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I'm looking to possibly add a choke/capacitor filter to the RM-9 amp and would like to know if anyone else has done the upgrade and was it worth the trouble?What value of choke to use?I know where to put it.Or does anyone have a mark II version with it already done?
Any help would be greatly appreciated.
Follow Ups:
The amp projects I'm starting now are all doublers. I'll be using a Hammond 155T after the doubler caps, then a reservoir cap. The choke is rated 0.5H, 300 mA, 30 ohm. This might not seem like much inductance, but it significantly reduces ripple and presumably noise. The second cap doesn't need to be too large. The doubler caps each pass 60 Hz current, but the reservoir cap is operating at 120 Hz. Also, because the doubler caps are in series, the load only sees half the capacitance of each in terms of storage and output impedance. In any event, a single 500V cap (or equivalent) will work well in the second position. As an aside, you might consider redesigning the bias supply to eliminate the Zener diodes. If the bias voltage can "track" B+ changes, potential fluctuations in output stage bias current will be minimized.
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Buy Chinese. Bury freedom.
Edits: 04/09/21
TK - would you say there are any advantages to 30 ohms DCR vs 10 ohms DCR given the same amount of inductance? I know you typically say the supply impedance is set by the final cap - so maybe the DCR isn't terribly important?
What should the value be?I've read if the capacitance is too high in this position-the B+ may go too high.I have a 100mf/500v and a 470mf/500v.
"I've read if the capacitance is too high in this position-the B+ may go too high."
The voltage won't move substantially higher, but it will sag less under load. That's what we want for an AB1 amplifier, because it tightens the bass response and reduces IMD. There's a point of diminishing returns, of course. I suspect most of these power supplies reach an optimal value when the capacitance after the choke roughly equals the capacitance ahead of it. IOW, if the doubler consists of two 200uF caps in series, about 100uF after the choke would be appropriate. That's not any sort of rule, just my own gut feel for all this.
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Buy Chinese. Bury freedom.
The RM 9 MKII had two chokes after the voltage doubler, one for each channel. Following the chokes were two 1000mfd 250vdc caps wired in series, which yielded 500 mfd at 500vdc. Roger Modjeski did not reveal where he purchased the chokes, but he did tell me that the DCR was 5 ohms. Given the size, they could not have been more than .3 henry (300 millihenry). The additional chokes and caps did make a noteworthy improvement. This power supply improvement and fusing each output tube are the differences between the RM 9 and RM 9 MKII.
Don't forget Edcor USA, they have a range of low inductance fairly low DCR chokes at reasonable prices too.
Will they ever stop painting their transformers blue? The parts might be excellent, but Edcor is an economy brand, and the distinctive color immediately identifies anything built with their products as an economy amplifier. Then there's the fact I don't want major components on top of my amps to be blue (or red, yellow or green, either). It's such a PITA to repaint black, I'd rather just buy Hammond and pay the Canada fee.
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Buy Chinese. Bury freedom.
This one is #159ZA 300mH 1A 6ohms 500vdc 2.5lbs
from Mouser.I think this on should work.Any comments?
It would not fit in the crowded confines of the RM 9.
I have a deeper case that I made years ago.It's 4" deep.
Edits: 04/09/21 04/09/21 04/09/21 04/09/21
NT
IN addition,I sheilded the PS cord and turn-on switch,put in Hexfred diodes on mains,low voltage Schottky (idea from Reference Audio Mods) 4 in parallel to bias,solid core 28 ga copper to filaments of 6550.Recently added Vishay
TX2575 into audio pathway from inputs to input tubes grids and plates.Major improvement throughout. No brightness but gobs of details and expansive soundstage. Almost wonder what could be better!
You'll have the best RM 9 on the planet when you are done.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
bogus subject
Music Reference did provide a Kit for this with the chokes-
it is a tight squeeze to fit it in, but works - and yes, where you highlighted the Schematic-
I'll dig through my notes to see if I have more info on this
and if there are any of RAM chokes available...
Happy Listening
Can you post a schematic?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
copy of schematic
OK. Where would you put it? If directly after the voltage doubler then the B+ to the output stage will be lower. You could put it in place of the 2.2k resistor and add a resistor to make up the difference between the choke's DCR and 2.2k and then the B2 and B3 voltages would be unchanged.
Why do you want to add a choke?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
After the voltage doubling caps,connect a choke in series to a capacitor connected in parallel to ground and then to the B1 supply.
Why?No real reason other than possibly making amp sound better.Tweaking.
That would probably work. The DCR of a decent choke should be low enough that it won't lower the B+ voltage much at all.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I'd suggest a Triad C40X. It's 10 ohms and .32H... Small. Around $12 plus shipping.
I think a few people here were using them in retrofitting other classic push pull amps with doublers.
JDM suggested those little Triad chokes years ago for LSES applications.
I still have 2 of them.
DT 667
Is .32H enough inductance to really do anything?The Hammond 193J is 10Hy 200ma and only 82 ohms DCR. Of course it wouldn't fit under the chassis but it would be the real deal.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 04/09/21
The glasses are sitting on the power transformer. The choke to the right is the 10Hy input choke. The potted choke in front is the 7Hy filter choke and the open frame choke is part of the 300b filament supply. All of these power supply parts just to operate one 300b. Overkill?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre',
are you using the 7H choke after your 10H input choke? How many uF following these chokes?
What output transformers are you using with your 300B?
Always enjoy seeing others DIY amps up here.
"are you using the 7H choke after your 10H input choke? "Yes.
"How many uF following these chokes?"
A lot! I don't remember exactly, I'd have to look but none of them are in the signal path. I cross at 200Hz before the input stage and I have a UltraPath film cap in place.
The reactance of that UP cap at 200Hz is tiny vs. the "reactance of the last cap in the PS in series with the resistance value of the 300B's cathode resistor" (no cathode bypass cap). So, for all intent and purposes, the signal path is cathode, plate, output transformer primary winding, UP cap and back to the cathode.
Without the UP cap there would be a cathode bypass cap and the signal path would be cathode, plate, OPT primary, last cap of the power supply, cathode bypass cap and back to the cathode.
"What output transformers are you using with your 300B?"
ElectraPrint Partial Silver, Single Secondary.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 04/23/21
The last pair of amps I built run a UTC S37 and a big C for its single-stage LC filter. 550 mA/8 Hy. Tested as an input choke delivering 650V at 350 mA without any signs of distress. Not overkill at all...though it could be that the CG-105 would have worked just fine at the 350V/250 mA operating point I am loading it with.
Need more damper diodes...LOL
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Tre',
You were the one that influenced my preference for L-critical supplies. I'd agree - with a fresh supply design I'd go with a choke that would be more substantial.
In tight quarters with an existing supply that works I'd go with what fits and doesn't change B+ voltage much.
You can get 500+V electrolytic caps now - no need to series IMO with regards to the rest of the upgrades on this amp in question.
You can also get Panasonic 50uF film caps at 500V pretty cheap - and they are small!
"with a fresh supply design"
I always go off on a tangent.
It looks like the OP did make some additional room by providing a deeper case but with limited space you can only do what you can do.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
With existing stuff like a Dynaco chassis, there is not much room for 'improvement'. Just a bit too much of 'built to price point' for my taste. Now a St.70 converted to monoblock operation is quite another story. Swap an OPT for a choke, and install dampers where its EL34's used to live and you are now free of needing a GZ34, or a bigger power trans.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
This is a big little amp. S271S output. S37 choke, Beckmann D/U power iron, and 6CJ3 rectifiers. Input stage is 25HX5. Balanced input. It is about as heavy as I am comfortable with... :)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
good to see pics of your builds douglas!
custom shelving needed!
I'm guesstimating 38" in length ... ?
Nah, only 31 x 11.
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I would say as a complimentary choke in a design without one yes.
Smaller choke good for HF hash? I don't know. I think either McShane or Samara (spelling) liked them.
I've used them.
RAM wants about $400 to put together a kit. I found this choke that looks good but I'm not sure of the proper parameters.
The inductance of the Mouser chokes you linked is way too small for B+ filtering.
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