ENGL e530 build help/advice

[Bill_Nephew]

I am in the planning stages of building the rare gem that is the ENGL e530. As I looked over the schematic, there were a couple of questions that came to mind:

http://www.freeinfosociety.com/elect.../Engl_E530.pdf

1) In the input stage, besides the resistors that are specifically labeled for a certain wattage, what should I use? Carbon film or metal film? and how many watts? 1/4 or 1/2?

2)As for the tubes themselves, I have read that the ecc83 is the european equivalent to the 12ax7. So, that means I can use 12ax7 tubes, i assume. As for the brand, which one would you guys recommend? I have heard great things about JJ tubes, but this is my first experience w/ tubes other than my Crate TubeDriver 70 combo.

3) In the power supply section, I noticed that the voltage I need the primary x-former voltage to be is included, but the VA rating is not listed. Are there any calculations I can refer to so I know what transformer to buy for this?

[Chuck H]

1) In the input stage, besides the resistors that are specifically labeled for a certain wattage, what should I use? Carbon film or metal film? and how many watts? 1/4 or 1/2?

It's not as important as you might think. I use metal film 1/2 watt. I don't know what Engl uses.

2)As for the tubes themselves, I have read that the ecc83 is the european equivalent to the 12ax7. So, that means I can use 12ax7 tubes, i assume. As for the brand, which one would you guys recommend? I have heard great things about JJ tubes

My experience with the JJ's is that they sound fine. not amazing and are sometimes noisy. I like the Sovtek LPS but they're expensive and too prone to microphonics to be used as first gain stages. The first gain stage is important because the tube needs to meet all criteria. It needs to sound good, be quiet and non microphonic. I have my best luck with NOS for this most often.

3) In the power supply section, I noticed that the voltage I need the primary x-former voltage to be is included, but the VA rating is not listed. Are there any calculations I can refer to so I know what transformer to buy for this?

Not being an EE I've always gone with specs I find for similar amps and then adjust accordingly, though roughly, up or down depending on specifics. I havent had any problems. Figuring roughly you need to have secondary current ratings that will exceed whatever the maximum current draw will be. For example, this preamp has two 12ax7 type tubes. Each filament will draw .3 amps of current. So you need .6 amps + safety margin for the 6.3V PT secondary. The more over rated you go with the secondaries the cooler the PT will run. Not as much a consideration with a preamp but closely rated PT's can also contribute to "sag" which is considered partly responsible for the attack envelope in some amps. This preamp uses a generous amount of transistors so I would say over rate by at least 30% on mA secondary rating to guarantee the regulated voltages don't fall below spec at any time.

[Bill_Nephew]

What would you say would be the maximum secondary voltage needed? I found this transformer that outputs 6.3vAC at 3A. That might be overkill, but would it guarantee a cool running transformer that doesn't pose a safety hazard? It was the only transformer I could find on mouser with the primary and secondary voltages i needed.

[Chuck H]

Well since there are no voltages spec'd for the transformer, and I'm not schooled in transistors, I can only say that for the HV on the preamp tubes typical for a preamp only unit would be 200V to 300V secondary. The Engl PT has four secondaries. A more common way of doing it would be to have a PT with a 6.3V filament, B+ HV secondary and a 50V bias supply secondary. Then you would need to design regulators peripheral to those secondaries suitable for your transistors. The transistor specs should clue you in as to the voltages you need to achieve and peripheral regulated supply designs are multiple and varied. Unless you know how to design this you'll need a Engl PT for this project. Otherwise you would need the exact voltages for the schem and three or four seperate transformers.

[exclamationmark]

Apparently ENGL are notorious for not providing the right schematics (ie, missing components and wrong values) and it's quite evident from the 47nf coupling caps and 22uf bypass caps this is the case. A pre-amp design using these values would suffer from horrible blocking distortion, making the thing basically sound like a fart machine. I seem to remember something about the ENGL powerball missing smaller coupling capacitors in series with the 47nf's in the schematics, and I'd assume this would be the case in the e530.

[JacksonRR]

Yeah I had ENGL send me by e-mail a scheme of the E625 Fireball, and it was not correct. A buddy of mine who's better than I am at looking at what's happening in a scheme told me there were way too many things wrong with it and it would sound horrible. He suggested I just lay it to rest until I can either buy one or find someone who has had direct experience with them. Internet searches will bring up more horror stories than success rates on ENGL builds.

[Bill_Nephew]

Should I abandon this one then?

If the schematic is incorrect, is there any other preamp out there that has that good of a high gain tone to it that uses only 2 tubes? Does marshall normally have good schematics?

[exclamationmark]

I don't know of any pre-amps that come close to the e530 in the gain department with only 2 tubes. There's the JMP-1 by Marshall but you might find it a bit hard to build due to the massive amount of midi channel switching crap in there. Similarly there is the ADA MP-1 (don't know about the schematics for this one) but I always thought it sounded like ass, haha. It too has lots of midi channel wizardry going on inside.

If we go up to 4 tubes, there's the Peavey Rockmaster (awesome sounding pre), reasonably complicated to build though, and then there's the SP-77, basically the pre-amp taken out of a SLO100 stuffed into a rack. Alternatively if you go over to the SLOclone forums or search Google hard enough I believe there are correct schematics for some ENGL amps that use only 2 tubes for the pre-amp section. You would just basically 'chop' the pre-amp section off before the phase-inverter section (unless they use some funky topologies).

Personally, if I were going through the effort of building something into a 19" rack, the most expensive part of the build (unless cannibalized), the extra cost of a couple valves, sockets, resistors and caps wouldn't bother me. Would likely end up costing an extra <$30, unless you have other restrictions.

[Bill_Nephew]

I might have found it...

Mesa Mark IIc+ Preamp : DIY Fever – Building my own guitars, amps and pedals

Since I am a petrucci fan, I think I should build this instead of the engl. Also, I could probably build this preamp into a lightweight head that can be used with the effects return of any amp I please. On top of that, it is a rather stripped down version of the actual preamp which leaves a lot of room for me to stick in any other features i want, (i.e. a 10 band equalizer or a noisegate) and even includes the parts list to go with it. I am probably going to have to modify the power supply section so I can use U.S. mains voltages with it, but that should not be too difficult. On top of that, the power supply doesn't require an ungodly amount of transformer secondaries. That is definitely a headache reliever to begin with. I also have a couple of large perfboard pieces I can use to build the circuitry on. 3 tubes is not bad either.

[JacksonRR]

=) =) =) POWERBALL! It's from the SloClone forums and has been built and verified as correct! Merry Christmas to all. I am going to also see what I can do with it as far as modding a Laney GH50L towards this design. I bought that amp for $150 and it just sits now that it's functional.



edit: Lead channel only with switching for high/low modes and bottom switch. Should, at least, be a good start with the high gain sound. I'm pretty sure you're not really bothered by having to cook up your own clean channel.

[JacksonRR]

I think the guys at the sloclone forum have been tackling the ENGL schemes for a bit now. They have the complete P-Ball, Fireball and E530 schemes up, tested and debugged.

[Hilli]

Hi,
this should be the original schematic. I have build the e530 as preamp and as 100W amp, they works fine.