Tuesday, September 9, 2008

Fender Pro Junior Harp Amp Project – Speakers

The original Fender Special Design speaker (made by Eminence) that comes in the Fender Pro Junior amp is very efficient and bright. Together with the high-gain 12AX7 tube in the preamp socket, the stock Pro Junior can be a feedback monster for harp players. A warmer-sounding alternative was needed for this project, but I wanted to keep the cost low. That meant I had to forget about the great Weber VST speakers and used vintage Jensens.

I’d tried the Jensen reissue P10R and C10Q speakers in other projects and didn’t like them. I’d also tried the Weber Signature 10 ceramic with smooth cone and loved it, so I decided to try its alnico twin in the Pro Junior.

Several players have said they saw a drop in volume compared to the original speaker when switching to the Sig10 alnico, and they are right, sort of. Ted Weber describes this speaker as “compressed at high volumes” and he ain’t kidding. This speaker has a nice blat for harp but in the Pro Junior it squeezes the dynamics down a bit too much for my tastes. This speaker is a touch bright (not nearly as bright as the original speaker), making the Pro Junior sound much better but still a little nasal; a little boxy. The compression made the amp slightly monotonous. I could see it in the wave forms when I recorded.

So, I swapped it out for the Weber Sig 10 ceramic I already had on hand. The difference was immediate. The ceramic speaker is a little warmer and less compressed. The amp responds better to mic cupping; it is less boxy, more open and lively; more articulate. To my ear, the ceramic sounds much better.

You be the judge. Here are clips of each speaker in the Pro Junior, recorded under identical conditions.

Weber Sig10 alnico, smooth cone
Weber Sig10 ceramic, smooth cone
NEW: Shure SM57 mic, Weber Sig10 ceramic, smooth cone

The smooth cone in both these speakers promotes earlier break-up and a warmer tone, ideal for blues harp. The amp is not stock: I have replaced all the tubes with harp-friendly options:

NOS JAN Philips 5751 preamp tube (lower the gain slightly)
JJ 12DW7 phase inverter tube (unbalanced wave form for a fuller tone)
Electro-Harmonix EL84 power tubes (warmer versions of the EL84)
I also disconnected the negative feedback circuit. (a little more “dirt” in the tone)

I like the way the Pro Junior sounds now, although I need to take it out and run it around the block in gigs or blues jams. So far, it sounds great for a low-buck project. Total for the used amp and new parts was under $300.

UPDATE: That great-sounding ceramic Signature 10 speaker from Weber is only $30.00, ten dollars less than the alnico version. The cost of this project is only $280.

: The Fender Pro Junior amp was set at volume on 4, tone on 4. The amp was mic'ed with an AT2020 condensor mic about 10 inches in front of the amp, slightly off axis. Harp mic had a Shure CM element; harp was Hohner Marine Band Deluxe in B-flat. No effects of any kind were used on the amp or in the recording or editing. The backing track was from a Boss DR-3 drum machine. No animals were harmed during the production of this test, but my dog looked at me kinda funny...


Joe said...

Did you notice a change in the tone when you swapped in the 12DW7 in the phase inverter? If so, what was the difference?

How loud can you turn it up before you experience feedback? Just curious on this. I could never crank it above 4 w/ the 12AY7 in V1 and a 12AX7 in V2. A speaker change didn't effect this for me.

I liked that amp for harp. I found myself not using it and had better use for $200, so I sold it.

Rick Davis said...

Hey Joe-

When, I first tried the 12DW7 tube in the phaser inverter socket (back when the rest of the amp was stock) I could not hear any difference. Now when I swap it for the original 12AX7 (after all the other changes) I can hear a slight change in color with the 12DW7. That could be because I have the amp calmed down now, and the subtle differences with the unbalanced phase inverter can come out.

How loud can I turn it up before feedback? It depends on the size of the room. If I stand right in front of it in a small room I can't get past 2. In a somewhat bigger room I can get to 4. When I stand outside the room with the mic I can turn it up as loud as I want without any feedback. I need to try it in a club venue to see how it reacts there.

I was interested in this project because I don't much care for EL84 amps for harp. I know some other players like them but I had the impression they were too harsh. I much prefer amps with 6V6 power tubes. But, so far this little Pro Jr is sounding pretty good for not much in the way of mods.

There are LOTS of good 5-watt harp amps for not much money, but when you jump to the 15-watt range the choices get fewer and a lot more expensive. This Pro Jr project amp may fill that niche nicely at a very reasonable cost.

Nat said...

Hey Rick,
Great help , I had the same project going at the same time. I had sent for JJ tbes harp replacement and was not thrilled , I had cut the C2 cap and was getting better but not pleased. Saw your project and then cut the NFL , sent away for Weber Sig like you recommended , Wow now I could hear some possibilities .Running on a budget (the wife) so I couldn't spend money on a 5751, traded some old junk for used 5751, put it in real loud Hum.Wife relented. Sent away to tube depot for 5751 and EL84EH should be here tomorrow.Tried FAB echo liked it turned all the way down , now looking into modding it for harp, More low end and speed control, So pretty much all your recomendations and counting, thanks

Rick Davis said...

Hey Nat, the Pro Jr makes a really good little harp amp with a few inexpensive mods. I'm more impressed with mine every time I play it. It is totally giggable. If you need more volume you can use TWO Pro Jr amps (still way cheaper than one boutique amp), or use the H&K Red Box for a good line out to the PA.

I've noticed this article gets a lot of hits, so my guess is there are quite a few people catching on to how cool the Pro Jr is for harp. I'm looking around for another Pro Jr for a different project: Two 8-inch speakers crammed into the PJr cabinet! Stay tuned for that.

As for the Dano FAB echo... it is not my favorite delay for harp, but it certainly is when you factor in price.

Anonymous said...

Hey Rick,
Yeah, it was the 15 dollar price tag that made the Danelectro attractive to me. Way too much gear, not enough dough in this world. Anyway, I got my delivery from Tube Depot (5751, EL84EH) today and had to hold my trembling right hand with my left while I put in my 5751. Total hum and the EL84's are glowing like crazy. This is without anything in the input jack. This is the third 5751 that did this to me. The first two were the ones that I traded for as mentioned above. The EL84's are the JJ's. I didn't even try to put in the Electroharmonix that came with my 5751s as it was humming too much. In the V2 position I have a 12DW7, again JJ, this is the one that I've been using with a JJ ECC81 in V1 position. So what gives??? Thanks again ... you have been very helpful and I would appreciate any further feedback.

Anonymous said...

hey rick ... sorry had to post as anonymous because couldn't log into my account ... duh. Nat

Rick Davis said...

Whoa, that doesn't seem right. I use the 5751 in lots of harp amps including the Pro Jr, and it never produces hum. It is just an industrial-quality version of the 12AX7 with slightly less gain. I don't really know what to suggest other than hitting all your tube sockets with some DeOxit. Also, check to make sure the metal shield below the volume and tone pots is not bent upwards and shorting anything.

Are you sure you have the 5751 in V1 and the 12DW7 in V2? V1 is farthest to the right when looking at the back of the amp.

Anonymous said...

Working!! I like the 5751 over the 12at7 in V1, I think it was a contact issue .Put tubes in right away without any contact cleaner on hand , quick and dirty . You called it . I consider this project a complete success, Will be playing it out Friday night(small club) and I am confident that I will be heard, not be blamed for feedback in the PA, and last will have a tone that I can get behind. Thanks for the help .

Rick Davis said...

Nat, send sound clips of your gig!!!