LR Phono Preamp and PS - PC Boards

stephie's place

Moderator: sbench

dave slagle
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Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
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Post by dave slagle »

i was looking at it from a slightly different direction. I figured since you already needed ot regulate the filaments, why not use a current source and kill two birds with one stone. the offset winding can then be sized to the filament current to reduce the DC flux by say 75%. Given the low AC flux we are talking about, we will still have single quadrant operation (not that that matters) and it will allow the iron to operate with a larger margin of error. Part of me still says that the large gap required by direct feed is the key to wonderful sounding iron.

i'll also make note that you have (with good rerason) accepted much lower inductance values than most would. at some point people will want double the inductance and the ability to provide that makes the whole thing much more versitile. it's easy to add 30% more turns to double the L but that puts us at the point where things start to get ugly quickly. The c3 guys preferred a 2:1 that I was embarrased to send. I almost didn't send it because it could come back to haunt me. Well it did... but in a different way. I truly hate it when something that measures worse sounds better since it proves we still do not know what to measure.


dave
Johnny
Posts: 62
Joined: Wed Jan 26, 2005 3:43 pm

Post by Johnny »

Hi Steve,

Way Cool!!! I can't wait to get the boards. Congratulations.


Johnny
sbench
Posts: 296
Joined: Fri Jan 28, 2005 3:45 pm

Post by sbench »

Attached is the schematic of the power supply that agrees with the layout. Dave, the only problem with the 317 as a current source is it -er- sounds -er- lousy. At least every one I've built. :oops: Sooooooo, I've added a simple PNP into the sch and into rev B PCBs (next go). Those vintage usually sound pretty good (or I should say, don't impart a sound).

Next I'll post the schematics of the LR pre as layed out. (tomorrow?)

I'll be mailing off the PCBs to the C3 crowd in the next day or so.

Steve
Attachments
psu_lr.pdf
(23.93 KiB) Downloaded 1524 times
sbench
Posts: 296
Joined: Fri Jan 28, 2005 3:45 pm

Post by sbench »

As advertised, here's the Phono preamp per PCB layout.

I'm about to go stand in line at the post office... you coloradio guys oughta see your stuff soon.

Steve
Attachments
lrph_pcb.pdf
(27.13 KiB) Downloaded 1151 times
askchan
Posts: 1
Joined: Wed Apr 12, 2006 3:18 pm

D3a vs E810F

Post by askchan »

I know that both pentode tubes are designed for wide band amplifier but E810F is shock and vibration resistant. May I use it instead of D3a in Steve's LR phono?
hifryer
Posts: 1
Joined: Tue May 02, 2006 9:27 pm

Help re pre-amp details

Post by hifryer »

hi guys - newby here

I am very interested in Steve's full function LR RIAA MC capable pre-amp.

Steve, are boards available for purchase?

Is there a parts list with recommended suppliers?

Can you point me to attenuator and line stage details please.

Are there later schematics etc other than on your site?

Cheers
sbench
Posts: 296
Joined: Fri Jan 28, 2005 3:45 pm

Post by sbench »

Hi All,
Just a quick update. I have been focused on other priorities and this is, I think, the first time I've actually checked this site this year. Sorry about that.

The units came back from ETF in pretty bad shape. The Sowter version is currently operational, Ihave to repair the others.

I do not have any current PCBs. I DO intend to update the PCB, but my first priorities are elsewhere for a while.

What's in the pipeline for the LR is:
1. Slight modification of the circuit to eliminate the really long warm up time that some folks have noted.
2. New PCB to correct my original mistakes.
2a. New PCB will also allow for those shock mount sockets.
2b. New PCB will provide for Lundahl, Sowter, Slagle and Tribute iron.
3. Power supply will be slightly different.

No, I don't have an estimated completion date yet.

Current schematic on this site has values for Lundahl/Sowter and Slagle iron. I finally did get some Tribute transformers, but no inductors yet.

Best Regards,
Steve
agent.5
Posts: 12
Joined: Sat Apr 08, 2006 3:50 am

Post by agent.5 »

Steve,

Do you have the PCB for sale?
sbench
Posts: 296
Joined: Fri Jan 28, 2005 3:45 pm

Post by sbench »

At present, out of PCBs.
agent.5
Posts: 12
Joined: Sat Apr 08, 2006 3:50 am

Post by agent.5 »

sbench wrote:At present, out of PCBs.
Thanks for your reply. I will point-to-point your design then. May I ask you a question about the bias?

The question that I have are resistor R10 and R23. On the schematic posted on this page, the values are 1K. 402 ohm with the Slage irons. I will be using Slage irons and D3A for both the first and second stage amplification, so I will refer to the 402 ohm value.

Please correct me if I have any errors. 2.1V bias for the first and second stage. Diode bias only for the first stage. In the second stage, a hybrid diode/resistor bias is deployed,

with 31.3ma (12.6/402) to bias the second D3a. How do you determine the value of 31.3ma?

Can you tell us the reason of using two different bias scheme?

I am just trying to learn what is going on.
Steve Kaufman
Posts: 35
Joined: Wed Jan 26, 2005 6:00 am
Location: Fort Collins, Colorado

LR phono stage

Post by Steve Kaufman »

Hi Steve

I'm just getting around to building the phono stage with the original PCBs and Lundahl iron. Have there been any mods, including those alluded to in the June 6, 2007 post?

Thanks

Steve Kaufman
jeanlucdemarc
Posts: 3
Joined: Sun Dec 20, 2015 11:47 pm

PCB preamp fix

Post by jeanlucdemarc »

Here was "old version" of pcb whit mistake... After I complete the amp I will send back with all informations to PCB Express.
Attachments
B+   mistake ; (was grounded )
B+ mistake ; (was grounded )
B+.jpg (119.72 KiB) Viewed 10462 times
alfijan
Posts: 5
Joined: Mon Oct 31, 2016 3:17 pm

LR RIAA Consultation

Post by alfijan »

Hi Stephie,

A lot of time has passed since you posted Rev.3 LR RIAA schematics in November 2005.
Since I plan on building an authentic version of your project, using Sowter iron, I was curious whether there were some improvements, updates and/or general comments/reviews regarding this project.
I haven't been able to find much info on this topic, or read about people's experiences with crafting such a RIAA, so any additional info would be of great help, as the project is fairly expensive and requires quite a budget to get built.
So, before going into all of this, I would like to know what to possibly expect along the way.
As far as I'm concerned, I don't mind upgrading the project as much as possible and then sharing that experience, but I wouldn't like to waste time on things that someone already figured out before I did.
Also, I'm thinking about visiting Germany soon and meeting with Thomas Mayer, but that seems possibly unnecessary if there is anyone who can tell me more about this whole thing.

I hope I'm not bothering you with this, your reply would mean a lot.
jeanlucdemarc
Posts: 3
Joined: Sun Dec 20, 2015 11:47 pm

Post by jeanlucdemarc »

Rendering with Sowter transformators
Attachments
PCB-main.png
PCB-main.png (585.01 KiB) Viewed 8196 times
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