Secret of the big headroom?

[Leevi]

I have built several SE amps using 12AX7 and EL84.

One of my last projects was based on Bad Cat Mini schematic.

The sound of this amp differs from the others with its big headroom.
The amp is still very loud. What are the essential factors that make this possible?
For more information see the schematic:

http://www.freestompboxes.org/viewtopic.php?f=2&t=1756

/Leevi

[kagliostro]

Hi Leevi

which transformers did you used on it ?

have you find a layout or have some photo to share ?

Thanks

K

[Leevi]

Hi Kagliostro

PT: http://www.tube-town.net/ttstore/product_info.php/info/p527_Toroidal-50VA.html
OT: http://www.hammondmfg.com/jpeg/125DSE_B.jpg

I think I made some small changes in the tone stack.

/Leevi

[Leevi]

have some photo to share

/Leevi

[kagliostro]

Nice Cab and big magnet on that Speaker 

Thanks for the PT & OT data

No Amp Porn ? 

K

[echuta13]

I would think the tone-stack is dropping gain and giving some headroom there.  The slightly higher uf bypass cap on the output might help a bit.  The power supply is also very stiff.  Other than that, I would think a beefy output transformer (125DSE being  beefy), and the relatively efficient speaker would be factors.

Might be misreading the schematic, but it looks like the 220k resistor (from grid to ground) might be reining in the second triode as well.

[DummyLoad]

there is no path to ground for DC in the EL84's grid leak ckt. as shown in the schematic.

--pete

[stratele52]

IMO it is the circuit desing . Seems very original to me.

It is not the power transformer or output transformer wich are very basic.

[echuta13]

The Valve Junior or Champ have what I would consider a pretty basic output transformer rated @ around 50ma and weighing in around .75 lbs.  The DSE is rated for 70ma and weighs in around 2lbs. That's quite a difference IMO.

[jazbo8]

I don't think there is any secret... it is just a low gain amp, with nicely center-biased gain stages, and a well bypassed screen supply for the EL84. None of the stages breaks up easily thus the perceived big headroom.

Jaz

[DummyLoad]

very nice work leevi!

 

--pete

[stratele52]

The Valve Junior or Champ have what I would consider a pretty basic output transformer rated @ around 50ma and weighing in around .75 lbs.  The DSE is rated for 70ma and weighs in around 2lbs. That's quite a difference IMO.

Ok it is not a basic OT

[Leevi]

Thanks for your responses.
I think there is not any special trick but it's a sum of different solutions also mentioned in this thread.
E.g. the 220k ground resistor and 100k+2.2n cap on the EL84 grid
affect definitively.

/Leevi