What parts determine tone?

[pbman1953]

In a preamp what parts should be experimented with when trying to contour tone-


I have tube preamp pedal that's based on a B15 preamp. My question is, what is the determining factor that makes it a B15 emulation ?
 
  The resistor or cap that is connected to certain pins on the tube?

• Parts after the tube?
• The eq circuits?

   
I’m wondering , if it’s simple to change a value in the right place to make it more like a Fender or Sunn. The B15 s nice but I like a softer midrange, where Ampeg always seemed to have a stronger mid compared to most others.


Thanks

[acheld]

In a preamp what parts should be experimented with when trying to contour tone-

As a first step, I'd suggest going to http://www.duncanamps.com/tsc/ to check out the tone stack calculator. You can experiment with different components and/or setups given your question, which seems to point toward the tone stack.

"Gain" related tone is an entirely different discussion . . .

[WimWalther]

I have tube preamp pedal that's based on a B15 preamp. My question is, what is the determining factor that makes it a B15 emulation ?

There are many factors that can affect the sonic qualities, or "tone" of an amplifier, but they fall into two main categories: circuit topology and component choices.

So the particular circuit used can have a very large effect on the sound. After this, things like tube / transistor / op-amp types, capacitors, resistors, pots / controls, chokes, transformers and even wire and solder all contribute to the final sound to varying degrees.

Now I don't know what makes your preamp sound / behave like a B15 - there are several approaches to this goal. But chances are that the pedal shares the same basic circuit with the B15, and the components used are modern approximations of those found in the original.

Or at least that's how I (and probably others, here) might approach it. But in today's world of powerful yet cheap & ubiquitous electronics, digital modeling can't be overlooked.. but as the saying goes, that topic is beyond the scope of this discussion. ;-)

[pbman1953]

The pedal is an Arkham Oracle and the tone circuit info is here-


www.arkhamsound.com/james.html

[WimWalther]

The pedal is an Arkham Oracle and the tone circuit info is here-
www.arkhamsound.com/james.html

Apologies if I'm misreading you, but it seems like you're asking two different questions, here..

1) What makes my specific B15 emulation pedal "B15-like'?

2) How do different topologies and component choices affect the sound of an amp / preamp?

Which is it that more interests you? Which would be more helpful?

ETA: Many edits

[pbman1953]

The pedal is an Arkham Oracle and the tone circuit info is here-
www.arkhamsound.com/james.html

Apologies if I'm misreading you, but it seems like you're asking two different questions, here..


Both in a way-

1) What makes my B15 emulation pedal "B15-like'? What are parts that make it B15 like? Parts before the tone controls or after? Are there values that can be changed on the tube that could soften the "Ampeg" sound?

2) How do different tone stacks affect the sound of a preamp? I think tampering the tone stack would not be a good idea. I was hoping that changing a value on the tube may be the solution

 

[pbman1953]

Between this pedal and  other Ampeg inputs , pin 7, the Ampeg Normal channel use a 47k. This pedal uses a 1M

[Williamblake]

hth

[acheld]

The pedal is an Arkham Oracle and the tone circuit info is here- www.arkhamsound.com/james.html

Lots of good info on your pedal's information page, and how they've approached their tone. 

[WimWalther]

Between this pedal and  other Ampeg inputs , pin 7, the Ampeg Normal channel use a 47k. This pedal uses a 1M

If those are resistance values from input to ground, they are two very different loads, and likely to have a noticeable impact on sonics.

[pbman1953]

Between this pedal and  other Ampeg inputs , pin 7, the Ampeg Normal channel use a 47k. This pedal uses a 1M

If those are resistance values from input to ground, they are two very different loads, and likely to have a noticeable impact on sonics.

I was wrong on that one. The 1M is out of the circuit when the jack is plugged in

[HotBluePlates]

... The 1M is out of the circuit when the jack is plugged in

Not according to Arkham:

Specifications:

IN: 1/4" TS, Input Impedance = 1 Meg ohm

That said, the B15N schematic shows an input impedance of either ~5.6MΩ (Normal channel) or ~150kΩ (Bright channel).

The lower resistance of the latter would normally roll-off treble from the pickup (due to interaction with the pickup's L-C-R), but the upper leg of the 100kΩ/47kΩ voltage divider is bypassed with a cap to retain highs at full-strength.

[passaloutre]

2) How do different tone stacks affect the sound of a preamp? I think tampering the tone stack would not be a good idea. I was hoping that changing a value on the tube may be the solution

I would say it is precisely the tone stack that makes this sound like an Ampeg and not a Fender or a Sunn.

[AmberB]

The type of tone circuits that an Ampeg preamp has are quite different from the Fender/Marshall/Sunn type tonestack.
The Ampeg type tone circuit has the capability to boost the affected frequencys of the bass and treble controls from "flat" as well as to cut them.  Generally speaking, the frequency response is closest to flat when the tone controls are at about 5 on the 1-10 scale.
The Fender type tone stack is all cut, no boost.
That is one of the differences in the "sound" of the different amps. 
The RCA tube manual shows a typical tone circuit of the Ampeg type, it's almost like Ampeg just used the RCA circuit descriptions for a lot of their amps.
Bogan also used the RCA type tone circuits in a lot of their PA amps, especially the CHB series.
Also, there is an RCA type tone circuit that has a midrange control as well as bass and treble.  It's quite interesting.

[pbman1953]

... The 1M is out of the circuit when the jack is plugged in

Not according to Arkham:

Specifications:

IN: 1/4" TS, Input Impedance = 1 Meg ohm

That said, the B15N schematic shows an input impedance of either ~5.6MΩ (Normal channel) or ~150kΩ (Bright channel).

The lower resistance of the latter would normally roll-off treble from the pickup (due to interaction with the pickup's L-C-R), but the upper leg of the 100kΩ/47kΩ voltage divider is bypassed with a cap to retain highs at full-strength.

I was looking at my 70's B15 schematic and it doesn't have the 1M resistor, to ground, but here on the Hoffman site I see the early 60's versions do with a 120k resistor.

[pbman1953]

The type of tone circuits that an Ampeg preamp has are quite different from the Fender/Marshall/Sunn type tonestack.
The Ampeg type tone circuit has the capability to boost the affected frequencys of the bass and treble controls from "flat" as well as to cut them.  Generally speaking, the frequency response is closest to flat when the tone controls are at about 5 on the 1-10 scale.
The Fender type tone stack is all cut, no boost.
That is one of the differences in the "sound" of the different amps. 
The RCA tube manual shows a typical tone circuit of the Ampeg type, it's almost like Ampeg just used the RCA circuit descriptions for a lot of their amps.
Bogan also used the RCA type tone circuits in a lot of their PA amps, especially the CHB series.
Also, there is an RCA type tone circuit that has a midrange control as well as bass and treble.  It's quite interesting.

Based on what you said I'd never be able to cut the frequencies I need on this design.

[pbman1953]

The company is with holding the schematic. I can't blame them for not wanting their unit to be altered.


Would it help if I made a diagram to show signal path and the parts used?

[pdf64]

...
I have tube preamp pedal that's based on a B15 preamp. My question is, what is the determining factor that makes it a B15 emulation ?
 ...

1/ It's not marketed as being a B15 emulator. Rather it's "inspired by the iconic Portaflex Bass amps of the 1960's" https://arkhamsound.com/oracle.html
So from that, I wouldn't expect it to be an exacted copy of any particular B15 preamp circuit.

2/ A valve guitar/bass amp is a system, not just a preamp; what's the rest of your system?
In the absence of a power amp, speaker and cab that respond closely to those of a B15, even if it was an exact copy, a B15 preamp shouldn't inherently be expected to sound like the full amp. eg a B15 preamp into a full range flat response rig won't sound like a B15.

...The B15 s nice but I like a softer midrange ...

How about inserting a good graphic eq device between the preamp and the rest of your system?
That may be by far the simplest and most effective way forward.

[pbman1953]

Great responses.


I use a Bergantino 212 cab and Sumo Class D amp


I'm thinking of getting a parametric eq. Please keep in mind that both my B15 and SVT have switchs to filter out the peaky mids. This has the sweep range pot which doesn't lower the peaks.

[pdf64]

The type of tone circuits that an Ampeg preamp has are quite different from the Fender/Marshall/Sunn type tonestack.
The Ampeg type tone circuit has the capability to boost the affected frequencys of the bass and treble controls from "flat" as well as to cut them.  Generally speaking, the frequency response is closest to flat when the tone controls are at about 5 on the 1-10 scale.
The Fender type tone stack is all cut, no boost.

I disagree with several points above.
1/ it seems contradictory to describe the Fender tone stack as being 'all cut', whilst describing the Ampeg as being able to both 'boost and cut'.
As I see it, all such tone stacks enable at least treble and bass to be adjusted above and below some notional nominal level.
2/ If Fender is cut only, then so is the Ampeg.
3/ Rather than the Ampeg being quite different design to the others, all such tonestacks use a network of passive RC low and high pass filters to achieve their effect.
4/ on a 1-10 scale, noon or halfway or 50% rotation is at 5.5.
But pot tapers of the low spec pots used in MI gear are completely untoleranced, so it shouldn't be expected for that point to align exactly or even closely with the corresponding resistance on the published taper chart.

This site has more tonestack simulations than most versions of TSC https://www.guitarscience.net/tsc/info.htm

[pdf64]

Great responses.


I use a Bergantino 212 cab and Sumo Class D amp

Such an amp should be pretty 'transparent', zero natural compression, with a high damping factor keeping the speaker cones under tight control. All those will characteristics be very different for the B15 power amp.

Does the cab have tweeters?
Whatever, I'd expect much faster attack than from the B15 cab.

I'm thinking of getting a parametric eq. Please keep in mind that both my B15 and SVT have switchs to filter out the peaky mids. This has the sweep range pot which doesn't lower the peaks.

How about the 'hi' switch, by the gain control?
I guess that with hi engaged, balancing the gain and master will help to fine tune the hi mids.

[pbman1953]

The high switch makes it too bright. No tweeters on this can. Dont need them.


Please take 5ge can out of the equation. The sound of this pedal, let's say, sounds like an Ampeg type sound. Very strong in the midrange. I didn't realize it would be that strong but, it sounds better than anthing I've heard or played with.


I'm trying to draw up the wiring diagram. I have all parts Id'd so I'll send this drawing soon


Thanks to all!

[HotBluePlates]

... an Ampeg type sound. Very strong in the midrange. ...

You do realize that Ampeg's way to scoop-Mid is done by cranking up Treble & Bass, right?

Turn Treble to max, turn Bass to max.  Still mid-heavy?

[pbman1953]

... an Ampeg type sound. Very strong in the midrange. ...

You do realize that Ampeg's way to scoop-Mid is done by cranking up Treble & Bass, right?

Turn Treble to max, turn Bass to max.  Still mid-heavy?

You're 100% right. Arkham told me to max both the bass and treble and still it's barky in the midrange. I'm using my tube amps as a comparison. Comparisons were made with my Fender Studio bass head and my Sunn 2000s. Much smoother in the 600-1k area

[pbman1953]

I made a very crude drawing so I apologize first.


2 drawings- Input and tone controls.


You will see this "Point "B":


4 parts are connected together on a terminal:


.004uf cap- terminal from the treble pot
.001uf cap from the Low Boost sw
220k resistor from the Bass control pot
.002uf cap from the pin 1


Please let me know if this makes sense and if it does, would changing any these values help my issue? If not thanks very much for looking!

[pbman1953]

Anyone want to take a stab at this?

[passaloutre]

Playing around with the TSC, turn both Bass and Treble up to ten, then back off the bass to like 7-8 or so. That cuts out a lot of those lower mids without losing the fundamental.

[pbman1953]

Playing around with the TSC, turn both Bass and Treble up to ten, then back off the bass to like 7-8 or so. That cuts out a lot of those lower mids without losing the fundamental.

I've worked through many of the suggested adjustments from Arkham and others. Still nothing truly moves enough mid out to be satisfied with.


The next question is, from the drawing, if any of the parts could be subbed, or look for another preamp unit

[AmberB]

Here's something that may be of interest to you.

[AlNewman]

I've built a few amps with the James tonestack, and it's very versatile, that being said, everything has an effect on tone and gain.  I think it's fairly similar to the fender TMB stack, with the mids on 10 all the time.

If I were trying to reduce mids, I would look into reducing the value of the 22k resistor at the bottom of the bass control.  It's fairly easy to experiment with, as you can parallel different value resistors to find what you're looking for. 

[pbman1953]

I've built a few amps with the James tonestack, and it's very versatile, that being said, everything has an effect on tone and gain.  I think it's fairly similar to the fender TMB stack, with the mids on 10 all the time.

If I were trying to reduce mids, I would look into reducing the value of the 22k resistor at the bottom of the bass control.  It's fairly easy to experiment with, as you can parallel different value resistors to find what you're looking for.

You're a genius!


Yes that worked and made a difference to take some of the honk out of the mods. It is suttle, but could be enough. I started with all controls flat, all boosts off with a 15k, then 10k, then 5, the 1k and I settled on 470 ohm.


Thanks for taking on the challenge  with me!

[pbman1953]

Any other parts hat come into play?

[AlNewman]

I wouldn't have thought that 470 ohm would have been the value chosen, but if it works for you then that's good.  Try playing it for a while, and figure out what works for you.

[pbman1953]

I wouldn't have thought that 470 ohm would have been the value chosen, but if it works for you then that's good.  Try playing it for a while, and figure out what works for you.

What would you of expected?

[AlNewman]

Whatever sounds good.  I would have probably went with a 10k resistor to test.  470 ohm, I would think you're basically dumping all your signal at certain settings. 

[roseblood11]

Why not use a pot?
Carvin hat some amps with James tonestacks with B25k mid control, for example the Nomad, Vintage 33 and Bel Air.

[pbman1953]

Why not use a pot?
Carvin hat some amps with James tonestacks with B25k mid control, for example the Nomad, Vintage 33 and Bel Air.

Maybe that's what the Range pot is doing. It's controlling the 2 caps on the bass control and a resistor

[AlNewman]

If you want a fender sound with 2 knobs, build a deluxe reverb tonestack.  It will likely perform how you want.  As I mentioned earlier, everything is reactive in your James tonestack.  Just look at where the volume is positioned. 

[pbman1953]

If you want a fender sound with 2 knobs, build a deluxe reverb tonestack.  It will likely perform how you want.  As I mentioned earlier, everything is reactive in your James tonestack.  Just look at where the volume is positioned.

Thanks for all your help, but I've decoded to sell it t. I put it back to stock, resistor wise. Since better weather is coming,  I'll deal with taking out my tube amp, a Fender Studio Bass head. Weight wise it's not so bad and I'll get exactly what I want. Meanwhile I'll research more for something that suits my tastes.


Thanks!