VTA PH15 Build thread PH14

Regarding OPA 637 oscillation, if you still have it, I tried 2 things that helped for me. First, in addition to the standard 0.1uf decoupling caps on each of the op-amp's +/- power rails, I added 0.01uf and 0.001uf (to remove the higher frequencies). I also bypassed the NFB resistor with a 10pf mica to limit high frequency RFI from entering the loop from the backside. I tried this after reading an article about taming noisy op-amps and it seemed to eliminate the "hashy" noise my phono pre would make during loud complex passages.
The values I chose for the decoupling and bypassing capacitors were not calculated, I guessed and used what I had around.

@heyraz i was able to eliminate the oscillations in the Parasound, its covered somewhere on that web page. but thanks. what you suggested is pretty much what I did.

I now have all the upgraded parts for the PH15 as well I am going to put "nude" bulk-film and caddock resistors in key places on my MK3's along with the V-Cap CuTF's in the phase splitter and a Jensen CuPIO to couple the gain stage to the phase splitter. Its all about a $700 upgrade to the MK3's and should bring them up to snuff.

I did put the V-Cap CuTF's in the MK3's to burn in. My expectations were low in that I expected when I put them in and tried them out right away that I would be faced with a very subtle difference and the part of my brain that *wants* them to sound better would lose, as usual, against the part of the brain that has to admit there is not a sonic difference (I exercised the ability to be objective about audio when I did extensive A/B/X testing many years ago with speaker wire and interconnects). Well, the audible difference with the V-Caps was immediate and apparent - there was no subtly at all. I also experienced this going from Multi-caps to Jensen AlPIO however that "upgrade" was a little more subtle than going from the Jensen's to the V-Caps.

The V-Caps sounded very clear and detailed. I was hearing way more nuances than I ever had. I could definitely also hear a "hardness" or "strident" quality which I think is from the caps being fresh and no broken in. For the first 10 hours or so, they were definitely a major step up from the Jensen Al PIO's I had in there for 10 years. Things like more detail in the recordings of room sound (reverb), the nuances of the bow and fingers on violin and acoustic guitar strings, etc. just more sound and not colouration or "phantom" sound - more actual real qualities in the recordings. of course the quality of the recording has to be high too. so definitely so far sold on the V-Caps. Before listening to them I felt a little like a fool for shelling out $550 for these caps but now, so far at least, I think its an easy and well justified upgrade for the price.

After about 20 hours the sound went down hill. it was like the sound was trying hard to "get through" and losing. like if you break your way through a brick wall, by the time you get through you are still you but you are worn, haggard and bleeding. however, i have heard that this is not uncommon with caps that there are phases during burn in where they can sound bad. these caps apparently need 400 hours (17 days @ 24 hours a day) to burn in. so i have my MK3's running 24/7 now with a set of "junk" tubes and Caddock 8 ohm 100W film resistors on the speaker terminals. I am not running them full power, only enough to make the resistors "very warm" to the touch. I am also burning in the other set of V-Caps going into the PH15 so they are ready or close to ready when the kit arrives and I am ready to solder them in. Those caps are in a 12AU7 pre-amp I have with outputs running to ground. I am using the same burn in track I created that I mentioned before: equal mix of 1-22kH 10s sweep, 1-22kH 0.2s sweep and white noise all repeated.

So, totally surprised by the V-Caps, and like I said, I don't just say something sounds better unless it actually really sounds better to me - if its a subtle thing then I err on the side of it just being psychological and if I can't do a real blind A/B test then I will even more err on the side of non-objectivity. That was not the case with the V-Caps - very apparent and different sound. I am not going to say "better" yet because they need to burn in.

For the MK3's, the V-Caps are in and burning in. Once they are burned in I plan to spend a few weeks listening to it extensively. then i will do the resistor upgrades and see if there is a change there. I am skeptical about it but we'll see. I can understand how caps can make an audible difference but resistors, not sure.

Resistors probably contribute the most noise to a circuit. There's a couple of articles out there describing the different types and what situations to use them in. I spent a lot of time researching that when I built my ST70. In another amp I have, metal oxide was too harsh, carbon film was just plain noisy, and metal film was just right. Each situation is different (plate-grid-cathode) so research the article. When I replaced carbon resistors with metal films in the signal path of my phono preamp, it was very noticeable. Much quieter, more air and depth to the music.

The PH15 kit arrived today. It looks really good. There are no step by step instructions, only schematic, board layout and parts list. That's fine for me but for others who need step by step, sorry. Here are some pictures of the contents. The parts quality is decent, it will at the very least get you started. There are no cheap resistors and caps here - only quality 1% resistors, many are Dale (one or two steps above run of the mill 1%'s), the film caps are Wima's which are "ok" and the electrolytics appear to be good quality too. Everything is sorted out very nicely so that will help with picking the right parts when populating the board, however you should still double check before you plop a part on the board. check and double check and re-check.

I am going to cut the board to separate the PSU from the phono stage because I want to put them in separate cabinets. as you know I am going "full bore" with this build - most of the parts Roy supplied I am going to be using top quality parts for. I know its a bit of a waste but I wasn't sure about what I was going to replace while the board was in transit so I decided to just get the full kit and whatever is left over I can put in my parts drawer. As mentioned I will be using V-Cap CuTF's, Jensen CuPIO, Auricaps, Caddock MK132 and TX2575 bulk film "nude" resistors. Around $1000 in parts upgrades.

The build is done, at least as far as the PCB's are concerned. I can't do much more until I get the cases, so likely 2-3 weeks. Alas. I might hook up some RCA's and test it out at some point but for now, enjoy...

Had to try it out. So its just hanging off the wires. Works well and less hum than I expected considering its just sitting in open air. The sound is definitely a big step up from my modded Parasound PH100. Wider soundstage, more depth of image, more detail gets through giving instruments and voice more "layers" in the textures of the sounds. I am hearing more things, nuances and in some cases instruments in recordings I am well acquainted with. I am also hearing more tape hiss from the master being pressed into the vinyl, where I haven't in the past. Just more detail is getting through, and deeper quieter sonics are being resolved where before they were not.

The whole thing needs burn in time. The V-caps have 100 hours on them and they need 400 to be officially burned in.

You are hearing exactly what I was hearing when I upgraded to the PH14! I have bypassed the electrolytic on the grid of the first tube with a 2 uf film cap, seemed to me it really opened up the sound. Next I tried eliminating the voltage divider and electrolytic completely and biased the tube with a 9 volt battery, sounds fantastic, haven't been inclined to mod it any more since! I left the grid reistor in place.

Warmed up, the PH15 sits at 115.5VAC @ 0.25A or 29W. However a 0.5A regular blow fuse will pop on start up, some of the time. So I switched to a 1A fast blow and that seems to hold ok.

@TMadden Can you explain in more details your mods and also explain what each does and why it improves performance? I just want to learn as much as I can.

OK, well I'm no engineer but here's my understanding of it. The first stage of the ph14/15 is a j-fet cascoded into a grounded grid triode. This gives us the low noise of a j-fet combined with the sonic signature of a triode. I don't have the schematic in front of me, but you have the grid of that triode being held at about 9 volts by using a voltage divider composed of 2 resistors and an electrolytic capacitor. Electrolyitc capacitors are handy for lots of capacity in a small package but they are not ideal sonically. Hence the film bypass. To take it one step further as done in the Loesch style preamps, you can eliminate the voltage divider and cap entirely and just use a 9 volt battery to bias the triode. If you google "Loesch preamp" or "Oz Loesch" you will see several variations on this, all in very high end, highly regarded designs. I just borrowed the idea!

Build time for me on the PH15 was 5.5 hours to get all the boards together and do a smoke test on the PSU. I took my time and ensured each solder connection was sound, top and bottom. Also measuring series and parallel resistors to get the odd values to ensure the channels were balanced within 0.5%. Bending all the resistors pins to fit also took a lot of time. Another 1.5 hours was spent hooking it up, powering it up and getting it connected in the system for a preview.

Special thanks to Parts Connexion for all the help and stock of the upgraded parts I used, high quality wire, connectors, etc. A great resource and a pleasure to deal with.

@TMadden - great thanks for that. I am actually learning about tube amp design right now and although tube circuits are simple when you look at the schematic, they are very complex devices - even more tied their own "physics" than transistors, it seems. So any little details like this are helpful in further understanding. thanks!

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