[dsavitsk]

Something else I have been tinkering with for a while. The "case" is temporary. It is the second breadboard iteration to check for proper layout. The amp is modular in that the tubes are attached to little replaceable circuit boards (with terminal blocks for the wire connections) so that different tubes can be swapped in and out. So far there there are modules for 6n6p/6h30/6n1p/6dj8's, 6sn7/12sn7's, 5687/7119's, 6c45's and 5842's and can be either resistor or led biased. It is shown with the 6n6p's.

The circuit is just a tube, a transformer, and two resistors. The cathode bias resistors can be bypassed, but so far I am using it cap-less. The PS is a Welborne Lab PS-10 with a tube rectifier and an additional pi filter in front of it. Clearly there is still work to be done, but since it is working and doesn't hum and sounds pretty good, it seems like a good point to post a progress picture.

-d

 

[hifihaxor]

lets see the schematics please!

whats the cost been so far?

 

[dsavitsk]

 

[jbloudg20]

I love it! want to share some more info?

 

[nikongod]

those look like VERY sweet output transformers.
what brand are they? standard, or tweaked?

 

[FallenAngel]

Quote:

Originally Posted by dsavitsk /img/forum/go_quote.gif

Oh Yeah! I love that schematic, now why can't the HPDAC be the same

 

[dsavitsk]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif those look like VERY sweet output transformers. what brand are they? standard, or tweaked?

Not sure what sort of tweeking would be done ... They are James transformers 5K:8. I am using them with Grados with a 33R resistor in parallel (both to set the operating point and to offer a safety margin in case the amp gets turned on with no headphones plugged in), so they are running about 10K on the plates. It is hard to compare transformers directly in the same circuit, but James' are good budget trannies. Probably not as good as Electra-Prints or Magnequest, but better than Hammond. I think the story is they are made by former Tango people, though that's just hearsay.

Obviously, I hope, the actual schematic is a little more complex than the one I posted, though not much. For the dual triodes, I just have both sides parallel which keeps the gain the same but doubles the output current.

Heaters are all AC. I found that if I grounded the heater center tap it got rid of the last bit of hum, so everything runs very quiet.

The PS has a 5ar4 rectifier, though there is plenty of voltage headroom to use some others. The transformer is 500V -- and is hopefully being replaced with a James power transformer soon (as soon as I can source one) to match the others -- which gives about 330V after the tube. Lots of this is dropped over a RCRCLC filter. Then there is a string of zeners and a mosfet that regulates the PS to 160V. I used a regulator since different tubes will draw different current which would lead to too much calculating for various operating points. I chose 160V as this was a reasonable plate voltage for most of the tube I want to use. The 6N6p's have been the default, but I am waiting for my 6c45 boards which have a little more gain and similar power to the 6n6p's, and since they are single triodes, will hopefully have more cohesion. We'll see. The 6N6p's sound pretty good though.

I put the output transformers in the front both for the practical reasons that that's where the headphone jack goes and to be far from the power transformer, but also because I always liked that Jadis does that, so this is my little homage. I think transformers look cooler than tubes anyway.

 

[tyre]

That's a nice amp dsavitsk, simple and elegant. Any chance you could draw a more complete schematic, with the power supply and part values?

 

[SoundGoon]

Quote:

Originally Posted by hifihaxor /img/forum/go_quote.gif whats the cost been so far?

x2

 

[Voodoochile]

How are you liking those james transformers so far? I've been curious for a while about those. Euphonia seems to have updated their offerings a bit recently.

 

[PeterP]

Very nice amp. I’ve always toyed around with an amp that could take a wide range of tubes but never could come up with an “adaptor” plate that I liked. I see you like the James OTs. Did you use any other OT during your testing? Is that what you plan on for the "final" volume control? What is it? (I see you grounded the VC frame. Sure hums without grounding.

) What are your thoughts on either a balance control or dual volume controls?
Looking forward to seeing the final amp.

 

[dsavitsk]

Quote:

Originally Posted by Voodoochile /img/forum/go_quote.gif How are you liking those james transformers so far? I've been curious for a while about those. Euphonia seems to have updated their offerings a bit recently.

They are quite nice for the money -- very clean midrange. Unfortunately, the impedance ratio is not quite ideal in this setup so when they are scaled up the bass is rolling off a little more than I'd like. I think I am actually going to get a pair of Electra Prints custom wound with 32 ohm taps for the final version. I figured with the amount of time and money i have in this thing, I might as well get it right. Not sure what I'll do with the Jameses -- maybe keep them around for breadboarding, or sell them off or something.

Quote:

Originally Posted by hifihaxor whats the cost been so far?

If you have to ask ...

Seriously, as with anything like this, a lot of money is eaten up in experimenting, and thus parts that don't go in the final version. However, if one were to build what I think will be the final version and not invest time and money in designing top plates and adapters and circuit boards and burning up power supplies, and swapping in different ouput transformers and multiple power transformers, I'd say about $800 in parts. Actual cost has been higher, but many of those parts will find their way into other projects, or will be used inother breadboards.

Quote:

Originally Posted by PeterP I see you grounded the VC frame. Sure hums without grounding.

Not sure I know what a VC frame is ...

Quote:

Originally Posted by PeterP What are your thoughts on either a balance control or dual volume controls?

I know Rick does the dual volume control think, but i've never really found a need for it. This amp does not have a hair triger, so the pot seems to track well enough for me.

 

[PeterP]

Quote:

Originally Posted by dsavitsk /img/forum/go_quote.gif Not sure I know what a VC frame is ...

I mean to say that you have grounded the metal frame of the volume control. Most of the time I end up with a volume control mounted on something other than a metal chassis. In those cases you need to ground the frame of the volume control pot to keep hum out of the system (especially when touching the volume control. Anything that you can touch should be grounded, however in this case it's not only a safety issue.)

 

[dsavitsk]

A little update. This would be the 3rd iteration. I replaced all of the iron with custom wound Electra-Print transformers. The outputs are 5K:32R and can handle about 35mA of current -- the James' were 5K:8 being run at 10K:16 with a resistor in parallel to the phones. The power transformer has essentially the same specs as the Hammond that was there before, but is at least twice as heavy. Sound has improved accordingly.

Pictured here with the 5687 tube modules in place. I think it is ready to go, and I am going to order the real top plate in the next few days.

 

[Voodoochile]

The word 'massive' comes to mind!
Looking good, can't wait to see the end result. Is Jack pretty well caught up this time of year?