VTA PH15 Build thread PH14

@Avinunca Yes the 22k 3W resistors get quite hot. i raise them off the board to help prevent board damage and give more airflow to the resistors.[/quote]

I was going to raise those - just wondered about the 1/2 Watt

Avinunca wrote:

@Avinunca Yes the 22k 3W resistors get quite hot. i raise them off the board to help prevent board damage and give more airflow to the resistors.

I was going to raise those - just wondered about the 1/2 Watt[/quote]

I didn't bother raising the 1/4W ones.

anbitet66 wrote:
Plexus, what version of audacity do you use? I have 1.2.6 and I don't see any way of saving as a FLAC. Do you have a newer version?
Tony

Time to update. Current stable Audacity is version 2.0, quite a few improvements.

@GP49 thanks for that. i updated. so far I'm not noticing much difference other than I get digital drop outs now. : /

I am about to order the wood-side cases for the PH15, one for the PSU and one for the phono-stage including the step-ups. They will have nice Bolivian Rosewood sides. I also have some copper mesh and tape coming so I can properly shield the inside of the cases and I will use the mesh as the heat vent. I am going to have to cut all the case holes myself and I don't have the tools to cut narrow vent slots. so my idea is to cut out a rectangular hole above/below the board and use copper mesh to provide airflow. it should look pretty good too.

I expect it to take a few weeks to get all the case stuff. I also have to build the power umbilical to connect the two, I have the parts for this. I am going to use a plastic shell twist on 4 conductor cable with 12ga wire for both B+ and FIL. each supply will also be fully shielded in the umbilical to prevent EMI from getting it - not that it will but might as well "bullet proof" the design. I always like to do all the cheap and easy things I can to eliminate interference and otherwise provide the best quality possible.

Last night I listenedd to a re-press of Mingus Ah Um. Wow. it sounds like they band is right there, so clear. i can hear all the nuances of the horns, like the spit rolling around in the sax as its played. yeah, that's my audiophile benchmark: can i hear spit? if you can hear spit you're doing well. I was feeling that building this PH15 is sort of like building a musical instrument - its all in the nuances and rich deep character when you get to this kind of quality of sound. the cap and resistor selection, making every solder connection count, etc - it just feels like making a fine instrument rather than slapping together an electronics kit. the final pay back is listening to Ah Um and feeling like, the next day, I saw Mingus live at a local jazz club.

I've been messing around with step up transformers. what a black art. having no experience with them its been a big lesson is hooking small coils of wire to larger coils of wire and determining what the heck goes on with that. talk about non-linear. naively i bought a pair of used Jensen 34Ks which have a 38:1 ratio, 31dB. I figured it was just about gain and getting the right load on the MC. partly true. but there is a lot more at play because when you load the MC you lose gain. but you also change the sonic character of the whole MC+SUT system and this is what feeds the phono stage.

My MC is a Benz Ruby 2 with a 40 ohm internal impedance. apparently it sounds best with a 200-400 ohm load on it. so in order to get that on the primary of the SUT, i have to use a 430k resistors because the reflected load on the primary is (reflected primary load) * (turns ratio)^2 = 300 * 38^2 = 433k.

So theoretically 430k on the secondary will give around 300 on the primary, in the middle of the generally accepted range that works best with the Ruby 2. thing is, it sound bad: very bright, airy, lots of detail but smeared instruments, no body and lacking bass. through trial and error I found 100k on the secondary sounds good but that theoretically load the MC with around 70 ohms.

So there is more going on here. Impedance, inductance, coils of wire driving other coils of wire... its a black art. but its fun to learn. "they" say that a 10:1 or maybe 20:1 is better suited to MC's with an internal impedance of <40 ohms and that SUTs like 38:1 are best for < 5 ohm. why? I am not sure but I am sure there is math somewhere that explains it.

For now I am running the 34K's with 100k despite the fact that it should sound like its loading the MC down too much, it sounds really good with the PH15. better than I have ever heard. Its the closest thing so far that I've had where my system sounds like a live gig. The hope is that a "better matched" SUT will sound better. I've ordered a pair of Lundhal LL9226's which can work as 5:1, 10:1 and 20:1 so I will try that out and if they sound better I will swap the 34K's out.

I also rolled in a pair of EH 6922's (low noise) that I burned in for about 100 hours. They sound pretty dark compared to the Amperex JAN's I have in the PH15. I will do more listening and report. I am going to try and get my hands on the reputed best sounding 6922, the Amerpex white lable PQ pinched waist but try and find those for less than $200 a tube, used.

But so far the PH15 is sounding much better than anything I've used in the past. I'd like to do some comparison with other tube phono stages at some point and also a stock PH14/15 with the stock parts compared to mine with the crazy hot rod parts.

Oh and I ordered the cases: 11"x7"3.5" with bolivian rosewood side panels. should have them in a few weeks. I made up the power umbilical last night. that took 2 hours because it was so fiddly getting the pins in the connectors. the parts just for the power cable cost me around $70. but it will be a sweet high current capability, shielded twist lock connection between the PSU and preamp. there is about 0.2 ohms on each line so not too bad all things considered.

You might want to get a pair of the PC boards for small transformers shown on this page:
http://www.kandkaudio.com/accessories.html if you haven't already. Makes it much easier to work with the Lundahls.

Yeah I got those boards too

I have settled on Jan Philips 6922's and RCA clear top 12AU7 in my PH14. You can pick up the Jan Philips pretty reasonable if you want to try them. Sounds very good to my ears!

Lundhal LL9226's arrived and I will install tonight. the hope is these mate with my cartridge better than the Jensen 34Ks I am using. I do get some "edge" on high level signals off vinyl and I am hoping this will fix that. they were $100 each. The next step up is the LL1931 which are about $250 each and above that is the LL1931Ag which is silver wire wound and I am told those are $800 each! backing up a bit, I was told (by a knowledgeable party) that the 9226 is not "embarrassed" by the 1931, it just sound a bit better. and a bit better more is the silver wound one. can't wait to hear what this sounds like.

I've been using the K & K step up transformer kit with the LL1931 in it. I have nothing else to compare it with, but I'm sure pleased with the sound of my analog system. Assembling the thing was quite fun as well. It's a good little kit, straight forward to build.

You're looking at a $2000 phono stage kids. Roy's PH15 with all the goodies.

I was watching a used pair of Amperex white lettering pinched waist 6922, apparently the holy grail in 6922's. they sold for about $540US for the pair. INSANE! I will live with my lowly Amperex JAN 6922's :/

http://www.ebay.ca/itm/251044599175?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

From what I am read in order from best to worst:

- Amperex 6922 pinched waist white lettering
- Amperex 6922 PQ white lettering
- Amperex 6922 PQ orange lettering
- Amperex 6922 PQ all others
- Amperex JAN 6922 white lettering
- Amperex JAN 6922 all others
- All other 6922's

This doesn't include the 7308's which are a mil spec version and also shuffle into that list where basically the 7308 version is better than the 6922 version.

I might splurge on the PQ white lettering one day. they are around $100 a tube from what I have seen.

Update. Had 3 custom enclosures made by Keith Kirby with Bolivian Rosewood side panels. They arrived monday and as of today I have the chassis parts installed. The internal wiring+work needs to be completed which I hope to have done today. The enclosures are just amazing - very high quality workmanship from Keith and the materials are top notch. I used an optical centre punch and cobalt unibit for the round holes and a nibble for the IEC hole which was a lot of work because of the thick gauge aluminum Keith uses. I also EMI shielded the wood panels on the inside with copper tape.

Here is the over-all "look" of the system. The top case is the PH15 power supply, the middle is a passive line stage and the bottom is the PH15. They PSU and PH15 connect with a 4 conductor umbilical shown in the other picture.

Some interesting features of this design: note the 3 large holes on the top edge of the PSU and PH15 - this allows the power connector to be moved so you can run the umbilical however you want, the open holes will provide some extra ventilation. Also, Keith's cases assume that the cover plate will be the bottom - there are more screws and they are not counter sunk like they are on the top. typically you'd use the cases to make a tube amp and have the tubes sticking out the top so the removable panel makes sense on the bottom. in my design, all the electronics are in the enclosure and I want the cover to the top to gain easy access to the tubes etc. what I did was make the cover the bottom for the PSU (the board will be mounted on the bottom plate) and for the PH15 the cover is the top. the reason for this is, that when stacked with the PSU on the top, it looks better from the top. When stacked it doesn't matter what the PH15 looks like and its better to have the cover be the top for tube access. if you have them side by side, then ok, the top of the PH15 wont look as nice, but i think typically they would be stacked and the PH15 be on the bottom. hence the decision to do it this way.

Tonight I will finish this up and report back with some nice pics.

Oh and I did end up getting a pair of Amperex USA white lable PQ 6922's and they do sound smoother and more extended. i did some measurments of them compared to the green label and the EH's and i can see why.

I've got the PH15 operating. its amazing. anyway before i get into details, a question: i am getting about 50C/125F ambient temp inside the enclosures. would this be ok for solid state devices in the PSU and the 6922/12AU7 in the phono? It will be a real issue to create ventilation holes in the enclosures so i am hoping to get by without them.

those temps sound just about right, all the SS devices are rated at 100C, or 212F
of course the tubes themselves usually run about 250-350F, so don't touch!!

I haven't posted any final shots of the build because I am still evaluating etc. I will post some pics soon. needless to say the project turned out really well. better than I expected. the PH15 sounds really great and is a major step up from what I was using for a phono stage, and that was a pretty high end solid state phono stage. I still get some hum but its bearable however the hum output is considerably lower than the install in the temporary case - i think the PSU was sending EMI to the phono stage, right side, that it was closest too. that hum is gone but there is now an equal amount of hum at a lower level coming through. i *think* its coming in from the turntable but i am not sure.

I also am having some serious microphonics. but that's the tubes. i have some dampers on order so hopefully that will help.

like the guy in the SP14 post mentioned, i too have been staying up late listening to LPs especially during the final stages of the build. and since the PH15, i have basically not been listening to anything but LPs!

Nice to see a big renaissance in vinyl too! lots of really nice pressings out there.

Try some NOS military tube types, preferably with triple mica and added support rods to reduce microphonics. That made all the difference in the world for me.
Rich

@heyraz can you tell me specifically what tubes you are using? initially i got a pair of Amperex JAN 6922 green printing and then I read that the Amperex PQ with white printing sounded 2nd best to the coveted "pinched waist" version. I saw a pair of "pinched waist" tubes go on ebay for $550! im not spending that kind of money on these tubes. but the PQs sound good, better than the "green printing" Amperex's - I also did a spectral analysis of the PQ tube and it has a smoother response and is flatter on the high end so this accounts for the sound difference. but, they are quite microphonic.

Good sounding 6922's seem to get quite expensive. well, $500-600 for 2 of the apparently "best sounding" 6922's around (the pinch waist). there was even a "pinched waist" that the seller said had sonic issues in his amp (noise, clicking) but it still sold for around $150. yikes.

Anyway, let me know what you are using and I'll see if I can find any.

In the meantime I ordered some dampers and hope that will help. if not the company offers a money back guarantee.

TubeDepot.com has a good selection of 6922 types (including several different Amperex) and they can be pre-tested
for low-noise and low-microphonics, which is very important for this tube type.

Hi Roy. I know, I also got a pair of EH 6922's from tubedepot.com, low noise/microphonics. they sound ok but the Amperex PQ's sound much better, smoother, clearer. I find tubedepot's vintage tube prices quite high however, generally speaking, compared to ebay or classified. but then again its a crap shoot for microphonics.

another good supplier for new and used is Brent Jesse, AudioTubes.com
some nice Telefunken's for $175 a pair

wow those are insane prices. i don't have first hand experience with anything but the 6922's i have which are: new EH, vintage JAN green printing USA, vintage PQ white printing USA. The green print were $100 for the pair and the PQ's were $150 for the pair. from what i have read the PQ's are second best sounding to the pinched waist tubes which are $500-600/pr. but this is just what I have read. pretty much everyone who has tried the pinch waist and the PQ says the same thing: #1 pinch waist, #2 PQ, after that they are less distinct in terms of sound quality. so outside of spending $500 on 2 used tubes (NOT!) i got the PQ's. i will try dampers for the microphonics but really i can live with the microphonics because they only occur at loud volume levels. but granted microphonic tubes could cause sonic issues even at lower sound levels. i'll try and the dampers and take it from there...

maybe one day i'll get a pair of pinch waist and try them. i understand from reviews that the telefunken and mullard 6922's are "meh". but in the 12AU7 world Telefunkens are some of the best sounding.

My situation is a little different as my preamp uses 12ax7's. In my situation I use a Sylvania Gold Brand 5751. The 5751 has a lower gain than typical 12ax7, but it's the military build that really makes the difference. I try to use a vintage military tube whenever I can and like pretty much anything made by RCA and Sylvania. I get them from ebay and have been lucky so far. I don't mind collecting a few extra tubes here and there because sometimes you need a tube that you don't care about if you're testing a component you're not sure about. Having a few extra tubes around also lets me "voice" the component. Kind of like changing the strings on a guitar.
Rich

I am listening to a vinyl transcription I made using the PH15. As you may know from my previous posts I do have a bit of hum when listening to the PH15. I have installed parallel output jacks on the PH15 so I can go into my Dynaco MK3's and into my tube preamp/ADC -> computer. So the output of the PH15 drives both simultaneously.

What is startling to me is that the transcription has NO hum on it! so the hum I am getting is not coming out of the PH15. The other output of the PH15 goes into my passive attenuator box, through a rotary switch and then through the passive attenuator. When listening to the PH15 through the amps, the hum level is affected by the attenuator, so I assumed that the hum was originating out of the PH15.

This appears to not be the case, as the recording has no hum, recorded simultaneously as listening through the other outputs. Any ideas how I can trace this hum down?

EDIT: I assume its a ground loop issue. all the components are plugged into the same grounded power bar. i guess its a matter of ground loop tracking down - unplug, try cheaters, etc. good news though that its not the PH15. in that sense the PH15 is dead quiet.

I am going to make some recordings of just the PH15 output with no audio. I also want to test out the dampers I get to see if they help with the microphonic tubes - again I will make digital recordings of with and without to compare. I will post the results here.

Very nice. I'm about to start on my own PH14. I'm going to boprrow some ideas from you and Pigface and do some things different myself. I'm probably going to cut the board. Single chassis, I have the 16" widebody one. I'm giving serious consideration to a paired set of inputs to allow the use of RCA mounted load plugs.

I studied your upgrades, you didn't use the Vishays for R4 and R13, can I assume cost being a factor and it being hard to arrive at the correct values without using several?
Can I ask you what the board trace surgery and jumpers are for in the area of R13?

Thanks.