Pink Triangle PT Too - Modifications and enhancements

[JaS]

An essential guide for PT Too owners by Abandonflip, with some useful tips for any turntable DIY'er

Pink Triangle PT Too - Modifications and enhancements

Comments, questions or suggestions?

Feel free to use the comment form at the end of the article or post in this thread.

Regards,
JaS

[uktel]

Well done Flip
A good informative and useful article for all PT users
How many of these mods have you done to your own PT?
I no longer use a PT but if I did it would be in bits by now after reading this!
Terry Dale

[Abandonflip]

Thanks Terry.

My poor old PT was the donor for all of these mods. I had tried some of them before, but never all in one go.

I had also tried other materials when building one-off's 15-20 years ago. I used all sorts of bits & pieces, but was most proud of my suspended TT based on a Luxman PD284, using some Thorens springs and an SME3009. This was donated to a friend and may still be around even now.

What has been difficult, of course, is trying to gauge the difference each incremental change has made. Given unlimited time (or maybe just a second PT to play with) I might try making measurements and subjective comparisons after every change - that sounds like a winter project to me.

One thing it will never be is an Anniversary, sadly, and it won't compete with a Vector'd PT either. However, I'm more than happy with the results so far, and IMO all of the mods have enhanced the PT attributes that I most like.

Perhaps there's no reason to go further or spend more...

[uktel]

Isn,t it a shame that we have to sell components to help pay for the next one
I,d love to hear my old PT TOO with my graham arm and the carts I now have in my present system.
I reckon it would sound pretty good!

[satanfriendly]

Mr Flip, you don't know how close you could have come to having a second PT! Minus a bearing of course.

I learnt a lot from your little paper and what parts I did use were most valuable. I've still got one or two tweeks to go through (arm board experimentation), but apart from being pleased to actually 'get there', time was running out. I never did get the 'butch' tile spacers instead having some rather fairy looking pink objects from the top of a tupaware box.

Back to work next week so at least I can return on the 27th December as against to the end of January.

I can assure you there is more fun to renovating a shagged out old PT than repairing shagged out pipelines at 2000m.

A bit like you at the moment, I don't see how spending anymore could result in any better sound. Get used to what I have, like it, love it and use it!

[Mark Kelly]

This is a phot of a PT TOO PS modification I did for BK.

His summary:

" thanks to your work I have the PT TOO turntable working better than ever now".

The boards used are available as a kit, except the little veroboard which makes the PT toos 0-5V logic talk to the -5 to +5V logic I used ( I don't like having Vss at ground in a mixed mode circuit, too much noise injection into the analogue ground)

[Abandonflip]

Mark,

What was the purpose of the PSU mods, and which circuit board 'kit' are you referring to?

It's interesting to see something done with the PT Too supply, other than putting it in the bin when it goes wrong! It seems to me that even Funk aren't particularly interested in repairing PT PSU's (their argument is normally that certain parts are no longer available) and would rather sell you a DC motor conversion instead.

The only other option currently available is to use the Hercules supply (which has just been made available for the PT Too in the UK), but this is a relatively simple affair compared to PT's original.

Also, what do you see being involved in adapting the PSU to battery power? AFAIK the 'bridged' DIN socket at the rear was intended for connecting a battery pack, but this never came about and the whole unit was eventually replaced by the Pacesetter.

[Mark Kelly]

The PT TOO PS is fairly primitive so the idea was to bring it up to a more modern spec. This expanded along the way so it now has some features that I haven't seen on other power supplies. Mine are the boards with the green solder mask visible in the phot.

The main thing BK wanted was fine adjustment of speed, so the output frequency was made adjustable in steps of about 0.01 Hz. Brian says his PT-TOO runs at correct speed with the drive at 50.08Hz. I insisted on including adjustment for quadrature angle, the PT TOO allows for differential phase voltage so that feature was retained.

The overall output voltage changes with speed and there's an adjustment for a voltage reduction after a delay timer (also adjustable) on the 33 speed. I found that fine tuning the level of third harmonic in the drive waveform had a small but interesting effect on the motor so I included that adjustment too. There's also an option for 78 RPM but that requires a major revision.

The boards and some necessary parts are available from me as a kit, I have an ad up on Audio Asylum classifieds.

The problem with running the PT TOO on batteries is that the original spec output amps (TDA 2004) require about 19V to get enough drive voltage for the motor and this makes a battery supply a little cumbersome. My kit was designed from the ground up to operate on a 12V battery supply so it includes an output board with a different amp (TDA7266). This is much easier to do than changing over the PT-TOO. By the way the newer design measures better as well, I think this is because I was more careful with PS layout than the original PT TOO designer.

BTW I think PT are misinformed, I do not remember a single part in the PT TOO supply which is non-standard. It's a bog ordinary CMOS logic circuit with an LM10 switched cap filter and a TDA 2004 output amp.

[Abandonflip]

The PT TOO PS is fairly primitive so the idea was to bring it up to a more modern spec.

I think you're absolutely right, although of course it was seen as being quite advanced in comparison to its main competitor at the time - Linn's Valhalla.

In fact, a good indication of PT's overall ineptitude with electronics is the fact that Arthur K apparently runs two of his own integrated amps to achieve stereo, as one channel of each amp is inoperative and he can't seem to repair them!

I would be interested to take this further Mark, but do you think there's any inherent benefit in improving the AC supply, or is it easier/better to go along the DC route?

[Mark Kelly]

Assuming you are talking about the supply to the PT controller rather than AC vs DC motors, as I see it there are two options.

First is the solution shown in the phot, with the supply and the output amps from the original PT TOO PS retained but the electronic speed regulation upgraded. This is the cheapest option (an experienced tech could do this for less than $USD200 / 80 quid).

I don't see it as worthwhile to try to do battery supply or whilst retaining the PT output section. It would cost you more than doing a complete conversion, use more power and not perform as well. The same comments apply double for upgrading the existing AC supply; taking the motor controller "off the grid" has huge benefits IMO.

The TDA7266 seems to perform better than the TDA2004 and it's a BTL chip so it can be directly wired to the output transformers (no honking great output caps).

The second solution is therefore to gut the PT supply completely and replace the innards with the full Synchrotron kit. This is somewhat more expensive (a bit over $USD200 , call it 100 quid) but you also have to stump for the battery and the charger which will add around USD70, say 30 quid)

All these prices assume that you are comfortable ordering the parts and building the kit on your tod.

[Wulf]

Hi Abandonflip,

Nice article, made me think of some hints to give PT owners who like to 'get under the hood'

Mark Kelly,

Very interesting piece, and no doubt very enlightening for those who insist on messing with crappy AC motors, you have to jump so many hoops and spend more money than it's worth to get them to run smoothly (think Atlas, Lingo, etc). There's one thing you can't get away from and that's the fact that AC motors want to vibrate, inject stray fields into the deck and generally add noise right where you don't want it. It also means you have an alternating magnetic field somewhere near the cartridge which can't be a good thing. The designers who I respect such as Arthur K. of PT/Funk Firm and Mark Baker of Origin Live have it straight - DC is the way to go. However, you clearly know your electronics so I raise my hat to you for showing alternatives to PT Too owners whose PSU may be dead or otherwise unsatisfactory.

I bought two PT decks off Ebay, the earlier one, PT 2296, is the one I kept as it's got a beautifully-polished teak plinth with the little pink triangular perspex logo on the front (there's a hole through the plinth behind it, might put a lamp in there one day) and a pink-tinted lid. It was "upgraded" (haha) to PT Too spec by its previous owner. Still with its original box, and what's more I went all the way from Norwich to Brum on a train to collect it. Man did my arms ache when I got home!

The other one, PT 4212, a DC version, arrived with a broken lid and several other issues, but it all worked out well in the end as this one had the HR-100S on it which I still have. To cut a long story short, I rebuilt 2296 with all the DC kit and the chassis and bearing from 4212, added the Alphason and Music Maker 3 and haven't looked back since. As a side benefit, I put 4212 together with the PT Too bits and sold it to a mate for £100 so we both won in the end.

To this day, 2296 runs sweet and true and never fails to give me a smile or a tingle, plus it looks dead gorgeous (4212 was un-logo'd and rather plain-looking by comparison). Bass (especially) on the DC version is much more intelligible and 'organic' without any hint of 'one-note' syndrome. I love this deck so much as it's now totally original, and being an early version has the better (IMO) hard acrylic suspension supports and wedges, later ones are made of nylon and don't feel as good when you slide the parts against each other. Being an engineer means I'm a picky SOB when it comes to materials and construction standards

Might post my hints in another topic as this little ramble is in danger of straying far from its intended direction

[Abandonflip]

...I raise my hat to you for showing alternatives to PT Too owners whose PSU may be dead or otherwise unsatisfactory.

That'll be most of them

Bass (especially) on the DC version is much more intelligible and 'organic' without any hint of 'one-note' syndrome.

Without doubt the DC versions have snappier bass, and you have to work hard on matching and setup to get back some of that performance with the Too. People have mis-conceptions about the Too though, and because it's seen as more 'traditional' they quite often - wrongly - assume it sounds like an LP12.

I love this deck so much as it's now totally original, and being an early version has the better (IMO) hard acrylic suspension supports and wedges, later ones are made of nylon and don't feel as good when you slide the parts against each other. Being an engineer means I'm a picky SOB when it comes to materials and construction standards

The expression 'sample variation' doesn't even begin to cover the apparently random changes that PT made throughout their production of, well, everything! No doubt Arthur would say that the nylon parts are deliberately more compliant, whereas the truth is likely to be that they hadn't paid their usual supplier.

Might post my hints in another topic as this little ramble is in danger of straying far from its intended direction

You should do that - it all helps to keep the PT flag flying!

[Mark Kelly]

Wulf

I design DC drives as well as AC ones. My interest is to see how far the two technologies can be taken.

The challenge with DC is to get stable speed over both the short and long term. No-one's done this yet because they tend to attack one or the other rather than both at once.

The challenge with AC is to get rid of both cogging torque and torque ripple without paying $500 for a motor. The principles are well known, the implementation can be expensive.

Watch this space.

[Wulf]

Mark,

I design DC drives as well as AC ones. My interest is to see how far the two technologies can be taken.

That's cool, all is balance

The challenge with DC is to get stable speed over both the short and long term. No-one's done this yet because they tend to attack one or the other rather than both at once.

The challenge with AC is to get rid of both cogging torque and torque ripple without paying $500 for a motor. The principles are well known, the implementation can be expensive.

Points well made, DC speed drift IS a pain, but leaving the PSU switched on/plugged in helps. DC-driven PT's have the control board inside the plinth so this may be of dubious benefit, depends on how many of the crucial components are powered with the speed switch in the Off position. Come to think of it I may do a drift-test on mine and report back to you

You now got me wondering if there's any point asking you if it's worth building a better DC supply given that the first PT I owned responded pretty well to being run from a custom-built brick sh*t-house PSU made from a power amp

Then again, batteries are cool, but Mark Baker at Origin Live maintains that a well-designed DC regulator can outperform them... the thot plickens