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Technics SU-V9 Restored ... now the questions

M

mateiux

New Member
Hi to all the awesome community at Audiokarma, this is my first thread after a few posts, sorry for the long in depth description, but I'm by no means an expert, and I'm afraid not to miss something.

Just finished restoring the SU-V9, a brief history:

Esthetics:
I got the unit in a "meh" condition, but working. Face and knobs dirty but no physicals scratches, lots of "electric" scratches though. Glass with a broken left corner, the side of the unit was badly scratched.
EXTREMLY dirty on the inside, with what looked like coffee/water spills on the amp board, dust, corrosion and the 40 years of wear and tear.

Functionality:
The unit powered up, worked ok but the speaker selector relay was inconsistent, sometimes it did not engage.

Rebuild process:
I pretty much took everything apart every single board, cleaned off the dust, deoxit, checked all solder points ... etc. put it back together and the trouble started, no relay click, thank to this forum, I got it going again ... in the process my wife threatened me I will sleep on the street along with the amp :)

What I changed from original:

-power transistors (Q331-334) are now equivalent parts: 2 x 2SA1494 and 2 x 2SC3858
-ALL caps are Nichicon won't go into details, but the good audio ones :), main caps still original.
-Initially changed (Q327-328) to "similar" 2x2SA1859A and 2x2SC4883A then I decided to change back to original parts (What do you think should I put the new "similar" ones or keep the originals ?)
-Fixed a loose wire inside speaker selector relay and cleaned the contacts.
-Fixed a bad soldering point that I missed J21 on the speaker selector switch board (main/remote). I consider this to be the issue for the relay inconsistency, it is super sensitive here, for example if there is a short even by finger touching the soldering points while in operation it triggers the relay to disengage. Yeah not a good idea to touch anything in operation ... ;)
-Flowers for my wife ...

Now the questions with regards to adjustments and other stuff that I don't understand after countless hours of reading about it and google translations from Japanese ....

  • Speaker selector switch voltage adjustment is exactly as per manual TP702 -0.1 Vdc and TP701 0.0 Vdc. here is the question: What relays are engaging, when and what do they do ...? I have the one on the selector board (RLY701) and then there are 2 remote ones from the main amp board (tap relay, why 2 ???? could not find this configuration in the manual online, only one RLY601) if voltage is greater then -0.1 Vdc then ONLY RLY701 clicks - the unit works fine ... If the voltage as per manual then BOTH relays click still the unit works fine. I'm confused on what is going on, I thought what I hear is the unit going in protection but, no ... what is it and how does it operate ?
  • Supply voltage perfectly stable at 54.5 Vdc (Q327 collector and ground at TP502) - no issues here.
  • ICQ Adjustment ... this is where the manual uses the word "about" 1 minute, if I read the other languages there is no confusion on semantics it's just "after" not "about". Here is the issue, after 1 minute I adjusted VR301/302 to be at 1mVdc ... voltage was almost there anyway, I left the DMM there and the voltage slowly goes up, do I have an issue, how stable should it be ???
... this is my story and my concerns ...
 
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mateiux said:
Speaker selector switch voltage adjustment is exactly as per manual TP702 -0.1 Vdc and TP701 0.0 Vdc. here is the question: What relays are engaging, when and what do they do ...? I have the one on the selector board (RLY701) and then there are 2 remote ones from the main amp board (tap relay, why 2 ???? could not find this configuration in the manual online, only one RLY601) if voltage is greater then -0.1 Vdc then ONLY RLY701 clicks - the unit works fine ... If the voltage as per manual then BOTH relays click still the unit works fine. I'm confused on what is going on, I thought what I hear is the unit going in protection but, no ... what is it and how does it operate ?
Click to expand...

This amp has auto impedance detect.

if you have 2 sets of 8ohm speakers it will work like this
Amp is on - spkrs switches are off.

you hit main speakers, you will hear speaker protect relay (RL701) click off then back on - this serves 2 purposes. 1: in off mode, speakers connected to output of speaker relay are momentarily connected to impedance comparator, which senses (over iirc 6 ohms or so) in this case, it leaves RLY601 in Hi Tap mode (AC46V windings) and 2: it saves the contacts in the speaker switches from under load arcing. —you will hear effective 2 clicks.


if then you switch on Remote speakers Again, you will hear 701 click off Then you will hear 601 click to Low Tap (AC 38V windings), then 701 re engage (you will hear 601 fall back to Hi Tap if going back to 1 pair of spkrs) — you will hear 3 clicks in this mode
 
SVI2004A said:
This amp has auto impedance detect.

if you have 2 sets of 8ohm speakers it will work like this
Amp is on - spkrs switches are off.

you hit main speakers, you will hear speaker protect relay (RL701) click off then back on - this serves 2 purposes. 1: in off mode, speakers connected to output of speaker relay are momentarily connected to impedance comparator, which senses (over iirc 6 ohms or so) in this case, it leaves RLY601 in Hi Tap mode (AC46V windings) and 2: it saves the contacts in the speaker switches from under load arcing. —you will hear effective 2 clicks.


if then you switch on Remote speakers Again, you will hear 701 click off Then you will hear 601 click to Low Tap (AC 38V windings), then 701 re engage (you will hear 601 fall back to Hi Tap if going back to 1 pair of spkrs) — you will hear 3 clicks in this mode
Click to expand...
Thanks, great, that is exactly how it behaves and now I get it ... or I think I do anyway :)

One down, one to go:

How stable should the voltage for ICQ adjustment be after 1 minute say 5 minutes ?
At the moment at ~ 1 minute, 1min 30 sec to be precise the voltage gets to 1mV, and then slowly goes up at about 3-4 minutes I get 1.5mV ...
 
I remember most sets were around 15-20mv

I did some digging... years ago I checked an original V9 and it was 17mv after 20 min both channels
 
Mine is way lower, also noticed it is temperature depended, so after 20 minutes left channel 1.80mV and right 1.83 mV
 
That’s way underbiased - after a few minutes adjust In increments... - adjust a little then let it sit for 5 mins... check emitter volt drop - when it keeps stable at 15-20mV you’ll be set

⚠️ I highly recommend using new good quality trimpots... these dropping open circuit can cause havoc
 
New Bourns trimpots installed and a week of chasing the right bias both channels stable at around 16 -17 mV at about 20-25 minutes - sounds really good, cannot compare to how it should sound since I did not use it too much in the original state, I have a Yamaha CA-810 and a Technics SU-C3, lower power, but also really low detail compared to this amp.

The SU-V9 has a fair amount of highs, sound bright, but I find that it is precise, mids are not shy or muddled, stereo separation is phenomenal, and bass response is fast and is there when needed, there is always the "super bass" control ready if needed :).

I have a cheap oscilloscope and sound generator (hobby stuff from Amazon) I will try to test it and see if all is fine, not sure how :) , next on my "to learn" things.

Glass was cracked in one corner luckily the broken glass corner was saved by the previous owner, so I printed some parts to cover the "fix" and look "factory" ...

Really pleased with the results, worth the effort invested, the speakers (SB-X700A) are rebuild and modified, crossovers with film caps, cabinets (really bad original) are fully braced + dampening on all walls, tweeters are ribbon and fitted inside the original bracket so they look original on the outside, woofer baskets reinforced with putty (HUGE change in sound, I was shocked by how much it changes) the TT SL1600-MK2 another full rebuild and back to original state ... and now all reunited with the SU-V9 they are all happy to "play" together again.
1.png 2.png 3.png 4.png 5.png 6.png 7.png 8.png
 
Neat setup. Good to see it’s all running to spec

nifty idea w/ the glass.... I took one of mine to one of the better glass suppliers locally and had them replicate the one I had... had a few made

a V9on X700s ought to sound very smooth

oh was your V9 a PA PC or PX region?
 
I love the aesthetics of those particular pieces together and that set up. stunning visually.
if you ever sell, holla@yaboi
looks like something out of the old stereo salon catalogs
or ikea (take that the right way, they have a great catalog of pix)
 
Oh the green new class A usually is on those regions

region codes are on serial sticker

like this (SPA = Silver Far East PX (PA)) - this one made on 11th June 1994
ED119784-93B4-4D0F-87A3-F1C4741A723A.jpeg
 
grinx76 said:
I love the aesthetics of those particular pieces together and that set up. stunning visually.
if you ever sell, holla@yaboi
looks like something out of the old stereo salon catalogs
or ikea (take that the right way, they have a great catalog of pix)
Click to expand...

Haha, the tv stand / entertainment center is an IKEA "hack" I designed and build for this purpose from 2 KALLAX units and accessories I got online. It was the best option for this setup, wanted the 70s-80s vibe.

The speaker stands are my design and build, even the headphone stand is designed (modified from others) and build (the parts were 3d printed) by me ... so all custom :)
 
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