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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 03 Jul 2014, 12:42 
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Location: South East US - Tennessee
laurie54 wrote:
...... i have looked threw your entire build of this amp before.....


-- He threw the ball through the window -- ;)

Very nice, Mark! Very classic and refined appearance. I like. :smoking:

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The key to a successful build is to keep the smoke IN the circuit.
-Les

We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
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LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board


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PostPosted: 03 Jul 2014, 18:24 
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Les wrote:
laurie54 wrote:
...... i have looked threw your entire build of this amp before.....


-- He threw the ball through the window -- ;)

Very nice, Mark! Very classic and refined appearance. I like. :smoking:

In appearance this build followed on from Abstinence (6EM7 amp with Sophia mesh plate rec. tube) but under the bonnet very different. I will have to build something very different looking next to brake the dark run of amps.

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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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PostPosted: 05 Jul 2014, 21:20 
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While checking-out some component value inside Black Lace I decide to add a few tweaks. The HT to the driver tube was a little low so I drop the value of the limiting resistors to it. Remember this amp has split PSs so I had to change one resistor per channel. This brought the HT up to exactly what Suncalc had specced.

Usually I put a 0.1uf snubbing poly across Ck of the power tube (6V6) but in this build I didn't do this initially. So I put one in on each 6V6. I think it helps improve high frequency. Wife was out last night and I got the whole night to listen to the amp with new tweaks. I really wasn't expecting any big difference. Boy was I wrong. The sounded like I hadn't heard it before. It was like a totally different amp. Nothing else in the system has changed for months so I new how the whole system should sound.

For the life of me I can't imaging how those small tweaks could have made such a big improvement. The amp was clearer and cleaner than I have ever heard it. Bright and crisp and far more open sounding. I have been listening to this amp every day for months so I know how it should sound but now - fabulous. As I said usually I always snub Ck and always with a 0.1uf poly. I will never leave one off again. Ck on the 6V6 is a 470uf low ESR. I like to use non-polar caps here where I can but in this case it would have been far too big.

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PostPosted: 14 Jul 2014, 23:25 
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I had put Black a Lace to the CRO some weeks back but was not happy with some of the results so I held off posting any figures. I made some minor tweaks to Black Lace as posted above. Today I retested Black Lace and I'm glad to say much happier with the results. Not sure if my testing was off last time or magically two small caps can make a huge difference. Only the Gods know.

One, Black Lace is an extremely nice sounding amp. I'm very impressed with its overall musical sound. I'm listening to it now. Two, here are some results from the recent testing;

-3db frequency results into an 8.2ohm resistor (OPTs are 6ohm out); 26Hz to 86KHz! @1W
Channel separation; 2Vpp into the left channel and 10mV in right channel @ 1KHz. Would some one like to tell me what that is in db separation? But the 10mVpp is really the noise floor so I don't think this is an accurate test. In other words the noise level is 3.5mV RMS. That's not too bad.

SQR wave for 100Hz and 1KHz is not good but excellent at 10KHz. The amp is better with high frequencies than low. Listening to the amp without my subbies there appears to be plenty of bass though.

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PostPosted: 17 Jul 2014, 21:00 
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I asked Suncalc for some suggestions for other power tubes to place in this amp. 6L6 (and I would image 5881) was the main suggestion. I was warned to watch the current drain. My chokes are only rated to 50mA each and with the 6V6s in place that is exactly the drain for each choke (one per channel).

With the 6L6s in idle current rose to 63mA and same with the 5881s. Too much. If the idle current had of risen to 55mA, a 10% rise, I would have felt safe but a 16mA increase is way too much. I tried an EL34 for fun, again the idle current rose too much. So for now the 6V6s stay. This was always going to be a 6V6 amp and I really wanted to keep it an all Ozzie tube amp. Nothing lost!

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PostPosted: 05 Aug 2014, 18:17 
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I lumped a whole lotta gear out to friends house (Ron) who helped me with some initial testing of the Beyma based speakers (VoXConcentriC - now completed). I setup the speakers and initially with Abstinence, my 6EM7 power amp. Ron felt the treble a little dominant. I dropped the tweeter 4db and the balance appeared better. This is how I had the speakers initially but removed the L pad thinking it better. Not so.

Abstinence sounded great with all music types until I replaced it with Black Lace, my new 6V6 amp using very old Ozzie made tubes. It is another Suncalc design. Black Lace had a lot more grip on the big 12" Beyma coaxial driver and rounded the lower mids and bass out a lot better.

In fact Ron liked it so much he brought back his four driver 3.5 way speakers. Black Lace produces about 5W but it handled Ron's 88db efficient speakers with ease providing an excellent mid range and good bass. Lucky for me. When I got home a local Ozzie wants to purchase Abstinence. A happy ending.

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PostPosted: 20 Nov 2014, 06:07 
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Part of the Black Lace build was always going to be a black lace dust cover. Fashioned by my mother (who is very good with craft etc.) here it is complete with real glass smokey beads and hand crafted bows.
Attachment:
Lace.jpg


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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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PostPosted: 21 Nov 2014, 18:32 
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After a number of days listening to my new Class D amp, Mirage, I have swapped in Black Lace. Talk about absence makes the heart grow fonder, I feel back in love in the first 30 seconds of music. Such a fine amp. It doesnt have the supper lush sound of my 300B, The Silver Dragon, but a leaner, delicate midrange and great balance of sound and linearity right across the audio spectrum. It just sucks you right in regardless of material played.

It reminded me of how much I enjoyed Black Lace soon after construction. It will remain in my system now for a good while but will have to give up its seat to the Dragon eventually. Until then some fine listening to be had. The sound of carbon film and real old Ozzie tubes. Thanks Matt.

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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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PostPosted: 27 Nov 2014, 17:20 
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I was kicking-back enjoying an extended classic piece (and a good red) one afternoon and it went through my mind how good the Silver Dragon sounds. Then I looked across at my equipment rack to see Black Lace where I thought the Dragon was. I had been listening to Black Lace all that time thinking it was my big 300B. Just shows you how nice a simple and cheap amp can sound.

Black Lace through my now Xover-upgraded (3rd order) VoXDeuX (small 2-ways) cuts an extremely deep and very detailed sound stage. A great combo.

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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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PostPosted: 01 Aug 2016, 08:12 
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Just looking at my last post. Wow that was a while ago and much audio water has flowed under the DIY bridge. Now I have the very high efficiency 15" Beyma concentric speakers and two stage tube preamp, things are different.

I have been enjoying my 300B (Silver Dragon), Tamarisk (EL84 SE UL) and now Black Lace (6V6 SE UL). But recently when I hooked up Black Lace there was just too much hum to bare. I pulled it out after 5mins.

This is only the second week in over nine where I haven't had commission jobs. Time to see if I can fix the Black Lace hum ghost. Last thing first. I fixed the hum 90% but realised after adding 470uf of 400V electrolytic to the PS that one of the filter resistors is only 5.6 ohm and not 560!

But by adding an additional 470uf to the filtering stage, making 570uf in total on the end of a two stage filter, the hum is extremely low. My VoXGrandious are 99db efficient so any noise or hum in the system comes through. Next will be to upgrade that very low filter resistor and to add another to make the filter stage a three stage affair.

That means; 4uf (PIO) cap, 5H choke, 47uf cap, 100ohm resistor, 100uf cap, 100ohm resistor, 470uf cap. It's very quiet now but tomorrow it will be even quieter. And there are two seperate PS split from the first cap. So lots of filtering.

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