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New schematics

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Posted on September 11, 2014 at 07:28:51
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 I've just had the Schematics and Projects section of the webpage updated for the first time in years and years and will keep it that way going forward... There are three new schematics for which I will add some more info soon. In the meantime don't hesitate to ask questions.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

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RE: New schematics, posted on September 23, 2014 at 07:04:12
Tubelcain
Audiophile

Posts: 32
Location: Guernsey
Joined: January 6, 2008
 Dear Kevin.

Wow new designs and thinking on K & K Audio. Out with the mainstream US and in with Russian military surplus Tubes/Valves in classic transformer coupled circuits. Out also with three stage designs and DHT’s and dumper diode rectifier power supplies. Quite a revolution.
I must confess those oddball 6C33C regulator tubes have always intrigued me also due to they’re very low impedance, a Push Pull transformer coupled amp using your Da3/6J49P balanced driver arrangement could well be on the cards for the forthcoming winter.

Does your new two stage arrangement sound better than the old DHT designs or is it a matter of simplicity or economy? I recall reading that in your opinion your best amp yet was a 3 stage GM70 single, is this still your personal reference or has this now been superseded?

Thanks for the new ideas your input and new designs are always welcome. I think that I read somewhere on the forum you were thinking of supplying a PCB for these new driver stage designs. One for PP and SE just add an output stage of choice, I am sure they would be a winner $$$

Enjoy The Music.
Tubelcain

 

RE: New schematics, posted on September 23, 2014 at 09:26:59
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 These 6C33C SE amps have a special kind of easy "live" sound that is very beguiling. Originally developed as easy-to-build circuits, it was clear after building the first stereo amp that something special that I had not heard in my SE DHT amp forays was happening.

I would say that the parallel SE 6C33C monoblock amps I'm now listening to are in the league sonically with the PP GM-70 monoblock amps (and have nearly the same power output), but require much less angst and expense to build and maintain. Of course, they are different sounding, but offer similar musical enjoyment.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: New schematics, posted on September 29, 2014 at 00:17:38
chrismercurio
Audiophile

Posts: 155
Joined: August 4, 2008
 Kevin,

Did you rig up the PP/PSE switch yet?

Best,

 

RE: New schematics, posted on September 29, 2014 at 05:12:38
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 Not yet.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: New schematics, posted on October 30, 2014 at 06:45:07
JoshK
Audiophile

Posts: 820
Location: NJ/NYC
Joined: August 3, 2001
 What ever happened to the PP300B schematic? Did you take it down from the forum? I am still planning to build mine (when I finally get my workshop setup again). I think I may have a copy somewhere, not sure.

----------------
"When Khruschev said "we will bury you" I don't think he meant with surplus parts." zacster

 

RE: New schematics, posted on October 30, 2014 at 07:14:25
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 No, I've not taken any schematics off of the forum. When you're ready, holler at me and I will send you the latest.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: New schematics, posted on March 4, 2015 at 06:32:17
KurtP
Audiophile

Posts: 245
Joined: January 25, 2007
 Hello Kevin:

Curious about the 2-stage PP amplifier schematic and the headphone amp. I have a 3-stage PP amplifier with interstages that I am going to be modding. I have a desire to eliminate the input phase splitter xfmr, as it doesn't have ideal performance. Going fully differential with a CCS to a negative supply is likely my choice for the first stage, similar to your headphone amp.

Removing the first-second stage IT is another possible goal if I can gain a performance increase. This leaves only one IT for the driver to the 3rd stage 300B's. Your headphone amp is a good option to do this. How stable are the DC operating points over the course of a month? Is this a set-it-and-forget-it design, or do you find that periodic tweaking is necessary? I really like the idea of DC coupling the stages to avoid having a capacitor.

On the other side of the thought process, simply forcing the first stage to be fully differential (as opposed to the Lynn Olson design) could allow the input transformer to remain, with its benefits of shielding and galvanic isolation. As long as I don't require phase balance performance from the input xfmr, it performs well. In other words, it does well transforming differential signals with low distortion, but it fails to provide accurate gain and phase relationship between the two secondaries.

Your thoughts ? Currently using LL1692A/PP (2:1.75) for IT, and LL1620AM/PP for OPT. Input transformers are selectable between a Tribute and Cinemag. Thanks!!

 

RE: New schematics, posted on March 5, 2015 at 13:10:44
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 Are you feeding your amps a balanced or unbalanced signal? Feeding a balanced signal obviates the need for an input transformer. I typically install an input transformer and connect the RCA jack to the primary and the XLR jack to the secondary. The secondaries then act like a CT grid choke for balanced inputs.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: New schematics, posted on March 5, 2015 at 19:56:04
KurtP
Audiophile

Posts: 245
Joined: January 25, 2007
 Feeding amps with balanced output, actually from a LL1689AM/PP preamp. So yes, considering removal of the input transformer entirely (or having provisions to insert or bypass, depending on mood).

If going fully differential with a CCS in the tail, I wouldn't be concerned about balance in the first stage. But then the question is do I IT to the second stage or DC couple. Hence my question about bias stability.

 

RE: New schematics, posted on March 6, 2015 at 05:58:17
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 I have built several PP amps where I used direct coupling between the first and second stage. The problem that I encountered was not bias instability, but the consequences of imperfect first stage tube matching. If the second stage tube had low grid bias voltage, a small plate voltage offset in the first stage due to mismatch in the input stage tubes "ate" a fair amount of the voltage swing available to drive the second stage to symmetrical clipping. It's not that I envisioned clipping the second stage in normal use, as that would be bad design, but simply want to have plenty of "headroom" in this transaction. The least fussy solution I found was to use a driver (second) stage tube that had a high enough grid bias voltage that a few volts of plate imbalance wasn't a big issue. I ultimately settled on triode-connected EL34 drivers in those amps. Of course there are other ways to deal with this as well, short of adding another IT.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: New schematics, posted on March 6, 2015 at 16:23:39
KurtP
Audiophile

Posts: 245
Joined: January 25, 2007
 Kevin:

That makes perfect sense. I think that is what I will need to experiment with over the next few months; either DC couple with CCS or keep the IT. I will be using a trioded 6W6, so should have ample headroom at the grid, very similar to the EL34. Formerly using the trioded 46 as a driver.

The more I study the headphone amp schematic on your site, the more I like it. That trick with the input transformer, RCA on one side and XLR on the other, is slick. I will definitely go that route. You effectively force voltage balance through the coil inductance. Technically, one only requires impedance balance to have a balanced line; voltage balance is in theory irrelevant. The differential input handles that. However, by providing voltage balance you permit each triode to amplify similarly scaled signals, which are then passed on to the next stage. This prevents one side of the amp from having to do all the work. At least that's the way I envision it.

 

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