18Watt.com

Has anyone built the 36W layout per the Ceriatone Jan 2010 Revision Layout? I see lots of differences between it and the R5 circuit in the download section.

The Ceriatone Jan 2010 has what I think is sometimes called a 'treble peak' circuit after the TMB side volume (1M in parallel with 560pf). This seems like standard Marshall like tone shaping that I don't see in the R5. The R5 looks almost fenderish with the 1.5K/22uf on the V1 cathodes, but then does go cathode follower with Marshallish tone stack, so not so fender for sure.

So if anyones done the build, I'm just looking for how it came out and what mods you did. Right now I'm thinking to stick with the Jan 2010 layout and that 1M/560pf has my interest 'peaked'. JCM800's have a 470K/470pf instead in that spot, so I need to get the calculator out and see what is the peak frequency for both. I never mind tweaking values, even after its up and working, but again just looking to see who's done this exact circuit.

No replies??? Okay let me try this....

My main concern on the differences between Ceriatone <-> Richie R5 is that the Normal channel on the R5 runs through V2. This gives the normal channel more gain (has a second stage) and puts it through the TMB tone stack along with master.
So with the R5 you actually have two eq's (tone + tmb) on the normal channel and the volume becomes a preamp gain and the master controls the total volume. Interesting. I wonder what inspired this however, is it the fact the running the normal channel (with just one stage) directly to the other end of the PI just not enough? (as in the ceriatone design).

My amp is less than halfway done, about 1/2 of the board is done and last night I switched gears and did all of the heaters while contemplating changing the board to have the normal channel go through V2....
Can't seem to make a decision!!!!

What I do know, on my 18watt I built I can't get the normal channel loud enough compared to the TMB channel without it being 'dirty'. It just doesn't have the volume the TMB channel has. This is why I'm considering the change to put the normal channel through V2....

Okay -

I think this thread is just for my own reference!!!

I completed the amp to Ceriatone's specs with heyboers - gave it a few days listen, even a jam night too, my observations:

1. The NFB switch on/off seemed almost non-functional
2. TMB - seemed a little bright, fizzy???
3. Half power switch works fine
4. Normal channel, didn't seem so usable, not clean enough as I wanted to possibly a/b switch the channels if its possible with an a/b/y box

So - time to try Richie R5!!!
1. Once NFB R5 values were installed, the amp oscillated with NFB ON!!! Had to switch the OT primaries!! Why didn't it oscillate in the other config???
2. Left in half power switch, need to check again with more testing
3. Redid the preamp per Richie R5 values

Now:
I'm much happier with the amp
1. Nice almost 'glassly' tone before crankin it up and gettin it to breakup
2. NFB switch very usable, I like both modes
3. Normal channel seems much more usable, but I was diggin' TMB so more testing needed there.
4. New speakers for my 2x12 on the way, can't wait to test the full rig as planned, maybe a few more tweaks, but it may already be there!!!

I'll come back to update my note to self thread after speakers...

Congratulations!!! Glad you got your amp working more like how you want.

Ceriatone's 18W/36W designs are becoming somewhat of a mystery. Nik used to be involved in the discussions on 18watt.com. Now he does his own thing, without talking to anyone about it. And he doesn't publish any schematics, only layouts. Of course, he's perfectly entitled to do that if he wants, and his customer service is always excellent. But the downside is that there isn't too much detailed knowledge about his 18W family amps within the community here. So we mainly have to work on a generic basis when attempting to answer questions.

A couple of things. When you apply NFB, if the OT is phased the wrong way round, you get PFB instead of NFB, which is why your amp oscillated. Without any feedback, which is how your amp originally was, the OT polarity doesn't really matter. Also, the Normal channel was never intended as a Clean channel. It's just there to give the original Marshall 18W vintage vibe, with lots of power amp distortion.

A couple of things. When you apply NFB, if the OT is phased the wrong way round, you get PFB instead of NFB, which is why your amp oscillated. Without any feedback, which is how your amp originally was, the OT polarity doesn't really matter. Also, the Normal channel was never intended as a Clean channel. It's just there to give the original Marshall 18W vintage vibe, with lots of power amp distortion.

Thanks for the feedback phil (no pun intended...lol), I did start with Nik's latest circuit which does have a NFB on/off circuit, so I either did the original wiring wrong (I pulled the switch out and totally re-wired it for R5 values with this change), or his current NFB scheme is questionable. I'm thinking it was my original switch wiring because even though Nik's feedback resistor values are much lower (820/100) vs 27K/1.5K it should still apply a feedback voltage to the pi and have a sonic impact, originally my switch seemed to do nothing.

I've been building for a few years now, but a quick search confirmed the idea to try switching the OT primaries to fix the oscillation.
THANKS FOR BEING HERE 18WATT.COM!!!

... or his current NFB scheme is questionable.

There are some NFB mods around for 18W/36W amps, that only apply the feedback to the tail of the PI. These will have very little effect. I wonder of Nik's nFB mod is also designed that way. Richie does the NFB right, by applying the feedback to the PI's second input. This does mean that the two channels then have to be combined together and both then fed into tha PI's 'A' input.

Phil, you are all over this one. I knew I was combining both channels to the same input of the pi (which also gave me a second stage for the normal channel), but you know exactly why its so different now - I also made the R5 change which as you said, does couple the nfb to the second pi input. You da man with the knowlege!!!

Giving my ears a bit of rest after playing it for a while this morning. I'm still very happy with making the switch to Richie's R5!!! Both tones (NFB on or off) are very usable.