Yamaha Strange Design

[Richardjhy]

I have quite a few Yamaha vintage amps/receivers. Some of their design for impedance selection confused me.
AX-592 impedance selector shows 4 ohms min and 6 ohms min. Rail voltages are +-58v when selecting 6 ohms for speakers, and rail voltages are +-49v when in 4 ohms.

Older model RX-V1070 impedance selector shows 8 ohms min and 6 ohms min. When I measured rail voltages, +- 58v when selecting 6 ohms and 49 ohms when switching to 8 ohms.

Why 6 ohms speakers need higher rail voltages than 4 or 8 ohms speakers? Are 6 ohms speakers hardest to drive?

 

[Blumlein 88]

The amp in your first image has a 4 ohm or 6 ohm setting. It says A+B at 8 ohms (which will also be 4 ohms). It makes sense that a lower rail voltage into lower impedance might limit current to prevent the amp from having dissipation issues. 6 ohms would not draw as much current as 4 ohms speakers so a higher voltage would work without excess dissipation.

Are you sure you didn't get them backwards in the 2nd amp. It would appear to be backwards. Or maybe the old switch was labeled backwards.

 

[JSmith]

@Richardjhy the pasted image is fine, but you also attached an image file which contains your email address... you may want to remove same for privacy.


JSmith

 

[Richardjhy]

RX-V1070 was TOTL receiver by the time with huge transformer and heat sinks. It weights more than 40lbs.

 

[Richardjhy]

@Richardjhy the pasted image is fine, but you also attached an image file which contains your email address... you may want to remove same for privacy.


JSmith

Thanks. How can I do it?

 

[Richardjhy]

The amp in your first image has a 4 ohm or 6 ohm setting. It says A+B at 8 ohms (which will also be 4 ohms). It makes sense that a lower rail voltage into lower impedance might limit current to prevent the amp from having dissipation issues. 6 ohms would not draw as much current as 4 ohms speakers so a higher voltage would work without excess dissipation.

Are you sure you didn't get them backwards in the 2nd amp. It would appear to be backwards. Or maybe the old switch was labeled backwards.

I double checked my measurement. I emailed and Yamaha replied that their design is normal.

 

[Richardjhy]

I double checked my measurement. I emailed and Yamaha replied that their design is normal.

 

[Deleted member 48726]

AX590 switch is between 4 or 8 ohm and the higher voltage is measured at the 8 ohm setting. This seems correct.

RX-V1070 switch is between 6 or 8 ohm and the higher voltage is measured at 6 ohm setting. This doesn't seem correct and goes against common logic.

 

[Richardjhy]

AX590 switch is between 4 or 8 ohm and the higher voltage is measured at the 8 ohm setting. This seems correct.

RX-V1070 switch is between 6 or 8 ohm and the higher voltage is measured at 6 ohm setting. This doesn't seem correct and goes against common logic.

That's why I asked Yamaha but they said it's normal.

 

[Deleted member 48726]

That's why I asked Yamaha but they said it's normal.

A bit weird. Maybe referring to the service manual for the RX-V will explain why.

 

[Randyman...]

Strange indeed.

 

[Deleted member 48726]

Strange indeed.

Well the schematic shows that the 6 ohm setting indeed gives higher voltage from the transformer so Yamaha is right. Why the impedance selector behaves the opposite from all other amplifiers with a selector I can't answer.

SOURCE-->https://www.hifiengine.com/manual_library/yamaha/rx-v1070.shtml

 

[TheBatsEar]

I have quite a few Yamaha vintage amps/receivers. Some of their design for impedance selection confused me.
AX-592 impedance selector shows 4 ohms min and 6 ohms min. Rail voltages are +-58v when selecting 6 ohms for speakers, and rail voltages are +-49v when in 4 ohms.View attachment 302188
Older model RX-V1070 impedance selector shows 8 ohms min and 6 ohms min. When I measured rail voltages, +- 58v when selecting 6 ohms and 49 ohms when switching to 8 ohms.
View attachment 302189
Why 6 ohms speakers need higher rail voltages than 4 or 8 ohms speakers? Are 6 ohms speakers hardest to drive?

Well, that surely makes no sense to me.

 

[Galliardist]

I think I saw this explained somewhere before. I may be wrong... but

AX-592 has two pairs of speaker outputs A and B. When using both, you have to use the 8 Ohm speakers, and if you use one set only, you can then use 4 Ohm speakers. So it has the higher output.

The RX-V1070 has surround speaker outlets. The 6 Ohm output allows higher power in this case to all speakers. You shouldn't use 4 Ohm speakers with this amplifier.

However, what also happens is that when you switch to 6 Ohms, a stiffer protection circuit is switched in. It can draw more power in normal use, but can't manage to sustain peak output for as long: so it is protected against doing that.

 

[Cbdb2]

Yes looks like first Amp switch is for 4 or 6 ohms, second is for 6 or 8 ohms.

 

[Richardjhy]

I think I saw this explained somewhere before. I may be wrong... but

AX-592 has two pairs of speaker outputs A and B. When using both, you have to use the 8 Ohm speakers, and if you use one set only, you can then use 4 Ohm speakers. So it has the higher output.

The RX-V1070 has surround speaker outlets. The 6 Ohm output allows higher power in this case to all speakers. You shouldn't use 4 Ohm speakers with this amplifier.

However, what also happens is that when you switch to 6 Ohms, a stiffer protection circuit is switched in. It can draw more power in normal use, but can't manage to sustain peak output for as long: so it is protected against doing that.

Surround channels in RX-1070 use separate rails, rectifier bridge and filter caps from the transformer.