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Old 1st April 2015, 08:51 PM   #1
diyAudio Member
Join Date: Apr 2015
Default New amp build, initial thoughts?

Hi, I am planning out a low watt amp build, but am not well schooled in circuit designs, what can and can't be done, and even if it can be done, is it really such a good idea? I've been doing a ton of reading, looking at features of both production and custom amps, picking features that I know I want and some that just sound like good ideas. My head is spinning from it all, so I thought I'd put down some ideas and see which ones stick with you guys.

I'm looking to do more stereo /panning stuff, so flexibility in blending and I/O is important. So I want to do a common thing with many, which is to have two main sounds in one enclosure. In my case a super clean Blackface and a PLEXI with extra gain to take it to JCM800 territory. There's other stuff I will describe and ask if you folks are willing to walk through it with me! Starting here, what general setup is best? I came up with three options.

a) One amp with two pre-amp channels? (I would want two inputs, and two sets of speaker outs to run separate cabs.) Other "features" would be a buffered loop (one for each channel.) Also a line out for each. If both inputs in use, blending can happen with the independent volume controls, with yet another, separate set of speaker outs (that's three sets of two (4,8,16) outputs!)

b) Two Separate amps in one head shell. Two sets of speaker outs for each. How much can the amps share? Rectifier, tranny, etc? Or is it better if they share no components? Need to blend the amps somehow, preferably in board. I know there's all sorts of outboard gear, but trying to keep things tidy as possible.

c)A two separate pre amp set up in one head shell. Outputs and options as noted above. Each pre amp with two sets of speaker outs, line outs, buffered loops. My understanding is you can connect the output of the pre amps to either the main input of a clean amp (I have a Vibroking that I think would do it) or into the fx return of any amp. Using the line out, I could also plug into a mixing board/PA when needed.

The separate amps appeal the most for maximum flexibility, and also using the family of tubes best suited for each sound from each amp. No sharing of circuits and tubes, without different gain stages etc to differentiate the tones from each channel. Does that partially explain the main difference between one amp, two channels, vs two one channel amps? Thanks, I'm sure my questions/posts will get shorter after I get through the "big questions." Thanks again.
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Old 2nd April 2015, 12:42 AM   #2
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Join Date: Sep 2013
Location: Minneapolis, MN
For low watt, what do you mean? 15-18 watts, 5 watts? My initial thought would be a two channel amp voiced differently to get your sound that you want. If this is your first build, it might be best to keep it a little simpler than to do stereo, FX loops, panning,etc. Learn about lead dress, minimizing noise and hum, layout procedure, grounding schemes, etc. And not book learning, actual building experience. Do a Fender Blackface style channel and a second higher gain channel. This probably will be the most you want to do at first.
Some people might even suggest you do just a single channel amp with maybe 2 preamp tubes and either one or two power tubes depending on your power needs. It usually is a mistake to take on too much at first. Maybe a Lite IIb type amp and then graduate to more later. Just my opinion but I've heard it many times.
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Old 2nd April 2015, 12:43 AM   #3
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Join Date: Jun 2011
I think the only real reason to have 2 amps is for stereo effects. In that case you'll need to think about how you're going to manage that now. Footpedal? I would have thought identical amps in that case.

If you want different tones, then the modern approach is to use some kind of processor somewhere in the chain and switch tones using that. One amp would do, but you could have different processing for each path. Each amp must have it's own speaker, but 2 solid-state amps could share a common power supply, as could 2 tube amps, but that might be less desirable.

You could have 2 proprietary amps from different manufacturers, if you wanted particular tones, but better to buy them off-the-shelf.

The very last kind of option is to attempt to build 2 tube amps each to to meet a different 'sound' requirement and integrate that into a single device with roughly the same volume on each channel, which seems to be where you're headed.

Why not just assemble something like what you want with some borrowed gear and see if it lives up to your expectations. You could split the signal to 2 swell pedals, each to an amp. I would have thought you could mess around with this 'virtually' with a computer, soundcard and some plugins.
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Old 2nd April 2015, 09:54 PM   #4
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This is my first custom build (haven't picked the builder yet,) and am used to the common configurations on production amps. So, like any special order, I want to be as certain as I can that I choose the best sonic combinations when not limited by what a factory produces. boobtube, you are right, I have little live rig routing experience, but I do have some. I have developed likes and dislikes with gear and brands, and discovered what options are important to me by their absence in my present gear. So, like many, I want to roll all that into a custom amp order with a quality builder. Low watt means 5-8 watts. Counterculture, I get the "don't get over your head" comment, I really do. I think I need to back up a step and get an understanding of muti channel amp voicing v. Separate single channel amps. Example, Phaez amps builds a "Duophonic" which has two channels, voicing of your choice. In my case, one would be Blackface clean (Corona,) and the Pasadena (hotter SIBLEY and Jackal voicing.) Would the Duphonic Corona channel sound exactly as the standalone single channel Corona? Same question on the second Pasadena channel? If yes, that's where I am getting a little lost. How does such an amp get the exact tones from a shared set of rectifier, tranny, power tubes, etc? when as standalone they use different tubes, guts, etc? OK, so through some creative circuitry it gets done.

Then there are I/O considerations. I would like to have two sets of speaker outs for each channel, so I can set out a couple of 1x12's spread out a) one signal from one channel split to the two cabs b)same for the second channel. c) One channels tones to one speaker, the other channels sound to the second cab. d) something outboard to mix the sounds into one, which is split between the two cabs. I have rarely, if ever, seen the number and separate outputs for amp channels on a multi channel amp. I see multiple speaker outs on stand alone heads regularly.

That's what made me think of two independent amps. They will theoretically sound as expected, as they will use their own set of unique tubes as in the line of amps they are inspired by, and have all the I/O options I will need (or can easily specify in the build.) Put both in an oversized head shell and off I go. Is there a "primer" on multi channel amps and how they duplicate multiple tones from one set of parts/guts? Thanks, Andy
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Old 2nd April 2015, 11:25 PM   #5
sreten is online now sreten  United Kingdom
diyAudio Member
Join Date: Nov 2003
Location: Brighton UK

This is over complicating any sensible reality.

Anyhow you best bet is two 2x10's with seperate
and parallel socketry for wiring. Then you can do
the combined two channels quite easily, by using
a 10" in each cabinet for each channel.

rgds, sreten.
There is nothing more practical than a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
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Old 3rd April 2015, 12:15 AM   #6
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Join Date: Sep 2013
Location: Minneapolis, MN
So you are wanting to know what is possible to determine what features to ask your builder to put in your custom amp? You said "haven't picked the builder yet". If that is the case, you should direct your questions to him. He will be the one to determine what he can build and what he can't. When I answered to keep it simple for your first build, I assumed you were the builder. If you want to dream big, ask your builder what he/she is capable of doing. You should find a very talented one to pull off what you want. I tend to agree with sreten, a little over complicated.
I must admit this is the first thread that the OP is asking about what another builder can do. Unless I have misunderstood.
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