adding a midrange control to my YBA-3

[pbman1953]

It may be a long shot but I wonder if there is a way to add a Midrange control to my YBA-3. My ideal would to use one of the existing controls, like the Treble Expander. i have no use for it


Don't get me wrong,  the amp is great but a bit heavy on the midrange. I'm getting tweaky now but I figure around  800- 1k.  Right now the amp has that Ampeg full steam ahead tone.  If there was a midrange cut, I could get the amp closer to a Sunn 2000 . It would be awesome to have both tones in one amp.  I'd love to smooth out that midrange area


Can this be done easily otherwise or somewhat easily?






http://www.freeinfosociety.com/electronics/schematics/audio/traynor_customspecial_yba3b.pdf






Thanks

[sluckey]

That amp has very uncommon (for guitar) 'active' tone controls. I don't see any easy way to add a midrange control short of ripping out all the tone controls and building something more common. I would not do that.

[dnator]

I know of two (there could be more) stand alone mid controls you could maybe use.


One is in the Matchless Chieftain and was in some early Gibson amps.
http://el34world.com/charts/Schematics/files/matchless/matchless_chieftan.pdf


The other is in the Framus Cobra and IMHO sounds better than the Chieftain one.
http://i53.photobucket.com/albums/g57/chromaticdeth87/cobra.jpg


I'm not exactly sure where the best in your amp to put one would be. Maybe before the MV.

[shooter]

I was wondering about making R13? ,(22k from bass to ground), a pot.  Would that work sorta like the pots I've seen that guys call "meat control?"  I'm with Sluckey on this that is quite complex TS. I'm surprised with all the switch/pots for T&B they don't effect *mid* .

[pbman1953]

 The switches just make it brighter with no effect on mids. A little masked but not pushed out enough.


Thanks

[PRR]

Overall I sure agree. This is a very fancied-up amplifier and it resists neat/simple changes.

The "treble expander" network gives a midrange peak and rolloff even at "minimum" (max pot value). This is surely good for someone(*); but if you think the mids are distressing then you do NOT want this.

Hack below puts the 3rd stage dead-flat with average gain similar to before. It can be done with few snips and only one new part. Do that temporarily and see if it is more to your liking.

(*)Have you heard the bass-only mix of Yes' Roundabout? You do not hear it under the guitar and organ orgasms, but the bass line is VERY jangly. If it was a piano I would be pounding loose pins and installing new wound strings. This is the -type- of thing the YBA3b "treb expand" would do, and yes it sure worked well in the Roundabout mix, but could be very annoying with a less-crazed act.

[pbman1953]

Looks like you're taking the pot out of the system?

[PRR]

Taking the whole R-C twin-T network out.

The pot is a frill. It turns from more-mid to MORE!-mid. Just snipping the pot is not enough. All them other parts bend the response in the midrange. So bypass the whole enchilada with a several-hundred-K resistor, make it flat.

There may be other mid-boosts in the system. It looks like somebody played with a capacitor box for a long time. 

[pbman1953]

Looks simple. If you look at the picture I think all that has to be done , at least for testing is


Lift out the 47K resistor and the connected 120k


Lift out the yellow wire, which is the feed from the 100k resistor


Attach the new resistor to the yellow wire which connects to the 47k

[pbman1953]

I do have  some 220's, but going up in value will have what effect?


Thanks

[PRR]

More gain.

[pbman1953]

Please help me understand what more gain will do, subdue  or expand the mid?
Thanks

[pbman1953]

As far as the sound I'm looking for:


Tommy Shannon
John McVie-  Blues band days
Leo Lyons- Ten Years After




I have it with the my Sunn 2000s. Very smooth and deep


I'm always looking for: I'm here and you can see and feel the bass but not here I am, look out. This amp is scary dynamic  so I'm looking just to calm down the mid area


Thanks

[pbman1953]

Mod recap-


After trying many combinations with different resistor values I  ended up with a 250K pot instead. The stock pot, listed on the schematic, was supposed to be 250K. In reality it was 212k. I installed a tested 250k.  I set it up as a gain control not a volume . So the ground leg was opposite of a volume control. Overall I have 3 settings that work out well with out loosing that much gain . As far as the positions I have a 6:00 , 4:00 & 3:00. Anything under 3:00 cuts into the gain 


Thanks to all for making this a success!


And very easy

[jjasilli]

Checkout the manual, which can be found on this page:  http://www.0rigami.com/vb/models.html#customspecialyba-3


If you're treating the tone controls like the more standard FMV tonestack, the results will be unsatisfactory.  It appears that the amp's tone controls are "h-fi like".  I.e., with the treble & bass pots @ mid-position, tonal response is flat = no mid-cut.  Turning these controls down from 12:00 o'clock will further emphasize mids.  To "cut" mids, you instead need to boost hi's and maybe lo's too, past their pots' mid positions.  Then you can tweak the expander controls.  You may then need to re-adjust overall volume.  If you haven't tried this, it's worth a go.

[pbman1953]

I've had both of the YBA- 3 series amps and the only controls that really change things are the treble and bass. The Bass expander makes the mids worse. The Presence does open up the sound some and has no ill effect on mids. The treble expander makes the sound even brighter than it should be. After someone in an earlier post mentioned Yes, I can now see that the Treble boost and bass boost was a match made in heaven for that tone. I don't use them. Both of them increase noise.


The amp has an inherent strong mid like an Ampeg SVT does. I was only in line to calm that down some

[pbman1953]

Any comments on what I did?




Is there a similar tweak I can do with the Bass Exp?


There is quite a bit of mid when using that. I'd leave the Presence as is.


Thanks

[pbman1953]

Is there a similar tweak I can do with the Bass Exp?There is quite a bit of mid when using that. I'd leave the Presence as is. Thanks

[PRR]

> similar tweak I can do with the Bass Exp?

Same thing, of course. Jump the twin-tee network with a resistor to taste.

[pbman1953]

Thanks PRR for coming back!




Couple things-


Did you see my reply #14 on what I ended to do?


Also in the case of the Bass exp. the Presence is tied in. I'd hate to loose that but keeping it could complicate things. Otherwise, same resistor values?


http://www.freeinfosociety.com/electronics/schematics/audio/traynor_customspecial_yba3b.pdf

[pbman1953]

I just noticed something-


On the Bass EXP there are supposed to be 2- .01uf caps connected ( c22 & c23) where the Presence control comes in. I noticed that the caps are really .001 not . 01


What effect would  that wrong value have?

[PRR]

I think you are rather on your own with this amp and quest.

You have a soldering iron. If you think the 0.001 are a mistaken 0.01, tack in the "right" values and see/hear the difference. Likewise with bypassing tone-networks. It was all developed try-and-see, that may be the best way to re-develop it.

[pbman1953]

I think I get the right cap value in there and leave it


Thanks!!

[HotBluePlates]

I looked the tone stack placed between the plate of v2a and the grid of v2b, and found it close to the "E series" tone stack found in the Duncan Amplification.

They are more-different than alike.


The circuit at the plate of V2A is a feedback loop to the grid of V2A (which reduces gain of that stage). Inside that feedback loop is a twin-T network, and if the junction of C5 & R9 went to ground instead of the Treble Expander pot (and R44), then that network would provide theoretically infinite attenuation at one frequency. The relative values of the twin-T components (R7, R8, R9, C5, C6, C7) determine how narrow that notch is.


Because the "infinite reduction" twin-T is sitting in a negative feedback loop, it's really infinite reduction of negative feedback at that frequency (and a band around the center frequency). Which means boosting of apparent gain at the center frequency, and the band of frequencies around it (again, the twin-T values determine the narrowness of the notch, or the width of the band that gets boosted). There is resistance between the Expander pot (and the resistance of the pot itself) to allow some variation between a minimum-boost and a maximum boost; max boost should occur when the resistance to ground is the least.


PRR's 1-resistor change sets a fixed amount of feedback for all frequencies, and can be adjusted by raising/lowering the value of the resistor jumpering the twin-T network.


Repeat all that for the Bass Expander section. The Presence control is just another way to cut the feedback around V2B to boost extreme highs.


The Treble and Bass controls between V2A and V2B (C10-C13, R11, both R13's and the pots) are just a common James tone control. Max midrange happens when you turn the Treble and Bass pots to 0; minimum midrange happens when you turn the Treble & Bass pots full-up. In this circuit, midrange is essentially fixed at one level.

[pbman1953]

"Repeat all that for the Bass Expander section. The Presence control is just another way to cut the feedback around V2B to boost extreme highs."


So you're saying to cut out that whole section and a play with the resistors as in the first mod?

Also where is the cut point:

1) after  or before the .1- 400v cap from the volume control

2) The second point would connect to the resistor to the 220k that is connected to the terminal 2 of the V2B , right?

Thanks

[HotBluePlates]

On the Bass EXP there are supposed to be 2- .01uf caps connected ( c22 & c23) where the Presence control comes in. I noticed that the caps are really .001 not . 01

What effect would  that wrong value have?

Shift the range of one side of the twin-T notch, possibly changing the center-frequency of the notch (but now in NFB, so effective boost).

If you're thinking they're 0.001uF instead of 0.01uF, swap them out and see what you think it sounds like afterward.

"Repeat all that for the Bass Expander section. The Presence control is just another way to cut the feedback around V2B to boost extreme highs."

So you're saying to cut out that whole section and a play with the resistors as in the first mod?

If you're sure you don't like the effect of the expander controls, you can defeat them out of the circuit. The net result is none of the voicing of that circuit left in the amp's sound.

Essentially, the Treble Expander and Bass Expander are the exact same circuit, but with R and C values adjusted to act in different ranges. Through in a series R&C to ground in the Treble Expander circuit to keep a shelving boost for highs, through in a similar circuit in the Bass Expander to selectively boost highs for the Presence circuit.

Breaking a couple key connections and substituting a single resistor leaves the response essentially flat instead, so cathode bypass caps and coupling caps (along with tube internal capacitance) set the frequency response as in many guitar amps. You'll also listen to just the effect of the Treble and Bass control in the James tone circuit without all the extra mess (and get to evaluate if you like the operation of that circuit).

Also where is the cut point:

R14 should become ~470kΩ; it will have one end to V2B pin 2 and the other end to ground. C15 keeps one leg connected to V2B pin 1; the other end connects to a new resistor of ~220kΩ. The end of that new 220kΩ not connect to C15 connects to V2B pin 2. C20-C23, R17-18, R38 and the Bass Expander and Presence pots are no longer connected into the rest of the circuit; you could/should remove them from the amp or disconnect the wires from them to C15 and R14.

All this does is eliminate the Presence and Bass Expander functions and whatever tone-shaping they contribute which you can't dial out. Overall signal levels should stay about the same, except you may miss the "added gain" of the boosts which previously existed.

[pbman1953]

After thinking about this I've decided just to bring the Bass Exp/Presence back to stock at .01 uf.


Do any of these tone circuit changes require a re-bias?


Thanks to all who helped

[HotBluePlates]

Do any of these tone circuit changes require a re-bias?

No, re-bias not required.

[pbman1953]

Thanks, the amp is really cool now.




I've had the YBA-3A super and I thought it sounded good.I have a change of heart now that this amp has 6550's.  Some guys like the stock 6CA7 because it's crunchy. Give me the big bottle for the smooth big sound.

[pbman1953]

I have yet another question about this amp.




With the use of Humbucking type basses the amp is quiet. With a single coil ( Ex: Jazz Bass)  it's nosier/ hummy. With my Sunn 2000s both bass types are fine.




Is there something simple that can calm the hum down? Possibly an easy part swap?


Thanks

[HotBluePlates]

With the use of Humbucking type basses the amp is quiet. With a single coil ( Ex: Jazz Bass)  it's nosier/ hummy.

Same thing happens to me when I use Humbucker & single coil guitars. The noise difference is almost certainly the difference in noise-cancelling ability of the pickups.

With my Sunn 2000s both bass types are fine. Is there something simple that can calm the hum down? Possibly an easy part swap?

No, it's probably a matter of speaker or amp frequency response. Again, same thing happens to me when using humbucker/single coil guitars with different amps. Some make the noise present more obvious.

[pbman1953]

Thanks, I was just hoping to scale down.  Otherwise the amp is great!