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 NEW  Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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PostPosted: 01 Dec 2012, 15:17 
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Joined: 29 May 2011, 12:24
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Location: Netherlands
Since my sourcing of parts to build an EL34 Oddwatt amp is taking a while I had to start a smaller project, as my hands were itching to at least have something in my stereo system build, modified or upgraded.. and preferably with tubes. I stumbled on the lampizator website and decided to give it a go. So these are my first baby steps in the DIY tube hifi world. :smoking:

I scored an old Marantz CD50 cd player for 10 euros, and a used power transformer for the SRPP circuit for 15 euros. As for the rest of the parts I used what I had laying around. I took the signal from the TDA1541 DAC and made it switchable so I can switch the cd player back to stock, just so it's easy to compare what the modifications do to the sound. I then made an outboard SRPP circuit as described on the lampizator website, using UOS philips E88CC tubes which I pulled from an old oscilloscope. I added some cathode bypass caps as I prefered the sound with these caps, even though the original circuit left them out. After some comparison of OSCON, Elna Cerafine and other caps I thought the oscons sounded the best. Unfortunately I didn't have them in low values so I popped in some 15uf oscons, but will order a smaller value as 15uf is giving me a lot of extra gain.

The sound is definitly better than the stock CD player. It's much warmer, focussed, cymbals sound less shrill and less digital. I like it.

I had an issue with the heater voltage being to high, I got +/- 7,9 volts measured to earth. Now I seem to recall reading somewhere that in a SRPP citcuit the heater should be completely floated, but I can't find the article. I do have the - of the bridge rectifier connected to earth. I wonder if this has something to do with it? I would appreciate some input here. :idea:

If I were to build again I would use a larger chassis to accomodate the filter caps with a little more space.

Next build will be bruce's EL34 oddwatt to replace my cheapo sony amplifier. Looking forward to get started on that one.. ;-)


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Last edited by Steavis on 01 Dec 2012, 16:57, edited 1 time in total.

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PostPosted: 01 Dec 2012, 16:25 
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In an SRPP, the heater circuit at minimum should be floated. Best route is to bias the heater to the B+ to keep it with in the H-K range (50V for ECC88), especially in reference to the upper cathode of the SRPP.


Your wire dress looks great! :up: The only thing I see that kind of bothers me is that exposed lead of the electorlytic right next to the case - if it were me, I'd put some insulation either on that junction or on the case adjacent to that junction.

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

Science without religion is lame, religion without science is blind. - Albert Einstien
_________________________________
LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board
Current project: 6V6 "pseudo Champ" prototype
Still to come (On hold): 6CG7/12AX7 Guitar amp (modified FireFly)


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PostPosted: 01 Dec 2012, 17:17 
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Les, thanks for the reply. I'll completely float the dc heater supply tomorrow. Since I'm quite new to this I don't completely follow you on biasing it to the B+ (I'm used to guitar crcuits which always have 6,3v ac). I'll do some more reading on this topic as I'd like to learn.

I thought about the electrolytic cap's leads being exposed. I glued it in place but am not happy with it..if the glue will go the cap can easily short. I think I'll use some shrink tubing there. I also wasn't completely happy with the B+ supply being quite close to the chassis (on the left, where I put the blue electrical tape). It doesn't short, even without the tape..but still. Next time I would use a larger chassis so I don't have to squeeze it in so much.


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PostPosted: 01 Dec 2012, 17:23 
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@Steavis: Nice compact neat build. You are using the same cast Al chassis I sell at work.. They are Asian made but are cheap ans easy to work with.

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Projects: "Parley" - Tube preamp with Pass B1 buffer | "VoXConcentriC" - Beyma high efficiency 12" speakers | "Black Lace" - all Ozzie tube 6V6 Power amp - old school
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PostPosted: 01 Dec 2012, 17:33 
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Thanks Mark. The chassis is sold under the Velleman brand here and cost 22,50 euro. I'm sure they buy it from the Asian factory and sell it as their own!

Steven


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PostPosted: 01 Dec 2012, 21:26 
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Cool, those cast aluminum enclosures take paint quite well I find, very nice job. :up: I had one successful "lampiztor" attempt, sadly I retired that cd player for parts as the case fell apart.... lol I wonder why, I have a Kenwood one to try next.

Do you have a picture of inside the CD player?

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PostPosted: 02 Dec 2012, 00:11 
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Steavis, follow this link: http://diyaudioprojects.com/Tubes/EL84- ... -Tube-Amp/
Scroll down a bit so the power supply schematic is shown. You'll see a 100K resistor and a 220K resistor, which form a voltage divider circuit for "biasing" the heater to the B+. It is of vital importance that the voltage difference between the cathode and the heater be with in 50VDC for the ECC88. If the difference is too big, it will cause the cathode to fail prematurely = shortened tube life. Now, since we don't have the particulars of your power supply, you will need to figure the best voltage divider arrangment to get that H-K difference to less than 50VDC. Again, of particular importance is the upper cathode in the SRPP since that cathode is most likely to be well outside of the 50VDC range as it feeds the plate of the lower half of the SRPP. Your actual heater voltage won't change, it should be about 6.3V. What you're going to be looking at is the voltage difference between the cathode pin and either heater pin at the tube. This should be less than 50V. If your heater circuit itself is producing more than 6.3V (which it will if all you've done is put a bridge rectifier on your 6.3VAC transformer) you can either add some resistance between the bridge and the heater OR use a voltge regulator like an LM7806 in the heater circuit. The LM7806 is a 6VDC 3 terminal regulator that's simple to implement, just be sure to use a heatsink and keep it isolated from ground. You could also do as Bruce did in his power supply circuit which is to series connect 3 1N4001 diodes (or similar). Since these have a voltage drop of 0.7 each, 3 will give you 2.1VDC drop, which will bring your heater supply in to its proper voltage for the heater.

Hope I haven't confused you to much ;)

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

Science without religion is lame, religion without science is blind. - Albert Einstien
_________________________________
LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board
Current project: 6V6 "pseudo Champ" prototype
Still to come (On hold): 6CG7/12AX7 Guitar amp (modified FireFly)


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PostPosted: 02 Dec 2012, 09:56 
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Hi Les, thanks for the excellent info. I ended up with a voltage divider of 220k / 47k which gives me about 40V H / K difference. I have 157 volt on the plates of the E88CC's and with two 1N4001 diodes I ended up with 6,35 volt on the heaters. Perfect.

I'm listening to some jazz now and it seems to sound even better than yesterday now that all voltages are correct.

Attached is a picture of the finished product. After I took this picture I added some electrical tape as a precautionary measure to the sides, top and bottom on the left where the B+ supply is, and to the right next to the electrolytic cap for the heater supply. It's not an ideal sollution but it'll have to do for now. If I would build another one in the future I'll get a bigger enclosure.

In the future I intend to upgrade the wima coupling caps for some 2uf paper in oil type.. but first I'll enjoy it the way it is for a while. :wine:


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PostPosted: 02 Dec 2012, 10:05 
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Hi, Very nice, I have considered a tube stage on my CD player but since Oppos go for relatively large $$$ and the model I have was a Stereophile A list, I figure using all tubes after it will do for now.

A hint to all you builders out there..... if you need to insulate a high voltage terminal in a project there is a whole line of products that generally are called RTV. They are silicon based goo in tubes. There are various ratings but pretty much any will work at the voltages we usually see in diy. They look a lot like common silicon sealer but have special properties so they will not corrode metals and not break down under voltages. Do not use common silicon sealer. It will have unpredictable consequences depending on its composition.

Good listening
Bruce

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PostPosted: 02 Dec 2012, 10:19 
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CrazyAbtTubes, here are some chassis shots for you of the cd player. I upgraded the DAC capacitors with MKP type (those 14 red caps bundled together). I added some silver mica caps for the DAC's oscillator. I don't know if there's any need for this but I was having fun soldering and thought it wouldn't hurt to upgrade all caps around the DAC. All white MKT caps are bypass caps for electrolytic caps. Some caps that matter on the main board were upgraded to 47uf OSCONs. I also did the NOS (no oversampling) mod. I didn't really hear a difference before or after NOS mod I have to say.

I added a rubber band on one side of the clamp which keeps the cd in place to put some more even pressure on the cd to (hopefully) aid in getting less vibrations. Originally it had one spring on one side of the clamp.. now it'll be pushed down from two sides.


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