FX loops: When does an amp need one??

[makinrose]

Over the years I've installed a number of mixing FX loops based on the TUT Best All Tube FX Loops with a lot of success and find that design to be transparent and more useful than the serial loops in many amps.  I like the idea that the dry path isn't going through all the buffers, mixing circuits, etc. in the pedals as well. 

In general, I've only thought an FX loop is needed in higher gain amps but more and more I'm seeing them lower gain amps (Bassmans, Plexis, etc) and get requests to install them in.  At what level of gain is there enough benefit to warrant the effort?  I was hoping I could get some guidance  and opinions on the matter.  Thanks everyone for the help!

[Sherlok Ohms]

Hello Mr. Makinrose

I believe your own history of modification requests answers your question. The gain preceding the effects loop does not matter, and what the player seems to desire is that the guitar signal hit a tube grid before anything else, be warmed up, then go to the effects.

For example, in a Fender Twin Reverb amplifier, one might wish to add the Equal Weighting mod from TUT1 first, then add the effects loop between the channel mix point and the input to the reverb block. I believe KOC suggests this as the preferred order for an effects loop and a reverb. Each of the two-stage preamp channels actually has significant raw gain, but players do not really push them that hard. Consider that in most Fender amps the second stage drives the power amplifier input, which only requires 2-3V peak to be driven to clipping.

In a Fender Twin Reverb, the reverb block adds a bit of gain overall to the related channel, so the second stage is working less hard. Inserting the Equal Weighting mod reduces the output of each preamp, so they are both back up to what the Normal channel output level might have been in the stock configuration.

With all of the desk-top recording systems people have, there is an increasing demand for warming stages before or after processing, and these stage are usually tube gain stages set either for low gain, or with attenuators either at the input or the output or both.

Cheers

[makinrose]

Hello Mr. Makinrose

I believe your own history of modification requests answers your question. The gain preceding the effects loop does not matter, and what the player seems to desire is that the guitar signal hit a tube grid before anything else, be warmed up, then go to the effects.

For example, in a Fender Twin Reverb amplifier, one might wish to add  the Equal Weighting mod from TUT1 first, then add the effects loop between the channel mix point and the input to the reverb block. I believe KOC suggests this as the preferred order for an effects loop and a reverb. Each of the two-stage preamp channels actually has significant raw gain, but players do not really push them that hard. Consider that in most Fender amps the second stage drives the power amplifier input, which only requires 2-3V peak to be driven to clipping.

In a Fender Twin Reverb, the reverb block adds a bit of gain overall to the related channel, so the second stage is working less hard. Inserting the Equal Weighting mod reduces the output of each preamp, so they are both back up to what the Normal channel output level might have been in the stock configuration.

With all of the desk-top recording systems people have, there is an increasing demand for warming stages before or after processing, and these stage are usually tube gain stages set either for low gain, or with attenuators either at the input or the output or both.

Cheers

Thanks for the reply and all the helpful remarks.  I guess one of the things I'm weighing is amount of benefit that adding the loop would having vs. other features in a cleaner amp.   For example, having a loop vs. tremolo or tube reverb....there's only so much room.  Another concern is whether the loop in a cleaner design is going to have a big enough benefit vs. putting pedal through the front end especially considering many players are going to have drive pedals in front.  While I like the idea of hitting a tube grid first is the person playing it going hear a difference?  This may be case of build-and-see but I would be interested what other's experiences are.

[K O'Connor]

Hi Guys

When doing mods, you already have the input from the player, so his intentions and expectations are known, although you till have to discuss things as thoroughly as you deem necessary to make sure he will be satisfied.

If you are contemplating building amps ahead of orders, then your wonderment of what will be most useful may make you entirely confused. The fact is multi fold: whatever you build will be useful to someone; whatever you build will have benefits that you may not think are there. You have to describe each product in the glowing terms it deserves. I don't believe you can go wro9ng with your choice here, except that one model may sit on the shelf longer than another.

In my experience building amps and preamps, and from storied I've heard from other builders, it is usually the most subtle things that customers respond to most. For example, The first version of the SUSTAINOR preamp that I offered as a product ( described in TUT6 Ch.6, has cascaded triode stages at the input separated by an attenuator. The attenuator cancels all the gain of the first triode. So why do it? A switch allows the player to access the output of either stage, adding the veil of character of the second stage or not, per his choosing.

When you have a 2-stage preamp, as Sherlok Ohms described, the player may not be pushing either stage very hard - in fact, the first stage may be working at a higher plate signal level than the second stage - but each adds character. The order of effects and tube stages within the amp may sound broadly the same when the orders are changed, but the subtleties are still there for players to notice or not. Ultimately it is the daily user of the amp who will mine out and enjoy the nuances of tone.

Reverb is the most expensive effect to add to an amp, but to me, it is the most beneficial. If I had to choose between having only an excellent distortion or an excellent reverb with clean, I would choose the latter. If you want distinct echoes as a delay can produce, and wish to be able to control them in a natural way, then a mixing loop is the best solution assuming correct control of the loop. Whether this is pre/post tube preamp depends on how you perceive the overalll tone. Obviously, pre-preamp makes less sense than post-preamp except for the controllability option you might add.

Tremolo is a nice effect, but far less widely appealing than reverb or overdrive or chorus.

Have fun

[makinrose]

"If you are contemplating building amps ahead of orders, then your wonderment of what will be most useful may make you entirely confused."

Truer words have never been said. It is interesting how every player has their own priorities. For me if I was choosing between reverb and overdrive, I would pick overdrive/distortion over reverb. As cool as tremolo can be I so rarely use it that I does seem to be taking up room that could be used for other features. Nonetheless I have customers would think of it as an essential feature. It's all so subjective.

One thing that comes to mind is that these days digital reverbs have gotten much better yet sound different from a true analog reverb. A loop would be useful for better pedal-based reverb sounds as well.....