Tone control in Tweed Princeton 5F2-A Clone

[cathode]

I just build my first amp: a princeton 5F2-A clone from the Angela Instruments homepage. Following link gives you a schematic view:
http://www.angela.com/catalog/how-to...incetonsch.gif

Well, the project was easy to do. I put the chassis into an old Fender Bronco cabinet (Tweed!) and used a Weber 8-SigA-S4 speaker. The amp is a little eye catcher and only humming a little bit at highest volume levels (it's o.k. for me).

My problem is that following the Angela Instruments schematic the amp sounds really muffy. 'Angela' changed the 1M tone pot into 250k and this is the main reason for the muffy sound I think. (s.o. Brian Newman's threads)

Because of the sound I did two modifications:
a) I took out the tone stack and let it run as a '5F1 Champ'...
No solution - the amp doesn't sound much better. I still miss the treble frequencies (perhaps the speaker....?!?)
b) Because I just had a handful parts left and second 250k pot (and no 1M one) I modified the tonestack into a Brownface Tone Control with Bass and Treble pot
Much better! This is something to work (control) with! But the amp isn't as loud as before and this can't be the end of the line...

My questions: has anybody an idea for an usable tone stack with Bass and Treble pot that doesn't take so much signal level?
Is tone control first and volume control second the right order to save the best 'information' from the guitar signal?

Looking forward for some output (HEELLPPP!!) of your stock of knowledge

Carsten

[cathode]

Probably I did a mistake by connecting the volume stack and the tone stack together without a capacitor inbetween for decoupling the two circuits ?!?
I will check it out this evening...

But there is still the question if I have to install the tone stack first for a better quality...

Carsten

[MWJB]

Why not go back to the tone pot but at 1meg. A bass control is a good idea with bigger amps for paring off thuddy lows, that shouldn't be necessary with a 5F2A with a 6V6.

You're a bit limited as far as T(M)B tonestacks go as you only have 2x12AX7 triodes to play with, losses are pretty well inevitable. With another preamp tube you could go for a tweed style tonestack.

[cathode]

try the basic tone control with the 1 Meg pot is another opportunity I'd like to test out, but for this I have to order another 1 meg pot.

Anyway, in my circuit the 1 meg volume pot is directly in parallel to the 100k resistant and the 250k bass pot of the browneface tone control. The result is a big missmatch of the bass control and less volume output. I'm sure I can fix it with an input capacitor of 0.022uF in front of the tone stack.

I'll give you the results later...

[cathode]

Here we are with the results:

with that extra 0.022uF capacitor between volume and tone circuit the influences between the pots is gone. The volume losses decreased but are still well recognized, especially with a stratocaster. Playing an Epiphone Emperor (humbuckers) or an '67 Gretsch Nashville (filtertron) the volume is o.k. to me.

MWJB was right: for this brownface tonestack the amp needs another preamp tube. Otherwise it won't fit!

Now I'll order the 1 meg tone pot...

[Satamax]

Hi Carsten, in the mean time if you want to play, you could fit 470KΩ resistor between your 250K and ground. If still too bassy try 680, or more.

[Fabio]

Nowadays I had the same problems.
I replaced 12AX7 (gain = 100) by ECC82 (gain = 19) with 6V6 in power stage.
Tone and Volume work in all condictions
Ditortions ? Only cranked (with tone working fine).

FAB

[stingray_65]

I too have just built a 5F2A

I used an 8" fender speaker (ceramic magnet, ribbed cone, unkown origin)

it sounded a bit muffled too

I'm ordering a Weber Blue Pup as it will go in a champ sized cab too.

I had to say OMG! when I hooked it up to a Weber signature 12 alnico I have as a seperate extention cab.

loud , clear and punchy, the amp itself is very sensitive to attack and so many different tonal flavors can be achieved with different guitar playing styles.

the test guitar is a cheap strat squier.

I followed the schematic faithfully except for the heater wiring. it is EXTREMELY quiet, I can only hear the hum when i have my ear next to the speaker, and even then it's less than a wisper.

OH! I used a linear taper for the tone control (1M )

after I had it running good I made a mod to the NFB

on the Volume control I changed out the regular pot for a pot with a push pull switch

I hooked the wire that comes off the output transformer and spliced it into the switch

I then halved the NFB resistors resistance by piggy backing the same sized resistor ontop of it (i did it this way for ease of removal if I didn't like the results) (I liked it)

with the heavy NFB the amps a bit quieter, but the cleans are WAY cleaner and I have a percieved higher headroom.

whith the NFB switch out it has a very nice early breakup, kind of dirty gritty bluesy sound. really has an early ZZ Top sort of sound to it

by the very nature of the volume/tone stack design there will be interaction.

I often feel that playing with tweed tone stacks is a lot like using a OUIJI board

I'm not a fan of it having built a few tweed amps now, but when dialed in the tone is PURE VINTAGE FENDER

I'm anxious to hear the amp with an 8" speaker

I try to steer all the kids I build amps for toward Webers, they really have the best bang for the buck (IMHO) and all the ones who have tried them REALLY love the sound

OH! just curious did you buy the ceramic or AlNiCo?
On these small SE amps (Princeton/Champs) I think the ceramics are a better choice, but if you write to TED at Webers, He'll give you sound (pun intended) advice prmptly.

Just my .02 take it with the grain of salt

Ray

[Fabio]

Hello stingray_65,
I know the espeaker is a very important part of the ampli.
But, I'm using a 12" 8Ohm apeaker (METEORO http://www.amplificadoresmeteoro.com.br/site/) disigned for a 100W transistorized ampli. I don't know if it's ceramic or alnico. I thinhk it's FERRITE.
I tried with 8" 15W beherinher speaker too, and 15" old speaker that I had in my house, but the results were the same.
My 5F2A is only a head. I'm not looking for a cab (yet). I'm a begginer!

I was using a Gianinni with sigle pickusps Select EMG.
With Flying V, I got Heavy Metal.
I agree with you...Different guitars ---> different sounds.

I was looking for a clean sound with high saturation only cranked for most sort of guitars.

I'm using linear taper (1M) for tone control too and log for Volume (1M too)

IMO 5F2A has so much gain (with 12AX7) and needs to be calmed (and I gave him a valium).

I reach my objective with ECC82. Before it I tried ECC81 (gain 60) and I felt a good sound, for different speakers.
Then I decided for ECC82.
Try it too, may be will became surprise. (do not take you a valium)

FAB

[Fabio]

5F2A with ECC82 and wiring

5F2A with ECC82 and wiring
The wiring I founded at the web site
http://www.diycustomamps.com/princeton.htm

[stingray_65]

I'm building this amp as a gift for a very good friend

he has allowed me unlimited use of his shop for the last 5 yrs and I have built so many different things in it including a show winning custom chopper and every amp cab and chassis I've mad so far

the fun part of this is he is a guitarist and wants me to build him an amp, but he has never come straight out and asked.

He's seen every aspect of this build and was the person I had playing the guitar while I trouble shot the amp and dialed in everthing till it sounded great.

infact I just got back from there and have the cabinet peces layed out on his bench ready for glue tommorow morning

the mods I have made have all been by his suggestion, he had said it would be nice if an amp could have 2 sounds so I put the switch on the NFB and halved the resitance. He liked the snakeskin tolex I used on my son's 5E3 so it gets wrapped in snakeskin. he also has DJ equipment so I added a balanced XLR output off the 4 ohm tap on the OT. all the time I've been building this he has told me his story of his old VOX amp he had back in the 60's and how he had to sell it to make rent just after his first child was born, so I ordered Webers Blue Pup to give it a Vox flavor when he plays it clean with the heavy NFB

he was really blown away when I pulled out a vintage NOS set of RCA tubes for it.

I'll have to try that 12AU7 (ECC82) and look around for a NOS RCA if it sounds alot different just so he can have the variety.

Ray

[Bruce / Mission Amps]

In order for the tweed tone and volume controls to work right you must use two 1M audio pots.
Use a single 500pf to 680pF cap for "treble add", ...and to roll the treble down, at least a .0047uF cap, which is grounded at the tone pot.
If you want a warmer tone use a .01uF cap for the bottom of the tone pot and a 470pF treble cap at the other end.
The volume and tone pots are blocked by a .022uF cap after the 100k plate load resistor.
You don't need to make that any smaller or any larger for great tone.

[Fabio]

As I said I'm a begginer. Sorry!
The NFB resistor connects the circuit to the Output Jack to the wire of the OT?
If YES, Did you install a 22K resistor on the NFB resistor 22k reaching a 44K resistor ?

Really, it's cheaper than a tube.

I'll try it too and maybe come back to 12AX7 SOVTEK

Thanks
FAB

[stingray_65]

the NFB (Negative Feed Back) resistor is the 22K resitor between pin 8 of the preamp tube and the secondary side of the output transformer.

It is usually mounted on the tagboard

I've drawn a picture so you can see how I made the modification

when you mount a resitor in this fashion it is said to be connected in PARALELL

the formula for figuring resitors in parallel is R1 x R2 x R3 / R1 + R2 + R3

so 22k x 22k / 22k + 22k = 11k NOT 44k

by lowering the NFB resitor you allow MORE of the output signal (which is 180 degrees out of phase to the signal at the preamp tube) to react with the preamp.

this has 2 effects

first it stabilizes the signal to the power tube allowing the signal to be amplified more before it distorts

second it lowers the over all output volume by it's dampening nature at the preamp tube

I'm pretty new to tube amp theory also so I hope I am conveying this correctly. I'm sure that if I need correction one of the more knowledgeable members will let us know.


The reason I mounted the resitor " piggy back " was so that if I did not like the change I could easily remove it.

I've often wanted to experiment with a resistor and a potentiometer in series to make a variable NFB loop

Ray

[Fabio]

Hello Ray,

Thanks very much by the explanation and the opportunity to discuss about 5F2A amplis.

I did the modifications!
The amp (with 12AX7) is calmer than yesterday.
The experience shows that you are right in all you said with NFB=11k !


But....
Let me see if I undestood your ideas: You are saying me that the power-stage (6V6) starts distort before the complete pre-amplifications stage arrive the top in 5F2A ampli, insn't it ??

Using 12AX7 and NFB = 11k you can better profit the 12AX7 pre-amplification satage before the 6V6 starts distort (alleviating the 6V6 tube).
In this way, (and in my case) the ampli became cleaner and calme about 10 or 15% and more amplified before it distorts. But in both cases, the pre-ampli stage and power-stage distort at some point.



On the other hand, based that the distortion may happens only in pre-ampli stage, (and based in my experiences), if you plug a tube with less gain like ECC82, the power-stage (6V6) supports (maybe) the total signal of the pre-amplification stage, and the distortion comes from only the pre-amp tube signal when saturated.

Obviously the total output volume is lower.

I prefer use ECC82 yet, but It's only myself opinion.

Regard's

FAB