So I decided to do some modifications to the PXA-H701.
I'm not happy with the sound of the stock unit.

This is the work so far on the processor
The service manual is quite different in a lot of resistor and capacitor values from the actual board, although the basic circuit is the same.

Before:
Standard guts of the H701 Processor
Click to view attachment

Processor Board Removed to show Analog (Right) and power supply (Left)
Click to view attachment

These little capacitors are all through the processor - yucky
Click to view attachment

So it was time for some special attention and TLC for the precious analog circuits:
Click to view attachment

Replaced:
JRC4560 opamps with OPA2134.
All electrolytics in signal path with Blackgate Hi-Q NX capacitors
Decoupling electrolytics (3.3uF) with Rubicon XYF, higher values (47uF) to match the manufacturer's specs for the volume control I.C's
Board-mounted RCA sockets with insulated panel mount units.

Added:
100nF polypropylene across the electros
10uF electros + 100nF poly caps on each opamp for improved supply decoupling/stabilising

Removed:
Navi Mix circuit (including 1 opamp stage on front1/front2 outputs)

Click to view attachment

may think about soon:
Output mute transistors replace with fast switching signal relays
replace Burr Brown PCM1608Y DAC chip with "K-grade" version
The only reasons I'm not doing the DAC now are:
1. won't make much difference in sound
2. SMD is not for fun.

must say though, Alpine have used a very good board for the build - takes a lot of heat to destroy the pads.

not yet

As far as cost goes, I think I'm up to about $250 so far (including the new DACs) - and that's (almost) enough bits for 2 processors.

edit - this gives an indication of the size of the parts on the PCB
Click to view attachment

nice work simon - what sort of audible/functional improvements are you hoping to achieve with the pxa mods?
also, have you noticed any improvements, sq-wise, with the roof deadened?

NICE.... finally, an update..

heard about the PXA changes prior to commencing.. but would be interesting to hear the difference it makes..

good work with the deadening of the roof...

It's meant to be lower noise, lower THD, more useable dynamic range, and better resolution of low level signals.

The stock PXA is pretty woeful in those areas, when compared to good Home stuff.

awesome work! would you be interested in doin the same work to other people's PXA's for a fee?

haha I havent even bought one yet and I'm already thinking of modding it. good work

impressive stuff. indeed i hope it translates to 'audible' benefits.

maybe you should do a comparison between modded vs unmodded.

That's the plan - to have it just running straight-through, and A-B compare to my other (still stock) PXA.
Although if the changes are as much as I hope, there should be no problem hearing the difference.

my only real concern is that the evil noise may be introduced by the processor - nothing I can do there... maybe

Awesome work Simon.

I'd be interested if you ever felt like doing these upgrades for my 701 for a fee/

I remember reading somewhere that the weakest part of the 701's chain is the clock?

i'll post the link if i can dig it up again.

The clock isn't the best, but replacing it may be a little trickier than usual, as the system uses rising and falling edges of complementary outputs.... have to see once I get this one up and running.

id be interested in having my 701 upgraded if you are interested in doing it for a fee.......

More updates - nearly done for now, should be working by tonight for initial testing.

Top - now with decoupling caps on I'Cs
Click to view attachment

Bottom - also done.
Click to view attachment

just got to wire the new RCA's and start testing...

Nice work Must have taken ages!

About 3 months

Anyways, it's done now:

Click to view attachment

sounds fantastic. No noise, fuller bass, very clean.
Mwahahahaah!!!!!

tricky!

I'm excited

OMG!!!
I wonder if I can switch mine with yours behind your back without you noticing

hrmmm....

oh!, wait.............. no.

How good is good simon?

Is it worthy of putting into the home system now?

Hey, wait a tick..

i just realized your're using the optical-in, have you tested to see if your mods have improved the analog in quality too?

I'm interested in reducing the noise floor of the analog in's so i can use my old school transports.

So was this in use yesterday Simon?

Nice work simon.
Good to see someone doing some modding.

Yes, it's as good as the home DAC (as far as I can tell without my new amp and speakers running)

haven't checked the analog ins - I think it'll be the same, as I didn't change the input circuits at all.

Kirk - yes, it was running yesterday at the comp.

next mod will be the head unit I think - still a source of noise (poor noise floor hiss - even from the digital output, might be the clock or the power supply)

i have upgrade my pxa too, i am using the same op amp as you. caps are mixed of blackgate nx, elna n sanyo os con for the digital. I have modded the clock as well (reclock using 20ppm crystal) the biggest difference was the reclocking! much smoother sound.

HI ReVVoU, welcome to the forum and good to see another 701 modded!

Why don't you post some pics so the rest of us can see how your mods look like.

Hi ReVVoU,
It certainly is good to see another modder on here - not too many of us I feel

I am interested in the clock mod - did you have to separate the Dolby clock from the Yamaha chips, as in the circuit they are running off opposite sides of the clock signal (Xtal)???

I have a clock module here ready to go in, but I am wary of that aspect.

Where do you source these higher quality components? I have an old active crossover I'm using for my system that I wouldn't mind modding up to get a clearer signal.

overseas generally.

What I can't get from local distributors (Arrow, Farnell, RS, RPG, etc.) comes from Digikey, Parts Connexion or other places.

Very interested in these mods.

Some H701mod pics I found on an Italian site,
http://www.perryhificar.it/tweak/tweak.htm

Any updates on the mods? I'm especially interested in the reclocking mod.

still busy enjoying the sound, and playing with crossovers

The noisy head unit will be the next target, as I am developing now a replacement output stage - completely new board from the DAC to the RCA's.

Preliminary work so far, it will be based on Wolfson WM8740 DAC's and Burr Brown PGA2310 volume control chips. The switching power supply (for DACs and output stage) will be external from the PXA. The clock becomes less relevant as these DACs have much better jitter rejection than the one in the PXA.

Pulse-R,
Did you get my PM re: H701 schematics?

Thanks!

where is golf_bht in this disscussion

yes, sorry I read it now

The set of circuits are >100MB for the Alpine service manual (Circuit diagrams are A3 and A2 size). bit too much to email. They can be bought from Alpine easy enough on a CD-Rom.

Any idea why there is a pair of opamps for the front 1 and front 2 outputs where as the rear and center/sub outputs only use one?

WOW,...
Greap work everyone. This reminds me that I've forgotten so much about electronics. Excelent results guys. Would love to get back into this.
I used to be set-up for surface mount (digital blower, paste, glues, sucker, removal tools) to do SMT IC's. Stolen now.
Well done & well reseached. (can i suggets you remove all flux resideu, I was tought that it absorbs moisture, but perhaps you have already done that )

the extra op-amp stage for front speakers is for the Navi-Mix (GPS) input. now gone.
As part of the same circuit, the centre, sub and rear speakers are reduced in volume by 6dB - gone too

A few questions (I finally obtained the schematic!):

What would be the easiest way to bypass the navi-mix output circuit, could I just solder jumpers from the outputs of the front 1 and front 2 opamps to the outputs of the navi-mix opamps and just remove those opamps?

How do I remove the -6db from the rear, sub, and center outputs?

Last for now, what is your opinion of AD8066 opamps? I'm considering replacing the stock NJM opamps with these.

Thanks for your help!

sorry, I'm a bit slow this week.

That's what I did

remove the transistor Q310, but I looked and it's only for the centre channel - rear and sub are left alone (no navi-attenuate).

no idea on those op-amps, I used OPA2134 because I had some lying around. LM4562 or LME49720 are good too.

I should probably get off my ass and look at doing something like this myself!! The noise is driving me insane! lol

Also if you like I'm more than happy to host those circuits if you like. Throw me a PM and we can sort something out

Hi there,
I'm also have this unit on the workbench. I saw some different mods at various websites, nice!

I think you can just drop the whole output section, and connect the DAC (BB PCM1608Y) output to a decent analog output stage. Each channel with his own multiturn volumepot. No remote volume, but all for SQ..
The volumecontrol TC9482 and a lot of C's and opamps less in the signalpath...

Also, two questions:
1.
The powersupply is +/- 9V. The LM4562 is at +/-15V on top of it's performance. Is it possible to change the voltage to +/-15V without "smoke" something..?
2. Service manual please...

Rob.

The +/- supply is only for the vol. control analog section, and the op-amps in the output. so 15V is ok (I have an external converter for modifications.V2)

Also in Mods V2 is the complete re-design of the output stage with PGA2310 volume I.C.'s and possibly changing the DAC to multiple Wolfson parts (depends on what SW mode is used in PCM1608).

Ok Thanks. I bought a service manual at www.manuals-in-pdf.com for a PXA-H700.

I wonder the TH9482 is worse then the PGA 2310 volumecontrol..?

Rob.

From what I have heard, the PGA2310/CS3310 is far superior, as the TC9482 changes gain slightly with changes in program level - i.e. is not very linear to changing amplitude signals (such as music) - due to the nature of the silicon resistors inside. The PGA and CS parts have different internal structure of the silicon resistors to combat this problem, with very good linearity across varying signal levels. (more even dynamics).

also the PGA/CS part has internal high performance op-amp, so reducing the need for extra stages of opamps. the total signal path is then DAC->Filter (op-amp)->Volume control->Output. also can remain fully balanced from the DAC to the output for +10dBm balanced outs, and no caps in the signal path

Apparently, the Service manual is available here:
http://filestore.nealedgeworth.com/PXA-H700_PXA-H701/