Stancor A-4408

[craigmorris74]

I recently scored a great deal on a NOS Stancor A-4408. I'm looking for the best place to put this beast.

One option would be to use it to replace the input transformer on my KT-2A opto. Not sure this would be a huge upgrade, since it sounds fantastic with the stock Midas transformer and an RCA tube in the V1 position.

Option two would be to use it on the input of a nice old American style tube preamp. If I took this route I'd like to build one that is a known great sounding design, but isn't crazy difficult to get right. I've built a few P2P tube guitar amps before that have turned out very well, so I have some experience with tube builds.

Any advice would be appreciated.

Craig

 

[Whoops]

Maybe you should post some info and specs on that transformer then it would be easier to understand it's best uses

 

[craigmorris74]

The image is from the catalog.

 

[j.colt]

Let us know how it sounds. I have one too laying around. Looking at the catalog, these were about 1/3 the price of the High Fidelity series which were UTC A- and LS- series clones. I imagine the A-4408 doesn't spec as well as a WF-22 or HF-22 but could certainly have some desirable non-linearities for today's use. I was thinking about making a passive DI box with mine.

 

[craigmorris74]

It will probably be this summer before I get to trying this out, but will post here when I do.

 

[j.colt]

Here’s the doc in case another lost soul wants to wire this obsolete beast…

 

[j.colt]

Well this got me curious so I put it on the scope with a 600ohm signal at about 1v and following the instruction for a 500ohm primary. I still haven’t listened to it, so there’s that. But what I can see is pretty massive roll off outside the 100hz-6khz band. Definitely not hi-fi like the WF/HF series but probably in line with recording playback from the 40s. The square wave shows quite a bit of low frequency loss in the « good » range, which is not surprising. I would not put it in the n an LA-2A but it’s gotta be good for something!

 

[Bo Deadly]

Well this got me curious so I put it on the scope with a 600ohm signal at about 1v and following the instruction for a 500ohm primary. I still haven’t listened to it, so there’s that. But what I can see is pretty massive roll off outside the 100hz-6khz band. Definitely not hi-fi like the WF/HF series but probably in line with recording playback from the 40s. The square wave shows quite a bit of low frequency loss in the « good » range, which is not surprising. I would not put it in the n an LA-2A but it’s gotta be good for something!

If the primary is 600 ohms, that just means that the characteristic impedance is 600 ohms. The source impedance of the driving signal is not necessarily 600 ohms. A dynamic mic like you might use with a phantom-less pre could be more like 300 ohms. A line source will be more like 100 ohms or less. So if you're using a 600 ohm resistor in series with your signal, that is not representive of a real signal source. If you drive it will 100 ohms, you might get a considerably wider response.

 

[j.colt]

If the primary is 600 ohms, that just means that the characteristic impedance is 600 ohms. The source impedance of the driving signal is not necessarily 600 ohms. A dynamic mic like you might use with a phantom-less pre could be more like 300 ohms. A line source will be more like 100 ohms or less. So if you're using a 600 ohm resistor in series with your signal, that is not representive of a real signal source. If you drive it will 100 ohms, you might get a considerably wider response.

That’s a good point… I should have strapped the secondary because the scope is unlikely to have an 80k load! Forget everything I wrote!

Edit: I strapped an 82k resistor on the secondary and the frequency response is much improved! Still no HA-100X, but very cool looking. Sorry about spreading fake news.