EF86 Modern Classic tones

[AleS]

Hello everyone, long time lurker, new joiner - first post here

I've been toying with the idea of building my own for a while and getting very close to pulling the trigger now. I'm keen to go down the full DIY route rather than kits as there is plenty of layouts and resources on here for me to be able to put together something that should fit my needs.

One design that caught my eye is the Modern Classic with the EF86 on the Normal channel as per this thread: viewtopic.php?t=25606

As a lover of Vox tones as well as retro Marshall I'm hoping that might bring a touch of that character and, more generally, simply provide a fairly different sounding pair of channels. I'd probably look to go TMB rather than trem on the second channel.

My question here is, how different would the EF channel be compared to the 12AX7 TMB one?

And lastly, am I looking at biting on a little more than I maybe can chew for my first project and should perhaps look at a lite IIb/superlite TMB?

Thanks a lot in advance!
Alex

[JMPGuitars]

Hi Alex, welcome to the site!

The current design of the EF86 Modern Classis has the classic EF86 Lite circuit as the first channel. There are a ton of demos of that on youtube, or the Hear It! section of this website.

Personally, I prefer the newer EF86 circuit version I designed in the EF86 Xtra. I will eventually make a Modern Classic with that version of the EF86 channel, and a 2nd version with the TMB. Not sure how soon that will happen though.

You can mix and match the channels from any of the modern classics without too much trouble if you know how to read a schematic.

All that said, I highly recommend the latest docs version of the Superlite TMB as your first build here. It's a wonderful amp, and by the time you're ready to build the next one, I might have new docs ready. Maybe.

If you're relatively new to amp building, or want to brush up on your skills, I highly recommend you review the soldering and grounding threads in my signature.

Thanks,
Josh

[AleS]

Thanks for the reply! I had seen the EF86 Xtra but looking for a low gain base amp, so the more the headroom, the better, and seen as it's described as HIGH GAIN (in caps!), I'm inclined to look elsewhere. The Marshall (and Vox to be fair, since there is a touch of overlap here to a point) tones I love aren't the rock'n'roll, higher gain ones, but rather the beautiful cleans, edge-of-breakup and light crunch valve goodness that comes before that, so my thinking follows the idea that maximising that range would be optimal for me.

I've been looking at the Sluckey Dual Lite as a way of putting together an amp with a couple of flavour but nonetheless a tried and tested project with a low BoM: https://sluckeyamps.com/dual_lite/dual_lite.pdf

I'd probably have Hi and Lo inputs for both channels, as this should give choices in terms of headroom/gainyness and give the opportunity to play with jumping.

With regard to the EF86 channel - the Matchless style tone control (which is effectively a high pass through different coupling caps) looks great to me, as cutting low end should go a long way to lower saturation by removing low end frequencies and help achieve some of the chimey, sparkly, September Gurl-esque edge-of-breakup cleans I enjoy. I was looking at this great diagram from the downloads section to establish the values: storage/EF86.gif - I'll be looking to stay into trad Vox or stray into Matchless territory but was wondering, how do these values affect gain and headroom? Would I be right in thinking Rp and Rk would be the likely suspects I should look at for tweaking that?

As per the 12AX7 side - the Trinity SIII seems a well regarded, cleaner amp and I was looking at that: https://www.trinityamps.com/wp-content/ ... ic-v12.pdf - once again a question about headroom to help me understand the process: what is it in this circuit that makes it a bit cleaner? As per the EF86 circuit, should I look at those here marked as R4 and R5? On top of that, a very simple modification I can see, which wouldn't add much complication, could be having dual single and parallel inputs - since I'd only use the classic Trem channel tone control I wouldn't be using the second half of V1 for the tone stack.

Last couple of questions if I may - some schems have a resistor in series with all inputs, ranging from 10k to 33k - how do these affect the tone and design of the amp?

Also, going through a DC30 schem comparing preamps, I ended up following the path all the way to the power section and saw it features a push/pull on/off master volume, which could be a great and potentially simple add on. This is the schematic: https://www.thetubestore.com/lib/thetub ... ematic.pdf - Now, looking at this, would I be correct in thinking that I could add a MV to the Sluckey Dual Mini by wiring a 1M pot with lugs 1 and 2 connecting to the 0.005uF and 470K and lug 3 to the Cut pot and the other 470K R?

Hope all this makes sense! I'm hoping to mock up a schematic tomorrow, which should hopefully add a slight new variant of flavour of 18 watter, if a slightly bastard one!

[JMPGuitars]

Thanks for the reply! I had seen the EF86 Xtra but looking for a low gain base amp, so the more the headroom, the better, and seen as it's described as HIGH GAIN (in caps!), I'm inclined to look elsewhere. The Marshall (and Vox to be fair, since there is a touch of overlap here to a point) tones I love aren't the rock'n'roll, higher gain ones, but rather the beautiful cleans, edge-of-breakup and light crunch valve goodness that comes before that, so my thinking follows the idea that maximising that range would be optimal for me.

I wasn't suggesting you build the EF86 Xtra. The high gain aspect of it is that there's an additional gain stage after the EF86, before the PI. My suggestion was to change the EF86 section for better sound, not to add a gain stage. (Side note re: EF86 Xtra- with the 2nd gain knob off, you can get low gain also. Still not recommending it for you though.)

Any amp version, from this website or others, can be tweaked for headroom. However, if headroom is your only real concern, you should consider building higher wattage. A 36W build will give you more headroom regardless of the circuit you choose.

You'd want to look at optimizing your B+ for the response you're looking for. A lot of your questions / circuit comparisons are related to the preamp, and you can do a lot there, but the magic of the 18W stuff is in the power amp. Typical B+ target is 345VDC +/- 5V. Lower B+ will give less headroom, higher B+ will give more headroom. There's a balance between headroom and overdrive, and crunch vs. mud depending on how far you go.

Thanks,
Josh

[AleS]

Thanks for yet another quick and helpful response Josh! Much appreciated.

I wasn't suggesting you build the EF86 Xtra. The high gain aspect of it is that there's an additional gain stage after the EF86, before the PI. My suggestion was to change the EF86 section for better sound, not to add a gain stage. (Side note re: EF86 Xtra- with the 2nd gain knob off, you can get low gain also. Still not recommending it for you though.)

Apologies, my misunderstanding, and that makes a lot of sense

Any amp version, from this website or others, can be tweaked for headroom. However, if headroom is your only real concern, you should consider building higher wattage. A 36W build will give you more headroom regardless of the circuit you choose.

An important bit of information I somehow forgot to mention is that this would mostly be a studio amp, used for recording and often used through a dummy load and into IRs for quieter practice/songwriting, so overall volume is not a huge issue per se

You'd want to look at optimizing your B+ for the response you're looking for. A lot of your questions / circuit comparisons are related to the preamp, and you can do a lot there, but the magic of the 18W stuff is in the power amp. Typical B+ target is 345VDC +/- 5V. Lower B+ will give less headroom, higher B+ will give more headroom. There's a balance between headroom and overdrive, and crunch vs. mud depending on how far you go.

Absolutely - having read your article (which is linked in your signature) about issues with modern voltages from power supplies I think I might hedge my bets and stick to stock for now as it looks as thought I might already get to hit a little higher than 345 with a tube rectifier. I can then use that as a starting point. The power amp saturation and it's effect on the overall tone is another reason why the MV option is temping to me - though it might not be something I end up necessarily using often it might just be a great way to learn more about the power valves' behaviour, tone etc

Thank you very much for taking the time to share your experience!

[JMPGuitars]

An important bit of information I somehow forgot to mention is that this would mostly be a studio amp, used for recording and often used through a dummy load and into IRs for quieter practice/songwriting, so overall volume is not a huge issue per se

If you're building a studio amp, then headroom is useless for you. More headroom means you need to crank the amp LOUDER to get the good tones you want. That's the opposite of a good studio amp. You want to have a small range of clean tones, then a decent range of dirt without making your ears bleed. Dummy loads are okay, but having a good speaker option is obviously important too. In your case, I might consider using an attenuator with a line out and speaker motor built in (that's what I use when I don't want to hear a loud speaker).

I think your idea to build the 18W stock(ish) is a good idea to start with. If you want a TMB (and you're okay with a single channel amp), I'd look at the Superlite TMB, as that's a fantastic sounding amp with great distortion in both the preamp and power amp, and it's a fairly simple build on the grand scheme of things.

Another important point... You can crank a well built 18W amp into dirty dirty dirt, and roll off the guitar volume (or lighten pick attack) for excellent shimmery clean tones. Here's an example with the older style EF86 preamp: https://youtu.be/dj0RL4XVv6A - keep watching for a minute, and you can see/hear after he turns down the guitar volume knob.

[AleS]

Following up quickly after mocking up a schematic (attached), made by botching together Steve Luckey's original Dual Lite schem and a few more from the Downloads forum as per below:

Dual Lite - the heart, core and starting point of this design: https://sluckeyamps.com/dual_lite/dual_lite.pdf

The EF86 values chart (from a comprehensive EF86 post by zaphod_phil): storage/EF86.gif

Trinity Amp's SIII TMB V1a circuit (for -hopefully- a slightly cleaner flavour of 12AX7 18w): https://www.trinityamps.com/wp-content/ ... ic-v12.pdf

Josh's 18watt Lite IIb - borrowing the single + parallel inputs design to add the possibility of a higher gain flavour of 12AX7: storage/18wattLite2b.gif

Curious to hear if the design looks cohesive and sensical to better trained eyes than mine!

[AleS]

You want to have a small range of clean tones, then a decent range of dirt without making your ears bleed.

I guess that's where my needs differ from those of many Marshall users - I'd rather optimise the range to have better control dialling clean to low gain tones as I wouldn't be using anything past what many hard rock players would call "midium-low gain"
Bue of course as you say, that's no deal breaker - ultimately those cleans are there regarding how much total gain is on tap and indeed using the guitar's volume or even underboosting can clean up these amps beautifully!

In therms of cabs I'd be plugging this into an open back 2x12" with Greenbacks when needing to hear it, which should still be plenty loud to use in a practice room just past that controllable edge of breakup if need be. Or of course I can bring in the heavy artillery and crank the old AC30, then I sure won't run out of volume

[JMPGuitars]

I don't have time to review your schematic right now (maybe somebody else will) but I'll say your target voltage at A is too low. That's the first B+ measurement point (DC voltage coming from the rectifier), and 325VDC is going to be in the muddy range, with less headroom. Look at the Downloads section for one of my voltage charts for better targets. 345VDC should be your minimum, especially with you still thinking you want more headroom.

[AleS]

I don't have time to review your schematic right now (maybe somebody else will) but I'll say your target voltage at A is too low. That's the first B+ measurement point (DC voltage coming from the rectifier), and 325VDC is going to be in the muddy range, with less headroom. Look at the Downloads section for one of my voltage charts for better targets. 345VDC should be your minimum, especially with you still thinking you want more headroom.

I WILL get my headroom! *evil laugh*

Jokes aside, thanks again for the valuable pointers and being one step ahead - the power section is maintained from Sluckey’s schem and you’re right, looking low and probably down to the fact his original project revolved around repurposing an old Hammond transformer from an old amp if I’m not mistaken.

Having said that, the power section of the Lite IIb is probably what I’d look for, the A voltage of 360 looking reassuringly above 345 Evening here in the UK but will look at piecing together a v2 schematic tomorrow.

[AleS]

Didn't get much time yesterday for anything but realising that, having put together chunks of other schems, the power section I'd drawn up didn't make sense and things did not add up, which sent me down a rabbit hole of comparisons for voltages on different designs that resulted in no decision being made. One for the weekend I suspect

For the above reasons I removed the previous mock up schematic for posterity - should anyone land on this thread they won't be faced with an incongruous design which might be a curveball rather than an inspiration/idea.

[AleS]

Another day of reading up, comparing schematics and learning for me.

Lowering the grid leak resistors from 470k to 220k in Vox/Matchless style seems another good way to get a little more headroom and is probably something I'll explore.

Then again, the fettler in me is wondering... Would it not be a great mod to have 220k grid leak Rs and wire a dual gang 250k pot in series as VR to go from Vox to Marshall value and anything in between? Or would it just end up being a fairly tame secondary gain control that isn't neither here not there? Or would a Matchless style 1M VR MV in parallel do effectively the same job?

[JMPGuitars]

I have a mod I call the "stupid simple master volume" that does essentially what you're talking about. I connected a 1M pot to the 470K resistors like this:

Stupid Simple Master Volume.jpg

That will accomplish what you're asking about. It does work as a master volume / headroom tweak, depending on how much you turn it. I built it in 1 amp, it worked fine, but there was nothing exciting about it enough for me to repeat it. The cool thing is that you can install it, and decide if you like it or not and keep or remove it without making any tedious changes to the circuit.

Experiment for yourself. You might find that you like it in only a specific position, then you can measure the resistance to ground and replace the 470ks if you want to.

[Bieworm]

I experimented with this stupid MV a week ago, in preparation for a client’s demand. It works fine… although you loose that magic twinkle in the overtones a little. But it serves well enough

[AleS]

Thanks both for your input and expertise! I've seen that MV often implemented as either a or a click to turn push pull on/off pot, which should mean the original character can still be there. As Josh mentions, it's such an easy add on that I recon I'd just have it there to begin with and see how much use it gets, most chassis have multiple pot holes anyway and I'd probably wait before ordering a faceplate until I'm happy with what I've got.

Another pair of schematics I've started looking at are the EF86 Lite 2P and the Trinity TC15, both of which again use the EF86 and tweak the power amp into a Voxy direction: files/JMPGuitars_18W_EF86_Lite_2P_Schematic.pdf | https://www.trinityamps.com/wp-content/ ... tic-v9.pdf

Josh, out of curiosity - looking at the EF86 Lite 2P, I see the infamous 220k grid resistors are there - any specific reason why? Did the amp come out better suited for a slightly more headroomy vibe or is that implementation of EF86 preamp saturating more than a regular 18w, thus needing less power tube push?