Best location for a choke

[pbman1953]

I was advised to install a choke in my Traynor YBA-3a because it doesn't have one. I was wondering the best location.


I sent the link to look at the schematic.  I'm replacing the 470 ohm resistor ( R42 -10W) with a 3 mh choke.




http://www.freeinfosociety.com/electronics/schematics/audio/traynor_customspecial_yba3c.pdf


I mounted it in the chassis now behind the volume control and any hum I had has increased.    Before the choke install I had some hum and with with Ed's help it has reduced some. Before the choke,  the hum would increase with the master and the volume control would amplify it. After the choke install, the master still governed the hum but  the volume does not amplify the hum at all.


I may unscrew to move around to see if the hum changes.  I have the choke inside, if need be I'd install it tube side and install a grommet for the wires


Any suggestions?  Space is limited

[sluckey]

A 3mH choke ain't very effective at 60Hz. You need something like 3 to 10 H.

[PRR]

> replacing the 470 ohm resistor ( R42 -10W) with a 3 mh choke.

1) If Pete thought it would be better with a choke, he wudda choked it.

2) to get more than 470 Ohms worth of buzz-reduction the choke has to be nearer/over 1 Henry, 300 times bigger than 3milli-Henry.

So basically where Pete put 470r+20uFd or 7:1 of buzz filter, you have nearly none. Screens are not real sensitive but they are not deaf to PS buzz.

That's not considering the ill effects of putting any power supply points near a sensitive audio point like a volume contro.

[pbman1953]

I have back peddle a little- It's a 3 Henry-


http://www.classictone.net/40-18058.html




Update on the hum. I un-soldered so I could move the choke around. The amp didn't like where I picked and moved it to the rear and the extra hum went away.




In the past Ed told me to prob around with a wooden chop stick to see if wires were to close to others to find the hum source. . After some probing , with not much force, the   1K- 20 watt resistor broke about 1/4" from the body end.


I have to buy a new one, would you suggest to stay with the original value?

[shooter]

would you suggest to stay with the original value?

If this was an original amp, I'd stay with original values, you can bump the wattage, I use dale 25W riveted to the chassis.  If this is a new build, I'd want to know why it failed 1st.

[sluckey]

1/4 inch should be long enough to solder another lead to that resistor. But if you have to replace it get the same resistance value and same (or higher) power rating.

[pbman1953]

It is real short and due to age, I'll go for a new one.

[pbman1953]

Actually I looked at the resistor again and was able to hook on another wire to get the amp going again.

[Ed_Chambley]

> replacing the 470 ohm resistor ( R42 -10W) with a 3 mh choke.

1) If Pete thought it would be better with a choke, he wudda choked it.

2) to get more than 470 Ohms worth of buzz-reduction the choke has to be nearer/over 1 Henry, 300 times bigger than 3milli-Henry.

So basically where Pete put 470r+20uFd or 7:1 of buzz filter, you have nearly none. Screens are not real sensitive but they are not deaf to PS buzz.

That's not considering the ill effects of putting any power supply points near a sensitive audio point like a volume contro.

PRR, I have read you state that any amp above 15 watts you would consider needing a choke.  What about this design would not fall into this category?
The OP has been chasing hum and I have been helping with some improvements and I suggested he get a 5 Henry, 200ma choke for the screens and he decided on the smaller 3hy, which will work.


Should it not have a choke?

[sluckey]

Yes, it will benefit from having a choke. PRR's statement was based on the info that the OP used a 3mH choke, which is totally useless for smoothing 60Hz or 120Hz ripple from a power supply.

[pbman1953]

Ed did suggest a 5 MH, but I went with a 3 due to space . It fit inside and is flush with the chassis rim.   Should I have gone with the 5?

[Ed_Chambley]

Ed did suggest a 5 MH, but I went with a 3 due to space . It fit inside and is flush with the chassis rim.   Should I have gone with the 5?

The choke is fine Rich.  It is a replacement for a 100 Watt Marshall, so it will be fine.  The one I suggested is just a different Marshall.

[pbman1953]

Thanks Ed,


At least by adding the choke the amplifying of the hum, from the volume control,  stopped.


Now,  I just have to deal with the master .


Sound wise it's great!

[Ed_Chambley]

Thanks Ed,


At least by adding the choke the amplifying of the hum, from the volume control,  stopped.


Now,  I just have to deal with the master .


Sound wise it's great!

Yea Rich.  Just keep looking at the parts one at a time and you WILL find it.  It is very possible you have more than one thing contributing to your hum, but you can bet it is around the V2 area.  We know of at least 3 different things now, 2 of have reduced the hum somewhat.


Other than decreasing some of the hum, can you tell any difference in the way the amp responds having the choke?  Also, keep in mind your work can help others who may be lurking, so keep posting your progress.

[pbman1953]

I'll keep plugging at the hum.


I'll know better Thursday night, because I'll using it in a band setting. For the time leading up to this it's mainly been low practice volume.


Thanks

[PRR]

> you state that any amp above 15 watts you would consider needing a choke.

I can't sit well and may have mis-typed. Please point to where you saw this.

> did suggest a 5 MH

*Please* keep your units straight.

In your paycheck, 5 bucks and 5 milli-bucks (half cent) are very-very different.

While a 5 cent paycheck might "obviously be a mistake", 5 milli-Henry chokes are readily available for lo-volt hi-amp chores.

[Ed_Chambley]

> you state that any amp above 15 watts you would consider needing a choke.

I can't sit well and may have mis-typed. Please point to where you saw this.

> did suggest a 5 MH

*Please* keep your units straight.

In your paycheck, 5 bucks and 5 milli-bucks (half cent) are very-very different.

While a 5 cent paycheck might "obviously be a mistake", 5 milli-Henry chokes are readily available for lo-volt hi-amp chores.

I looked and cannot find the comment about chokes, but I remember the topic.  No you did not state 15 watts specifically, but in reference to the 5E3 vs 5E5.  I was just lurking and not commenting on the thread, but was building a Trainwreck at the time and testing it without or with a choke as Fisher never used one.  Some were saying the 5E3 has no choke and this is when you contributed.


Anyway, what I remember may not be correct, so if it is not or did not come from you I apologize for quoting you.  What I remember is simply you saying you would consider using a choke especially on any larger wattage amp.


I searched and you name with choke or 15 watts brings up too much stuff.  It was a few years ago, but now is now and since now is now, if you were designing the amp in question or if I were would you suggest a choke?  If so, what would be the purpose for not using one other than costs?


The reason I remember is so well is I did not use a choke, and since have omitted using them, but I always worry because of reading your comments. 

[Ed_Chambley]

> you state that any amp above 15 watts you would consider needing a choke.

I can't sit well and may have mis-typed. Please point to where you saw this.

PRR, I found the thread, but you stated you are not a fan of chokes for small amps, but here it is a good idea.  Here meaning a KT88 push pull power section.
I took from that comment you meant something like any amp over 15 watts because I think of "small" amps as any Push Pull that uses small tubes.  Even the 22 watt Deluxe I consider a small amp.


The thread is here:
http://el34world.com/Forum/index.php?topic=15436.msg148745;topicseen#msg148745

[PRR]

OK.

IMHO, at modern prices, no-L filtering is perfectly practical up into the 100W level. Which is what that thread was about. As you get to 100W, you need to sharpen your pencil and compare cost/weight for a C-only design and a C-L-C design. Even then there is no "do this": those 300 Watt Bogens I had used no choke.

[pompeiisneaks]

OK.

IMHO, at modern prices, no-L filtering is perfectly practical up into the 100W level. Which is what that thread was about. As you get to 100W, you need to sharpen your pencil and compare cost/weight for a C-only design and a C-L-C design. Even then there is no "do this": those 300 Watt Bogens I had used no choke.

As I understood it, didn't the choke use back in the day come from cost?  Chokes were less expensive than high watt resistors?  Or is that completely out of nowhere (my brain :D)

Why would they use chokes vs resistors then, and why is it better to do resistors now per this suggestion.  It's one of those topics I've never fully understood.  (sorry for the hijack)

~Phil

[sluckey]

Chokes were more available than big electrolytic caps.

[Ed_Chambley]

OK.

IMHO, at modern prices, no-L filtering is perfectly practical up into the 100W level. Which is what that thread was about. As you get to 100W, you need to sharpen your pencil and compare cost/weight for a C-only design and a C-L-C design. Even then there is no "do this": those 300 Watt Bogens I had used no choke.

As I understood it, didn't the choke use back in the day come from cost?  Chokes were less expensive than high watt resistors?  Or is that completely out of nowhere (my brain :D)

Why would they use chokes vs resistors then, and why is it better to do resistors now per this suggestion.  It's one of those topics I've never fully understood.  (sorry for the hijack)

~Phil

Here is a good read on choke usage.
www.aikenamps.com/index.php/chokes-explained

And a simplified version

http://www.300guitars.com/articles/chokes-what-are-they-what-do-they-do/


In practice experience on building the Trainwreck circuit, when I added a choke the amp tightened up and this circuit is all about distortion and being able to clean up by reducing signal.  The difference with the choke is the Bass became tighter and the amp lost the greasiness.  It also had a effect on the overall sound, feel and reduced the overall distortion.


The reason I mentioned adding a choke to the Traynor was he has modified the amps plate resistors adding more gain and changed from EL34's to KT120's.  Being familiar with the Bass extension that comes from the KT120's and my experience with adding and removing chokes is why I suggested adding a choke since the OP was doing quite a bit of modifying the circuit.  These modifications somewhere along the line have added noise and the OP is chasing noise.


As you can see, the OP's amp has gotten quieter since the choke addition.  Not saying you couldn't get it quiet with a resistor.  I am sure Traynor had their reasons for designing the Bass amp without a choke, but when you begin modifying an amp you are no longer following the designers outline.

[Ritchie200]

I'd like to hear that Traynor when it's done!  Please post sound clips!

Jim

[jojokeo]

Ed,
That 300 guitars link gives incorrect info in a few places and is worthless compared to Aiken's site. Also Aiken's link doesn't work. Try this instead: http://www.aikenamps.com/index.php/chokes-explained
 
I don't care for the 'wreck's "greasiness" and over the top distortion character myself. Recently, I doubled up the reservoir cap & carried the other's nodes down on the string since there was an available cap on one of the cans not being used. BIG improvement. This had a 1k/25w resistor and the amp tightened up greatly with the caps wiring changes.
Without knowing your friend should employ shielded wiring where appropriate, get those grid resistors on the tube sockets, minimize grid wire lengths, etc... and ALWAYS go through the grounding scheme very thoroughly. Putting a choke and any other power supply wiring, & OT wiring anywhere near a Vol control is "rookie mistake 101" as pbman will now know. As for lurkers...you mean like me?! 

[HotBluePlates]

The 300guitars explanation missed the mark; however, Aiken had the info.

Simple explanation:
If you have a 5H choke with a d.c. resistance of 150Ω, then it looks to ripple as though it were a ~3.8kΩ resistor, but only has the sag impact of a 150Ω resistor.

Chokes are used when you want a large impedance to alternating current but very much smaller impedance for direct current.

Big series resistors can knock down ripple in your power supply, but they also cause the supply voltage to fall if current draw increases, as it does in class AB amps. Yes, you might get some cool compressed sounds, but you also zap your amp's power output capability if you opt for the big resistor instead of the choke.

A choke is also valuable when your supply voltage is fairly low and you can't afford the B+ voltage drop due to a resistor as-big as as the choke's reactance.

But what PRR is saying is Traynor almost certainly considered the issue, and didn't find a choke warranted in that amp design.

The reactance of a choke is given as
X_L = 2*Π*f*L
f = Frequency in Hertz
L = Inductance in Henries


I just did something silly and used a 150H choke in an amp feeding 2 triode stages. The cap afterward is 10μF. For 120Hz (ripple frequency), the choke looks like ~113kΩ while the cap looks like ~133Ω. Ripple output following the choke is about 1.2-thousandths of the ripple at the input to the choke. The choke itself has 3.7kΩ of d.c. resistance, but current draw is steady around 7mA total.

My B+ is less than 140vdc (this is a PRR 1/3-watt variant). I couldn't replace the choke with a resistor of the same size as the choke's reactance because a 113kΩ resistor will drop 791v when passing 7mA. In my amp, it drops ~26vdc (7mA through 3.7kΩ).

I chose to use chokes in my amp because I wanted a super-clean B+ rail, my starting B+ voltage was small (only ~168vdc), and I deemed the chokes used to be small enough and cheap enough to be viable (under $30 for a 150H and a 15H). I also chose to use polypropylene filter caps, so getting high-valued caps was not practical because of their huge size. So like classic tube electronics, I was using smallish cap values which made chokes "sensible".

[pompeiisneaks]

Thanks that's a ton of great info.  I should have clarified that I understand what a choke does to the amp, it resists changes in voltage, so it smooths the ripple, but the pros/cons you've shown make a lot of sense, and definitely seem to change some of the tonal characteristics of the amp. (I'm pretty sure I've read almost everything on aikenamps.com like 3 times :D)

thanks!

~Phil

[HotBluePlates]

... I understand what a choke does to the amp, it resists changes in voltage, so it smooths the ripple ...

It resists changes in current; a cap is the item which tends to resist a change in voltage.

But therein lies the challenge: there's several ways of looking at/understanding component parts & what they do, so the practical application gets obscured.

[pompeiisneaks]

Oh thanks, yeah that's something I'd misunderstood too :P

~Phil

[Ed_Chambley]

Ed,
That 300 guitars link gives incorrect info in a few places and is worthless compared to Aiken's site. Also Aiken's link doesn't work. Try this instead: http://www.aikenamps.com/index.php/chokes-explained
 
I don't care for the 'wreck's "greasiness" and over the top distortion characteor myself. Recently, I doubled up the reservoir cap & carried the other's nodes down on the string since there was an available cap on one of the cans not being used. BIG improvement. This had a 1k/25w resistor and the amp tightened up greatly with the caps wiring changes.
Without knowing your friend should employ shielded wiring where appropriate, get those grid resistors on the tube sockets, minimize grid wire lengths, etc... and ALWAYS go through the grounding scheme very thoroughly. Putting a choke and any other power supply wiring, & OT wiring anywhere near a Vol control is "rookie mistake 101" as pbman will now know. As for lurkers...you mean like me?! 

My friend is the OP and his amp.

You simply do not like wrecks and I really don't either as they are not versitle. I don't have one, but I can build one.