Fryette Effects - SAS EF86 Overdrive

ppluis0 · Post by **ppluis0** » 14 Mar 2012, 02:28

WOW man...

What a nice solo...

Look forward to hear these same pre, plus your guitar, pick, and fingers, driving a 2555 amp

I´m agree with diagrammatiks about the assumption that the boostasio must be a close cousin of this unit. At least the supply, bypass, and tube sections does not differ too much of the same sections of the SAS unit, and will be easy to trace the internals of this booster.

Also I think that any little pentode can be employ to clone this unit, without the expense of buy a new or NOS EF86. Perhaps a NOS radio or TV pentode as 6AU6, 6BA6, 6CB6, or the like can sound closer (or perhaps better or worse... who knows ?) than a real EF86.

Why use a Hi-Fi tube to create a distorted sound, when a cheap one can sound the same ?

Cheers,
Jose

drbob1 · Post by **drbob1** » 14 Mar 2012, 03:43

I've heard it said that a rail to rail distortion on an op-amp isn't very good sounding, OTOH, rail to rail distortion from a tube generally does sound good (or at least pushing it into the non-linear ranges) and distortion from a non-linear pentode in general, will have more lower order harmonics than a triode. So the idea of using an EF86 is cool. Further, running a harsh clipping like a pair of diodes to ground, into a non-linear tube stage is generally going to even out some of the harshness (for example a D+ into a dimed Marshall). I respect what he's done here, although I'd love to hear the results of the EF86 pushed into cutoff without the clipping diodes... Not enough to canabilize the pedal, though.

Next step is to try it with my Watkins Westminster (same circuit as the Dominator) which is a very dark amp, I suspect the combo of clipping and brightness of the EF86 will be just the ticket!

drbob1 · Post by **drbob1** » 14 Mar 2012, 03:47

Oh yes, I think it'd be fair to think of the EF86 as V2 in this configuration, with V1 being the op-amp driver.

Also, if someone is interested, there are pentodes designed to run on 12-25v B+ from car radios (like the 12K5, of which I have a couple lying around). Might make for an easier build since you only need to rectify the AC power from a 12v adapter, not transform it)!

mat · Post by **mat** » 14 Mar 2012, 22:01

ppluis0 wrote:WOW man... What a nice solo...

Look forward to hear these same pre, plus your guitar, pick, and fingers, driving a 2555 amp

I´m agree with diagrammatiks about the assumption that the boostasio must be a close cousin of this unit. At least the supply, bypass, and tube sections does not differ too much of the same sections of the SAS unit, and will be easy to trace the internals of this booster.

Also I think that any little pentode can be employ to clone this unit, without the expense of buy a new or NOS EF86. Perhaps a NOS radio or TV pentode as 6AU6, 6BA6, 6CB6, or the like can sound closer (or perhaps better or worse... who knows ?) than a real EF86.

Why use a Hi-Fi tube to create a distorted sound, when a cheap one can sound the same ?

Cheers,
Jose

Thanks Jose for Your kind words, I think I'll build the pedal with switch to bypass the IC/diodes..
Unfortunately I don't have recording equipment where the amps are. Might try to record with the iPhone..

mat

ppluis0 · Post by **ppluis0** » 15 Mar 2012, 01:27

mat wrote:Unfortunately I don't have recording equipment where the amps are. Might try to record with the iPhone..

mat

I'm not in a hurry, so take your time to do a normal recording session.

It´s also a great chance to compare the previous set up with the new proposed combination of preamp and amplifier and judge both sounds, if both tracks are recorded in a similar manner.

Cheers,
Jose

mat · Post by **mat** » 15 Mar 2012, 21:55

The sound was superb ! Very much like the NAMM-video. Great harmonics and really joy to play. Only problem was terrible noise on the OD-channel (maybe due of the prototype layout of the 86-Special). The noise is acceptable when playing the 86S by itself but going into 86S and from pre out into 2555 guitar input the noise is crazy.

mat

mat · Post by **mat** » 24 Mar 2012, 13:10

Ok! I ordered parts for the build. The transformer specs are:
Pri: 230 V
Sec1: 200 V @ 0,015 A
Sec2: 6,3 V @ 0,6 A
Power: 7 VA

I will use full bridge rectifier. Could someone advice how to calculate the right resistor (Wattage/Resistance) to get 9V from the high voltage and how big fuse to use ?

Thanks,
mat

ppluis0 · Post by **ppluis0** » 27 Mar 2012, 02:12

Hi Mat,

Perhaps is a better solution to make a voltage doubler (you know: two diodes and two electrolytics) at the 6,3 volts secondary instead of obtain 9Vdc from the high voltage filters.

But also you can drop from the first filter cap using a series resistor of 27K rated at 4 watts adding a 9 volt zener in parallel of the pins 7 and 4 of the op amp, just to avoid overvoltages.

Be safe !!

Cheers,
Jose

mat · Post by **mat** » 27 Mar 2012, 14:16

Thanks Jose for the tip. I think I'll use the voltage doubler and 9V regulator. Any specs for the diodes and caps to use in this kind of schem (first pic): http://www.coolcircuit.com/circuit/voltage/index.html

Also how big fuse should I use ?

mat

ppluis0 wrote:Hi Mat,

Perhaps is a better solution to make a voltage doubler (you know: two diodes and two electrolytics) at the 6,3 volts secondary instead of obtain 9Vdc from the high voltage filters.

But also you can drop from the first filter cap using a series resistor of 27K rated at 4 watts adding a 9 volt zener in parallel of the pins 7 and 4 of the op amp, just to avoid overvoltages.

Be safe !!

Cheers,
Jose

ppluis0 · Post by **ppluis0** » 27 Mar 2012, 18:46

You need to put a fuse in the primary side to protect all the supply related components including the transformer. I guess that a slow fuse of 200 mA will be enough.

mat · Post by **mat** » 27 Mar 2012, 20:14

ppluis0 wrote:You need to put a fuse in the primary side to protect all the supply related components including the transformer. I guess that a slow fuse of 200 mA will be enough.

Ok, slow 200 mA it will be then. I think I have some 16V/1000uF caps and 1N4001 diodes for the voltage doubler. I will get the parts in few days and start the build. Picks and clips will follow when the pedal is ready.

Thanks for the advices,
mat

ppluis0 · Post by **ppluis0** » 27 Mar 2012, 22:20

Hey Mat !!!

You need to have high voltage to feed the tube. Four diodes and several RC sections with the values we seen in the schematic will do the job.

Also you need 9 Vdc to supply the op amp, and 6,3 Vdc or ac @ 200 mA to the heater of the EF86.

Bear in mind that the filament needs some reference to ground and can´t be left floating.

Please draw what you intend to build to obtain the low voltage supply sections to help you in this matter, if I can.

We need (I think) more tube based pedals in this forum, so go ahead with this clone !!!!

Cheers,
Jose

mat · Post by **mat** » 28 Mar 2012, 20:31

Hello again,

I was thinking that the 6.3V secondaries (not having a center tap) will need 2x100ohm to ground reference but how will it work if I take the IC's 9V supply from 6.3V taps trough voltage doubler and a 9V regulator? I'll try to draw something on paper.

mat

ppluis0 wrote:Hey Mat !!!

You need to have high voltage to feed the tube. Four diodes and several RC sections with the values we seen in the schematic will do the job.

Also you need 9 Vdc to supply the op amp, and 6,3 Vdc or ac @ 200 mA to the heater of the EF86.

Bear in mind that the filament needs some reference to ground and can´t be left floating.

Please draw what you intend to build to obtain the low voltage supply sections to help you in this matter, if I can.

We need (I think) more tube based pedals in this forum, so go ahead with this clone !!!!

Cheers,
Jose

mat · Post by **mat** » 28 Mar 2012, 20:57

http://mattitee.kuvat.fi/kuvat/6.3VACto ... idestart=0

mat · Post by **mat** » 28 Mar 2012, 21:00

mat wrote:http://mattitee.kuvat.fi/kuvat/6.3VACto ... idestart=0

Forgot the 100R's from the heater taps to ground from the picture..

mat

ppluis0 · Post by **ppluis0** » 29 Mar 2012, 19:21

Hi Mat,

I think that´s better to implement the voltage doubler named Cascade, that appear in second place in the link you prevoiusly posted: http://www.coolcircuit.com/circuit/voltage/index.html

The reason is that the lower wire is the same ground for the start of the transformer secondary that is connected to GND. At the same time you wiil have one side of the heater voltage referred to ground wich sometimes is enough to avoid hum.

BTW the secondaries of the transformer you ordered are effectively wired in series ? or there are several isolated windings ?

Cheers,
Jose

mat · Post by **mat** » 30 Mar 2012, 07:26

Just got the parts for the pedal

The trafos secondary windings are independent isolated ones. The HV measures 530ohm and the heater winding about 1.2ohm. They are not connected to each other (no readings between the HV and heater windings).

I'll start to build the pedal on next monday.

Thanks for the tip of the voltage doubler !

mat

mat · Post by **mat** » 01 Apr 2012, 21:08

Hi Jose,

I was thinking of putting just a bridge rectifier (with 1000uF cap from rectifiers + to ground) connected to 6.3V taps to get 8.9V for the IC. Should I put a small ohm resistor in series of the bridge to the IC and another smaller value cap to ground just before the IC ? What do You think of this option ?

Part layout planning on the chassis: http://mattitee.kuvat.fi/kuvat/IMG_0555.jpg

Thanks,
mat

mat · Post by **mat** » 01 Apr 2012, 21:38

Here is the planned power section: http://mattitee.kuvat.fi/kuvat/sasPWR.png Any comments ?

Thanks,
mat

ppluis0 · Post by **ppluis0** » 02 Apr 2012, 02:31

Hi Mat,

I think that you can replace the 1 ohm resistor to another one of 56 or 68 ohms rated at 1/4 watt, and increase the size of the 47uF cap, maybe, to another 1000uF in order to have low ripple.

Considering that a single TL071 draws only 2.5 mA from the supply, the 56 or 68 ohm resistor of the RC cell result in almost 7.2 Vdc to feed this IC. In the datasheets I can`t find what is the lowest value reccommended to make this IC work reliably.

Perhaps any forum member can tell us about how to supply a TL0xx family chip.

Cheers,
Jose

Fryette Effects - SAS EF86 Overdrive [traced]