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So, I have been wearing Stephen out with questions about the TC-15 (judging from the time stamp on his replies, I don't think he sleeps). The TC-15 seems to be everything I have been looking for, with one exception - an effects loop.

Much of the time I play in a CCM (Contemporary Christian Music) setting and that typically means using (lots of) delay. My experience using delays in front of the amp has been less than satisfactory. Loops, however, don't really seem to be a topic of much conversation from those building [insert dual-EL84 architecture] amps (thread about three postings away from this aside). Is it that few are using delays in the way I am, or is it that delays sound fine in front of these amps given that much of the overdrive stems from the power section?

I have read about the one loop per channel Matchless concept of handling this and can't get my head around how that would work (other than having delay and modulation effects available only on one channel). Surely there is some way to insert a single loop before the power section(?).

Thanks everyone. I have enjoyed learning from the many posts so far.

Let's see if we can get Tom to give us an update...

viewtopic.php?t=1321

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I read that with intense interest while you and I were emailing. That seems absolutely brilliant, but also way more than I was considering.

I am sure that I am showing my ignorance, but is there no way to have a single effects loop that would be parallel with respect to the two preamp channels, thereby allowing whichever channel in use access to the effects prior to entering the power stage? That is the way that my current amp seems to do it.

The Matchelss design is actually pretty simple. One 1/4" stereo jack per channel. When you plug in, it routes the signal to your effect and back to the amp. When you unplug the jack, it bypasses 100%.

Not sure you want to mix two channels together into one jack.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I use two analog delay pedals in front of my TC15 with excellent results. I use the MXR carbon copy set to long, multiple delays and a Goudie FX analog delay set to a single faster delay. Both are last in the effects chain, and I have no issues.

AJC

Thanks for the input. The frightening thing for me about putting my delays in the front is that it hasn't worked well for me with other amps. Might be gold with this one, but I wouldn't know until complete.

Would the generic tube-buffered effects loop kits work with the TC-15?

I haven't had a lot of luck with delays (or modulation effects) in front of amps either. I find they tend to be very noisy & the "clocking" effect can be a problem. The noise is especially problematic when overdriving the pre-amp. I guess if you used a noise gate at the end of your chain before the amp's input it might help.

It depends on the pedal. Some work fine (the Carbon Copy being one), while others are a nightmare (the Diamond pedals have given me grief). I have a Line6 Echo Park that is unusable unless running full wet in a series loop.

If you're getting your dirt from an OD or distortion box before the delay (or whatever) I find it works better. Generally speaking if you're running clean it's not a problem, but some boxes still are too noisy or have that clocking issue.

I would like to have a loop in all my amps. I'm planning on adding one to my 2204, but it's pretty simple in that case (being a single-channel head). I expect it would be relatively straight-forward in the Triwatt too (insert the loop before the master volume), but I'm certainly not the expert around here! Actually, I expect it would be pretty simple to add a loop to any master volume design.

The problem with the 18w, TC-15 & probably the Deluxe as well is you have two physically separate channels, as it were. One could easily add a loop for each channel. However, I've never understood why a loop couldn't be inserted after the channels get mixed prior to going to the output stage. Maybe Stephen or Phil could explain that one?

Am I crazy (well, obviously), but did I read somewhere that one could use the "jumper" between the channels as a parallel loop & use the volume of the jumped channel as a return/mix level or something like that? Still sounds like you're basically inserting the effect before the input stage though so I don't know that you'd be gaining anything.

My train of thought, exactly. I've seen the Matchless - separate loop for each channel solution - but I can't see how that would work for me. The output from the two preamp channels must come to one point at the common master volume - couldn't it be inserted there (asks the guy who has never put an amp together - please forgive and continue to suffer my ignorance)?

Not sure what ever became of this guy...
viewtopic.php?t=1321

Stephen prodded him a while back but no response

Joe G

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Brain sold separately...

One thing I'm gonna try is an effects loop blender pedal....basically a parallel loop between the guitar and the amp. I found one that's available as a kit here:
http://www.woundedpaw.com/catalog/product_info.php?cPath=27&products_id=141

It'll be a while before I get this assembled, tho......I still need to wrap up my TC-15 build.

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Especially as the Triwatt, unusually for most amps, but like all Hiwatts, has a further preamp gain stage after the MV which makes for a handy FX recovery stage.


The 18W and TC15 (as well as AC15 and AC30) mix the channels together inside the phase invertor, which directly drives the power tubes. So there isn't anywhere to insert the loop "after the channels get mixed prior to going to the output stage". Basically the loop has to be inserted before the phase invertor. The Deluxe mixes within the preamp, so it doesn't have this problem.

Yes, that's mainly something used with classic/tremolo 18Ws, and basically provides a kind of parallel FX loop between the inputs of the channels. You can'tdirectly jumper the two channels of a classic/trem 18W together, as they're out of phase, so you need some kind of FX in between. This doesn't apply to TMB versions.

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I have been holding this question since the term was first mentioned in this post. I have reached the point where I can hold it no more. At the risk of being deemed the most ignorant participant on the board:

Why does the TC-15 need/use a phase inverter if it is running in class A?

First of all it's a push-pull amp and actually running in Class AB. Next, there are many similar Class AB amps out there, Vox, Matchless, Marshall 18W, etc, which the marketing guys call "Class A" for their own misinformed reasons.

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Because it isn't running is class A

So far, all of the Trinity amps are class AB push-pull amps

Some companies use the term for marketing reasons for cathode biased class AB amps without negative feedback because "people believe" that class A amps are better than class AB amps.

There is a lot more to this and hopefully someone else will chime in

I believe technically you can run class A push pull so you'd still need a PI.
Stew

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thank you all for the extremely gentle responses. Your grace is noted and very much appreciated. I have obviously fallen victim to marketing hype.

I learned to read schematics in high school, but haven't done anything of this magnitude with it since. I'm now mid-40's, so the assumption was that, since Vox and Matchless amps were class A (hype!) and this was a Vox/Matchless-style circuit, V3, even though it appeared to me to be a phase inverter, had to be something else.

See, I have learned something beyond what I originally set out to learn. Thanks!

Edited to add: thanks, Stephen, for the Last Word on Class A, you posted while I was responding, above. Very informative and much of it even made sense! I feel like Neo after taking the red pill. I see now how absolutely correct the responses to my question were. Thanks!

Now, back to the effects loop...

I just thought I would like to chime in.

Hi folks!

OK, I'm done now.

OK, a little more seriously, I think some of your confusion was also probably due to getting Class A amplifiers mixed up with Single-Ended (SE) amplifiers, since SE amplifiers are usually true Class A. However, as Stoo points out you can in fact also have true Class A push-pull amplifiers, although their efficiency benefits aren't nearly as good as Class AB ones.

Now here's another little understood fact, if you can handle another red pill. In some applications it's also possible to have single-ended Class AB amplifiers. Conventional wisdom says that's not possible, but this conventional wisdom only applies to high fidelity audio, where all forms of distortion are to be avoided, and not to guitar amps. In hi-fi all Class AB amps must also be push-pull, so that while one power tube goes into cutoff, the other one carries on amplifying the signal. Then they swap places. In guitar amps we actually like the sound of a power tube going into cut-off, as that gives some real nice power tube distortion. So we can break the conventional rules a little by just using a single power tube (and therefore no phase invertor) and allowing it to go briefly into cutoff. The Fender Silverface Champ, popular as a recording amp, is a great example of single-ended Class AB. I expect the same will apply to Trinity's "Tramp", when we get around to finishing the design.

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I thought that was the case. I was looking at the schems after I posted that & I saw there was no mixing going on until the PI. Thanks for verifying!

So, in order to make a shared loop work in an TC or 18w, one would have to insert that mixing point before the PI and then basically feed the mixed signal to the PI. I assume that would require some re-thinking if the PI itself to make it work satisfactorily. I also assume that it will impact the tone too, so even with the loop bypassed the amp would still sound a little different from stock.

Interesting... Think I'll leave that challenge to someone a little more technically adept than myself!!!

You would have to mix the two channels by means of a pair of resistors after each channel's volume control, like in a Triwatt/Hiwatt or Marshall Plexi. However, this also has the effect of somewhat attenuating both channels. The spare input of the PI then has to be grounded via a 0.1uF cap. And yes, it would change the sound of the amp a bit.

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Great tones come in small glass jars!