2x 807/1625 or 2 x 6L6GC)

http://el34world.com/Forum/index.php?action=dlattach;topic=17282.0;attach=44133

Franco

[VMS]

Hi Franco,

I throw one more power section to think about (last page on the datasheet):

http://frank.pocnet.net/sheets/127/5/5881.pdf


-v

[kagliostro]

Thanks VMS

but I'm not a great fan of UL configuration

Franco

[MakerDP]

Ciao Jim

the guy who is interested on this thing now uses a PSE with 2 x 6L6GC as power section and the AX84 clean as preamp

I'm just curious... why doesn't he like this setup? Not clean enough for him or just wants to try something different (G.A.S.?) That preamp with a nice Push-Pull power section should have lots of headroom.

[kagliostro]

He says it isn't clean enough 


K

[MakerDP]

Wow ok. Maybe the PI and/or the power amp is being driven too hard? Or even the speaker for that matter. I can't imagine a 6L6 with a conservative-gain design preamp like that one not being able to get "clean enough."

[HotBluePlates]

the guy who is interested on this thing now uses a PSE with 2 x 6L6GC as power section and the AX84 clean as preamp

He says it isn't clean enough 

Wow ok. ... I can't imagine a 6L6 with a conservative-gain design preamp like that one not being able to get "clean enough."

A 25L15 is a very clean amp. Fender clean sounds fuzzy to me after I built the Standel.

But notice something important about the AX84 Clean Preamp... It has all the low-gain, high-input tubes but keeps the tone controls at the end of the preamp, like a 5F6-A or Marshall amp. The 100L15 schematic posted shows a T-filter between the 1st and 2nd gain stages (which will cut mids) and has a feedback loop around the tone controls which reduces the gain of V2a (and the size of the signal into V3a.

So there is 1 gain stage with higher gain than used in the AX84 preamp, but the Standel has 2 places where tone circuit reduce gain. I don't know what kind of cathode voltages the AX84 clean preamp has, but I suspect it doesn't get as high as 3v for a 12AT7 stage or 7v for a 12AU7 stage. Those large bias voltages (taken with the small plate loads, especially at the phase inverter) keep things clean throughout.

[kagliostro]

but keeps the tone controls at the end of the preamp

Yes, I see, that is really an important thing HotBluePlates

Thanks for pointing that out

that way the first triode can push the second, instead, if the TS was placed between the first gain stage and the second, all will be different

All this remembered me this amp that is declared to be a good clean



---

I tried to collect all the info I've found in the net about the 25L15 and derivated amps and put it in a puzzle schematic

but I doubt I can arrive to something concrete without any help



Lot of doubt about preamp section and also PS, PT and OT

(at this purpose, which will be a correct primary impedance for the OT to be used here ?)

Many thanks

Franco

[HotBluePlates]

Before going much further, you may need to ask your friend something about the power of the parallel-SE amp you built him. Does he need more power (more volume) than that amp, or is he only looking for less distortion (at the same or similar volume)?

If the overall power level is okay, you don't need to build an entirely-new amp. You could just modify what is delivered to the 6L6 output stage (by changing the preamp).


One potential pitfall of both the Double Six and the Standel Puzzle you've assembled is the Bridged-T filter. On the Double Six, this is between V1b and the output tubes and is made of R15, R16, C13, C14 and the Middle control (usually a fixed resistor when the bridged-T is used in, say, Gibson amps).

The Bridged-T filter imposes a set mid-range cut, somewhat like fixed settings of a Fender blackface tone stack. The Middle control in the Double Six will vary how deep the midrange cut is, though it may not eliminate it entirely (I'd have to build or simulate the circuit to know for sure). If it's designed well, that mid cut is right between the Treble and Bass ranges of the James tone circuit between V1a and V1b.

Just something to keep in mind.
The Double Six has only 2 gain stages, with 2 stages of tone control (cutting). That seems like a formula for clean, though I haven't built or heard the circuit.

I don't know if it is similar enough to the existing parallel SE amp you built to just be a matter of dropping in this preamp circuit to try. That looks like an easier path than building the Standel (a push-pull amp with new-everything). Which is why I asked about your friend's perception of whether the overall power in his amp is enough (allowing a preamp change).

[kagliostro]

Thanks HotBluePlates

I'll ask to my friend to clarify if is a question of power or distortion

as I've understand him till now, is a question of distortion, but he insists on using his Gibson Less Paul ......

The amp he is using was built by him, not me, the schematic of the pre is this

http://www.ax84.com/static/corepreamps/Clean/AX84_Clean_Preamp_Schematic.pdf

and the power section on which is based the power amp (that as told uses a pair of 6L6GC) is this

http://www.ax84.com/static/corepoweramps/20W_SE/AX84_20W_SE_Poweramp_Schematic.pdf

After I've an answer about what he really needs/wants, I'll be back here to report it

Thanks

Franco

p.s.: for better or for worse this are a pair of samples I've found about the DoubleSix


http://www.youtube.com/watch?v=x0h7Bj2ly4c

http://www.youtube.com/watch?v=K1jFyDhik9c

[MakerDP]

Just another suggestion to think about...

I don't think his "problem" is with the preamp. It sounds to me like there is just not enough power from that 20W SE power amp to stay clean at the volume levels he needs. I've been thinking about this a bit and I bet he's not going to be happy with the clean headroom of much of anything unless he gets into a 50W or more power section.

Maybe keep that AX84 preamp and go with a more beefy power amp. If his amp was built strictly to the AX84 layouts then the preamp, power amp and power supply should be on three separate turret boards. If so, it would be relatively easy to modify -not change out altogether- the existing power amp and power supply boards to the 50W push pull design from AX84, drill an extra hole for another octal, replace the PT & OT, and drop it into the chassis. That should give him lots of room to have loud clean tone and be much cheaper/faster than building a whole new amp. That's the cool thing about the AX84 core projects... you can mix and match trying different combinations to find the one that works without having to build a whole new amplifier.

Well, the power amp board will probably need to be replaced not modified if he went from SE to PP now that I think about it. But still, a WHOLE lot less work and money.

[HotBluePlates]

the guy who is interested on this thing now uses a PSE with 2 x 6L6GC as power section and the AX84 clean as preamp

Do you know the supply voltages for the clean preamp, and the bias voltage of the output tubes? We can do a quick analysis of the existing amp and see whether it might not be as clean as it could be. Or maybe figure out your friend really does need a bigger output section.

EDIT: Nevermind... I'll use the power amp schematic you linked, and assume he got the same supply voltages listed.

[MakerDP]

Browsing old threads about the AX84 Clean Preamp I found one by the creator of the circuit where he said it was not well-suited to drive a single-ended amp... not enough output to drive it effectively... much better results with a push-pull amp... but he intended to address that in the future. Not sure if it was ever addressed.

Food for thought.

[kagliostro]

Thanks HotBluePlates & MakerDP

not enough output to drive it effectively... much better results with a push-pull amp

not enough output didn't seems a reason for the amp to don't stay clean

Franco

[Mike_J]

I constructed a tweed Deluxe.  It had some hum so I decided to try modifying the power supply.  Placed a 32uF cap on the HT, then added a choke and one or two more electrolytics and upgraded the OT to one Mark at Magnetic Components said had more bandwidth and beef.  Anyway,  the amp is very clean and quiet up to a fairly loud level, for a 12 watt amp.  I need to use pedals to get distortion but it handles them well.  Has a Jensen reissue P12Q and sounds a lot like a 5f6a Bassman played at pre-breakup volumes.

This amp is not what I originally wanted to build but is a lot of fun to play.

Thanks
Mike

[kagliostro]

Thanks for sharing your experience Mike

Seems that the interest is to try the Double Six and the Standel circuit

at the moment components for the Double Six were ordered

Franco

[drgonzonm]

K,
whats your budget? what is your application?. what speakers are you planning to use? 

What I am thinking is an ultralinear audiophile conversion to an instrument amp. 

Crowhurst, RCA and others have some decent audiophile amps that can be converted. 
 

[kagliostro]

What I am thinking is an ultralinear audiophile conversion to an instrument amp

That has a sense and is a good idea, but my friend decided for the Double Six amp and ordered the parts, I don't know if he want to modify his AX84 amp or want to build a new one, because at the moment he is out of Italy

from my part I was intrigued by the Standel Amp and at the moment I'm in contact with a guy that can help me

only I can't reveal any thing about

Franco

[drgonzonm]

It is my understanding that Fender did make a UL amp, mid 70's in the twin lineup.  power at 70 or 135 per a quick web search. 

[kagliostro]

Well, my friend returned in Italy and we can go on

1° He ordered the material for a Double Six, but it is to be used for a new amp not to modify the existing one

2° He would like to trim the amp he is using as to have less distortion
(the AX84 clean preamp + AX84 20W SE poweramp modified in PSE with 2 x 6L6GC that uses an homebuild 4630ohm OT)

The schematic of the preamp is this



and this is the schematic on which is based the power section



The undesired distortion appears with the volume control at half way and increases increasing the volume

Ive think to insert a gain control between V1 and V2 (V7 and V6 in the schematic) maintaining the 470k leak resistor

What do you think ? Have you concil as to tame the undesired distortion and reach a clean sound ?

Thanks

Franco

[kagliostro]

I forgot to add that the problem of distortion is more present (as can be imagined) when a Les Paul is used, less whit a Fender


K

[MakerDP]

The fact that it gets "worse" as the master volume increases in my mind means you are getting all the overdrive from the power amp.

Is the homebuilt OT not up to the task? Has he tried more efficient speakers? Has he tried using a 2x12 or 4x12 cabinet to get more volume without pushing the power amp too hard? Tried colder biasing on the 6L6's?

If it were me, I'd reconfigure the amp to a push-pull design with negative feedback. It could be done without adding a tube. Use a MOSFET for the cathode follower and the now extra triode for the phase inverter. Of course, it would need a new OT.

[SILVERGUN]

In the preamp, I would get rid of the Sparkle/Grit control, and just center bias that 12AU7 triode with a 2.2K without a bypass cap.
On the Clean / Blues switch I'd raise the value of the 680R (clean side of the switch)  to 1K or higher.(for humbuckers)

In the power amp, I'd change the Master Vol. to 500KA and adjust the VR1(s) down to 120R so that the combined cath. resistance is around 220R for each 6L6.

I would think those steps would clean it up some.

 

[kagliostro]

Thanks MakerDP & SILVERGUN

@ MakerDP

I don't know if he can use other type of speakers, however I'll say him to give a try to something elese if possible

@ SILVERGUN

interesting, this thing will be tried as soon as possible

Thanks

Franco