Hey Paul, I don't thinks there's need for apologies. You're being very open as to where you're standing and we appreciate that. I guess some of us are so excited with this new project that we can become a PITA with our posts. Please take all of them as suggestions. In the end you know we'll find a way to mess around (while not necessarily improve) your final product. I think part of the fun of building BH kits is that. I'd never replace my BH amps with "finished" products for that reason!
SR45 amplifier
- Thread starter debk
- Start date
tsingle999
New member
Paul, i can't conceive of my sr-45 being flawed. It is one of the great pleasures of my meager existence! But if you can improve it in some way i am all ears
Paul Joppa
Moderator
I guess I haven't addressed the impedance question very well yet - I was feeling pretty crabby last night (for which I apologize to anyone who might have felt offended. Completely unrelated reasons.)
Anyhow, in my opinion, or according to my analyses depending on how you like to phrase it, 4000 ohms is as close to ideal as you can get for a 45. A 3K load exacerbates the already poor damping factor of the 45. On the other hand, getting full power from a 5K load would require a higher plate voltage than the tube is rated for.
By designing at 4K, a range of about 2800 to 5600 will work quite well (I calculate that as the square root of 2, multiplied by or divided into 4K) - that is, they will all produce similar power and distortion, with a slight tradeoff of higher distortion and greater power at the lower impedance, and vice-versa at the higher impedance. In my opinion, this is the best available compromise; those who wish to use different iron are welcome do so as long as they can figure out how to mount the components safely and effectively - and don't expect Bottlehead to guarantee the result! :^) In many cases that will require a new, larger chassis plate - but that's always been the case, and probably always will.
In the original SR45, I jiggered the operating point (lower voltage and a little too much current) to work best with a 3K load, since that was the only available quality iron for the Paramour at that time. Stretching that to 5K was a bit much, so I offered some adjustments, mostly just reducing the current. It increases the distortion a bit, leaves the power unchanged, and extends the tube's life a bit. I'd like to stress that all the above are quite small effects - I think most audiophiles might hear them but would be hard pressed to choose which is best.
Incidentally, in my current draft layout there is more room than usual for capacitors. But as I said, I haven't even shown this draft to Doc B yet.
Anyhow, in my opinion, or according to my analyses depending on how you like to phrase it, 4000 ohms is as close to ideal as you can get for a 45. A 3K load exacerbates the already poor damping factor of the 45. On the other hand, getting full power from a 5K load would require a higher plate voltage than the tube is rated for.
By designing at 4K, a range of about 2800 to 5600 will work quite well (I calculate that as the square root of 2, multiplied by or divided into 4K) - that is, they will all produce similar power and distortion, with a slight tradeoff of higher distortion and greater power at the lower impedance, and vice-versa at the higher impedance. In my opinion, this is the best available compromise; those who wish to use different iron are welcome do so as long as they can figure out how to mount the components safely and effectively - and don't expect Bottlehead to guarantee the result! :^) In many cases that will require a new, larger chassis plate - but that's always been the case, and probably always will.
In the original SR45, I jiggered the operating point (lower voltage and a little too much current) to work best with a 3K load, since that was the only available quality iron for the Paramour at that time. Stretching that to 5K was a bit much, so I offered some adjustments, mostly just reducing the current. It increases the distortion a bit, leaves the power unchanged, and extends the tube's life a bit. I'd like to stress that all the above are quite small effects - I think most audiophiles might hear them but would be hard pressed to choose which is best.
Incidentally, in my current draft layout there is more room than usual for capacitors. But as I said, I haven't even shown this draft to Doc B yet.
2wo
Active member
I built my SR-45 with the BH-5, and BCP-15's, however I may not have wired to the speaker, as Paul had intended. I wired for highest load.
I acquired a pair of nickel EXO-45's, put them in and like them. Understand, I like nickel and run them full range. I am not asking them for the very deepest bass. To that end I often run them with no cathode bypass cap on the 45...John
I acquired a pair of nickel EXO-45's, put them in and like them. Understand, I like nickel and run them full range. I am not asking them for the very deepest bass. To that end I often run them with no cathode bypass cap on the 45...John
howardnair
New member
having ordered my-output transformers from magnequest-power transformers from bottlehead-triad chokes for power supply via [i forget where] and plate chokes from heyboer{using jim redmonds 60ma. 80H suggestion}-i am getting ready to order the rest of the parts i need-my question concerns the power supply caps which show to be 47uf--is there any benefit in increasing the value of the power supply caps
thanks howie
thanks howie
Paul Joppa
Moderator
The value of the 450v capacitors in the power supply is not critical, once the choke has replaced the 270 ohm resistor and especially in a regulated PSU. I wouldn't go lower than 25uF, myself, or over 220uF, but the true answers come from PSUD (the simulation software) and from your ears.
howardnair
New member
it seems best results using psud are 47uf for c1 and150uf/ 200uf for c2 --i am unable to put the first 470k resistor in place per the schematic but psud puts a 10m in series right after the rectifier for me-which after changing the values of this R1 around the 10m seems to be the ticket-is there a way to duplicate the power supply exactly -i seem to be able to insert only a circuit not a specific component and not parallel to c1
howardnair
New member
ok!!!-i managed to removed the one 470k--never having fooled with psud what exactly am i looking for-what i have on is a 10m resistor in series rt after the rectifier -a 47uf cap the choke then a 200uf cap with a load of 60ma-the caps are across the b+/b-this gives me on the graph simulator--at 0 a nice slightly upward curve then a 45ish degree line and then a gentle curve that then flattens at just below 400v--there does not seem to be any info to inform one of what it is we are looking for--i can infer from here and there on the net but nothing specific-it seems what i have modeled is correct as the curve is gradual with a steep but inclined climb and then leveling off --this is a little exasperating but a great deal of fun--realizing no-one has seen my yard -but i have lots of gardens and yard-trees to trim-- windows to paint--but nooo!!!! i sit here fooling with psud
Paul Joppa
Moderator
Yeah, PSUD has a steep learning curve. Two things I look for:
1) no ringing, or at least not very high or for many cycles. This usually happens in the first few seconds.
2) To check the ripple, model after a delay of a few seconds so the voltage has reached a steady state. Then you can see the ripply, and the table will show max and min values.
There are extensive discussions (and flame wars - wear your flak suit!) on the TubeDIY board at Audio Asylum. There are kernels of wisdom there, but more chaff than wheat. For a SR amp, the regulator will take out most of the ripple anyhow, so my advice is a quick check for ringing (you've done that), then head to the garden in the spring sunshine.
1) no ringing, or at least not very high or for many cycles. This usually happens in the first few seconds.
2) To check the ripple, model after a delay of a few seconds so the voltage has reached a steady state. Then you can see the ripply, and the table will show max and min values.
There are extensive discussions (and flame wars - wear your flak suit!) on the TubeDIY board at Audio Asylum. There are kernels of wisdom there, but more chaff than wheat. For a SR amp, the regulator will take out most of the ripple anyhow, so my advice is a quick check for ringing (you've done that), then head to the garden in the spring sunshine.
howardnair
New member
thanks paul--i have one more question-the psud puts a 10m ohm resistor in right after the rectifier-i take that this is correct-what is the necessary wattage for this component
Paul Joppa
Moderator
Change from an RC filter to a C filter, and the resistor will go away.
Unless you are referring to the capacitor's ESR, which you can find in the cap manufacturer's data sheet.
Unless you are referring to the capacitor's ESR, which you can find in the cap manufacturer's data sheet.
howardnair
New member
i got it --thank you--
Paul Joppa
Moderator
Good timing; I was just going to spend some time today pulling together my scattered notes - I've been out of town a good deal lately, and grabbing a few free hours here and there to work on aspects.johnsonad said:
This thread has a bit of a split personality, so in this post I'll only talk about a the new amplifier design being developed which will implement the fully shunt-regulated high voltage power supply concept. At this point, it is an entirely new design, not an upgrade of the original limited-production semi-kit of several years ago. Doc B. and I have conferred extensively on where to go with this, and concluded that the regulated approach should be matched with an equivalent level of performance, reliability, and utility.
One consequence is that this design is optimized for performance, rather than being an experimental platform. Not that you can't play with it of course, but we'll put better, more expensive parts in without worrying about making it easy to change them. Here are a couple examples:
1) All the power supply capacitors are going on a single large PC board - the "capacitor farm". They'll be premium long-life parts, and the layout places them away from the heat-generating parts for longer life. Probably on the same board there will be a set of sequenced power control relays and timers.
2) The cathode bias and the master current source bias resistors both get hot and dissipate a lot of power. So this time I am moving them to a second "heat-sink farm" board, well removed from the capacitors and with a large cooling vent immediately adjacent. At this time I expect to use Caddock TO-220 resistors on large heat sinks. It will be difficult to replace these with (for example) your favorite Mills NIWW, but on the other hand the Caddocks are damn good resistors to begin with.
3) On the other hand, I have allocated a large space around the tubes for the capacitors that carry signal current - interstage, parafeed, and cathode bypass. Those will be easy to swap out - this is still a Bottlehead amp, after all!
The performance improvements are relatively small. Based on the recent BeePre work, I'll try a second generation regulated filament power for the output tube, along with regulated heater power for the driver/shunt regulator tube. That should reduce hum and noise, and also overall operating point stability - which is IHMO a major part of why regulation sounds good. The operating points are optimized for performance, without compromise for available voltages or a variety of transformers and chokes. Again, not that you can't play around with iron, just that the design is built around specific parts. I intend to put in some better-quality signal capacitors from the start, as well.
For convenience, I want to have output impedance switches and input level trim to optimize system balance. And the power sequencing relays and timers will protect the output transformer from being magnetized by startup and shutdown transients, so the amp should sound good very quickly - no more "run it with music for 30 minutes before critical listening"!
For reliability I have already mentioned the cooling flow and parts location design. There are a lot of electrolytics in the low-voltage power supply, but with temperature control and careful parts choice (and some conservative, mil-spec design practices) you can get a theoretical lifetime of well over 100,000 hours. The sequenced power will extend the life of the tubes, as will regulating the filament and heater voltages.
Appearance is still being worked on. I'd love to have all the connections on the back panel, and a hefty thick front panel with only the power switch, perhaps with wooden side panels. It looks like a basic chassis plate 10 inches by 16 inches will accommodate the layout fairly well, and could be done optionally sideways for rack mounting if anyone actually wants that. But at this point, all that is speculative.
I should mention that there are some other features and directions being worked on; I can't go into them until I get some more research done, but the bag of tricks is not yet empty!
tsingle999
New member
Wow sounds like its going to be amazing! Cant wait Paul!
I would like to request grid chokes in the amp or designed so they can be added later based upon the transformation of my current sr-45 when i added them.
I am listening to it now and it is just so good i dont know what to do with myself
its hard to listen n not dance! I put the subwoofers n amp for sale today - no need anymore...
I would like to request grid chokes in the amp or designed so they can be added later based upon the transformation of my current sr-45 when i added them.
I am listening to it now and it is just so good i dont know what to do with myself
its hard to listen n not dance! I put the subwoofers n amp for sale today - no need anymore...Paul Joppa
Moderator
Hey Taran - what are you using for a coupling cap upstream of the grid resistor?
I'll give that some thought - with the longer chassis it may be possible to find a quiet location for a grid choke.
I'll give that some thought - with the longer chassis it may be possible to find a quiet location for a grid choke.
