Phono Amplifier

[soulmerchant]

Hi All,

I just want to thank all the experienced posters here for sharing their kind advice in this forum.

I have build a few end stages, usually with small modifications to known schematics. This is the first time I built a phono stage, and it really sounds great.

Zero hum thanks to star grounding and a nicely regulated DC heater supply. I do have a little RF hash, but it is very minor and easily fixed with a few matched low value resistors on the grids.

I experimented with some cold cathode voltage regulators (OD3A's have a wonderful glow) but found it to be more dynamic and life-like without them. Maybe it was due to the different mains transformer. I tried Hammond iron with an expensive full wave rectifier and OD3A's, but this version uses Lundahl iron with a 6BY5GA in a hybrid bridge.

I still have to do a few small things, like build a cover for the (admittedly ugly) Lundahl transformer. Right now I am using budget China tubes but they will be probably be replaced with something matched of higher pedigree.

Again, I would just like to thank all experienced posters for their input and advice in this forum. I don't post much, but do read the forum frequently and have learned a lot over the years. Thank you.

Kind regards
Ian

[data]

Looks very nice mate, well done

I need to do something similar, do you have a schematic for this build?

[SemperFi]

Very nice man! Good job.

[soulmerchant]

Originally Posted by data

Looks very nice mate, well done

I need to do something similar, do you have a schematic for this build?

I used a modified schematic similar to that of the EAR834p... not so complex really.

If you look up this 'romy cat' circuit online you will find he uses air tuning caps in the RIAA correction. The sound is very good with these, but I am using Amtrans AMCH instead.

The power supply for mine is also slightly different, using a Lund LL1649 transformer I happened to have. I added 2x 100 ohm wirewound resistors in series to the HT secondaries to reduce current inrush to the rectifier. It is a hybrid FW rectifier circuit with a 'virtual' center tap made of a 6BY5GA and two CREE silicon diodes. The added serial resistance smooths the response curve nicely. The 15H chokes are Hammond 159M, and most capacitors are motor run type.

I have also made a separate circuite to de-charge the caps when it is in the off position.

I breadboarded a few different schematics before deciding to put this one into my chassis. One deciding factor is that I have a lot of ecc88 and ecc83 type (various brands). So schematics I experimented with utilized these valves. There are a lot of great designs out there. I am sometimes astonished at circuits that are branded 'new' that actually have been done ages ago...

Ian

[kevinkr]

Very nice job, I did however notice that that is a Lundahl power transformer with exposed contacts - this is a bit of a safety hazard, and you should install a protective cover over the transformer to prevent potential shock and electrocution.

[data]

Thanks Ian

[soulmerchant]

Originally Posted by kevinkr

Very nice job, I did however notice that that is a Lundahl power transformer with exposed contacts - this is a bit of a safety hazard, and you should install a protective cover over the transformer to prevent potential shock and electrocution.

Yes, I noted this in my first post. The Lundahls sound great, but building covers for them is a bit of a pain.

[data]

Had a look at 'Romy the Cat's" site and what a cool site, love his TT set-up

[Cassiel]

Zero hum thanks to star grounding and a nicely regulated DC heater supply. I do have a little RF hash

Yeah well, mine has a star ground and regulated DC heater supply and it HUMS. No hum and just a little RF hash (just like you) if no input is connected but when I plug in any kind of source (turntable, guitar, mp3 player) I get a loud hum. Anyway, that's my problem (still don't know what's going on). I just wanted to ask you if you like the sound and if the gain isn't too much for your cartridge. Mine has 6.5 mV output voltage and I have too much gain. I'm thinking of adding a voltage divider at the output. Not much of a difference between yours and mine. My RIAA cap is 100pf not 110pf.

[kevinkr]

Originally Posted by soulmerchant

<snip> The Lundahls sound great, but building covers for them is a bit of a pain.

So's electrocution.. Seriously though you can probably get a suitable housing on line, or contact the vendor you bought the transformer from - they should be able to help out. You'll know exactly what I mean when you inadvertently brush against one of those pins.. I've done it too many times..