VibroChamp / Pro Junior Boxy; Suggestions?

Fender Amp Discussion

Moderators: pompeiisneaks, Colossal

Post Reply
Bombacaototal
Posts: 1669
Joined: Thu Oct 06, 2016 5:53 am

VibroChamp / Pro Junior Boxy; Suggestions?

Post by Bombacaototal »

I am starting to think of a new build which will have a VibroChamp AA764 type circuit 5Watts

I once had a Pro Junior III limited edition from Fender (10" speaker - measurements 14.5”H x 15.25”W x 8.75”D) which sounded really really boxy and sold within a month

I played a silverface 70s VibroChamp (8" speaker - measurements 14”H x 17”W x 7.5”D) which was much sweater than the Pro Junior but still fairly boxy

I know the easiest would be to make it as a head and then use a 2x12 cabinet but given I want it as a small combo I would like to know if anyone has suggestions. I would like to avoid a 1x12 combo due to weight

I was wondering if I made the VibroChamp on a slightly bigger combo for a 10inch speaker with greenbacks which have a bit more bottom end if it would maybe be less boxy. Also thinking if other woods like Birch Ply or Poplar versus the fender Pine would perhaps help improve the sound

Has anyone experimented along those lines?

Lastly I am considering replacing the tremolo by a Tremolux AA763, which is fairly similar but in my opinion slightly better. Any thing to keep in mind?

Thoughts or suggestions?
brewdude
Posts: 651
Joined: Mon Mar 31, 2008 6:26 am
Location: Napa, CA

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Post by brewdude »

I've come to believe that the reason some speaker cabs sound "boxy" is that they are too small for the speaker. Perhaps, a larger combo can with a smaller speaker would help. Or, maybe the porting or amount of opening in the cabinet could be tuned better.
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Post by xtian »

Agree. The reason the Pro Jr and Champ/Vibro Champ sound boxy is because of the box, and small speaker.
I build and repair tube amps. http://amps.monkeymatic.com
Bombacaototal
Posts: 1669
Joined: Thu Oct 06, 2016 5:53 am

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Post by Bombacaototal »

Thanks for the replies

I am thinking what is the alternative. If it is to make a cabinet as big as a Deluxe Reverb one might as well put a 12" speaker. But then might as well build a Deluxe

If building a small head I am not sure 5Watts would really push a 2x12 100watt cabinet

Ideally would be to find a sweet spot in between. Maybe a 10" on a cabinet half way between a Deluxe and a champ?

I really wonder if the choice of wood might help as well
User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Post by xtian »

Bombacaototal wrote: Sat Mar 25, 2017 8:51 pmIf building a small head I am not sure 5Watts would really push a 2x12 100watt cabinet
Totally untrue. A 0.1w amp will push a 4x12 cabinet just as nicely as a 1x8.

The Princeton Reverb cabinet is a nice size, between Champ and Deluxe. You can easily fit a 12" speaker in there. Pine is a wonderful material for open-backed cabs.
I build and repair tube amps. http://amps.monkeymatic.com
68strat
Posts: 32
Joined: Fri Sep 19, 2008 6:48 am

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Post by 68strat »

Pine is a wonderful material for open-backed cabs.

Yes thats how leo did it. Who is to question that!? LoL and sounds great, classic.

How different does a small combo amp sound built of quality plywood sound vs pine?
Bombacaototal
Posts: 1669
Joined: Thu Oct 06, 2016 5:53 am

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Post by Bombacaototal »

xtian wrote: Sat Mar 25, 2017 9:53 pm
Bombacaototal wrote: Sat Mar 25, 2017 8:51 pmIf building a small head I am not sure 5Watts would really push a 2x12 100watt cabinet
Totally untrue. A 0.1w amp will push a 4x12 cabinet just as nicely as a 1x8.

The Princeton Reverb cabinet is a nice size, between Champ and Deluxe. You can easily fit a 12" speaker in there. Pine is a wonderful material for open-backed cabs.
Noted with thanks

I think I just might buy a massive attenuator and run my deluxe reverb head to the 2x12.

If I really decided for the combo the Princeton size looks loke a good idea. Not sure if I would build a vibrochamp circuit or a princeton tho

As far as combos these are the measurements:
1) Deluxe Reverb: Height: 17.5" (44.45 cm), Width: 24.5" (62.23 cm), Depth: 9.5" (24.13 cm)
2) Princeton Reverb: 16"H x 19-7/8"W x 9-1/2"D

It is interesting that the sizes are not proportional
User avatar
rp
Posts: 2528
Joined: Sun Apr 25, 2010 4:21 am
Location: Italy

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Post by rp »

Try running the little amp you don't like through a bigger cab, but you said the Blues Jr is gone. But if you find something small too boxy try lower filtering, a lot lower, no more than you need to not hum - like 5f1 style. That silverface among other things sounded sweeter because of the old caps, but it's still boxier sounding than a tweed cause of the higher filtering. Little amps and lots of filtering are going nowhere fast IMO, a little amp will never move a lot of air so setting them up for tight and punchy is silly to me, better to set up loose and fat. Crappy old molded microphonic coupling caps help too :lol: they add 3d swirl
User avatar
M Fowler
Posts: 14017
Joined: Wed Jan 16, 2008 2:19 am
Location: Walcott ND

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Post by M Fowler »

I have a stock Fender Black face VibroChamp and it sounds great for what it is, my practice amp or noodling amp.

I often see these being put into taller 1-12 or 2-10 combo cabinets so I would think that would be the thing to do.

Mark
User avatar
jjman
Posts: 753
Joined: Sat Oct 06, 2007 2:33 pm
Location: Central NJ USA

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Post by jjman »

Tremolux AA763 trem is the roach type. You won't have the negative bias to send to the trem, to keep it "off," which is only one "issue" with using that trem in a VC type build. I like all Fender trems. The only drawback with the VC trem is the fact its intensity control also changes the bias of the 2nd preamp triode stage. So turning the trem up also increases the dc on that 2nd gain-stage cathode, cooling down its bias & amplification. Try adjusting the control with the trem switched "off" via the rear jack and you will notice it. I tried blocking this problem with a big cap once but it would have to be too huge to preserve all the trem strength.

There are many trems out their that can modulate grids of preamp or output tubes. I ended up settling on one for a homebrew with some modifications to maximize strength. It includes the speed indicator light as shown on the Valve Wizard site. That light also functions as a DC-indicator for the amp which is nice. Its base came from the Brown Tremolux 6G9(x.)

The value of the pot is important since it is in the path of the impedance the signal sees. The grid leak resistor’s ground side goes to the pot wiper instead of ground. For an SE output a 250K pot may make sense with a normal 220k grid leak resistor. Mine is PP output
You do not have the required permissions to view the files attached to this post.
If it says "Vintage" on it, -it isn't.
Bombacaototal
Posts: 1669
Joined: Thu Oct 06, 2016 5:53 am

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Post by Bombacaototal »

@Mark: thanks for the note. The more I think about the more I am convinced of a 1x12. The question now is Vibro-Champ or Princeton circuit :-)

@jjman: thanks for the explanation on the tremolo circuit and the further considerations. The 6G9 sounds like a good option. Was your homebrew a VC?
User avatar
jjman
Posts: 753
Joined: Sat Oct 06, 2007 2:33 pm
Location: Central NJ USA

Re: VibroChamp / Pro Junior Boxy; Suggestions?

Post by jjman »

The trem on the homebrew provides the "ground" connection to a Larmar Post PIMV on a ~5E3~ output.
If it says "Vintage" on it, -it isn't.
Post Reply