DIY Audio Projects Forum

"Lacewood" Amp V2.0
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Author:  mwhouston [ 06 Jul 2017, 06:54 ]
Post subject:  Re: "Lacewood" Amp V2.0

I have never found Hz an issues. I think it is deeper.

Take to tranniamp miles way to a friends or relations house and measure it there. I think the question is mains or tranni.

Author:  HT Performance [ 06 Jul 2017, 09:11 ]
Post subject:  Re: "Lacewood" Amp V2.0

john55 wrote:
John; I am beginning to think that this problem is with your mains supply and not the Edcor transformers.

Hi Matt,
I live in a small Spanish town that was completely rewired approx 10 years ago. All properties are fitted with smart meters. There is no heavy industry in this area. I would agree with you that the chances of getting 3 bum transformers is ridiculously low, BUT, I bought a Hammond 370FX locally. It's the same as the 270FX shown in the power supply schematic, but has twin primaries with various taps to allow for different mains voltages. I've wired it to run off 240v mains so it is running under the same set of rules as the Edcor transformer. The 370FX wired up, stand alone on the bench, with 225v applied to the 240v windings and no load gave me readings of 260v-0v-260v exactly what I was expecting. The 6.3v winding was bang on 6.3v and the 5v winding was 4.7v (I'm not sure why the 6.3v hadn't dropped a little but an approx 6% under voltage on the primary gave an approx 6% drop on the secondaries). So, using the 370FX I'm having no problems at all. I've been listening to the amp every day now for 3 weeks and enjoying every minute.
I've just looked up a post I put on the 6EM7 thread last year. This was the first amp I built. “All valves are glowing, all voltages are low eg. 235V instead of 250V, 245V instead of 260V and 31V instead of 35V”.
Highly confused.
Update: I've just wired a Hammond 369EX transformer, standalone on the bench. Again I've used the 240V tappings even though my supply is 225V-230V so it is running with the same set of rules as an Edcor transformer. This is to build the 4S pre-amp. The secondaries are spot on. 190V-0V-190V HT and 6.4V for the heaters. So, as it stands..2 Hammonds working perfectly. 3, possibly 4 Edcors all giving low secondary voltages. I'm not knocking Edcor, everyone on this forum speaks very highly of them, I'm just trying to find out what is going on.

Hola John!

I also have the same issues here in Portugal.
The output voltages are lower than specified when running almost at full load.
I really believe it´s an issue with transformers when we´re running 50Hz instead of 60Hz. The transformer also heats-up too much.
The same issues happens at work when I use 60Hz power relays on 50Hz on industrial machines.


Author:  john55 [ 06 Jul 2017, 12:55 ]
Post subject:  Re: "Lacewood" Amp V2.0

Hola Miguel,
Hopefully we can sort this out with the help of the forum and Brian Weston at Edcor.


Author:  john55 [ 18 Jul 2017, 12:57 ]
Post subject:  Re: "Lacewood" Amp V2.0

This weekend I've wired up a 4S Universal preamp (I'd already made the case), and rewired the power supply on the Lacewood V.2. In both instances I've used Hammond Power Transformers. In previous posts on this thread I've been attempting, with help, to solve a low secondary voltages problem with an Edcor Power Transformer used in the Lacewood V.2. I know (after being told) that there can be many reasons for this, 50Hz instead of 60Hz even though the transformer is rated for 50Hz. Dirty Mains etc. As I can get Hammond transformers locally I thought I'd try a couple out to see if I had the same problem.
Mains in............ 225v (I've wired for 240V as voltages were high at 230V taps).
Volts to preamp..257V (Matt shows 250V).
12AU7 Vp............70V left 67V right
12AU7 Vk..............2V left 2V right
12AU7 Vp+k........67V left 62V right

Mains in.............225V (I've wired for 230V)
Volts to amp.......288V and 255V (Matt shows 300V and 265V.)
6SN7 Vp..............98V
6SN7 Vk.............3.9V
6SN7 Vp+k..........91V
6V6 Vp..............280V
6V6 Vk................17V
6V6 Vp+k..........263V
Left and right channels pretty much identical.

I've had both amps running together for two days now. No hiss or hum, more volume than I could ever need and crystal clear sound. The full system is as follows: FLAC files on remote harddrive – (Raspberry Pi – Hifiberry pro+ DAC – Rune Audio OS as a stand alone media player) - Fostex plate amp driving 4.5 subwoofer – 4S preamp – Lacewood V.2. - Fostex FE126En drivers in bass reflex/backloded horn, hybrid cabinets.
I would say that the Hammonds are doing the job. I also know that things aren't that black and white. Any thoughts?

Author:  mwhouston [ 18 Jul 2017, 18:47 ]
Post subject:  Re: "Lacewood" Amp V2.0

I use a Pi under rune with DIY AK 4495, Xmos USB DAC and local 2T USB drive.

Very pleased.

Author:  Longhorn [ 26 Jul 2017, 21:03 ]
Post subject:  Re: "Lacewood" Amp V2.0

Lacewood V2 Longhorn attempt.JPG
I finally completed my Lacewood V2 project and it turned out pretty good for my first venture into vacuum tubes. I changed the layout a little bit and managed to arrange the power supply stuff on the left half and the amplifier stuff on the right side. Volume and vintage power lamp on the front, IEC connector on left back, speaker outputs on right back. I kept the RCA inputs on the right side – close as possible to the volume pot and the 6SN7. All-in-all, a good layout and eye-appealing symmetry.
The wood case is mesquite. It is available in Southern Arizona where I live at local sawmills. Mesquite is hard to work with but is beautiful and grows wild in the Sonoran desert. (It is hard to find a straight piece more than a few feet long though!)
There was a bit of hum at first power-on but that was traced to the twisted, shielded wire I used from the volume pot to pins 1 and 4 of the 6SN7. When that was replaced with regular 22 gauge solid wire, the amp became dead quite (no input and volume control turned to full on). It remains hum and hiss free today.
I did have some strange results with my power supply. It was producing only 271VDC @ B+ output. I bridged the 350R 5W resistor and it jumped up to 295V where it remains today. Here is a table of the loaded voltages – similar to Matt’s and others who have shared – except for the 5U4GB output.
AC Mains: 118VAC
Trans HT: 279/279VAC
5U4GB, pin 8: 310VDC
Input, 1H chokes: 300VDC
B+ to 6V6S’s: 295VDC
B+ to 6SN7: 264VDC
6V6S, pin 4: 293VDC
6V6S, pin 3: 289VDC
6V6S, pin 8: 17VDC
6SN7, pin 2: 102VDC
6SN7, pin 3: 4.0VDC
6.3VAC heaters: 5.85VAC (transformer yellow wires)
5.0VAC heater: 5.82VAC (transformer brown wires)
CD player audio out: 4V P-P max

Performance: The amp has excellent volume (Driving a pair of HSU HB-1 surround speakers stolen from my movie room : 92dB/1M/2.83V). Driven by a Vizio BD player with CDs through the audio outputs.) The bass is strong and clean. Soundstage and imaging is outstanding. But… there is detectable “shrillness” in the upper end. The degree of the “over-brightness” seems to vary with the CD and volume level from barely noticeable to tiring. It becomes worse at higher volumes (overdriving the 6SN7?).
I know that some speakers can do this (although I never noticed it from these HSU HB-1s in the movie room). Being a new guy to tube music, I am wondering as if there is something I need to check or fool around with? I used good parts in the construction (including Nichicon KZs and some Audyn caps that I could barely fit in the case).
Any thoughts would be appreciated.

Author:  mwhouston [ 27 Jul 2017, 00:05 ]
Post subject:  Re: "Lacewood" Amp V2.0

Randy, good work. First of many tubers I hope.

Author:  Longhorn [ 31 Jul 2017, 14:49 ]
Post subject:  Re: "Lacewood" Amp V2.0

Thank you Mr. Houston.
Any ideas what might be causing the "shrillness" in my highs? I would appreciate hearing any thoughts you might have...just point me and I will do the rest to track it down.


Author:  mwhouston [ 31 Jul 2017, 18:39 ]
Post subject:  Re: "Lacewood" Amp V2.0

I'd say it is rare for a tube amp to sound shrill in the treble. Tubers usually sound smooth, sometimes too smooth, in the treble. Are you sure the sound is not coming from your preamp? I use a DIY two stage tube preamp which I love. Try different interconnects between preamp and power amp. Also put the amp on the CRO and take a look at the treble response. Most of my tube amps go beyond 32KhZ. My latest 6L6's upper 3db point is 47KhZ!

Also you may have oscillation and you should be able to see it on the CRO. Try a larger grid blocker resistor to the 6V6 or try a carbon film grid blocker. I remember reading many years ago that carbon film resistors make better grid blockers but can't remember why. Try the grid blocker first.

Good luck.

Author:  Longhorn [ 01 Aug 2017, 12:44 ]
Post subject:  Re: "Lacewood" Amp V2.0

Thanks for your insight Mr. Houston. Your thoughts will give me a place to begin looking. Couple of more questions if I may...

I wasn't clear but I am not using a separate preamp at this time. That was to be my next project.

I am running the audio output of my Blu Ray player directly into the Lacewood. That signal goes thru the volume pot directly to the 6SN7 signal tube (which in essence acts as the preamp I guess). I have noticed that the Peak-to-Peak voltage of the Blu Ray audio out going into the Lacewood is as high as 4V. Can that be overdriving the 6SN7 resulting in the shrillness at high volume levels? Would changing the 6SN7 bias to operate at a different point on the tube's load line possibly help? Would adding a preamp help or perhaps worsen the effect as you note in your response above? What kind of audio input levels should I be feeding the Lacewood to "make it happy?"

Meanwhile, I will investigate the issues you suggest with the o-scope.

Thanks again,

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