Technics Integrated Amp SU-Z760 vs. SU-V76

[vferdman]

I am not sure if this is the appropriate place for this thread. I hope so. I am looking for some info and possibly a source of service manual (hifi engine did not have it) for a Technics SU-Z760 integrated amp. I scored it for next to nothing on a tag sale and there is really nothing wrong with it a bit of DeIxit F5 didn't fix. I put it on my bench and measured solid 100 watts per channel into 8 ohm load from it. Frequency sweep from 20 Hz to 20 kHz showed a fairly flat response and the listening test was surprisingly pleasing! Even though this thing looks like a typical 80's "plastic" black face unit, it is actually a very well put together machine based on opening it up and poking around. It has a very heavy transformer, a cooling system I have never seen before with fins attached to a copper pipe and extending way out into the chassis. I think it may be a partial class A amp as it does get very hot when pushed and consumes just under 30 watts from the AC outlet at idle. It has a very high quality feel once you get passed the 80's plastic faceplate. The PCBs are very well made and the chassis is solid and somewhat compact in footprint. It has two tape in/out, CD in, tuner in and Phono in. It also has a "Super Bass" button that actually sound ok. Other than that, nothing crazy, but a solid 100 WPC machine. I looked around online and came across a SU-V76 that looks identical, but has a "New Class A" badge, which my SU-Z760 does not. But looking at pictures of inside of V76, it looks identical. There is an IC for the output section, which is mounted to that crazy heat sink with a copper pipe. Same as mine. I am having a really hard time getting any info on these units. Has anyone found any technical info on either or both of these? I would appreciate the reference very much. Also service manuals. I do not need them at the moment, but would love to have one if it's available just to look at the electronic design.

 

[coonmanx]

We do have somewhat of a Technics expert on here. I do not believe that those two are the same.
@SVI2004A

 

[coonmanx]

New Class A is not Class A at all. It is Class AB. So that was just a marketing name for their particular implementation of Class AB. They did do a good job with it anyway. They will also run a bit warm at times.

Overall they are decent. Nothing special but they get the job done. However the speakers are wired in series instead of parallel. So only 8 ohm speakers should be used with it.

 

[coonmanx]

Pretty sure that your amp also came with a rack system. Definitely not the same quality overall as some of the earlier silver face Technics units, but once again fairly decent for an amp that is only going to run one set of 8 ohm speakers. I used to have an SU-V75 but I gifted that to a friend.

 

[vferdman]

New Class A is not Class A at all. It is Class AB. So that was just a marketing name for their particular implementation of Class AB. They did do a good job with it anyway. They will also run a bit warm at times.

Overall they are decent. Nothing special but they get the job done. However the speakers are wired in series instead of parallel. So only 8 ohm speakers should be used with it.

I noticed the strange speaker arrangement yesterday when I hooked up two pairs of speakers. If there is no speaker connected on one of the sets of terminals and they are selected along with the ones that are connected, sound disappears, which suggests series connection as you said. I have never seen that before. I imagine that can not be good as one of the speakers will act as a sort of a filter for the other one, depending on order of series connection. It is just plain wierd. Not to mention that it adds the impedances of the two speakers. So two 8 ohm speakers will appear as 16 ohm. And two 4 ohm as 8 ohm. I tested the amp on my dummy load 8 ohm and got honest 100 WPC of very clean response at pretty much the entire frequency range from 20 Hz to 20 kHz. But the arrangement of the two speaker sets in series surprises me. I would love to see the schematic to confirm this is what they've done. It makes no sense, but the behavior of the speaker selector buttons sure suggests such an arrangement.

In any case, this thing sound great, performs great after a bit of pot cleaning and I got it for $5 at a tag sale. I will give it to my son, who will connect it to his movie projector setup as he does not have a sound system for that yet. I ran a pair of old EPI bookshelf speakers I restored a while back and they sound very good. Again, if there is a service manual for this thing floating around, please let me know where I can get it. Would love to see the schematic for the amp and that funky speaker arrangement. As I understand it, the "New Class A" marketing thing was to describe the biasing scheme of the class AB amp where the signal passes through just one side at low levels and operates in class A mode and at higher levels goes into class AB mode. Hence the warmer running temps and 30 watts of consumption from the wall at idle. Again, I am goin on what I read and have not seen the actual schematic of the thing. I know Pioneer did this with one of their older power amps, so it's not anything new. Just want to learn a bit more about this particular model. Still don't know the differences between z760 and v76.

 

[SVI2004A]

Iirc the V76 / Z760 were effectively the same… this seemed to be a common occurrence of the time
same thing with V66 / Z600 / Z610 / Z650… V78 / Z780… V98 / Z980 for a few that quickly came to mind..
iirc the V76 / Z760 used SVI3105 power amp

 

[vferdman]

Iirc the V76 / Z760 were effectively the same… this seemed to be a common occurrence of the time
same thing with V66 / Z600 / Z610 / Z650… V78 / Z780… V98 / Z980 for a few that quickly came to mind..
iirc the V76 / Z760 used SVI3105 power amp

Yes, that looks like the power amp IC in there, but I did not go in deep enough to read the nomenclature on the chip. Thanks for the reply. Do you know of a Service Manual for this thing? I am very curious about the speaker switch arrangement. So far I really like this machine. It's about 40 years old and runs like new after a bit of DeOxit F5 love.

 

[SVI2004A]

A driving force of those series connected speaker setups was the cooling couldn’t keep up… which certainly was the case in the later V78/98 sets..though the heat sink should be good on this… - possibly due to them being in rack cabinet setups…. But key is to prevent blockslide
I’ve seen other sets using SVI3105 on 4 ohm ratings

 

[vferdman]

A driving force of those series connected speaker setups was the cooling couldn’t keep up… which certainly was the case in the later V78/98 sets..though the heat sink should be good on this… - possibly due to them being in rack cabinet setups…. But key is to prevent blockslide
I’ve seen other sets using SVI3105 on 4 ohm ratings

The heatsink on mine is certainly impressive. Copper pipe with aluminum fins on it occupying half the enclosure. I did try loading it with my dummy load of 4 ohms just to measure power output. I did not run it long on that, but it did get very warm. Even on 8 ohm load running at 100 watts it got warm. And at idle with volume set to 0 it consumes about 30 watts from the AC outlet. So it's definitely a bit of a toaster, but as long as it's not choked for air I feel it should be just fine with that heatsink.

Still no luck on the service manual. I have looked quite a bit now...

Anyway, can you tell me how in the world two speakers connected in series can run without altering the signal to the last in line? I am not sure that's a great thing. In any case, I would not run it in 4 speaker configuration. But I am confident it can handle 4 ohm speakers (1 set) just fine. Especially at reasonable volume. I mean 5 watts output into 8 ohm speakers is VERY loud for me. I am not even sure what the whole power wars were all about. Any decent 20 watt amp from the old days is plenty good enough for most applications. Unless some unusual speakers are being driven (electrostatic?).

 

[coonmanx]

I just saw a couple of service manuals on the Bay for the SU-V76. Looks like the one from Germany might be the better one but not sure...

 

[coonmanx]

The heatsink on mine is certainly impressive. Copper pipe with aluminum fins on it occupying half the enclosure. I did try loading it with my dummy load of 4 ohms just to measure power output. I did not run it long on that, but it did get very warm. Even on 8 ohm load running at 100 watts it got warm. And at idle with volume set to 0 it consumes about 30 watts from the AC outlet. So it's definitely a bit of a toaster, but as long as it's not choked for air I feel it should be just fine with that heatsink.

Still no luck on the service manual. I have looked quite a bit now...

Anyway, can you tell me how in the world two speakers connected in series can run without altering the signal to the last in line? I am not sure that's a great thing. In any case, I would not run it in 4 speaker configuration. But I am confident it can handle 4 ohm speakers (1 set) just fine. Especially at reasonable volume. I mean 5 watts output into 8 ohm speakers is VERY loud for me. I am not even sure what the whole power wars were all about. Any decent 20 watt amp from the old days is plenty good enough for most applications. Unless some unusual speakers are being driven (electrostatic?).

Yeah, I really don't think that running speakers in series is a good idea. It can be done if necessary and I remember when a friend did it and it was OK. But if I am running four speakers it is always on an amp that can handle a 4 ohm load. And there are plenty of those out there. In fact my early 80s MCS 3842, which is actually made by Technics, can handle a 4 ohm load. I was previously running two sets of speakers on it but right now there is only one set on it.

 

[adowns]

Multiple speakers in series are perfectly safe.
Multiple speakers in parallel can overload the amplifier.