No fluorescent lighting, but there might an issue with the power supply of the Sony (a 400 disc changer) affecting the amp. It sits on top of the changer, and the various cables run parallel to each other. I’ll have to rearrange them & move the amp.

However, I don’t think that would explain the change in the loudness of the hum as I move my head.

Could the problem be the grounding of the amp? 

I’ll have to check whether the unit can be grounded.

I have rearranged the amp & cables, so we’ll see this afternoon.

Regarding a new amp: Would an SRM -1/MK-2 be a good choice? How about a T1?

1 hour ago, Sisterray said:

I’ll have to check whether the unit can be grounded.

I have rearranged the amp & cables, so we’ll see this afternoon.

Regarding a new amp: Would an SRM -1/MK-2 be a good choice? How about a T1?

srm-1/mk2 is good, but t1 is better, in terms of colouring of sound and texture. But since 207 is just an entry model so it doesn't matter much.

7 hours ago, Sisterray said:

Regarding a new amp: Would an SRM -1/MK-2 be a good choice? How about a T1?

I am not an amp expert, but I've been using an overhauled SRM-1 Mk2 as backup (PSU improved and some capacitors/resistors changed) for quite some time. It sounds dynamic, powerful and neutral, but still has a "rough" or "raw" character compared to a finer amp like the BHSE (which costs 10+ times the price, so...). It can drive an SR-007 pretty well though,  which smooths out things a bit, it's not a bad pairing. The 009 is definitely not a good pairing (since it takes up and even hyperboles the character of the amp driving it), neither are most of the Lambdas. The amp is not bright per se, it's just a bit more raw if you compare it with much better amps. I like it more (after mods) than the 323 and 353, at least it's not worse, and feels powerful and dynamic, so it survived both of them. In fact this is my only transistor energizer currently, for some reason I still prefer tubes, even in these rather exciting SiC and GaN HEMT times, out of personal preference or sheer bias, I don't know (don't war over this, please).

So I agree the T1 would likely be better, at least smoother, especially after mods (IIRC JimL described some mods to it either on HF or here, I don't remember).  Of course the best would be if you could compare them and figure out your own preference.

Good SRM-1/Mk-2 units pop up on eBay frequently. 

Both the SRM-1/Mk2 and T1 are old enough that replacing all the electrolytic caps would be recommended routine maintenance. I have no experience with a SRM-1, but a couple friends and I compared my modded T1 with an SRM-727 with global feedback mod. We all felt the T1 was more refined, and we all preferred it to the modded 727.

That’s interesting. I might hold out for a T1. There isn’t one on eBay right now that’s in North America. I’ve seen the listing for the Stax amp service. It does seem mandatory after so many years.

Getting back to the original problem...

I noticed the hum only after switching from an Onkyo C-7030 single-disc player to a Sony jukebox. The Sony has a plastic cowling or cover on the back, presumably with the power supply inside. (I haven’t popped the covers, yet.) I had my cables draped over it when I noticed the hum. So after rearranging the amp & cables, the hum has lessened,  but it’s still there. About two-and-half feet separate the amp from the power supply section of the Sony now.

Well, I can imagine some types of music where "raw" might be preferred.

Speaking of T1, I noticed that some of the earliest T1s have two transformers replacing the voltage divider in most other later T1s. Will this lead to sonic improvement?

I have just made a prototype of my O1 clone. Now I am working on standardizing the procedure of making this headphone as well as its headphone box so that it doesn't look DIY

Beautiful work!

Your clone reminds me that I’m looking for some DIY approach to replacing the “headgear” of my 207 earspeakers. Outstanding transducers, cheap-looking execution. I often fear I’m going to break something by simply handling them. I don’t want to change the transducer housings, just everything else. The pads will be changed to the leather 507 pads in a couple of months.

54 minutes ago, bwck2000 said:

I have just made a prototype of my O1 clone. Now I am working on standardizing the procedure of making this headphone as well as its headphone box so that it doesn't look DIY

They don’t look like DIY to me.  Well done!  Can you tell us more about it?  What is the dimension of the driver?

 

5 hours ago, chinsettawong said:

They don’t look like DIY to me.  Well done!  Can you tell us more about it?  What is the dimension of the driver?

black-anodized CNC aluminium case, sheep skin with memory foam earpad, copper electrode with 25% more open area than typical stax models, carbon fiber skeleton on the electrode and plastic parts made of industrial grade 3D-printed nylon. The electrode design is similar to the omega driver I posted eariler in this thread.

Regarding the diaphragm and the coating, I can't  speak too much but the coating is nothing similar to what you can buy in Walmart or Amazon. the diaphragm's active area is 90mm. The sensitivity is similar to 007 but lower than that of 009. 

Its sound quality is very interesting. its tonality is similar to 007mk1 and less darker but the clone's detail revival ability and soundstage size surpasses 009. The only weakness I noticed is the bass. 007 gets more punchy bass and some people might prefer how the bass is presented on 009 more. IMO stax sacrifice quite a lot of other aspects of sound quality to produce a better bass on its top model.

7 hours ago, bwck2000 said:

Speaking of T1, I noticed that some of the earliest T1s have two transformers replacing the voltage divider in most other later T1s. Will this lead to sonic improvement?

There is no difference to the amp section, it just how they did the tube delay on the early units. 

Speaking about tube delays, my SRM-600 delay is like 2x - 3x longer than my SRM-T1S. Any reason for this, EC99 takes longer to warm up?

There is nothing about it in the datasheet but in my experience it is a bit longer but not by much. 

Is $400 a good deal on a “C” model SRM-1/Mk-2 with dual pro bias sockets? It was pulled from a studio. I don’t know its age. If my offer is refused, How high should I go?

A method I use to determine average prices is to go to eBay, look up an item, click on "Completed Items" and look at how much people actually paid (those are the auctions and Buy It Now items where the price is green - if the price is in black it didn't sell). I also add in the shipping cost if that is listed.

It’s an eBay listing. He wants $479, plus $20 for shipping. That combo is too expensive for me. 

$400-500 US is pretty typical of late for a SRM1 MKII. 

Getting back to the hum issue, have you tried borrowing a different source?

Those old multidisc cd players are getting up there in age. 

 

I’ll do that tonight.

I’m not sure a 25-year-plus amp is worth the cost of purchase & refurbishment. That could end-up being $700-$800, if professionally done. I can get an SRM-353X for around $1K, made for North American line voltage, from Elusive Disc.

Drop $1200 and you can have an official stax mafia product!

https://mjolnir-audio.com/products/ 

I tried my Onkyo with the stats this afternoon. The hum developed, but weakly, and then disappeared. I couldn’t hear it when I switched back to the Sony changer. A mystery.

More on a better amp:

Would moving from an SRS-252S to an STM-1/Mk-2 be an improvement, since the 252S is a much newer amp?