LR Phono pre with Slagle iron

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

LR Phono pre with Slagle iron

Post by sbench »

Thought I'd start a new thread.

Dang, Dave, I don't see how we're gonna do much better than this.

Slagle iron, Bench LR phono preamp PC board values:
T1/T3: Dave's 2:1 xfmr
T2/T4: Dave's 3:1 xfmr
L1/L3: Dave's 1.0Hy inductor
L2/L4: Dave's 1.8Hy inductor
Tubes: this version built with all D3a/7721
R1/R14: 169k 1%
R7/R19: 13.3k 1%
R2/R15: 5.62k 1%
R8/R20: 750 1%

Bias: D1/D2/D3/D4/D5/D7/D8/D9/D10/D11 = UF1007
R10/R23: 402 1% (1/2w)
pots: mine are set around midscale (100 ohm for the 200 ohm pot)

Gain matched within about 0.1dB by swapping tubes :-)

Frequency response shown here. It should be noted that I saw NO variation in response with level change... congrats Dave!!!

Steve
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papagenohyun
Posts: 7
Joined: Mon Aug 22, 2005 5:26 am

Post by papagenohyun »

very good results!
congratulation , Mr.S bench.
i think Slagle iron is the best match with your circuit.
i think it is most difficult thing to choose appropriate two set of interstage transformers.

anyway, Hello, Mr. Dave Slagle?
would you reply on my inquiry e-mails on transformer and choke inductor?

best

from south korea.
sbench
Posts: 296
Joined: Fri Jan 28, 2005 3:45 pm

Post by sbench »

L i s t e n i n g T e s t s:

O my! What can I say. This one is easy to listen to, but not as laid back as the original. Detail is outstanding... I think I'm being limited by the rest of the components in the system, but the detail seems to be better that with the Sowter iron, and the detail with the Sowter iron was much better than the original. Bass is wonderful (Bob James: One: Feel Like Making Love). Right now I'm listening to the wonderful Mono Mercury Olympian recording of Concerto in F/Rhapsody in Blue (Bob Fine engineer) with one channel on orig and one channel thru the Slagle iron.

Soooo, I now have 3 versions of pretty much the same thing, and all sound amazingly different.

Too early to tell for sure, but the Slagle iron version appears to be best in every aspect... detail, smoothness, response, dynamics. What's new? Bass is distinctly better than either of the other versions - fuller but if anything, tighter. Very high treble is amazingly smooth, clean. The one aspect I liked about any of the versions of the LR is that it gives me back about 20 years of hearing, and this version is even more so. There's some hum I want to track down and destroy but I'm not sure where in the food chain it's entering at present.

Steve
Raj Gupta
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Post by Raj Gupta »

Sounds like you're gonna give the Eurotrash a treat, Steve.

-j, wishing he was further West right now
sbench
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Joined: Fri Jan 28, 2005 3:45 pm

Post by sbench »

Found the hum. Part is a design issue, most is simply yours truly who can see worth beans.

The power supply build in resistors (R3,10,16,23) are supposed to be 523 ohms. I had 330 ohmers in them. This caused more than expected current to flow, and excited a design problem in the PS.

In the power supply, R1 needs to be 50 ohms instead of 100 ohms. This provides more margin for the regulators. R2 can be either 50 or 100 ohms.

Back in the preamp, changing those resistors lowers the overall current slightly and believe it or not, actually improves the response... Setting the pot for 0 dB at 20 Hz makes the response at 18Hz -.3dB, the response at 15 Hz -1.3 dB and the response at 30-50Hz (highest peak region) +.4dB.

Steve
dave slagle
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Post by dave slagle »

Raj Gupta wrote: -j, wishing he was further West right now
can you listen to vinyl east of the East river? Steve has offered to ship something eastward, but my garard is to the west (west side of the hudson)
I think we all agree that the more ears the better, and rumor has it the ears in brooklyn...fuggeddaaabouddit.

dave
Raj Gupta
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Joined: Fri Feb 11, 2005 2:19 am

Post by Raj Gupta »

In a word, yes.

Steve - I use a step-up (Altec 15095) 1:10, any problem with that? My Denon DL103D seems happy with the ~470R reflected load.

-j
sbench
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Post by sbench »

I am likewise using a 1:10 stepup from Denon DL103.

Do you'se guys want me to send both Sowter and Slagle iron versions? To whom and when?

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

Sowter and Slage Versions

Post by Johnny »

Hi Steve,

Congratulations! Sounds like you have come up with something very special. I would love to hear both. I was just talking with Steve Kaufman about gettting a chance to listen to them. There's going to be a bunch of people here for the Rocky Mountain Audio Fest from around Sept. 25-Oct. 7. It would be real nice to have them then so we could let others take a listen as well.

All the Best,

Johnny
dave slagle
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Post by dave slagle »

IF a version or two make it to the RMAF, why not do it up. I could get a set of amorphous L's and IT's that match the 49% nickel ones. My slated delivery time for the right sized cores is Sept. 27, so that might be cutting things close. Let me know if there is interest, and i'll see what i can come up with.

I have already planned to make amorphous versions that will take the same mounting footprint and this might be a nice place to get some more ears on experience.

dave
Steve Kaufman
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Location: Fort Collins, Colorado

Post by Steve Kaufman »

Hi Dave and Steve

I have sent you both private e-mails about our wishes. We would love to have Steve's phono stage here to share with the Rocky Mountain AudioFest mob, many of whom will be hanging around for the week after the show. Frank Schroder will be staying with us for the week and he has particularly good ears. He is familiar with Steve's LR concept and is very interested in hearing it. Most of our local geeks and gurus will be around as well. If we can get my rough version of the phono stage done, necessitating a set of the same iron you just sent to Steve sent to James then we can have all the fun with gaps, cores, and bobbins. There will be lots of time for this the week after the show. I know Steve wouldn't want us mucking around with the iron in his unit. All the changes can be rough on the clips.

Thanks

Steve
sbench
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Post by sbench »

Quick comment... I know youse guys are chompin at the bit but please note 2 things...

1. I've been reporting on things as they happen here. My time is currently severely limited for a bunch of goofy reasons.
2. I'm still optimizing things out. See next paragraph.

After changing the build in resistors, I mentioned the response was "even better". Listening gave subjectively TOO MUCH bass. I'm adjusting the biasing a little yet. Need a little more time to finalize.

Dave, *if* you do get the amorphous Ls to behave, I'll put a switch on it and mount them on top of the other inductors so we can A-B.

Overall, what I plan to send is...
1. The Dave iron version + power supply.
2. The Sowter version + power supply.

Steve
sbench
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Post by sbench »

OK, here's what I ended up with for all the variables in the circuit...

RIAA values (unchanged)
R1/R14 = 169k 1%
R7/R19 = 13.3k 1%
R2/R15 = 5.62k 1%
R8/R20 = 750 1%

Biasing:
R10/R23 = 402 1%
pots --> set about mid scale... adjusted for about 0.5dB boost at 40Hz and about 0.3dB loss at 20Hz.
D1/D2/D7/D8 = 1N4148
D4/D10 = 1N4148
D3/D9 = UF1007
D6/D12/D13/D14 = shorted out as previously described
D5/D11 = UF1007


This version in my system is outstanding. I'll appreciate comments (good and bad) from others.

Steve
©
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Location: zurich

Post by © »

i'm fortunate enough to be able to compare steve's two LRs with slagle and sowter iron plus my own (built on steve's PCBs; using sowter sowter iron. my mods compared to steve's sowter version: pearl iso sockets for all four D3as, pearl tube coolers for the two input tubes [not enough room around the two output tubes :( ], all resistors tantalum, LL1670 grid chokes, siemens 10uf MP caps instead of the 33uf lytics, 470nf bypass caps right at the x.former primaries, 10nf bypass caps for the heaters at the tube sockets plus custom wound toroids with two electrostatic foil shields each [one shield connected to chassis ground, one to audio ground] in the power supply).

the tantalum resistors make a HUGE difference - the sound is at the same time more detailed (but not clinically analytical), smoother and more natural. replacing the 47k grid leak with lundahls grid choke added dynamics and openness. the iso sockets and the tube coolers really help with the microphonics. the heater cap mod is not necessary, the 470nf bypass caps removed some hf hash i previously didn't notice. of all the cap mods the siemens PIOs yielded the biggest improvement - they added that much sought-after ....uhm... oily quality :wink: (two pix: the innards (still with the unshielded wires and the original caps and my LR_no© in the lansing enclosure)

comparing steve's sowter to slagle iron in my system (blue thunder horns in passive config with 6080 pp amp or 300b SE, benz ebony HO cartridge), i noticed the slagle version to be a tad more detailed, to have a bit more finesse and a slightly more open sound. but contrary to steve, i prefer his sowter version over the slagle (sorry, dave... ;) ), the sound is less refined but more visceral. if i were to compare it with cars, dave's iron would be a merc 500sl, sowter's a 2005 corvette--both are fast, both are powerful, but you either like the benz or the 'vette. (now if only dave could make the LR behave like a supercharged viper... :lol:

an interesting observation: if i were dj in a club, i would use neither nor. both have very well controlled deep bass, that is a tad too polite and lacks that kick-in-your-stomach-quality prerequisite for house music 8) )

something i noticed with all three LRs: they're terribly sensitive to hum pickup. i guess it's those unshielded gapped ITs since the slagle and the sowter version both hum alike, with the latter having mu metal encapsulated inductors vs. dave's open frame inductors.

place the LRs within 50 centimeters of a mains transformer, and you'll have HUM (i measured 33mv hum in one channel with the LR sitting 25 cm above a toroid...). i noticed that the sensitivity is higher in the vertical than in the horizontal axis. rf is another issue - at first i tried unshielded twisted pairs for inputs and outputs leads, but that was looking for trouble - the output leads still are unshielded twisted pairs, but the inputs needed to be shielded (btw i'm using the "bl ag interconnect" from partsconnexion which isn't exactely cheap but sounded clearly better than the meitner/museatex solid core twisted pair i tried first.

to make a long story short: steve's LR phono stage in either incarnation is quite simply the best phono stage i've had in my system so far. and there have been quite a few...

the only three aspects where i see room for improvement:
- higher immunity against hum pick-up (magnetic interference)
- more ooomph in the deep bass
- more in-your-face-macrodynamics

(with the ooomph and the macrodynamics clearly being a matter of personal taste; i'm complaining on a VERY high level here.)
maymymay
Posts: 6
Joined: Mon Sep 08, 2008 2:07 pm

Post by maymymay »

hi steve,

i try your circuit with the lundahl iron and now i switch to dave slagle iron, i just place order and wait for it, I use the 1660/18mA in the first stage not the 10mA, any news in your your LR riaa phono can share with us?

:D
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