Greetings everyone,
I'm looking for some input on upgrading a Nakamichi PA-5 power amplifier.
This subject was discussed a few times before; however, there is no thread with the complete list describing PA-5 mods in enough details and discussion on them. I tried to make one and would like to get the community opinion on it. Few mods like recap are simple; however, some others were just mentioned in different threads without specific as to how they were made. That’s where help is really needed.
So here is the list:
-Replace electrolytic capacitors in L and R amp PCBs with Nichicon Audio grade KW or KZ and limiter PCB with Nichicon PW;
-Replace trimmers with multi-turn Bourns;
-Replace two 47000 mkF/80V filtering electrolytes with new 47-52 K mkF 80 V or 100V. Here I don’t know where to source replacements; Mouser and Digikey have a few but quite pricey; eBay has some less expensive but could it be trusted?
-Replace a Toshiba 15G4B41 diode bridge with HEXFRDs or with something faster and low-noise. What replacement(s) could be recommended?
- Short the C102/C202 10 mkF/200V electrolytic capacitor at the input to make the PA-5 DC coupled, remove C101/201 and R101/201, and install a 500 K DC offset pot across R114, R115 and the middle to R109 as suggested by Lars Nielsen here: http://www.diyaudio.com/forums/construction-tips/191275-nakamichi-pa5-mk1-update.html
Alternatively, upgrade the C102/202 to 470 mkF to improve low frequency roll off from ~50hZ to ~2 Hz, as discussed here in the post#4: http://www.diyaudio.com/forums/pass-labs/163741-improve-sound-nakamichi-pa-5-a.html
-Do modifications mentioned by the member Stephensank in the recent thread here: http://www.diyaudio.com/forums/digital-source/216674-garbage-switch.html
Unfortunately, he was not very specific about these mods: “A Nak PA-5(w/LF corner freq 10uf film enlarged by addition of at least 150uf/50v Nichicon lytic to remove subsonic BW limit) would be a huge improvement” and “first PA-5 & PA-7 had the subsonic cutoff & oversensitive protection mute circuits (easy 2 resistor changes to cure that bit)”.
- Add cascode modifications to PA-5. Here I am completely lost. What are they and would they improve sound?
-Replace internal wiring. Jon Soderberg offers this for PA-5/PA-7 but he did not provide any specifics. Most likely he uses heavy gauge wiring. Anyone tried this?
-Replace input RCA jacks and output speaker terminals. For me, both seems to be of sufficient quality.
Any other ideas? Let’s post them here as well as discussions.
I have a service manual with PA-5 schematics but can’t attach it here since it’s too big. Hifiendgine has it or I can e-mail it to you if needed.
Thank you for your help.
I'm looking for some input on upgrading a Nakamichi PA-5 power amplifier.
This subject was discussed a few times before; however, there is no thread with the complete list describing PA-5 mods in enough details and discussion on them. I tried to make one and would like to get the community opinion on it. Few mods like recap are simple; however, some others were just mentioned in different threads without specific as to how they were made. That’s where help is really needed.
So here is the list:
-Replace electrolytic capacitors in L and R amp PCBs with Nichicon Audio grade KW or KZ and limiter PCB with Nichicon PW;
-Replace trimmers with multi-turn Bourns;
-Replace two 47000 mkF/80V filtering electrolytes with new 47-52 K mkF 80 V or 100V. Here I don’t know where to source replacements; Mouser and Digikey have a few but quite pricey; eBay has some less expensive but could it be trusted?
-Replace a Toshiba 15G4B41 diode bridge with HEXFRDs or with something faster and low-noise. What replacement(s) could be recommended?
- Short the C102/C202 10 mkF/200V electrolytic capacitor at the input to make the PA-5 DC coupled, remove C101/201 and R101/201, and install a 500 K DC offset pot across R114, R115 and the middle to R109 as suggested by Lars Nielsen here: http://www.diyaudio.com/forums/construction-tips/191275-nakamichi-pa5-mk1-update.html
Alternatively, upgrade the C102/202 to 470 mkF to improve low frequency roll off from ~50hZ to ~2 Hz, as discussed here in the post#4: http://www.diyaudio.com/forums/pass-labs/163741-improve-sound-nakamichi-pa-5-a.html
-Do modifications mentioned by the member Stephensank in the recent thread here: http://www.diyaudio.com/forums/digital-source/216674-garbage-switch.html
Unfortunately, he was not very specific about these mods: “A Nak PA-5(w/LF corner freq 10uf film enlarged by addition of at least 150uf/50v Nichicon lytic to remove subsonic BW limit) would be a huge improvement” and “first PA-5 & PA-7 had the subsonic cutoff & oversensitive protection mute circuits (easy 2 resistor changes to cure that bit)”.
- Add cascode modifications to PA-5. Here I am completely lost. What are they and would they improve sound?
-Replace internal wiring. Jon Soderberg offers this for PA-5/PA-7 but he did not provide any specifics. Most likely he uses heavy gauge wiring. Anyone tried this?
-Replace input RCA jacks and output speaker terminals. For me, both seems to be of sufficient quality.
Any other ideas? Let’s post them here as well as discussions.
I have a service manual with PA-5 schematics but can’t attach it here since it’s too big. Hifiendgine has it or I can e-mail it to you if needed.
Thank you for your help.
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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.
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.
Many thanks for your advice, Mr. Pass. I planned power supply caps change but didn't think about setting bias this way.
Actually, your bias guidelines mean that the best working temperature of the PA-5 amplifier is 50 C. Mine NEVER was that hot meaning it is (seriously) underbiased. Nakamichi in the PA-5 SM suggests turn the amp on, wait 20 minutes and then adjust bias to 40 mV.
Why Nakamichi did this?
Actually, your bias guidelines mean that the best working temperature of the PA-5 amplifier is 50 C. Mine NEVER was that hot meaning it is (seriously) underbiased. Nakamichi in the PA-5 SM suggests turn the amp on, wait 20 minutes and then adjust bias to 40 mV.
Why Nakamichi did this?
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.
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Did most of the mods listed above: changed small caps and large filtering caps, replaced with multiturn Bournes bias pots and installed DC offset ones, changed diode bridge to IXYS and implemented mods suggested by Stephensank (thank you Stephen for sending me the detailed info). The amp works, delivering 150W in 8 Ohm loads before clipping.
However, I got a couple of potential issues:
First, bias in one the channels didn't go lower than 59-60 mV while in the other one it could be freely adjusted in the 30-80 mV range. Before upgrade bias in both channels was easily set up to 40mV as per service manual.
This doesn't bother me much since I wanted to increase the bias anyways as per Mr. Pass advice. Now the temperature of fins is 41-42 C after 2 hours of idling with bias at 59 mV in both channels; I'll increase the bias to one that gives ca 50 C. However, why does the bias in ONLY one channel can't go lower than 59 mV? Could it be a serious problem? Both bias pots are new.
Second, The DC offset jumps to ~58 VOLTS at the moment of powering up the PA-5 and stays there for 3-4 seconds until relay click. After this, the bias is approx quickly revert to ~1 mV, set up this way with newly installed DC offset pots. Could this huge voltage jump at power up damage the speakers?
However, I got a couple of potential issues:
First, bias in one the channels didn't go lower than 59-60 mV while in the other one it could be freely adjusted in the 30-80 mV range. Before upgrade bias in both channels was easily set up to 40mV as per service manual.
This doesn't bother me much since I wanted to increase the bias anyways as per Mr. Pass advice. Now the temperature of fins is 41-42 C after 2 hours of idling with bias at 59 mV in both channels; I'll increase the bias to one that gives ca 50 C. However, why does the bias in ONLY one channel can't go lower than 59 mV? Could it be a serious problem? Both bias pots are new.
Second, The DC offset jumps to ~58 VOLTS at the moment of powering up the PA-5 and stays there for 3-4 seconds until relay click. After this, the bias is approx quickly revert to ~1 mV, set up this way with newly installed DC offset pots. Could this huge voltage jump at power up damage the speakers?
I'm seeing just PA-7 there
anyway - try to connect 8R/1W (or even smaller power) resistor across amp's output pre-relay , then measure voltage peak during powering up
it's most probably just miniscule current peak , normal for that amp
in fact , pretty normal for any amp , prior to connecting actual load on output
anyway - try to connect 8R/1W (or even smaller power) resistor across amp's output pre-relay , then measure voltage peak during powering up
it's most probably just miniscule current peak , normal for that amp
in fact , pretty normal for any amp , prior to connecting actual load on output
Yes, just tried this.
With 8R/200W (didn't have smaller W load) connected across amp's output pre-relay the voltage spike was 1.8 V max if measured pre-relay.
If the load was connected to speaker terminals, the voltage at them was 2 mV or so before relay clicks and increased to 57 mV R. Ch/43 mV L. Ch. AFTER relay was engaged. Then it quickly went down.
Thank you for clarificatoin of this issue.
Time to put this babe into the system...
With 8R/200W (didn't have smaller W load
) connected across amp's output pre-relay the voltage spike was 1.8 V max if measured pre-relay. If the load was connected to speaker terminals, the voltage at them was 2 mV or so before relay clicks and increased to 57 mV R. Ch/43 mV L. Ch. AFTER relay was engaged. Then it quickly went down.
Thank you for clarificatoin of this issue.
Time to put this babe into the system...
Guys,
Sorry for delayed replies: that was kind of crazy Christmas season.
Pat C: The CA-5 preamp in a great condition should worth not less than $300; the PA-5 in the same condition might go for $550-$600. The sale price AFAIK varies between different Websites: on Audiogon it will be lower than at the ebay.
Synth: I have no idea since I didn't see Nak PA-5 MKII schematics. In any case, you can replace electrolytes, potentiometers and diode bridge rectifier.
All: many of you probably interested how the PA-5 sounds after I modded it. The short answer is: MUCH BETTER!
Specifically, the"mugginess" at the bottom end is gone, the bass became much more tight and natural. Is this actually bass or a lower midrange I don't know. The soundstage is better now, instrument positions are better defined than they use to be. Not sure re. 3-D depth of the soundstage. The way how instruments sound (tonality?) is now more natural for guitar, jazz bass and, naturally, drums.
So overall I like the amp better than before and mods were definitively worth it. BTW, the output power is 150 WPC at the bench before clipping vs. IMHO 100 WPC before. However, to get the best sound I need to warm the PA-5A up for at least 1 hour; if I listen to the music just after powering up it sounds good but thin.
Again, thanks to all who was involved in helping me with this project. In the future I plan to change the input/output jacks to Cardas ones and increase the bias to perhaps 80 mV to get the amp working temperature in the 50 degrees range as Mr. Pass suggested.
Happy New Year to all!
Andrei
Sorry for delayed replies: that was kind of crazy Christmas season.
Pat C: The CA-5 preamp in a great condition should worth not less than $300; the PA-5 in the same condition might go for $550-$600. The sale price AFAIK varies between different Websites: on Audiogon it will be lower than at the ebay.
Synth: I have no idea since I didn't see Nak PA-5 MKII schematics. In any case, you can replace electrolytes, potentiometers and diode bridge rectifier.
All: many of you probably interested how the PA-5 sounds after I modded it. The short answer is: MUCH BETTER!
Specifically, the"mugginess" at the bottom end is gone, the bass became much more tight and natural. Is this actually bass or a lower midrange I don't know. The soundstage is better now, instrument positions are better defined than they use to be. Not sure re. 3-D depth of the soundstage. The way how instruments sound (tonality?) is now more natural for guitar, jazz bass and, naturally, drums.
So overall I like the amp better than before and mods were definitively worth it. BTW, the output power is 150 WPC at the bench before clipping vs. IMHO 100 WPC before. However, to get the best sound I need to warm the PA-5A up for at least 1 hour; if I listen to the music just after powering up it sounds good but thin.
Again, thanks to all who was involved in helping me with this project. In the future I plan to change the input/output jacks to Cardas ones and increase the bias to perhaps 80 mV to get the amp working temperature in the 50 degrees range as Mr. Pass suggested.
Happy New Year to all!
Andrei
Chris,
I don't know what are differences between Nak PA-5 and PA-5 MKII; however, both have electrolytic capacitors, a diode bridge and potentiometers. I think that replacing of those parts in PA-5A MKII will have the same positive effect as in MK I.
Regarding the effect of upgrade pls see my posting of January 6th. I have nothing to add to it.
I don't know what are differences between Nak PA-5 and PA-5 MKII; however, both have electrolytic capacitors, a diode bridge and potentiometers. I think that replacing of those parts in PA-5A MKII will have the same positive effect as in MK I.
Regarding the effect of upgrade pls see my posting of January 6th. I have nothing to add to it.
PA-7 LIST OF UPGRADES
HELLO A LOT OF DISCUSSION ON THE NAKAMICHI PA-7 UPGRADES
DOES SOMEONE HAVE A LIST OF THE ITEMS THAT HAVE BEEN USED WITH SUCESS
TYPE AND BRAND CAPS I AM TAKING MY AMP TO BE SERVICED AND NEED A LIST OF THE PROPER COMPONENTS THAT I WILL NEED TO REPLACE AND UPGRADE. AND LET HIM KNOW OF THE THING THAT GENRALLY FAIL
THANKS PAUL
HELLO A LOT OF DISCUSSION ON THE NAKAMICHI PA-7 UPGRADES
DOES SOMEONE HAVE A LIST OF THE ITEMS THAT HAVE BEEN USED WITH SUCESS
TYPE AND BRAND CAPS I AM TAKING MY AMP TO BE SERVICED AND NEED A LIST OF THE PROPER COMPONENTS THAT I WILL NEED TO REPLACE AND UPGRADE. AND LET HIM KNOW OF THE THING THAT GENRALLY FAIL
THANKS PAUL
I posted this on the solid state PA 5 forum:
Greetings!
I have been rebuilding a PA 7. It has been rewarding but frustrating since the info is scattered about. I am considering starting a PA 7 update page so that we can bring our collective knowledge together. I totally missed this PA 5 page and for a long time didn't have some key information.
Regarding the main cans, I was not completly satisfied with the sound even after recaping the boards with wima, muse, and cerifine caps. The amp still sounded rather closed in with soft bass and poor high end extension.
I have recaped many vintage recievers and have heard many of them sound really sub-par with the old cans. It is amazing what a difference they can make! Sometimes the old ones will reform and sound really good. I am using a HK 930 that sounds great with the origional cans! Often though, they will sound awful at first listen, really dynamicly constipated. Try turning up the volume and it's like running into a wall. Then after a few days the sound really loosens up. It seemed the same thing was going on with the NAK.
Replacement cap options are rather limited. Specs are: 33kuf @ 100v, 2.5in (64mm) dia, 6"h If you look at what's available, the Nicicons and most others are 3" dia. They will NOT fit in the PA 7! That leaves Rubicon Digikey: Not stocked minimum order of 10. $59.71 each. If someone can find them stocked Please let me know!
I ended up going with the TCI caps from an ebay seller. Very little info on them. They are US made and appear to be very rugged. TCI makes industrial power products and these are apearantly surplus. 2pcs TCI 100V 33000uF Computer Grade 105C Bus Capacitors New | eBay Less than $150 for 4. I took the plunge (out of options at this point) and have been very satisfied. You have to drill out the holes on the buss plate and use larger crimped rings since the screws are HUGE. The improvement in sound is really substantial. Much more linear. Tighter bass, better dynamics, much better on the highs.
Hope this helps.
Also, I just added Clairty caps 4.7uf @ 250v for bypass. I still need to change the bias pots and the 200v fb caps. But right now I am totally thrilled with the sound on my Newform RS 645's.
Thanks, dbear44!
I am in the process of a complete upgrade but have been a little hesitant as mine is completely original and have never been touched.
So far, I have waded into bypassing the PSU with 3.3µF of CDE 941 and 10nF of polystyrenes but next on the list would be the probably tired bridge rectifiers and wires. I see you have changed yours to what appears to be IXYS HexFred's. Am I right? What are they rated at and how would you rate their contribution to the improvement in sound?
Once the bridges are done, next on the list would be to bump C102/C202 to 470µF as in the Threshold 400A. These caps are noted as non-polar on the schematic so I still have to decide whether it's Mundorf ECap Raw or Muse ES. Unfortunately, I have yet to find any film cap that would fit in that space - the Mundorf at 25x38 barely
I would very much welcome comments and input. Attached is the picture of what my PA-7 looks like now.
Attachments
The IXYS bridges I got from PCX. I used VBE 26-12 NO7 which is rated at 32A and 1200V. This is probably way overkill since with the soft start circuit they are never stressed, but the price is not much different from the smaller ones so why not.
I can't say that it made much difference with the old cans. I think it is more like icing on the cake. If the cake is old and stale the best icing in the world isn't going to help much!
Which brings us back to those big cans. What condition they are in depends on a lot of factors. Was the amp used regularly or in storage for years? Was it kept in some hot attic or damp basement or unheated garage? My amp had not been used in years so maybe that is why I needed to change them. YMMV.
I do know that I tried bypassing them with .47uf Wima's (the only thing that I had 4 that matched) and was not happy with the results. The sound became bright and edgy on top while still being soft and congested in the rest of the range. I ended up taking them out. What was happening was when you put a very small value low ESR cap in paralell with an extremely large high ESR cap you are making a filter. The bypass only helps on the high frequencies leaving lower ones still straining to get current.
So what I am saying is if your cans are in OK shape you may be able to get away with bypasses if they are large enough to affect most of the frequency range. If the amp still sounds overly soft and sluggish with the bypasses then you should replace the cans.
I can't say that it made much difference with the old cans. I think it is more like icing on the cake. If the cake is old and stale the best icing in the world isn't going to help much!
Which brings us back to those big cans. What condition they are in depends on a lot of factors. Was the amp used regularly or in storage for years? Was it kept in some hot attic or damp basement or unheated garage? My amp had not been used in years so maybe that is why I needed to change them. YMMV.
I do know that I tried bypassing them with .47uf Wima's (the only thing that I had 4 that matched) and was not happy with the results. The sound became bright and edgy on top while still being soft and congested in the rest of the range. I ended up taking them out. What was happening was when you put a very small value low ESR cap in paralell with an extremely large high ESR cap you are making a filter. The bypass only helps on the high frequencies leaving lower ones still straining to get current.
So what I am saying is if your cans are in OK shape you may be able to get away with bypasses if they are large enough to affect most of the frequency range. If the amp still sounds overly soft and sluggish with the bypasses then you should replace the cans.