Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Popsleigh on March 28, 2016, 12:58:29 pm

Title: Which lower output amp would most closely emulate the tone of an AC30
Post by: Popsleigh on March 28, 2016, 12:58:29 pm

Hi all,

I have a beat up 1963 AC30 which I asked my brother to return to me (after 18 years) as I wanted to start playing again. I forgot how wonderful the AC30 is and it got me thinking that I had actually robbed him also of a great joy as I did not realise how much he had been playing it. Given that I have more means than he does I am considering building a smaller single speaker unit purely for own use and plinking on for my own pleasure. I will then give him the AC30.

So any views on which smaller unit would come close tonally, other than an AC15?

I had been looking at the Stout with reverb but this appears to have a Marshall pedigree. This will potentially be my first build.

Any opinions would be welcome.

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: sluckey on March 28, 2016, 01:28:37 pm

Quote

other than an AC15?

Why are you excluding the AC-15?

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: Popsleigh on March 28, 2016, 02:46:00 pm

Hi sluckey,

I had a very close look at your AC15 thread and it was of great interest. It looked a little intimidating as a first project but having said that I would probably not put the Trem/Vib circuit in and would prefer to insert reverb.

I will revisit your thread.

regards

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: kagliostro on March 28, 2016, 03:00:02 pm

I think that this link didn't solve your question, but is what I remembered when I read your question

Quote

The third member of the LoWatt family is based on a British original - the AC30. But - we didn't model the entire AC30 in minature; only the EF86 channel.

(http://i.imgur.com/oPAmFfq.jpg)

https://www.tube-town.net/cms/?DIY/LoW-Projekte/Molly_%28engl%29 (https://www.tube-town.net/cms/?DIY/LoW-Projekte/Molly_%28engl%29)

https://www.tube-town.net/cms/userfiles/media/low-molly/low-molly.pdf (https://www.tube-town.net/cms/userfiles/media/low-molly/low-molly.pdf)

https://www.tube-town.net/cms/userfiles/media/low-molly/low-molly-layout.pdf (https://www.tube-town.net/cms/userfiles/media/low-molly/low-molly-layout.pdf)

http://www.tube-town.net/ttstore/Kits/Verstaerker/TT-Kit-Molly::6008.html (http://www.tube-town.net/ttstore/Kits/Verstaerker/TT-Kit-Molly::6008.html)

Franco



EDIT: Sample

https://www.youtube.com/watch?v=e_Qut2iIz0I (https://www.youtube.com/watch?v=e_Qut2iIz0I)

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: sluckey on March 28, 2016, 03:08:02 pm

Yeah, that two channel AC-15 is a bear, all because of the complex vibrato. But, look at this Dual Lite...

     http://sluckeyamps.com/dual_lite/dual_lite.htm (http://sluckeyamps.com/dual_lite/dual_lite.htm)

It's a normal channel AC-15 plus a normal channel Marshall 1974 18W. It's pretty simple and if you only want the Vox preamp, it get's even simpler.

You had shown some interest in Hoffman's Stout which is based on the Marshall 18W. The Dual Lite gives you both. I prefer the sound of the Vox channel.

Having said all that, I have no idea if the AC-15 sounds anything like an AC-30.

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: VMS on March 28, 2016, 03:13:53 pm

Does the '63 ac30 have a top boost channel?

If not, then I would suggest spitfire:

http://el34world.com/charts/Schematics/files/matchless/matchless_spitfire.pdf (http://el34world.com/charts/Schematics/files/matchless/matchless_spitfire.pdf)

If you like top boost channel then lightning could be one option:

http://el34world.com/charts/Schematics/files/matchless/matchless_lightning.pdf (http://el34world.com/charts/Schematics/files/matchless/matchless_lightning.pdf)

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: kagliostro on March 28, 2016, 03:22:11 pm

+ 1 for the Dual Lite

Franco

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: pompeiisneaks on March 28, 2016, 03:26:06 pm

You could also just take the preamp section from Doug's AC30 build as it has a normal and a top boost channel, and then modify the power output to use just 2 tubes for the push pull and have the AC15 concept with the AC30 preamp.  I'm not sure how much 2 EL84's vs 4 EL84's would modify the overall tone of the amp.  Someone else could chime in, but I think you could literally just pull out the extra tubes and components and need to only adjust the bias resistor and be in good shape.  Maybe it would need power adjustment or just a slightly smaller PT and OT to handle the different impedances and current demands of OT/PT, but for the OT really you could just halve them right? or do two tubes have a higher impedance than 4.  Some of that part still escapes me. 

(maybe just look at Sluckey's AC15 output and mesh that with the Hoffman AC30 input?)

~Phil

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: Ed_Chambley on March 28, 2016, 03:39:38 pm

An AC15 and a AC30 if not top boost and both have the same EF86 pre, they sound similar.  To me, all 4 output tube power sections have a better sound/tone, but not if you choke them down with a Master Volume.  Volume becomes an issue with the 30 watt if you want a practice to small gigging amp.


A Peavy Classic 30 and a modern Vox AC30 are very similar.  With the AC15 you have the combination of an EF86 Pentode to 2 EL84 tubes without anything robbing gain.  That is the nice feature of the AC15 and also the Matchless types.


I added a additional tube socket to my AC15 and tried a 1 tube verb and removed it.  Distortion and reverb I do not care for and the AC15 distorts easily, but it is very open sounding and easily manageable.  To me, that is what the Vox is all about.  That and the Vib/Trem.


I have tried a lot of different EF86 amps and have only kept the AC15 and still use it as one of my main go to amps.  Of course, we are all different.

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: Popsleigh on March 30, 2016, 01:30:44 pm

Thanks to al.

The dual lite looks like a really elegant option.

I never use the normal channel on the AC30 so the dual lite with Marshal input and then the AC30 Bright pre-amp sounds like a plan for me?

Steve could that work?

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: pompeiisneaks on March 30, 2016, 03:18:15 pm

As an aside, I never used the normal channel until I jumpered the normal and top boost, and then got a whole lot different tone I really liked.  My experience may not apply :)

~Phil

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: sluckey on March 30, 2016, 03:21:58 pm

Quote

Steve could that work?

sure

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: mresistor on March 31, 2016, 03:33:58 pm

Quote from: sluckey on March 28, 2016, 03:08:02 pm

Yeah, that two channel AC-15 is a bear, all because of the complex vibrato. But, look at this Dual Lite...

     http://sluckeyamps.com/dual_lite/dual_lite.htm (http://sluckeyamps.com/dual_lite/dual_lite.htm)

It's a normal channel AC-15 plus a normal channel Marshall 1974 18W. It's pretty simple and if you only want the Vox preamp, it get's even simpler.

Steve  - this Dual Lite is really a great looking project, I might have to build one for my next project.  What is the iron you used. Do you think some Hammond iron would work? 

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: sluckey on March 31, 2016, 04:49:35 pm

All info is on that web page.

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: mresistor on March 31, 2016, 06:58:38 pm

My hammond PT is an A0-27-1  out of an S-6 Chord organ .

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: Backwoods Joe on March 31, 2016, 07:58:57 pm

Even though the ac15 is a somewhat similar circuit, if you like the big round open tone of the ac30 you will be disappointed. In my $.02, the 18 watt Marshall amps are over-rated. Build yourself the AC30 you would like or buy your brother something else to use. Let me commend you for your generosity!

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: sean_thornton on March 31, 2016, 11:53:03 pm

Okay, i am going to muddy the waters a little further here. How about a 3 watt version of the Vox Night Train? It uses  2 12ax7's and one ecc99. Very impressive little beast.


https://www.youtube.com/watch?v=lOb-RVET8So (https://www.youtube.com/watch?v=lOb-RVET8So)

Details are here

https://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/ (https://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/)

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: sluckey on April 01, 2016, 02:07:06 am

I like that little amp.

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: Ed_Chambley on April 01, 2016, 01:47:44 pm

Very nice and responsive.  Easy to puch into overdrive.  Got a good beat and I can dance to it.  I give it a 10. :icon_biggrin:

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: Willabe on April 01, 2016, 03:34:54 pm

Quote from: Ed_Chambley on April 01, 2016, 01:47:44 pm

Got a good beat and I can dance to it.  I give it a 10. :icon_biggrin:

 :l2:

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: sean_thornton on April 01, 2016, 09:33:50 pm

Quote from: sluckey on April 01, 2016, 02:07:06 am

I like that little amp.

I've played around with low wattage amps in the past and never really found any I liked. Until now. I have a parts order into Tube-Town to build one of these. The Vox Night Train is based on Ken Fischer's Trainwreck Express, and to my ears this thing sounds like a Mini Trainwreck. It is a little beast, and the video with the Les Paul is an eye opener.
Finally found a low watter I like.

https://www.youtube.com/watch?v=1en5tWR3d20 (https://www.youtube.com/watch?v=1en5tWR3d20)

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: Popsleigh on April 03, 2016, 04:41:55 am

Who would have the time and patience to check my hybrid circuit. I have no circuit design experience so merely tried to take existing bits of circuits and to wedge them into Sluckey's Dual lite.

AC30 Brilliant channel Pre-amp in for the AC15 Pre-amp.
Added Tore T's reverb circuit

The component numbering is incorrect as I have moved components all over the place will start renumbering now. The values should be correct.

(http://i1133.photobucket.com/albums/m582/CZ550/Dual%20Lite%20sans%20normal%20channel.png)

Regards

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: kagliostro on April 03, 2016, 05:12:32 am

Just this morning, while I was walking with my dog, I was thinking about your idea and how I would have handled the thing

As to avoid the use of one more tube (with an unused triode in the event of the use of a 12ax7 tube) I was thinking about the use

of a Souce Follower as CF (on the Top Boost circuitry)

(http://i.imgur.com/xUahm4p.jpg)

About your desire to add a reverb circuit, I think I'll use a pair of mix resistors (say 220k) and then a 2.7-3.3M resistor bypassed with a

small cap like in the Vox Cambridge Reverb circuit

http://el34world.com/charts/Schematics/files/Vox/vox_cambridge_reverb.pdf (http://el34world.com/charts/Schematics/files/Vox/vox_cambridge_reverb.pdf)

May be you can contain the number of tubes also using the One Tube Reverb often used by our friend Tubenit

http://el34world.com/Forum/index.php?topic=7957.0 (http://el34world.com/Forum/index.php?topic=7957.0)

Franco

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: sluckey on April 03, 2016, 06:14:43 am

The reverb driver usually gets B+ from node B (screen).

I don't see any way to get reverb on both channels since there is no common signal path. You could mix the two preamps together with two 220K resistors (ala Fender style) and fee that into a single input on the PI. Then you would have a common path to pickup reverb input.

How important is reverb to you?

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: Popsleigh on April 03, 2016, 06:27:00 am

Reverb is really nice but I suppose it falls under wants and not needs. I do have an older Ibanez AD9 Analogue Delay that I also use.

The thing with reverb is that it rather complicates matters.

Cheers

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: VMS on April 03, 2016, 07:35:08 am

I think you can take the reverb from plate of the first triode and from the plate of the preamp pentode.

It looks like you ground the input of the unused channel so that shouldn't affect the reverb.

It might sound interestin when using both channels parallel.

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: VMS on April 03, 2016, 07:39:09 am

...or you can put a selector switch to choose if you take the reverb from top boost channel or the ef86 channel.

Title: Re: Which lower output amp would most closely emulate the tone of an AC30
Post by: Popsleigh on April 03, 2016, 09:40:50 am

Had not though of that.