VTA PH15 Build thread PH14

wow... apparently Dr. Arthur Loesch passed away on the weekend.

Forum post about Dr. Aruthur Loesch

Obituary

Tonight, I will listen to a Proprius pressing of Mozart Requiem on the PH15 in memory of Dr. Loesch. I am remembering now that years ago when I was researching for mods to my PH100, I did find a number of citations related to Dr. Loesch - he's done a lot for high fidelity audio amplification design and had a real focus on phono stage and RIAA.

nice job Brett, and who needs a chassis when you've got V-caps?!! I see that Telefunken output tube also! And I envy your turntable!

Yeah the chassis will hide the V-Caps. Alas. I am also using a set of Amperex 6922 PQ's along with the Telefunken. The turntable is nice but the Benz Micro Ruby 2 really matches well with the phono stage I think, so far. I noticed that with the Jensen step-up transformers, I was over-driving the phono stage - this is odd because I need those with my solid state phono stage when set to a gain of 55dB. So I wonder what's going on there - the PH15 seems to have enough gain to manage the Ruby 2's 0.3mV output. It might be a loading issue too. I have to get the loading worked out eventually.

Really nice.

I'm running a Benz Micro Glider SM with my PH-14. It outputs .8mv. I thought I had plenty of gain until i used a pair of Lundahl step-ups to double the signal to 1.6mv. Great improvement, the sound became much more dynamic and punchy.

I was thinking about this. Anything other than a very thick silver wire, and even with that, the audio signal is going to be distorted in some way. it maybe so minute that we can measure or hear it, but it will be just by the nature of what we know about physics. so in audio, i strive to eliminate as many things in the signal path as possible. i say "i" instead of "we" because everyone has their choice and some people prefer to colour their audio. in fact, when selecting components, the PH15 is an example, I choose components based on what I expect their colouration to be. knowing what a part is likely to do to the signal i then make a decision based on the cumulative effects of each part. its usually an educated guess and so far i have been pretty accurate determining the final "colour" from the pallet of "colour"(ation) I choose. I digress...

Not having to use a step-up transformer with the PH15 is preferable than using one. despite them being high quality they are really going to mess with the audio (take a look at a phase distortion plot for one of these). But then there is the question of cartridge loading too. however, you can get the same cartridge loading without using the step up with resistors. so i am not seeing any compelling reason to use a step up.

In your situation TMadden, maybe the over-all distortion of using the step-up produced a more accurate signal than not because of loading. but then you could load the cart with resistors and eliminate the step ups. or, maybe for some reason the dynamic characteristics of the step up and the cartridge worked in such a way as to provide the added dynamics you hear and the other distortions introduced were just not irritating to you?

I will work with connecting the Jensen step-ups to the PH15 but my preference is to not use them. Initially i tried them, as they were mounted in a project box with RCAs just to give it a shot, and they appeared to over-drive the PH15. taking them out of the path, loading my Ruby 2 with about 960 ohms (which it likes) gives me enough gain with the PH15. more would be nice so I'll try again with the step-ups but I have a feeling I will run without them. Lets say they make a more pleasing sound than without - that will still not work for me as I'd rather hear as undistorted a signal as possible and unless I find out otherwise, I don't step-ups are going to increase the quality the of signal vs not using them.

I've been messing around with the step-ups. I am using Jensen JT-34K-DX with a ratio of 1:37 or 31dB of gain. I am comparing using these with not using them and putting the PH15 into high gain instead (MC jumper). It been a real challenge getting the loading right with both configurations. So far the best loading with the Ruby 2 and the Jensens is 6.8K in parallel with the secondary, using R1 pads on the PH15 board to solder the resistor. Without the Jensens, I use 960 ohms to load the Ruby 2, again with resistors on the PH15 (in this case 22k in parallel with 1k).

I am using the Cardas test record which has 1kHz track recorded at 0dB so I can test distortion. I am also using SignalScope on my iPhone with a Tascam IM2 dock mic using the FFT to see distortion.

Its easy to overdrive the PH15 with the Jensens. The idea was to find a resistor which would load the Ruby 2 in a decent range and not overload the PH15. It took trial and error and so far 6.8K is the best compromise. I think what I need to do is put a pot in there and adjust it until i get minimal distortion and highest level and then sub resistors in for the value on the pot. Right now 6.8K is what I am using.

I don't use a pre-amp but rather a DIY line stage with a multi-position switch for input and a Khozmo 48-step shunt attenuator with Dale resistors.

I can get about 8dB more signal with the step-ups than direct however the higher order distortion goes up a bit at 0dB which I am not too happy about. I may just opt to run it in MC mode with no step-up and sacrifice the 8dB of gain. On the bright side its good to know the PH15 will work with the Ruby 2 to a decent volume level because if I can avoid using the step-ups I would prefer that. I just need to listen to it and determine what the best compromise is. My gut is telling me "no step ups" so we'll see.

Temporary home, for now...

I got kind of lucky with my transformers, I bought them with he intention of using them as phase splitters at the input of an all transformer coupled amp I was going to build. They are Lundahl amorphous core low level signal transformers, with quite wide bandwidth and low distorion. Looking at the specs, I noticed that they could be set up for a 1:2 step up, so I decided to try them, seems they were just about perfect for my cartridge and phono pre. I would agree that no step up would be ideal,since no transformer is perfect, but for my setup I would need a phono stage with nearly 60db gain. I do have somthing brewing down in the lab though!
If I recall, I loaded mine with a 1K resistor on the secondary of the SUT, the cartridge "sees" roughly 250 ohms.

I just did a lot of listening back and forth between high-gain/no-step-up and low-gain/step-up. I used 1K with no step-up for loading and 5.1k with step-up, because with the secondary, it works out to about 960 ohms, so close enough. There is way more noise, hum and this weird sporadic clicking when NOT using the step-up. the clicking is coming from the cartridge side. with the step-up its quieter, still some hum. sonically I find (I think) that with the step-up it sounds more accurate. although I don't think I am getting as much depth of image. however that depth of image perception could be colouration. thats my gut feeling + experience talking. i am going to live with-step-up for awhile and later switch to do more evaluation.

Either way the PH15 is a major step up from my PPH100. now that solid state phono stage had been upgraded using the most expensive highest quality precision low noise opamps you can get for audio, and all passives were replaced with Wima, hand matched 1% resistors and Solen output bypass caps. so it wasn't just off the shelf. still I am getting just so much more detail, clearer harmonics (which cause rich textures to sound more realistic) and more soundstage and depth and ambiance detail. finally I feel like the phono stage is better matched to the cartridge/phono set up and amp/speaker set up (i felt it was my weak link until now).

It's been fun following your thread, especially since what you are hearing so closely parallels my experiance. Great job hot rodding that phono stage! Tube based gear lets you get so much closer to the music. IMHO, the only time solid state is superior is driving woofers and subwoofers, where current handling is the priority.

I have been transcribing vinyl to FLAC's using a dBx 386 tube preamp ADC in 96/24. I did Fleetwood Mac Tusk a couple weeks ago using the Parasound PPH100 plexus hotrod version. Tonight I transcribed side 1 using the PH15 plexus hotrod version. So now I can compare them. I have to say they are closer than you might think. But for sure the PH15 sounds better: its clearer, instruments are more defined and there is more detail in the low level sonics like on attacks, the sounds of human's touching strings, the resonating texture of acoustic instruments and room sounds, and more dynamic, faster, transient response. however I will say we are in the realm of "golden ears" here - your average person not acquainted to high fidelity would likely be hard pressed to hear the differences. it's one of "those" things. but for me, yes, its enough of a refinement that its worth the money. and now I can consider selling the PPH100 and have something to compare it to.

In the interest of science and the quest for high accuracy audio, here are two 60s snippets in 96/24 FLAC of the beginning of my vinyl transcriptions as described above. the one with PH15 in the title was made with the PH15 detailed in this thread and the PPH100 is the Parasound PPH100 I upgraded. both using the same pre-amp and ADC. no processing at all was used. All other variables other than swapping out the phono stage are the same.

VTA PH15 flac sample (18.5MB) <-- note this was recorded with the wrong load on the Ruby 2. The sound here is very restrained. Look for a later post for updated samples

Parasound PPH100 flac sample (19.1MB)

I grant there is some noise and hum on these tracks peaking at around -45dB. I have to iron that out. I am hoping separating the PSU from the pre-amp will get rid of the hum, although it may be a grounding issue.

I am experimenting with cartridge loading. now that I have a good sounding phono stage, its time to really get a handle on the cartridge loading. the problem I had before where there was distortion was not because the step-ups were overloading the PH15 but rather the output of the PH15 was overloading the Mk3 driver. Installing a suitable attenuator solved this. after some experimentation with loading resistors on the secondary of the step-ups, i'm settling on 22k for now. this gives a primary load of 16 ohms to the cartridge, which has a 40 ohm impedance. I did work with 50k secondary load (36 ohms on the primary) however there was too much mid-high brightness and lacking bass.

I also had a 200k series input resistors on my shut attenuator but that sounded reserved. i replaced it with a 10k TX2575 and that really helped.

so i guess there is theoretical (40 ohm cartridge sounds better with a 16 ohm primary load) and a 270k input on the mk3 driver sounds better with 10k on the attenuator. let your ears to the walking.

I updated the FLAC above with the current loading on the PH15.

Have you ever messed with HDtracks? They sell 96kHz/24bit and some 176kHz/24 bit music. What are you using for your flac playback and when you convert an album to flac does it maintain the character of the album?

yeah I have purchased a lot of HDTracks products. I not only enjoy the music but also listening to the mastering to digital to learn and tune my ears to the various issues that digital has. I am using a Macbook pro and use either Enqueue or Fidelia for playback. For recording I use Audacity.

I find my transcriptions to sound decent. At the moment I have a lot of hum in the right channel of the PH15. I am hoping its related to the right channel being closer to the PSU in the case I am using. I hope. so unfortunately right now my transcriptions come with some -45dB hum in the right channel.

Overall, going from vinyl to FLAC using what I have, the results are pretty good. there is the usual lost of fidelity listening to digital but its pretty good. at work i listen to a pair a Stax Lambda 407's with a dBx DAC and so its a good way to have some vinyl recordings to listen to at work or elsewhere when I am not home.

Download and listen to the FLACs I posted and let me know what you think

with your cartridge I believe you need a step up with 20-24db of gain for LO-MM mode, or about 8db less gain (12-16 db) in HI-MC mode.
I think if I were in your position I would try another pair of step-ups in that gain range, a very nominal $$ amount compared to the cost of a pair of those capacitors. Just IMHO.

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

Plexus, are you related to that guy on CAM called Erik by any chance?

Hi. I'm new to this site and to tube amp building. Just started building my PH15. Looking at photos on this thread I am wondering if I have made a mistake mounting my resistors right up to the pcb instead of leaving a stand-off gap for cooling.
Only done the two sets of R10 to R15 so far. Do any of these run hot?

@tubes4hifi I have it sorted out. it was all in the loading. so even though the 34k step-up are an aggressive 31dB of gain, they work really great with the PH15. the PH15 pumps out a very hot clean signal. I should put it on a scope and check out some waveforms from stylus to PH15 output.

@anbitet66 1.3.14-beta on a mac

@Captain Coconut no relationship

@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.

@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.