DIY Audio Projects Forum

A question about other power transformers in the 4S preamp.
The one specified in the design is Hammond 269EX. In another subforum "Super Simple single stage tube preamp"
here viewtopic.php?f=9&t=3266&start=320#p36812 , in response to another poster Matt said this ......



http://www.edcorusa.com/xpwr136

http://www.edcorusa.com/xpwr161

So, would either of those power transformers be a suitable choice for the 4S preamp ?
In both cases the secondary voltage is higher the Hammond 269EX so maybe resistors and/or zener diodes will have to
be used to reduce the voltage.

I'm asking because later on I'll be getting some Edcor transformers for another project and I could get one of these in the
same order.
I also have a preference for Edcor transformers relative to the Hammonds.
.

Yes to the XPWR136 no to the XPWR161. You could use the 161 but it is serious overkill. Please note that in my response I referenced the XPWR164 and not the XPWR161.

The important thing to realize abut the 4S is that the design works well with B+ voltages from about 230v up to about 330v. Personally I like to run my 4S stages at around 300V B+. They just seem to perform best there.

I hope this helps.

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog

Thanks Matt, I'll get the XPWR136. Also good to know about the B+ voltages.

I didn't notice that I inserted the wrong link to the XPWR161 instead of the XPWR164 which is the one I meant to link to.

I recently built the 4S preamp and did some measurements with ARTA STEPS using the Steinburg UR22 MKII USB audio interface. I buffered the 4S output with a AD822 as a unity gain follower to avoid loading the 4S output by the ARTA measurement system which only has about 9K input impedance. I tested the 4S with a 12AU7A (JJ Electronics), a 12AT7WC (JAN/Phillips NOS), a 12AV7 (Marconi NOS), and some others (unfortunately I could only attach 6 files). The JJ Electronics 12AU7 had the best THD at 0.293%, followed by a Sylvania 12BH7 at 0.362%, the 12AT7WC was the worst at 0.614% (though it did have the best gain). The frequency response was pretty flat from10Hz to 20 KHz. The distortion was primarily 2nd harmonic as expected but I was surprised it was so low? I also measured the 4S feeding my Lacewood V2 with volumes adjusted for best distortion and the THD was 2.73%. I'm hearing impaired, completely deaf in one ear and have a cochlear implant in the other ear. But I listened to Brahams concerto No. 1 in D minor for piano and orchrestra with the Cleveland Orchestra and Leon Fleisher and George Szell and thought it sounded awsome through the combined system but my wife complained it was way too loud clear upstairs in the kitchen (my lab is in the basement at the oposite end of the house).

Thanks for the data.

_________________
Projects: "Precision" - 300W Class AB Holton power amp | "retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp |

OK so here are some more results for the 4S with the 12BH7A and the 4S with the Lacewood V2 together. I forgot to mention that my 4S doesn't employ bypass caps on Rk. All the THD measurements mentioned above are at 1KHz. THD on the Lacewood rises for frequencies below 200Hz to about 5% @ 50Hz.

Here is my latest iteration of the 4S using the 12BH7 tube, the chassis is Padauk and top plate hand-punched and sanded. I am really impressed how it sounds, whether it is in front of a tube or S.S amp, very detailed. My speakers are a pair of Fostex 206en in BLH based on the Solo 206 design. The preamp is currently paired with my VTA120 amp. Kudos to Matt for a very cool preamp that allows for a variety of tubes to be rolled.



Patrick

If the question hasn't been asked yet (or if it has), I just wonder - what about parallelling the triodes in each glass bottle. I have a chassis that was used for another preamp (the Elektor from mid 80's) and all are in place - transformer, rectifier (at least) socket, psu details, connectors .... and TWO holes for preamp tubes. Was considering using 6N2P.

_________________
Magnus

“If you don't know where you are going, any road will get you there.”
―Lewis Carroll

Very nice.

_________________
Projects: "Precision" - 300W Class AB Holton power amp | "retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp |

To do this so that you get similar performance just cut the load and bias resistor values in half. Bias resistor becomes 600Ω and the load resistor goes to 50kΩ.

This yields the same electrode voltages with twice the current. Just make sure you use individual grid stopper resistors on each grid.

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog