[spritzer]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif Yeah. In mine, there's a post marked "117V" - the AC bias lamp is plugged into this, and the other side goes to AC neutral. The other side of the lamp is connected to the switch, and connects through to the center-tap on the ac bias transformer primary (not secondary). Near the "117v" post there is an empty hole in the board marked "230" - the traces under the board directly connect it to the 117V post, iirc. I'm used to seeing power transformers with dual primaries but the center-tapped primary is a variant i've not worked with.

I'm not sure how this could be converted. Koss could have made a special version for 230v and that could be the reason why your unit lacks the odd power connector. Was the powercord treminated with the standard US power plug or one of the Euro variants?

 

[ericj]

Quote:

Originally Posted by spritzer /img/forum/go_quote.gif I'm not sure how this could be converted. Koss could have made a special version for 230v and that could be the reason why your unit lacks the odd power connector. Was the powercord treminated with the standard US power plug or one of the Euro variants?

All i had was three frayed wires sticking out the end of the cord. I trimmed them down a bit and added an appropriately
retro-industrial looking black rubber three-prong plug from the hardware store.

I'm guessing that the wire that bolts to the frame of the rearward audio transformer is ground. hot vs. neutral is a tossup where the fuse is on one side and the power switch is on the other.

 

[edstrelow]

CRIMPING SUCKS

When I opened the cups of the SRX3's I noticed that Stax had used crimps similar to the God-awful crimps Koss was using on the ESP6 and 9. I took one apart, the bias I think, to check for corrosion, It looked ok but I gave it some Progold to be safe. However there was still the issue of the cable running from the amp, which is crimped to the crimp, if you follow me. So I just splashed some more progold on this too so it would soak into the crimp/cable bond. This seemed to help the sound.

Then I looked at my Sigma lowbias and splashed the crimps with more Progold and got a fairly noticeable improvement in treble. These were easy to access because the mesh inside the cup was gone and you just needed to poke under the damping material at the bottom of the earcups.

My question is didn't Stax stop using crimp connectors at some point? I think the 404 is soldered entirely, and what about the Omega?


On my other project the ESP 6 seems to be opening up with regular use. Tonight they had some real treble, and the volume swings, from what are I assume bias swings, seem to be settling down. I still want to open them up and give the circuit boards a final cleanup.

 

[spritzer]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif All i had was three frayed wires sticking out the end of the cord. I trimmed them down a bit and added an appropriately retro-industrial looking black rubber three-prong plug from the hardware store. I'm guessing that the wire that bolts to the frame of the rearward audio transformer is ground. hot vs. neutral is a tossup where the fuse is on one side and the power switch is on the other.

I can't really see how you can convert a center tapped trafo with a single primary to 117v. It is further complicated because they only used the live wire and grounded the center tap. I think a step up is the only course of action for now.

Quote:

Originally Posted by edstrelow /img/forum/go_quote.gif CRIMPING SUCKS When I opened the cups of the SRX3's I noticed that Stax had used crimps similar to the God-awful crimps Koss was using on the ESP6 and 9. I took one apart, the bias I think, to check for corrosion, It looked ok but I gave it some Progold to be safe. However there was still the issue of the cable running from the amp, which is crimped to the crimp, if you follow me. So I just splashed some more progold on this too so it would soak into the crimp/cable bond. This seemed to help the sound. Then I looked at my Sigma lowbias and splashed the crimps with more Progold and got a fairly noticeable improvement in treble. These were easy to access because the mesh inside the cup was gone and you just needed to poke under the damping material at the bottom of the earcups. My question is didn't Stax stop using crimp connectors at some point? I think the 404 is soldered entirely, and what about the Omega? On my other project the ESP 6 seems to be opening up with regular use. Tonight they had some real treble, and the volume swings, from what are I assume bias swings, seem to be settling down. I still want to open them up and give the circuit boards a final cleanup.

When Stax switched to molded cables they also started to solder the wires. Before the crimping there were the horrible tiny jewelers screws that made the contact. Believe me, crimping was a giant step forward.

 

[niels]

Got the Raytheon tubes for the 006t today.....

 

[pojen_h@hotmail.]

Hi, I have a question for 4070 owners...

I recently moved to a new apartment that have central AC, i.e., it generates huge noise during operation. My 404 can't help in this situtation.

I am consider 4070, can the owner comments on how good the isolation is?

Thx,

 

[ericj]

Quote:

Originally Posted by spritzer /img/forum/go_quote.gif I can't really see how you can convert a center tapped trafo with a single primary to 117v. It is further complicated because they only used the live wire and grounded the center tap. I think a step up is the only course of action for now.

It's not a center-tapped transformer with a single primary.

It's a single-secondary transformer with a center-tapped primary. Which is extremely weird. But that's what i see in my 220v E.9, and the schematic shows a center-tapped primary with one side floating for the 117v version.

I'm not confusing the primary and secondary - unless someone intentionally hooked up the transformer backwards. I have continuity from the AC plug to the leads on either side of the center-tap of the transformer, and the bias indicator lamp is hooked up to the center-tap of the primary. fwiw, the lamp is marked as rated for 117v, which is roughly what it would get if the outer leads of the primary were at 230v.

Had a chat with an EE last night, who got as far as "Oh, center tapped primary?!?!" before his spare time ran out.

Admittedly I might not be able to figure out what was going on in the head of whoever designed this thing until i get my hands on a 117v single-bias-transformer E.9.

A center-tapped primary is not unheardof, it's just that usually in that situation you're talking about an autotransformer, which wouldn't generally have a secondary.

 

[spritzer]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif It's not a center-tapped transformer with a single primary. It's a single-secondary transformer with a center-tapped primary. Which is extremely weird. But that's what i see in my 220v E.9, and the schematic shows a center-tapped primary with one side floating for the 117v version. I'm not confusing the primary and secondary - unless someone intentionally hooked up the transformer backwards. I have continuity from the AC plug to the leads on either side of the center-tap of the transformer, and the bias indicator lamp is hooked up to the center-tap of the primary. fwiw, the lamp is marked as rated for 117v, which is roughly what it would get if the outer leads of the primary were at 230v. Had a chat with an EE last night, who got as far as "Oh, center tapped primary?!?!" before his spare time ran out. Admittedly I might not be able to figure out what was going on in the head of whoever designed this thing until i get my hands on a 117v single-bias-transformer E.9. A center-tapped primary is not unheardof, it's just that usually in that situation you're talking about an autotransformer, which wouldn't generally have a secondary.

Someone could have rearranged the trafos but I don't see why. This is a very strange setup but you could always replace the trafo with a similar item. You also always fit a 10w stepup inside the E.9

I would post pictures of my E.9 if they would help but there is just a large PCB instead of the iron. It appears to have been modified by Koss because the cover still has the holes and screws that would attach to the upper platform where the other transformers are.

 

[ericj]

Quote:

Originally Posted by spritzer /img/forum/go_quote.gif Someone could have rearranged the trafos but I don't see why. This is a very strange setup but you could always replace the trafo with a similar item. You also always fit a 10w stepup inside the E.9

If i go that route, I'll just replace the trafo with a setup similar to the stax amps, and from the sound of it, your e.9.

 

[krmathis]

Quote:

Originally Posted by niels /img/forum/go_quote.gif Got the Raytheon tubes for the 006t today.....

I received a handful of NOS Raytheon tubes today as well. Which will be used in my SRM-007t.
Should be fun!

 

[spritzer]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif If i go that route, I'll just replace the trafo with a setup similar to the stax amps, and from the sound of it, your e.9.

I would also do that. I think they might sound much better in a real push-pull configuration.

 

[ericj]

Quote:

Originally Posted by spritzer /img/forum/go_quote.gif I would also do that. I think they might sound much better in a real push-pull configuration.

I only meant rebuilding the bias supply, but I've considered getting another E.9 to use while i dig the transformers out of the one i've got now and build an SRD-7 circuit around them.

One of my EE friends has suggested how to rewire the bias transformer in my e.9, going to give it a shot tonight.

 

[spritzer]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif I only meant rebuilding the bias supply, but I've considered getting another E.9 to use while i dig the transformers out of the one i've got now and build an SRD-7 circuit around them. One of my EE friends has suggested how to rewire the bias transformer in my e.9, going to give it a shot tonight.

You can always build a voltage quadrupler circuit for the bias and let the the transformers be as they are.

 

[edstrelow]

I was thinking about converting a low bias SRX3 to pro.

On a whim, I called the US Stax distributor and service center, Yamasinc and asked if they could rebuild a Stax SRX3 Pro. I was told that the drivers are out of production but could possibly be remade, persumably by Stax Japan, fpr about $400-500.00.

Still thinking.

 

[spritzer]

Quote:

Originally Posted by edstrelow /img/forum/go_quote.gif I was thinking about converting a low bias SRX3 to pro. On a whim, I called the US Stax distributor and service center, Yamasinc and asked if they could rebuild a Stax SRX3 Pro. I was told that the drivers are out of production but could possibly be remade, persumably by Stax Japan, fpr about $400-500.00. Still thinking.

That is quite a bit of change. I'm not so sure the SR-X Pro is superior on all fronts to the old version. I know it will sound different but I personally prefer the normal models for sheer musicality and enjoyment.

I have been looking into modding my set to a Pro standard and it can be done with the right spacers and some precision tools. All you have to do is enlarge the space inside the driver by 0.2mm in each side and drill new holes for the guide pins. This is easy but the real problem is the way the diaphragm is tensioned inside the driver by the driver housing. Modding that will be a pain but it can be done. They will sound different from the production version so it is in fact a new phone all together.