Two Things: Toroidal Transformers; And No Chokes?

[jet66]

I've seen them (toroidal transformers) used in a few amps here and there. Why are they not more commonly seen in guitar amps? Is it a cost thing, or a tone thing? It seems like they would be a good idea as a power transformer, at least.

Also, it seems like there are a good number of amps that forgo having an 'old fashioned' choke coil/inductor. What are they using in its place, and what are the pros and cons?

 

[talltxguy]

On the Boogie Board, I asked why Boogie did not install chokes on their amps, and I got no responses. Curious about this as well.

 

[hunter]

You can use a choke or a resistor (I think). I have no choke in my Conrforf Mk50 and I think it plays a part in its tone. It's more >smack< on the attack but still blooms nice on the decay/sustain phase.

Torroidal transformers have advantages for noise, but they don't sag like old fashioned ones. It can be worked around with other parts, some resistors here and there or whatever. At least that is what Larry explained in another forum.

I have seen torroidal amps that sounded great, especially the early Eggie/TOL or Laney GH50L.

 

[MARK2C]

What Boogie does not have a choke ?

As for the use of a resistor, I feel it adds more sag to the tone. To my ears at least.

Toroids are really just another way to wind a transformer IMHO and are more common in preamp designs
due to space. I think Laney used them for a while as well in production amps. I have never strayed from using
big iron so I cannot comment on the tonal impact.

 

[talltxguy]

Unless I'm mistaken, NO Boogies come with a choke from the factory. I've not heard any mention of this from anybody on the Boogie Board, nor did I see choke mentioned in any of their descriptions of their amps.

 

[jet66]

Torroidal transformers have advantages for noise, but they don't sag like old fashioned ones. It can be worked around with other parts, some resistors here and there or whatever. At least that is what Larry explained in another forum.

That sag is probably the/a good reason, then. Less noise and (usually) less heat/more efficiency were two things that I thought might be in their favor, but I know that doesn't always translate in to 'good tone.'

As for the use of a resistor, I feel it adds more sag to the tone. To my ears at least.

That would make sense, some arguments I've seen for adding a choke and cutting out the resistor/s (I wasn't sure if it was just one, or a network) was for a more constant voltage supply, which would have less sag, going on that logic. Might be a boon for someone wanting a tighter amp, then.

 

[MARK2C]

Every Boogie I have ever seen has a choke. Every one from the MK I to Road King.

The Resistor replacement for a choke should give you a bit more blur in the notes and a tad looser bottom end.

 

[ed the yak]

Yeah, my Rectoverb head has a choke on it. I just found this article about chokes.. pretty good read

http://www.300guitars.com/articles/chok ... o-they-do/


I was also on the Fryette board a little while ago and there was a question about the newer Deliverances not having chokes vs. the old ones. Support chimed in and said the difference was pretty subtle.

http://www.vhtusers.com/forums/showthre ... ight=choke

 

[glpg80]

normally you see toroidal transformers in areas where space is of concern. they have limits to their design compared to EI or C type transformers. however they can withstand inrush currents in a much more stable manner. if you design your power supply circuit properly you wont need to use them - but laney always over-engineers or you wont have enough room to take in those considerations leaving the reason why you are using a toroidal trafo in the first place.

also the winding of a toroidal is harder to control because proper guage difference deviances can cause problems close to completion - not being able to get enough winds in before the center reaches a particular tolerance point. so you have to choose the core magnet carefully and this takes experience, otherwise you wont be saving space at all.

another reason we dont use them is because we also do not have space limitations to go by since most of the 3-5KVA TRAFO's we use by design are mounted externally. we simply have no reason to.

also, toroidal transformers can be more expensive to make

 

[JerryP]

Every Boogie I have ever seen has a choke. Every one from the MK I to Road King.

The Resistor replacement for a choke should give you a bit more blur in the notes and a tad looser bottom end.

+1
Boogies use a choke.
Jerry

 

[novosibir]

There's not much mystery about chokes or their substitute by a resistor.

The biggest advantage of a choke in respect to a resistor is its very low DC resistance, while its AC resistance is very high (what's required, to smooth out the remaining ripple as good as possible).
This allows to have the screen supply voltage not to far off of the B+, a difference of 2...5 volts usually, what gives the output stage some higher output power. But the output stage then also is rawer sounding due to some more K3 (odd order harmonic) - the rawer, the less the choke's inductivity. Example: Late 60's Marshalls have a 10H choke -> smoother sound. Early 70's Marshalls have a 3H choke -> much more rawer soundwise. Of course that's not the only difference, but contributes not negligible.

Now use a resistor, i.e. a 470 ohms or even a 1K like in the Trainwreck Express. Result, much more voltage difference between the B+ and the screen supply - a smoother sound, more 'touch sensitivity' of the power stage, but a reduced power output.

But the major advantage of a resistor is costs and its small physical size in respect to an adequate choke.
A disadvantage of a choke - if choosen too small in respect of current capability - is, that it might saturate. In this case spontaneously its inductivity is dropping to zero and the choke is acting like a simple resistor with its usually very low DC resistance with the result of enhanced ripple and hum.

There are some other ways, to get a 'smoother' sound and a higher touch response, even by using a 3H choke - but this post shouldn't become a small booklet

Larry

 

[MOAAH]

There's not much mystery about chokes ...
Larry

Great post and amazing looking preamp on your site.
I totally dig the 'Pure Evil' knob!!!
If I didn't build my own stuff I'd be ordering that preamp today
-------------------------------------------------------------------------
As for toroidal transformers, AFAIK they have a very limited availability outside of power trafos. The only toroidal OP I know of is designed for HiFi and has some weird secondary impedance like 5 or 6 ohms.

 

[jet66]

The biggest advantage of a choke in respect to a resistor is its very low DC resistance, while its AC resistance is very high (what's required, to smooth out the remaining ripple as good as possible).
This allows to have the screen supply voltage not to far off of the B+, a difference of 2...5 volts usually, what gives the output stage some higher output power. But the output stage then also is rawer sounding due to some more K3 (odd order harmonic) - the rawer, the less the choke's inductivity. Example: Late 60's Marshalls have a 10H choke -> smoother sound. Early 70's Marshalls have a 3H choke -> much more rawer soundwise. Of course that's not the only difference, but contributes not negligible.

Now use a resistor, i.e. a 470 ohms or even a 1K like in the Trainwreck Express. Result, much more voltage difference between the B+ and the screen supply - a smoother sound, more 'touch sensitivity' of the power stage, but a reduced power output.

But the major advantage of a resistor is costs and its small physical size in respect to an adequate choke.
A disadvantage of a choke - if choosen too small in respect of current capability - is, that it might saturate. In this case spontaneously its inductivity is dropping to zero and the choke is acting like a simple resistor with its usually very low DC resistance with the result of enhanced ripple and hum.

Thanks! That's the kind of detail I was looking for. Some info I found on my own gave a lot of technical differences, but not how it reflected on the sound and feel of the amp itself.

There are some other ways, to get a 'smoother' sound and a higher touch response, even by using a 3H choke - but this post shouldn't become a small booklet

Larry

Hey, if you want to go on, be my guest. I picked up my first adjustable bias amp about a year and a half/two years ago, and coupled with having to affect some repairs on my own in that time, I have become much more interested in how each smaller section affects everything else. The advanced technical aspects of the components themselves are often a little outside of my current knowledge, but the basic properties of what they do towards an end result helps to advance my understanding. It also helps me to better articulate what I want or don't want for the sound and feel I am after.

 

[Jimmie]

- but this post shouldn't become a small booklet Larry

I can't speak for anyone else but I for one, surely appreciate everything you have to say, makes a lot of sense, Thank you.
Jimmie

 

[talltxguy]

Thanks for the clarification on things, guys.

 

[Deleted member 3860]

...

 

[TheMagicEight]

Unless I'm mistaken, NO Boogies come with a choke from the factory. I've not heard any mention of this from anybody on the Boogie Board, nor did I see choke mentioned in any of their descriptions of their amps.

Look inside the chassis.

 

[talltxguy]

I finally found a Boogie that doesn't have a choke - my TA-15. lol I'm having a Mercury Mags put on it though - should be ready in the next week!

 

[joepete77]

most amps u see with no choke is done for cost savings as the main factor

 

[chumbucket]

Every Boogie I have ever seen has a choke. Every one from the MK I to Road King.

The Resistor replacement for a choke should give you a bit more blur in the notes and a tad looser bottom end.

+1
Boogies use a choke.
Jerry

Jerry,
What inductance of choke do you like for the 5150's?