View Full Version : Nakamichi PA7 Mods & Repair


cobramatteo
08-13-2012, 11:40 PM
Hello All,

I am a new poster, but have been checking out this site for years !

Personally love the PA7 amp generation one. As a teenager was fortunate enough to have a family member who had one and lusted after the sound and looks.

Flash forward to now, I own 4 of these amps and want to get all four completely serviced and updated so they sound better than new and will last the next 25 years.

They will likely power 2 pairs of Polk SRS 1.2s I own, each handles 1000watts, so biamping them with 2 Naks per pair should be the ticket.

For a preamp, I have an Adcom GFP-750 - Is this better sonically than the Nak CA7 ?

I am not wanting to do this work myself, are their any fellow members up to the task that have experience with these amps ?

Otherwise, these will all go out to - Stereo Repair - In House Service Company - located in Cali. They have a PA7 specific repair/upgrade process.

Has anybody sent their PA7 amp in to these guys for service ?

All comments will be appreciated except any telling me how I made the wrong amp choice and should have bought 4 XXXXXXX instead of Nak PA7s.

I also have been collecting about 10 Adcom GFA 555 amps and will one day get each of them serviced/updated in the same manor.

Audio is a subjective hobby, IMO these Nak's are pretty unbeatable as far as in your face wow factor, solid construction, reliability [ oversensitive speaker protection circuit notwithstanding ], and great sound.

With some modern parts, attention to detail, and the right speakers, these four amps could be amazing !

NavinJohnson
08-14-2012, 09:18 AM
when you have all 14 amps stacked up is it nakatomi tower?

avionic
08-14-2012, 09:29 AM
Hello All,

I am a new poster, but have been checking out this site for years !

Personally love the PA7 amp generation one. As a teenager was fortunate enough to have a family member who had one and lusted after the sound and looks.

Flash forward to now, I own 4 of these amps and want to get all four completely serviced and updated so they sound better than new and will last the next 25 years.

They will likely power 2 pairs of Polk SRS 1.2s I own, each handles 1000watts, so biamping them with 2 Naks per pair should be the ticket.

For a preamp, I have an Adcom GFP-750 - Is this better sonically than the Nak CA7 ?

I am not wanting to do this work myself, are their any fellow members up to the task that have experience with these amps ?

Otherwise, these will all go out to - Stereo Repair - In House Service Company - located in Cali. They have a PA7 specific repair/upgrade process.

Has anybody sent their PA7 amp in to these guys for service ?

All comments will be appreciated except any telling me how I made the wrong amp choice and should have bought 4 XXXXXXX instead of Nak PA7s.

I also have been collecting about 10 Adcom GFA 555 amps and will one day get each of them serviced/updated in the same manor.

Audio is a subjective hobby, IMO these Nak's are pretty unbeatable as far as in your face wow factor, solid construction, reliability [ oversensitive speaker protection circuit notwithstanding ], and great sound.

With some modern parts, attention to detail, and the right speakers, these four amps could be amazing !

Welcome to AK...:worthless

Satch
08-14-2012, 09:36 AM
The PA-7 mkI had problems overheating. MkII version had solved this. That's about all I remember...

My own Threshold amp is also based on the STASIS-design by Nelson Pass and sounds great, so I imagine the PA-7 (with some TLC) must be pretty good. Let alone four of them...

shrinkboy
08-14-2012, 09:46 AM
why all the GFA 555's?

cobramatteo
08-14-2012, 11:30 AM
Well, the reason for all the equipment is, as a teenager, I lived in Germany as an Army brat with my sister and brother in law. My brother in law owned the PA7 & CA7 pre, along with a few Adcom GFA 555s.

My brother in law was in the army, but also moonlighted at the base Audio Video Photo club [a store on base in Osterholtz that sold both high end equipment to the soldiers]

He was the Audio section manager and over the course of those 2 years we had a variety of equipment come and go in our household. The PA7 and GFA 555s were always there and sounding good. I remember the PA7 sounding pretty amazing with a set of JBL 4312s. Also used were Infinity Kappa 9s, Carver amazings, Bose 901s, Infinity SM152s, Klipsch La Scalas, and tons of other great gear .

Well now, 20 years later I work overseas as a civilian technical adviser to the US Army. After being deployed to Iraq and Afghanistan for 6 years straight, I have the means to buy all the equipment that I wanted back then and used first hand.

So about 3 years ago, I began buying various gear up on Ebay and Audiogone. Kinda got carried away and bought a little too much, lets just say when I am home for good - a good chunk will find its way back on Ebay.

At the present, I own and mostly plan on keeping :

1 pair Klipschorns, 2 pair La Scalas, 2 pair JBL 4312Bs, 2 pair Polk SRS 1.2s,2 pair Polk SRS 2.3s, Several sets of Bose 901s series 1-6, 2 pair Bose 601 series 2, about 10 Adcom GFA 555s, 1 GFP 750, 2 Carver TFM 55s, 4 Carver M400Ts, Carver tube CD player, Bose 1801 power amp, several Klipsch KG series 2.0-5.2s, and lots more ....

I am even having a custom 5 channel tube amp built by Bob Carver to run an all Klipsch legacy horn based home theater setup.

Everything is being kept in climate controlled storage while I am away, but I know between a bedroom, home theater, living room, and garage setup - I will need all those amps. When the time comes, I will put up for sale everything not needed - will likely sell the Bose 1801 amp as it just does not fit my needs anymore. A great 400 watt beast though !

Always liked Adcom gear, IMO the only button a power amp needs is the on switch. If you have ever seen stacks of Adcom amps, you know what I mean - its impressive looking and sounding. Thank Nelson Pass !:music:

All the older gear I keep will get restored to better than new standards, just my 2 pairs SRS 1.2s will be a massive undertaking to update them with all the parts available. Even though Polk no longer makes these flagships, they still support them and the Polk forum guys have created every possible update one could want to improve an already great speaker.

Paid on average 300.00 per Adcom GFA 555 amp, with another 400.00 invested for all new caps, better speaker jacks, and some tweeking, I will have 700.00 max into a 200watt power amp that should last another 25 years. Best part is the new caps and resister tolerances blow away what was used back in the day, and the sound after updates should eclipse anything that can be bought today for less than 2500.00.

The PA7s retailed for 2500.00 new back then, I got mine for about 750.00 ea, and with 450.00 in updates done - 1200.00 per amp is a steal for Stasis tech and the looks and sound you get with the PA7.

The second version of the PA7 did little more than to clean up the wiring internally and loosen the restriction on the overactive protection circuit on the first generation. [Nak paid for a service update on the series 1 protection circuit] Most people think the PA7 1 sounded better than the PA7 2, myself included.

There is even a Pass designed new front end that can be implemented on these amps making them shine. Looks wise, very few solid state amps to me are so sexy as the huge heat sinks on the PA7. Plus that large power button rocks, best click in the world when you turn that beast on !

Many complain that the PA7 runs too hot, this is caused by the bias being out of spec - a calibrated PA7 sounds amazing and will drive anything you throw at it.

The problem these days is that many folks listen to vintage gear that has old leaked down caps, poor previous repairs - and say this or that model is junk.

Most of the gear I have bought, I heard new and am fully aware of whats its capable of.

All my opinion, and its coming from a bored guy sitting in a tent in the mountains of Afghanistan wishing he was rocking out with 800watts and drinking some cold ones !

I will be state side next month for 2 weeks in Michigan - and will enjoy every minute of it !

vga911s
08-17-2012, 12:20 AM
Welcome to the AK site. Nakamichi PA 7 are fine amps. Mine have been trouble free for over 20 yrs of ownership. What are the mods you are planning to install.

jhoyt
08-17-2012, 09:41 PM
I too am interested in any PA-7 mods. I've been running mine for a few months now, and love it. Dialing back the bias to spec DOES reduce heat by a considerable amount! Also, where are N. Pass's front end mods detailed? I'd do mine in a heartbeat.

Be safe in Afghanistan, and thanks VERY MUCH for your service.

kotofei
08-17-2012, 10:39 PM
I am also interested in the PA-7 mods. I have its little brother PA-5 but design is similar and would like to upgrade mine some day.

What I know from searching DIYAudio.com forums that PA-5 and PA-7 that it's sort of consensus on modification that could be done. First, it's some obvious things such as changing of all electrolytic caps and single-turn potentiometers to multi-turn Bourns ones. Then, it's changing of internal wiring to supposedly more heavy-gauge; this includes power and speaker wiring. Also it's replacing of rectifier diodes with the new ones and possibly some other mods in the power supply (I forgot which ones). Lastly, it's an electrolytic capacitor at the input that some people remove and claim it improves sound.

There is a guy named Jon Soderberg , website http://www.vintageamprepair.net/ that upgrades Nakamichi power amps. I e-mailed him asked for what specifically should be done with PA-5/PA-7 and enquiring about the possibility of buying these per-cut and terminated speaker wires from him. He didn’t give me any specifics and refused to sell wires, probably keeping his trade secrets.

Regarding bias adjustments, Nelson Pass himself in diyaudio.com explained that in PA5/PA7 it should be done after amps are “on’ for 2 or so hours.

Regarding Adcom vs. Nak CA-7A preamps I think that the latter will sound better after bias/idling current adjustments and with after market power cord. That’s what I did with mine and enjoy the music ever since.


To ALL: let’s keep this thread as a resource for Nakamichi PA-5 and PA-7 modifications, posting here all we found on the topic and/or did by ourselves or have someone do it for us. These are great-sounding amps!

vga911s
08-17-2012, 11:58 PM
I have in the past been warned by my trusted audio tech in Palo Alto to stay away frm this bias adjustment and to leave the settings as were when they came home and were new. I have never had a single problem with any of my amps following this advice and have made no changes. Nakamichi seems to have gotten mine right!!:scratch2::scratch2:

kotofei
08-18-2012, 08:19 AM
When I checked mine after 2 hours of warming-up it was almost on the spot!


I have in the past been warned by my trusted audio tech in Palo Alto to stay away frm this bias adjustment and to leave the settings as were when they came home and were new. I have never had a single problem with any of my amps following this advice and have made no changes. Nakamichi seems to have gotten mine right!!:scratch2::scratch2:

UncleAng
08-18-2012, 10:12 AM
Can't comment on the sound of the GFP-750, I've heard them in the past but never did critical listening or A/B'd them to the CA7A. But as kotofei said properly adjusted gear is a must to get the best results regardless of brand.
IMHO there are skads of great sounding amps & pres available out there; vintage & new and I consider the Naks one of them.

Vinylcalle
08-18-2012, 05:52 PM
Just beacuse the bias was set right when it left the factory some 20-25 years ago doesn´t mean it´s still right. It can drift over time. The important thing many times when setting it is to clean or change out the potentiometers that you use to adjust it with.

vga911s
08-25-2012, 12:34 PM
It so is true that the bias can drift as the yrs pass by and when this is found to have occured it should be adjusted back into the Nakamichi spec for the amp. What I am refering to are the wholesale changes to the bias that I have heard and read about that a few have said will make the amp sound better. That change is what I would never do to any of my amps. For me spec is good!!:yes::yes:

kotofei
08-25-2012, 02:50 PM
I decided to go ahead with modding of my Nakamichi PA-5 and set up a thread at diyaudio.com on the subject. I listed there what I would like to do and asked for advice.

Below is the reply from Mr. Nelson Pass, who as you might know invented STASIS circuit and designed PA-5 and whole lot of other amps:

"If it's older than 15 years replace the power supply caps with ones
comparable to the originals. Panasonic or Nichicon is plenty good enough.

Arrange to get the amplifier some serious ventilation and then raise the
bias until the heat sinks run at 50 deg C after an hour of operation.

Serious ventilation is what you think it is - a fan is not out of the question."






It so is true that the bias can drift as the yrs pass by and when this is found to have occured it should be adjusted back into the Nakamichi spec for the amp. What I am refering to are the wholesale changes to the bias that I have heard and read about that a few have said will make the amp sound better. That change is what I would never do to any of my amps. For me spec is good!!:yes::yes:

kzim229
08-25-2012, 05:41 PM
Below is the reply from Mr. Nelson Pass, who as you might know invented STASIS circuit and designed PA-5 and whole lot of other amps: "If it's older than 15 years replace the power supply caps with ones comparable to the originals. Panasonic or Nichicon is plenty good enough.
Arrange to get the amplifier some serious ventilation and then raise the
bias until the heat sinks run at 50 deg C after an hour of operation.
Serious ventilation is what you think it is - a fan is not out of the question."

I had my PA7 recapped by Jon Soderberg and was very happy with the result, although he used higher-end parts than those recommended by Mr. Pass, and I probably paid more than I would have at a different shop. At the time his was the only shop I could find that said they knew just what to do.
He also upgraded the input rectifiers and installed new multi-turn pots for adjusting the bias, so he earned his money.
When I bought the amp used, I would have sworn it was malfunctioning, the sound was like someone had turned down the bass and treble controls on the preamp. After recapping, it sounded great. Unfortunately, although the new caps are not expensive, it takes a bit of labor to put them in, so it's not a very cheap fix. But it was definitely worth it.
About heat: some AK'ers claim all heat is bad. This is not always the case.
The output transistors used in Pass' designs have a measurably more linear output when operated at their specified temp, which I believe is something like 170 degrees F at the transistor mounting point, which corresponds to about 125-130 degrees at the outer surfaces of the heat sinks.
They have those generously sized heat sinks for a reason, which is to allow the transistors to run at the optimum temp. So nothing is to be gained by adjusting the bias down to make them run cooler.
125 degrees corresponds to the temp of the heatsinks which you can just tolerate putting your hands on for 5 seconds or so. If your amp is running cooler or hotter than that, it needs attention.
Many thanks to Nelson Pass for his generous contributions to DIY Audio and of course for his wonderful amp designs over many years.
BTW - I don't use fans, can't stand the sound of them. I just make sure there's clearance around the amp in its rack. works fine.