LR Phono Preamp and PS - PC Boards

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sbench
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LR Phono Preamp and PS - PC Boards

Post by sbench »

Hi All,
Decided to do a PC board of the LR phono preamp and power supply. Expect to be ready to get some made this coming week.

The PS is similar to the original LR power supply. It is on a 6x5.9" PC board. It produces 12.6V@ about 0.7A regulated and 2 separate 220V @ about 50mA each regulated B+ outputs.

The preamp is on a 6x11.6" board, and is set up to handle 6GU5 or D3a input stage and D3a output stage. It is also set up to handle either Slagle, Sowter or Lundahl iron (each has different footprint).

Both boards are being done in PCB Express "production" format so will be double sided plated thru holes with solder mask and silk screening for part locations.

According to their pricing rules, if I buy about 10 each, I expect $50 for the power supply and $60 for the preamp board.

Any interest out there?

Best Regards,
Steve
mwiebe
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Post by mwiebe »

Steve,

Is the design on the PC board changed from that posted on your site with 7721s, or since you demoed it at the European Triode Festival?

You also mention the possibility of using Slagle, Sowter or Lundahl. I expect the iron in this project is where the cost is. How much will the iron run from Slagle? Which Sowter transformers will work? Are their any advantages or disadvantages of going with one brand of iron over another?

I’ve heard enough about the good sound of this design to be interested, but I would like to get a better handle on the costs of the project.

Thanks,
Matt
sbench
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Post by sbench »

The overall design is similar to what was demoed at ETF. I have made provision for slightly more flexible biasing. Also, the demo version used 6GU5 as input stage, the one laid out allows for either 6GU5 or D3a.

I have built up the version with Sowter iron. It is more forward and much more detailed than the original version, but the original is more relaxed.

I have had a couple folks over here, and I have taken the "road show" up to Laguna Beach and Allan Rosenthal's beautiful place where we listened to it thru his stacked quads (and my 813 matrix amp which beat out his 845 and his 300b amps - but that's another story).

Dave and I are just starting on the iron finalization for the "Slagle iron" version. There are 4 transformers and 4 inductors in the preamp. Dave, if you're tuned in... care to guess the cost?

Steve
Johnny
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Joined: Wed Jan 26, 2005 3:43 pm

Power Supply Board

Post by Johnny »

Hi Steve,

I'm in for the power supply board. I think I would rather have a hand wired signal board but if you get enough interest in the signal path PC board I would order one as well. Sounds exciting!


Johnny
sbench
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Post by sbench »

Will do. Anyone else in C3 land need either?

BTW, the two toroidal transformers in the PS are Digi-Key parts. Either the chassis mount or the PCB mount version will fit, since I mounted the transformers on angle brackets to get a better form factor. Also, I have improved the heat sinking on the regulators.

Steve
Steve Kaufman
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Location: Fort Collins, Colorado

Post by Steve Kaufman »

Hi Steve

Steve here in C3 land! Please count me in for one of each board as soon as they are available. If there any discrepancies from the D3a schematic on the web site please let me know what they might be. Hopefully Dave will be able to get his iron to us soon as well. We'll have a bunch of folks in the end of September for the Rocky Mountain AudioFest and it would be great to have this in a functional state by then. We're particularly interested in comparing the different brands of iron. If things follow their usual pattern, Dave's iron will elevate this phono stage to a new level.

Thanks

Steve
dave slagle
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Re: LR Phono Preamp and PS - PC Boards

Post by dave slagle »

sbench wrote:Hi All,
Decided to do a PC board of the LR phono preamp and power supply. Expect to be ready to get some made this coming week.
just curious, why did you choose the PCB route? I know they get a bad rap from a lot of people, but boy they sure make things simple. I see johnny voices some hesitation below and i get a bit nervous with the idea but for the life of me cannot rationalize why :-)

I guess i have yet to see the whole issue discussed rationally and suspect a well done PCB would outperform 90% of the point to point stuff out there. (remember i do my point to point with clip leads)

dave
dave slagle
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Post by dave slagle »

sbench wrote:
Dave and I are just starting on the iron finalization for the "Slagle iron" version. There are 4 transformers and 4 inductors in the preamp. Dave, if you're tuned in... care to guess the cost?

Steve
i would guess about a grand for the first few sets and then the price will go up. This assumes the design will allow for unshielded parts. If shielding is required, this will not change the iron design or packaging but it will require the use of proper layout and use of shielding foil. (gee maybe a PCB will make this easy ;-)

dave
dave slagle
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Post by dave slagle »

Steve Kaufman wrote:. Hopefully Dave will be able to get his iron to us soon as well.
if you are referring to the iron for the LR-riaa you did yourself a bit of a favor by asking for the 2:1 for the RS241's :-) this transformer and the 3:1's for steve's full function preamp have laid all of the groundwork for the two transformers needed for the "LRIAA" the inductors are 60% of the way there and as mentioned above, my only "fear" is shielding.
We'll have a bunch of folks in the end of September for the Rocky Mountain AudioFest and it would be great to have this in a functional state by then.
sounds like a nice "test run" for the ETF :-)
We're particularly interested in comparing the different brands of iron.
this is a slippery slope.. if we don't look beyond "what" soundes better to find the "why" how can we ever improve?
If things follow their usual pattern
outside of lemmings, when has that ever happend?

dave
Guest

PC Board for Signal Path

Post by Guest »

Hi Dave,

just curious, why did you choose the PCB route? I know they get a bad rap from a lot of people, but boy they sure make things simple. I see johnny voices some hesitation below and i get a bit nervous with the idea but for the life of me cannot rationalize why
I don't have any direct experience with PC boards verus hand-wired connects in audio applications. In high frequency digital applications the type of dialectric used in a PC board makes a huge difference in terms of capacitance and internal reflections. I like the idea of an "air" dialectric but I haven't done any careful comparisons. My choice of a PC board for the power supply and hand wiring for the signal path is just a compromise. The power supply wiring would be alot of work and the signal path would not be nearly as much work.

Johnny
sbench
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Post by sbench »

just curious, why did you choose the PCB route? I know they get a bad rap from a lot of people, but boy they sure make things simple. I see johnny voices some hesitation below and i get a bit nervous with the idea but for the life of me cannot rationalize why

I guess i have yet to see the whole issue discussed rationally and suspect a well done PCB would outperform 90% of the point to point stuff out there. (remember i do my point to point with clip leads)
Get about 2/3 done and all of a sudden I'm on Microsoft web site for IE "update" Geez, that's annoying. Now, lets try this again..........

There's several reasons I went this route.

1. Power supply. The overall power supply has proven to be cheap, simple and effective (with the 2 relatively inexpensive toroids from Digi-Key. With the filament regulators and the B+ regulators, I can easily tailor it for other voltage outputs, making it relatively universal. With a silk screened PCB, building up a supply takes almost no time: simply stuff a 1N5822 where it says 1N5822, a 100 ohm 2 watt where it says 100 ohm 2 watt etc. For the LR preamp alone, I'll probably end up building 4 versions. That's 4 of exactly the same PS modules. Can also control ripple and noise better by laying out the thing for no ground currents, so buzz etc is minimized without "playing".

2. Preamp. Mostly for convenience... I'll go to ETF with at least Slagle and Sowter iron, possibly Tribute iron. If I can come up with a nice layout, I have avoided many pitfalls. One of them you mentioned, Dave: the shielding of the inductors. I can effectively electrostatically shield the inductor so that at most I'd need a "magnetic cap" over the part, but I doubt it. I've layed out the board for analog performance, not for looks, so that the signal lines are well controlled. That's one pitfall for normal PCB layout.... everyone wants right angles, same size traces and beauty. I prefer the beauty of correct performance and PCB looks come in way down on the list. Changing things is easier. For instance, I've laid out the preamp for 6GU5 (7 pin) or 7721 (9pin) devices. They bias slightly differently, but simply changing the socket and a part value or 3 changes it. That's more difficult in point to point route, since I'd have to rewire an entire tubes worth of stuff. No high impdance point is long. That's more difficult to pull off in point to point unless you literally draw out the physics of the connections first, so that you can put things where they minimize that. With PC board, you're already DOING that as part of the layout, so that you can allow the low Z points to get longer in order to make the hi Z points shorter. Ground loops don't exist, if you're careful. That's harder in point to point. Finally, me,,, I'm a klutz mechanically. If I get the PC board right, I'm pretty much guaranteed that when I go to mount the transformers, they'll actually fit in the holes. When *I* have to drill out holes in a chassis or bare board, that's not a given :-p

Steve
sbench
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Post by sbench »

here's the power supply silk screen layer, to give an indication of what and where parts go

Steve
Attachments
i did a minor resize to prevent the dreaded scroll.... dave
i did a minor resize to prevent the dreaded scroll.... dave
pwrsup1_107.gif (49.87 KiB) Viewed 39581 times
pwrsup1_107.pdf
here is the original in all of it's glory :-)
(125.25 KiB) Downloaded 844 times
sbench
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Post by sbench »

PS boards due back here Friday. I'll check one out and make sure it does what I want, then submit the preamp if all OK. Here's the preamp PC board pix... the first is the silk screen, the second is a screen capture of all layers... yellow=silk screen, red=top, orange = both top and bottom (see thru sorta), green=bottom. Gives you an indication of the shielding on the board.

Steve
Attachments
another minor rotate.... dave
another minor rotate.... dave
lr_pre_278.gif (39.05 KiB) Viewed 39584 times
rotating the image boss.
rotating the image boss.
lr_pre1_106.gif (65.35 KiB) Viewed 39584 times
Steve Kaufman
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Location: Fort Collins, Colorado

Post by Steve Kaufman »

Hi Steve

I'd love a large copy of the color rendition for over the fireplace! Impressive work.

Thanks

Steve
sbench
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Post by sbench »

The power supply boards got here yesterday (at 6:00PM!) Hey, whaddya know, everything fits. :o

I'll put a couple together to check them out this weekend, if I get time. If OK. I'll go ahead with the preamp PCB fab. I haven't "submitted" that yet as I wanted to check the quality of work I get. So far I'm happy, the boards seem to go together quickly, the soldering is easy and they seem to be of good quality.

Steve
sbench
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Post by sbench »

Power Supply Boards:
Work just fine. In two spots where I have marked a 150k resistor, the real "stuffing" is 200pF in parallel with the 150k resistor. This is on the rgulators and provides better stability (read lower noise). It took me about 2 hours per board to put them together... I've put together three, just to make sure they will all work out OK.

Phono Boards:
Got EMail confirmation that they have been fabbed and shipped. Should see them Friday. I'll rebuild the Sowter version on one set (since I know how it sounds and performs), and if OK, will start with Dave's iron. (presume coming soon to a theater or drive-in near you).

Steve
dave slagle
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Post by dave slagle »

on the iron, i'm a gettin' there :-)

for future reference...

how are the filaments of the tubes powered? I could probably figure it out but i'm at home on dialup and it might take a few hours to dig through it. I assume they are voltage regulated and have had the thought that a nice STABLE current reg could be put to some additional use somehow :-) granted the thought of a current reg for a idt seems a little strange, but all we need is a crappy one that doesn't go nuts with an inductive load.

dave
Guest

Post by Guest »

Hi Steve,

Any PCB's left for the PSU? Or does it still have to happen?

Regards,
Bas
Bas Horneman
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Post by Bas Horneman »

Oeps...sorry was not logged in..the previous post was mine..
To infinity and beyond!!!
sbench
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Post by sbench »

I'm going to have to count up the requests between here and Joenet. There may actually be enough requests to do another run of boards. Want to get the preamp boards evaluated first.

On the filaments... essentially same as original LR... FW rectifier to 18V regulator (317) to 12.6V regulator (second 317). In the original circuit, I had grounded the +18 output (so I could derive a -18v bias if I wanted it) and in the PCB version I made a 3 pin header available so you could leave the filament regs float, ground the common (+12.6VDC) or ground the +18 (compatible with original circuit).

Steve
dave slagle
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Post by dave slagle »

sbench wrote: On the filaments... essentially same as original LR... FW rectifier to 18V regulator (317).
Steve
ahh... i know the 317's can be wired for current regulation, but i also know that they go nuts when feeding an offset winding. Don't get me wrong, i'm quite happy with the performace of the trannies as they are, but some might want a tad more inductance and a little better top end behavior never seems to hurt.

this is just another situation where the filament supply isn't that far from what is needed for an offset winding.

dave
sbench
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Post by sbench »

The phono boards arrived safe and sound. Look quite good so far. Tube sockets (both the 9 pin and the co-located 7/9 pin sockets) fit just fine. All seems to be OK. I'll rebuild the Sowter iron version on PCB as a test before shipping PCBs to anyone.
this is just another situation where the filament supply isn't that far from what is needed for an offset winding.
Hey Dave,
When I re-order PCB for PS, there is no penalty for laying down additional (non-stuffed) parts... I *could* include a current regulator... Specs?

Steve
papagenohyun
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Post by papagenohyun »

hello, mr S. bench.
i have always dream to build your lr phonostage.
it is very good news that you produced PCB BOARD.
BUT how about providing it as full kit without case?
because there are many people who have difficulties to source the pars.
if you have a plan to do this one, you can bet me as one of first customer.

best

kim from south korea
sbench
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Post by sbench »

i have always dream to build your lr phonostage.
it is very good news that you produced PCB BOARD.
BUT how about providing it as full kit without case?
I'd have to think about that. I'm not normally in the kit business, but could be persuaded given enough interest.

Steve
sbench
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Post by sbench »

Quick update on the PCB. Found a mistake where I got overly agressive with the ground plane and managed to ground one of the B+ supplies. (330k bleeder resistor shorted out) Quick pass with the dremel and a spot of super glue to seal the grind fixes the problem though. Still continuing the build. Time is what it is. Hope to have more news tomorrow.

Steve
papagenohyun
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Post by papagenohyun »

i would be very appreciated if you can supply all parts and pcb.
especially, here in korea, it is very hard to source all the parts needed.
it is most difficult obstacle to make amplifier.

best

kim
sbench
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Post by sbench »

OK guys, here's the good news and the bad news.

I've rebuilt the "Sowter version" onto the PC board as a check. All fits seem to be perfect. The transformers and inductors fit just fine. The delay and mute relay I built into the circuit works just fine. There are a couple mistakes on this version of PC board, so you have to "mess with it" a little...

1. There was a short B+ to ground where I got overly agressive with the shielding. I have fixed that with Dremel and sealer on all the current version PC boards. (so no additional action required)
2. I bleeped up the cathode biasing somehow. It's actually relatively easy to correct, since I provided for additional diodes for other biasing conditions. These were intended to be shorted by simply putting wire in place of the part. However, with the PC mistake the wire ends up being slightly different as...
2a. D13 cathode hole needs to be wired to D6 anode and cathode holes.
note that there is no D13 nor D6 used.
2b. D14 cathode hole needs to be wired to D12 anode and cathode holes.
note that there is no D14 nor D12 used.
2c. D13 anode and D14 anode need to be grounded. The ground plane foil is conveniently next to these pins.
3. Bottom of R18 needs to connect to top or R24. It "looks like" this is connected except if you look real close, the trace stops just short of R24. I don't know how I missed that one.

Other than that, the boards perform flawlessly. The additional benefit is that if anything, the response is slightly better on the PC board version... that is, there's less high frequency "squiggles" than the point to point routing, probably due to the shorted length and built in shielding.

Any comments? I presume these will be acceptable to folks..... let me know if that is not the case.

Steve
dave slagle
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Post by dave slagle »

hey steve,

on the current reg option, we (ok I) still need a good current reg that would be stable for this option. I'd quickly say just use a choke, but that adds size, cost and weight to the whole thing we have a problem.

i thought for a minute that the current reg for a IDT would have less impact on the sound, but then reaized it 'might' me heard through the step-up so a "good" one might still be needed.

at this point, the concept can easily be tested with a choke on the boards you have if someone is willing to try it. Am i right to assume that all that is needed is a tweek of a resistor to increase the voltage at the output of the reg to offset the dcr losses of the cancel winding and offset choke.

hmmm... now that i think of it, this may actually be a better option.

dave
Guest

Post by Guest »

Am i right to assume that all that is needed is a tweek of a resistor to increase the voltage at the output of the reg to offset the dcr losses of the cancel winding and offset choke.

hmmm... now that i think of it, this may actually be a better option
In principle, that's all that's needed. However, the makings of a much better current regulator are there. There's two constant voltage sources... 18V and 12.6 volts. Sooooooooo, if you hang the base of a PNP on the 12.6, and the emitter thru a resistor to 18V, the current available from the collector is about 4.8/R. What sorta currents did you need to regulate? For instance, a 480 ohm resistor will give you 10mA at any voltage up to about 13 volts, a 100 ohm resistor would give you 48 mA up to about 12.5 volts etc.

Steve
sbench
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Post by sbench »

OK guys, Here's pictures of the system...
1. Raw PCB (6"x5.75") + Stuffed board mounded in plastic case(!)
2. Power supply all buttoned up
3. The raw phono board (6"x11.7"). The black writing on the right is the "rework" instructions.
4. Stuffed board. Yes, it's tilted up. That's Brian Sowter's iron.
5. Board mounted in it's case. Both the PS case and preamp case are available directly out of the Digi-Key catalog... they're Hammond boxes.
6. Buttoned up front view of PS and Preamp... note that normally I would not place the PS directly on top of the preamp.
7. ditto, rear view. That's a DIN connector for the inputs as specified for the ETF shootout.

Steve
Attachments
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