[luvdunhill]

Tom/Doug:

I like the amount of wiggle room that the board has when inserted into the slots. What percentage of the maximum slot depth did you use when determining the width of the PCB? I'm working on a case/PCB combo and am fairly worried about tolerances preventing the "perfect fit".

 

[tomb]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif Tom/Doug: I like the amount of wiggle room that the board has when inserted into the slots. What percentage of the maximum slot depth did you use when determining the width of the PCB? I'm working on a case/PCB combo and am fairly worried about tolerances preventing the "perfect fit".

I'll have to check my e-mail files because we went back and forth on it - too loose, too tight, just right. Maybe it was the Goldilocks method.

Alternatively, you can measure it and compare to the published Hammond slot width. I'll do that tonight when I get a chance. I believe it's 1 millimeter of clearance on each side.

 

[eekimus]

So I had just purchased the SSMH PCB, and built my third SSMH.

I tested it out on a pair of Beyerdynamic DT770, 250ohm. With the 50K pot vol turned up fully, and source volume on full, there's a hum in the background, and barely any sound.

I have used 30 and 80 ohm headphones on the SSMH with good success, what's up this this one now? P2P wiring from tube sockets to PCB, jacks, plug sockets etc.

Internal wiring is done with twisted CAT-5 cable pairs. Soldering has all been checked and okay.

How does teh amp behave with 250ohm loads?

 

[tomb]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif Tom/Doug: I like the amount of wiggle room that the board has when inserted into the slots. What percentage of the maximum slot depth did you use when determining the width of the PCB? I'm working on a case/PCB combo and am fairly worried about tolerances preventing the "perfect fit".

The Hammond 1455N1201 has a slot width of 100mm (3.937").
The SSMH PCB width is 98.6309mm (3.883").

If you're looking for a percentage, that's pretty easy to equate with the Hammond millimeter dimension (100) - 98.6309%.

I think Dsavitsk actually tried for a millimeter and a half clearance - there may be some slight dimensional conversion errors in the DXF file (0.1309).

 

[tomb]

Quote:

Originally Posted by eekimus /img/forum/go_quote.gif So I had just purchased the SSMH PCB, and built my third SSMH. I tested it out on a pair of Beyerdynamic DT770, 250ohm. With the 50K pot vol turned up fully, and source volume on full, there's a hum in the background, and barely any sound. I have used 30 and 80 ohm headphones on the SSMH with good success, what's up this this one now? P2P wiring from tube sockets to PCB, jacks, plug sockets etc. Internal wiring is done with twisted CAT-5 cable pairs. Soldering has all been checked and okay. How does teh amp behave with 250ohm loads?

The SSMH has no problems at all with 300 ohm Senns, so 250 ohm Beyers should be a piece of cake.

Something else is going on ... It sounds like you're saying you've used 30 ohm and 80 ohm headhones, but perhaps not on this particular build. It may have nothing to do with the Beyers. Have you tried other headphones on this one?

One thing to check is the input wiring. If you've crossed up the grounds with signal, you can get the effect you describe.

 

[tomb]

All kits and cases (except the 2 or 3 who were shorted) have been shipped. I have some extra cases that did not have the top lid machined and will do those myself for the ones who were shorted, if they agree.

There are quite a few tubes left, so I've asked Hammond for a quote for more cases. So, there will be cases and some partial kits (minus the power supply) available in the future. I'll keep you posted.

 

[ludoo]

I just finished my PCB-based SS (sorry Tom for getting a proto PCB then waiting half a year to build it). As I wrote a few posts above, I top mounted the 4 electrolytic caps as my Cerafines were too tall. This led to an accident while drilling the top holes, and after much head scratching I managed to salvage the case by carving a large space on top with the Dremel. It's not perfect, and I had to move the fastening spacer below the board, but at least it does not look like a bomb went off inside the case.

On hindsight, I might have just let the tube sockets protrude a little bit more on top, which would have allowed me to mount the board on the second slot, gaining that extra bit of space below for the caps. Or I could have used a slimmer case, with the caps mounted on top as they are now.

I also had a bit of a scare as when I plugged the amp I had no voltage anywhere, just 3V on the power switch. After some measurements I found out I have a defective switch, what are the chances of that? I bypassed it and the amp powered up fine.

I tested it with the iGrados and there's a bit of noise at high volume (which curiously is still listenable and not extremely loud) I then switched to the Yamaha HP-3, and the SS is barely able to drive them to listenable volume. My two other SS built using Pete's original BOM are louder, so I guess I'll have to remove something.

Will it be enough to remove R14/R15 leaving R16/R17 in place? I had a few accidents with my other SS and a couple Alien DACs, and I seem to remember R16/R17 offer some protection for the source.

 

[tomb]

Quote:

Originally Posted by ludoo /img/forum/go_quote.gif I just finished my PCB-based SS (sorry Tom for getting a proto PCB then waiting half a year to build it). As I wrote a few posts above, I top mounted the 4 electrolytic caps as my Cerafines were too tall. This led to an accident while drilling the top holes, and after much head scratching I managed to salvage the case by carving a large space on top with the Dremel. It's not perfect, and I had to move the fastening spacer below the board, but at least it does not look like a bomb went off inside the case. On hindsight, I might have just let the tube sockets protrude a little bit more on top, which would have allowed me to mount the board on the second slot, gaining that extra bit of space below for the caps. Or I could have used a slimmer case, with the caps mounted on top as they are now. I also had a bit of a scare as when I plugged the amp I had no voltage anywhere, just 3V on the power switch. After some measurements I found out I have a defective switch, what are the chances of that? I bypassed it and the amp powered up fine. I tested it with the iGrados and there's a bit of noise at high volume (which curiously is still listenable and not extremely loud) I then switched to the Yamaha HP-3, and the SS is barely able to drive them to listenable volume. My two other SS built using Pete's original BOM are louder, so I guess I'll have to remove something. Will it be enough to remove R14/R15 leaving R16/R17 in place? I had a few accidents with my other SS and a couple Alien DACs, and I seem to remember R16/R17 offer some protection for the source.

The volume/pseudo-gain is entirely dependent on the values of R16/R17 and the impedance of the pot. (Well, to a lesser extent, the cathode bypass, too.) The last of our investigations of the DAC shorting seems to be a tendency of the SSMH to build up a charge on the RCA jacks. I seriously doubt that R16/R17 are going to offer any protection in that scenario. So, I'd remove them (use some jumpers). That should free up the gain issue.

EDIT: My experience with a wide variety of headphone impedances/efficiencies is that a 1 to 1 relationship with R16/R17 and the pot impedance is about as much as you want to go - probably less in the case of Ortho's - or no R16/R17 resistors at all. I've also not had much complaint about the pot mis-tracking, either. I suspect a lot of the earlier reports had more to do with tube mis-matches than pot issues. That's IMHO, though, I haven't made exhaustive measurements of the pot's tracking.

 

[ludoo]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif The volume/pseudo-gain is entirely dependent on the values of R16/R17 and the impedance of the pot. (Well, to a lesser extent, the cathode bypass, too.) The last of our investigations of the DAC shorting seems to be a tendency of the SSMH to build up a charge on the RCA jacks. I seriously doubt that R16/R17 are going to offer any protection in that scenario. So, I'd remove them (use some jumpers). That should free up the gain issue.

Thanks Tom!

And what about R14/R15? BTW my pot is a 50k one. For cathode bypass caps I'm using a pair of OSCONs, I think they are 680uF but I'll have to check.

Edit: yes I messed up things, I seemed to remeber you saying something about adding input resistors to protect the source, but they were probably connected to ground.

 

[tomb]

Quote:

Originally Posted by ludoo /img/forum/go_quote.gif Thanks Tom! And what about R14/R15? BTW my pot is a 50k one. For cathode bypass caps I'm using a pair of OSCONs, I think they are 680uF but I'll have to check.

Personally, I don't think R14/R15 have much of an effect - we're talking an entire magnitude of difference in resistance values and volume works exponentially anyway.
Quote:

Edit: yes I messed up things, I seemed to remeber you saying something about adding input resistors to protect the source, but they were probably connected to ground.

No - you didn't mess up anything. I'm not sure which would be better for protecting the DAC's output - but it's meaningless if the charge builds up on the RCA jacks. Nothing inside the amp is going to help at that point. Try disconnecting your source from the RCA jacks while the amp is playing music. I don't exactly know why, but you'll probably get a huge hum that won't go away until something touchs the RCA jacks and grounds the charge. That's what's been happening to the DACs. Unfortunately, grounding that charge fries them.

 

[luvdunhill]

Thanks Tom. Those numbers jive with my measurements.

Now the real question is, can I get you to PM me that rear plate that has a way to attach a Bantam to the rear plate with a pair of small, threaded angle brackets like FPE sells, a square hole for the USB jack, and then on the right side stacked power switch and power inlet? I know you have it

 

[tomb]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif Thanks Tom. Those numbers jive with my measurements. Now the real question is, can I get you to PM me that rear plate that has a way to attach a Bantam to the rear plate with a pair of small, threaded angle brackets like FPE sells, a square hole for the USB jack, and then on the right side stacked power switch and power inlet? I know you have it

Hmm ... my guess is that you'd be better off mounting the Bantam to the bottom of the case body, not the backplate - the USB jack has quite a bit of overhang, you know - almost perfect for the bezel distance on the Hammond case.

 

[ludoo]

Removed R16/R17 and everything is back to normal. This one is for my dad, who will also get my second pair of HP-3 and a y1. He is a huge classical fan, has a pretty good (Linn) setup at home and goes to about two concerts a week. His only headphones are a pair of ER4 I gave him a couple of years ago, it will be interesting to know his reactions to one of the great budget setups to come out of HF.

 

[revolink24]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif All kits and cases (except the 2 or 3 who were shorted) have been shipped. I have some extra cases that did not have the top lid machined and will do those myself for the ones who were shorted, if they agree. There are quite a few tubes left, so I've asked Hammond for a quote for more cases. So, there will be cases and some partial kits (minus the power supply) available in the future. I'll keep you posted.

Wow, that's very kind of you. I will send you an email (probably tomorrow) confirming my order

Cheers,

~revolink24

 

[kuroguy]

First of all, thanks to the guys who put the kits, cases, and boards together. Group buys are not a way to get rich. Especially when you are machining cases by hand.

Now, onto my problem. My SSMH has been working flawlessly for the last year. I recently relocated and when I set up my amp at work the left channel had a 60 cycle hum that gets louder when I move my hand near the left tube. if I touch the tube it is the loudest. If I ground my hand to the casewhile it is near the tube the hum goes away. In face, even a paperclip that touches the tip of the tube and a ground point on the case stops the humming. I switched the tubes around and the hum followed the tube. The room it is set up in has an audible 60 cycle hum without the headphones on. Is this a bad tube or a grounding issue? I suspect some aluminum foil around the tube should solve the problem, but that wouldn't be too elegant.

Any comments or suggestions?