Any Phase Linear Experts out there?

Correct! Thank you D3imlay. I am looking around then to find the right place. My plate was devastated a bit by audio recording studio in Germany, where they had to fit the P/L amp into a rack... But the second one amp I have is in perfect condition - so feasible to make a 'copy'.

Best regards!

What will you do about the Phase Linear logo on the faceplate ? I can provide you with a water slide decal if you'd like. I've used such decals on some of my DIY projects, including a few DC blockers I've built for people. The decal is printed on a transparent film that you soak in warm water, then slide off its backing onto the destination surface, and allow to dry.

Here's a draft in the Series 2 style lettering. I will play around with fonts and try to get it looking like the Series 1 style.

PL_logo.JPG


DIY DC blocker with decal:

DC_BLOCKER_02.jpg
 
Quasi complementary vs. full complementary

Don, I would like to know your own opinion about the two different topologies in the output stage.
As for me I can tell you about my experience with another great vintage amp: the Quad 303. I have three units. One is 100% original with its quasi complementary array of RCA transistors. The other two, running in a biamp system, were purchased by me in non working condition with the aim of upgrading them. Therefore I sent them to David Pritchard (Net Audio UK) who designed several mods for the 303 taking advantage of the original circuit. One of those mods is the replacement of the original transistors with new ON MJ15003/15004 in a complementary topology.
Well, I can say both the new and old 303s sound nice.:thmbsp: Anyway, while the upgraded 303s are rigorous, detailed performers with no fear of low impedance loads, the original one has such a "fashinating" sound!! That "something magic" beyond any description.:tresbon:
Does it apply also to early PL amps in comparison with the late production? Thanks.
 
PL 700 Series 2 front plate

What will you do about the Phase Linear logo on the faceplate ? I can provide you with a water slide decal if you'd like. I've used such decals on some of my DIY projects, including a few DC blockers I've built for people. The decal is printed on a transparent film that you soak in warm water, then slide off its backing onto the destination surface, and allow to dry.

Here's a draft in the Series 2 style lettering. I will play around with fonts and try to get it looking like the Series 1 style.

Hi, I thank you for the solution - looks nice indeed. My plan however was to engrave them. The brand requires a professional touch I think. Already found reliable place in Warsaw to do the job - all process steps at one place: aluminum plate cutting / drilling, logo+signs engraving, anodizing ready plate. I am waiting for a quote.... Still they asked me for types of fonts used. I guess the logo was in 'Palace Script', but not sure about the rest. Also Palace may be found in different versions (e.g. in MS Office there is MT one). Do you know maybe precise types of fonts used in P/L Series 2?
Many tx!
 

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Quasi complementary vs. full complementary

Don, I would like to know your own opinion about the two different topologies in the output stage.
As for me I can tell you about my experience with another great vintage amp: the Quad 303. I have three units. One is 100% original with its quasi complementary array of RCA transistors. The other two, running in a biamp system, were purchased by me in non working condition with the aim of upgrading them. Therefore I sent them to David Pritchard (Net Audio UK) who designed several mods for the 303 taking advantage of the original circuit. One of those mods is the replacement of the original transistors with new ON MJ15003/15004 in a complementary topology.
Well, I can say both the new and old 303s sound nice.:thmbsp: Anyway, while the upgraded 303s are rigorous, detailed performers with no fear of low impedance loads, the original one has such a "fashinating" sound!! That "something magic" beyond any description.:tresbon:
Does it apply also to early PL amps in comparison with the late production? Thanks.

I am curious of Don's opinion, too. What I can say from my own experience is that older quasi P/L 700 series II amp sounded more convincing in jazz high resolution recordings, such as from 'Mapleshade Records', so it does in my opinion the pre-amp P/L 4000 series II versus Carver C4000. Still very much subjective in other types of music - and I listen often to Pink Floyd, Led Zeppelin or King Crimson, but as well as Alter Bridge or Creed. I simply hear no difference compare to full comp. output topology (shame...).

I recommend an interesting article here to read about the quasi/full comp. comparison: http://ampslab.com/c200qc.htm. What is said there may sound a bit in contradiction to the opinion found I think on DYI regarding P/L 400 Series II converted into full comp. mode:
"First the output stage was changed to a full complementary type utilizing output transistors is an order of magnitude greater than the original devices.
Result 1: The amplifier is quite happy driving 4 ohm loads as well as reactive 8 ohm loads.
Result 2: The output stage now is far more reliable than the original.
Result 3: A phenomena known as "common mode conduction" is avoided when the amplifier is driven at high powers at high frequencies. With the original quasi complementary output stage design this is problematic.
What happens is that both the top and bottom power transistor banks try to conduct current as THE SAME TIME. This guarantees destruction of the output stages. With the fully complementary design plus active pull off circuits, this is avoided completely."

Even, if this is correct, not sure that the conversion is worth of effort taking into account audible differences, which are 'not huge' to me. The job is not trivial and bear in mind that not all the changes required were covered by P/L service bulletins on revisions to convert quasi into complimentary output stage (wiring). Of course for Quad can be different.
Regards.
 
Hi, I thank you for the solution - looks nice indeed. My plan however was to engrave them. The brand requires a professional touch I think. Already found reliable place in Warsaw to do the job - all process steps at one place: aluminum plate cutting / drilling, logo+signs engraving, anodizing ready plate. I am waiting for a quote.... Still they asked me for types of fonts used. I guess the logo was in 'Palace Script', but not sure about the rest. Also Palace may be found in different versions (e.g. in MS Office there is MT one). Do you know maybe precise types of fonts used in P/L Series 2?
Many tx!

The font I have is Palace script MT. If you can get the panel engraved that would be great.
 
PL 700 Series 2 front plate

OK. And the sign below the logo: Model 700 Series Two, etc? Any idea what fonts are there? Thank you Glen!
 
The proper font is probably a mix between Franklin and Arial. The correct shape seems to be the Arial one, basing myself upon the observation of the roundish letters like "d" or "o". In the Franklin font they are a little taller and oval shaped. Anyway the stroke of the Arial font should be a little thinner, like in the Franklin font. IMHO obviously.
 
I recommend an interesting article here to read about the quasi/full comp. comparison: http://ampslab.com/c200qc.htm.

I know that site, interesting amps there sometimes. Well that article tells us some undeniable truth:

"Quasi-complementary outputs came about in the early years of solid state designs where pnp transistors were few, costly and don't quite complement their npn counterparts. Nowadays, with modern complementary transistors sharing similar properties, this output topology is not often favored. One reason is probably due to the lack of performance of the early designs that left a bad impression. Nonetheless, quasi-complementary outputs do have their advantages, the most obvious being that all output transistors are identical, unlike npn and pnp, which in reality is never truly the same."

Maybe nowadays, with modern devices, quasi complementary topology could get its revenge over complementary. I've heard more than one tech asserting that a well designed quasi complementary output stage is better than an average complementary in terms of pure sound.
 
Franklin Gothic Book and Arial fonts look very close:

Yes, I think the proper font shape is somewhere in the middle. What about trying different options with, say CorelDRAW (spacing, font shape mngt.), and printing them on a transparent foil used for overhead projectors, and then to compare with the original plate placing the foil exactly over the right place? On my side no probs with the software trial download but not sure for the foil printing capabilities...

If anyone from 'P/L Fun Club' did or can give a try - let me / us to know, please.

Many thanks for all suggestions already shared!
 
Maybe nowadays, with modern devices, quasi complementary topology could get its revenge over complementary. I've heard more than one tech asserting that a well designed quasi complementary output stage is better than an average complementary in terms of pure sound.

I believe it goes to topology roots as well. Here is another interesting article: http://books.google.pl/books?id=EOE...onepage&q=quasi complementary output&f=false:
[...]
In many ways the quasi-complemenary output transistor circuit is preferable to the use of fully complementary output transistors, since, to quote J.Verker of Naim Audio, "NPN and PNP power transistors are only really as equivalent as a man and a woman of the same weight and height" - the problem being that the different distribution of N- and P- doped layers leads to significant differences in the HF performance of the devices. Thus, although the circuit may have a good symmetry at low frequencies, it becomes progressively less symmetrical with increasing operating frequency.
With modern transistor types, having a higher current gain transition frequency (that frequency at which the current gain decreases to unity), the HF symmetry of fully complementary output stages is improved, but it is still less good than desired, so the relative frequency/phase characteristics of each half of the driver circuit may need to be adjusted to obtain optimum performance.
[...]
If you add questionable pure sound audible differences, I'd stick to Good Old Quasi... :thmbsp:
Cheers!
 
Yes, I think the proper font shape is somewhere in the middle. What about trying different options with, say CorelDRAW (spacing, font shape mngt.), and printing them on a transparent foil used for overhead projectors, and then to compare with the original plate placing the foil exactly over the right place? On my side no probs with the software trial download but not sure for the foil printing capabilities...

If anyone from 'P/L Fun Club' did or can give a try - let me / us to know, please.

Many thanks for all suggestions already shared!

Yes, you could play around with spacing and font shape. One of my daughters is a graphic design major at college and I'm sure can duplicate the original PL logo exactly. I will ask her. IMO, you could get away with either of the above fonts. I think people would only notice a difference from the original in a side-by-side comparison with an original faceplate.
 
Yes, you could play around with spacing and font shape. One of my daughters is a graphic design major at college and I'm sure can duplicate the original PL logo exactly. I will ask her. IMO, you could get away with either of the above fonts. I think people would only notice a difference from the original in a side-by-side comparison with an original faceplate.

Thank you Glen, that would be just great! I would very much appreciate your kind help.
Best regards.
 
Thank you Glen, that would be just great! I would very much appreciate your kind help.
Best regards.

My daughter said she can match the PL lettering exactly. She just needs to know what file format you want (e.g., png, bitmap, etc.).
 
My daughter said she can match the PL lettering exactly. She just needs to know what file format you want (e.g., png, bitmap, etc.).

That's very kind. I've checked quickly and TIFF or PNG works fine. Could you please help also with the part of faceplate where it is said: POWER ON/OFF and DISPLAY NORMAL/-20dB? Many tx!
 
uhm...it seems Don left us with our doubts about the output stage topology... :D

Don, quasi-complementary or complementary? Which is the winner? Please take a look at the past posts. ;)
 
Sure...I was asking because I have a 700 Series II. It works nice but, for safety reasons, I would prefer to replace the mix of transistors in the output stage (complementary). Most of the output devices are the original Motorolas TP9054/MJ15025 but some Necs and Toshibas are running together with them.

Just few comments after retrospective reading:

1) Follow the amp. checkup procedure as very well described in P/L service manual + bulletins, use light bulb test when powering up - great advice of d3imlay that I appreciate.

2) As recommended in the P/L service manual ad further bulletins, output transistors (in each channel) should ALL be of the same type (e.g. MJ15024/25 or MJ21196/95 respectively for full comp. stage). In 700 Series II full complementary amp, the drivers and output transistors are the same. For example – the driver for the MJ15024 output transistor is a MJ15024. Same comment for the MJ15025 (PNP match for the MJ15024). In other words DO NOT mix different types of output transistors in a single channel. The previous statement is very important when doing service or repair work – not only with P/L equipment, but any kind / brand of amplifier.

3) In order to cure oscillations the capacitors a 22~47pF usually work well to damp out any such tendency. The factory recommended 150 ~ 270pF value might be too high, and can cause high frequency slewing at high output power. Ceramic types are recommended with at least a 100-volt rating.

3) I agree with d3imlay not to overshoot with a wide scale of replacements with all kind of kits generally available. My 'own list' for renovation musts, on top of output transistors mentioned above if mixed, includes however:
- electrolytic caps (for the PL-36 driver board I'd try to stick to one high class brand/make for audio applications; for power caps I'd go up to ca. 20.000uF paying attention to bridge rectifier and bypass small caps);
- IC LF356 replacement (might be done with your amp by the factory - TBC);
- resistors (per each channel: R1, R101, R103 - especially those getting hot may drift after 30Y+) and emitter resistors 0,33ohm (if you replace - pick HQ with 1% tolerance 5W);
- power cord (non-polarized - watch-out hum problems, valid for EU export versions)
- output protection circuit to be added - there are few options for P/L 700 series II (don't forget to reconnect RF circuit from speakers output...).

After the off-set regulation you will enjoy the sound of your beauty beast :)!

Regards.
 
Well done:thmbsp:. You summarized every advice Don gave us in this thread, which I took note of. Very useful!!:tresbon:

I'm going to purchase one of those repair kits just to have every component at the same time. Anyway, it is my intention to replace only the electrolytics and the major resistors which regulate the current to the ICs. Those are the upgraded LF351 in my unit, not the old LF356.
As for the power supply I've already purchased a pair of 22,000mF Vishay caps and I will replace the bridge rectifier with a 40/50A 600V with ceramic or Mylar caps across each contact. Maybe I will put mylar caps across the main filter caps also.

Just one more thing.

My unit got a grounded cable (not shielded) at a certain point because it was a disco mule. Is it good? If not, which type of power cable can I install? Any suggestion regarding the brand and where to find it in case? Thanks.
 
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That's very kind. I've checked quickly and TIFF or PNG works fine. Could you please help also with the part of faceplate where it is said: POWER ON/OFF and DISPLAY NORMAL/-20dB? Many tx!

Sure, no problem. Its going to be a few days, due to a busy schedule.
 
Well done:thmbsp:. You summarized every advice Don gave us in this thread, which I took note of. Very useful!!:tresbon:

Just one more thing.

My unit got a grounded cable (not shielded) at a certain point because it was a disco mule. Is it good? If not, which type of power cable can I install? Any suggestion regarding the brand and where to find it in case? Thanks.

Well, it was not straightforward for my P/L rack. When I put all the gears together and turned them on the hum was truly terrible. It appeared that 4 units were grounded via 230V IEC plug: CD transport, DAC processor, Tuner and the P/L Amp. Grounding loops created unbearable noise... After many tests I left wall socket grounding only for the DAC. So, my advice is not to use 'earth' ground for P/L amp. power supply cord.

Cable shielding was another specific topic in my case. Since for the signal carriers I use unshielded interconnects from DNM (http://www.dnm.co.uk/products.html), in order to avoid potential RF interferences - lots of cables behind the rack, the power cord in my P/L is shielded (http://www.gigawatt.eu/products3_c.html - and adapted to the amp chassis requirements). The setup works really fine now... The decision on types of cables for power/interconnect/speakers application is worth of some experiments, with no exaggeration though - some are too pricey and nothing amazing to offer in return. At certain point I had my short list (two brands) and was able to rent particular cables from a local dealer for tests at no charge. Then I could decide based on my own assessment...

Good luck!
 
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