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Sansui G-7500 - Convert 230V to 110V

JRH99

JRH99

Active Member
I have a G-7500 running a pair of Ditton 44 speakers and it sounds fantastic! I purchased the G-7500 about 6 months ago and it has be working great with daily use. Last weekend I decided to detox the switches and potentiometer's as they were overdue for a cleaning. The first thing I noticed when I took the cover off was that the voltage selector was set to 230V, not 110V. The unit does have the 230V sticker on the back, but has the standard 2 prong US type power cord.

So here are my questions:
  1. Should I switch it to 110V? The reason this is even a question for me is that the units sounds amazing to me as it is. I suspect it was never switched to 110V and has been running at 230V on 110V for the past 40 years. I'm concerned if it might create any issues by switching it now.
  2. What is the impact of running at 230V on the 110V? I understand it will have less power and the display lights might be dim. But is there harm in running it this way? Could there be any benefit to the longevity of the unit running at the lower power?
  3. What type of fuse do I need to use if I do make the switch to 110? I have searched this forum and all over the net to find the answer to this question. Mainly, should it be a fast or slow blow fuse? The service manual does not state which to use. This may be a dumb newbie question, but it seems this would be critical and I can find no definitive answer on it. I have determined that I need a 7A fuse based on the sticker that was placed on the F-2980 power driver board next to the F-604 fuse location. It states a 7A is needed at 100/120V and a 4A for 220/240V. The service manual states 5A is needed at 100/120V and a 2.5A for 220/240V. The current fuse is a 4A 125V.
I would appreciate any feedback on my above questions. Most of all to confirm about the correct fuses I should use when I make the switch.

Thanks!
 
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Well, USA power is 120V (Supposedly), so you need to set it to 120V. Sometimes units my have a 117V option, which is the one you want to use if that it is the case.
Always a fast blow fuse in an amplifier.
All these amps I have serviced usually have 7amp fuses in them.

No damage would occur since everything will be running at approx 50% voltage....

All Sansui units are manufactured with parallel two conductor power plugs.
 
kevzep said:
Well, USA power is 120V (Supposedly), so you need to set it to 120V. Sometimes units my have a 117V option, which is the one you want to use if that it is the case.
Always a fast blow fuse in an amplifier.
All these amps I have serviced usually have 7amp fuses in them.

No damage would occur since everything will be running at approx 50% voltage....

All Sansui units are manufactured with parallel two conductor power plugs.
Click to expand...

Thanks for confirming on the fuse being a fast blow, that is what I thought, but wanted to be sure.
I read a lot of conflicting comments on this topic with some stating slow blow if it is in the power circuit as the in rush current would blow a fast blow fuse when you power on. And that you should use fast blow on the driver circuits. The F-2980 is both the power and driver board, but only need to change the power fuse for the 230V to 120V conversion.

And yes, it is 120V, not 110V....
Thanks.
 
Kind of surprised it actually worked at half voltage. Be sure you have a new fuse of the correct ampacity. Typically, these units will draw twice as much current at 110/120V as they will at 220/240V and so the rating if the mains fuse needs to be adjusted accordingly. The back panel near the fuse holder will usually have a rating shown for each voltage to specify which fuse should be used.
 
Sansuiman said:
Kind of surprised it actually worked at half voltage. Be sure you have a new fuse of the correct ampacity. Typically, these units will draw twice as much current at 110/120V as they will at 220/240V and so the rating if the mains fuse needs to be adjusted accordingly. The back panel near the fuse holder will usually have a rating shown for each voltage to specify which fuse should be used.
Click to expand...

It works and sounds really nice! I expect it may sound better at higher volume and would likely go louder with the correct voltage set up. I was always surprised by the fact that it never gets warm, even when its been playing loud for hours. I hope it does sound even better and goes a little louder, I'm kind of excited to find out! I will get a 7A fast blow and let you know what I hear.
 
Funny that. I've had a few Sansui components that came to me set for 220V or 240V, and didn't power up/operate at all on 120V. I suppose it depends on the type of component and characteristics of the power supply. Does surprise me though that you got good sound out of it with the rail voltages at half of what was intended.
 
Sansuiman said:
Funny that. I've had a few Sansui components that came to me set for 220V or 240V, and didn't power up/operate at all on 120V. I suppose it depends on the type of component and characteristics of the power supply. Does surprise me though that you got good sound out of it with the rail voltages at half of what was intended.
Click to expand...

ghazzer said:
Wouldn't it be wise to at least measure the rail voltages before making any changes?
Click to expand...
The voltage selector is set to 240V and it is running with the 4A fuse. What could be of potential concern, that it might not actually be currently running at 240V that it appears to be set at? I know for sure my house is 120V. What would I measure, the power supply output or are you suggesting to measure the house power? I appreciate any insight / and feedback you have on this. I definitely do not want to damage a unit that up until I saw that voltage selector setting, I thought sounded beautiful and was working perfectly.
 
I guess we're a all taken aback by how well it appears to be functioning at half rail voltage. Have you run it at high output without detecting distortion? I certainly don't suggest you do that until this question is resolved, but have you run it at high output without distortion on the present setting?
 
It gets plenty loud and sounds sweet with the loudness on up to about 30%, which is pretty loud. After that with loudness it's a bit distorted. Loudness off I can turn it up to about 50% and that is typically too loud for me. I also noticed that the volume does not increase at the same rate after 40%. Only issue I ever noticed was what sounded like clipping when turned over 70% on a low input source(tv with cheap dac). So I never did that again...
 
Rail voltages will be 1/2 of what they are intended to be. Amplifier output voltages will be reduced accordingly. If there are any logic devices in there, they may be operating in the indeterminate range (not good). Other control circuits may be operating in indeterminate ranges also, such as speaker protection circuits, relay drives, etc. I would not operate the unit like this.

Look at the power transformer. If you see a pair of wires coming out of the transformer that are simply tied together, they may be connected to the primary windings. For manufacturers that supply units for various markets, they sometimes design power transformers to be used in units for those markets, to reduce part number counts and sourcing leverage.

Two identical primary windings can be wired in series for 230v and in parallel for 115v units. Phasing is critical, so be careful. Look at the schematic or service manual.

Look at the transformer wires and report back.

Rich P
 
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I made the comment because it seems like a very simple way to get a solid answer.

The schematic in the SM indicates that the rails should be ±63vdc. Half of that would be ~32vdc.
 
ghazzer said:
I made the comment because it seems like a very simple way to get a solid answer.

The schematic in the SM indicates that the rails should be ±63vdc. Half of that would be ~32vdc.
Click to expand...
I was not addressing your post. I was addressing the statements regarding how well it appears to be working. "Appears" being the operative term.

Enjoy,
Rich P
 
As Rich alluded to above, please verify the voltage selector is actually 'in circuit' and not bypassed. Unlikely though it may be, it is possible the transformer was replaced with a 120V only part and the setting of the input voltage selector is moot as a result. In that case, you've been operating on 120V all along and nothing needs changing, except maybe the value of the mains fuse.

This is a very unlikely scenario but not knowing the history of this unit, and having seen many strange things in servicing this old gear; it's worth looking at.
 
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pustelniakr said:
Two identical primary windings can be wired in series for 230v and in parallel for 115v units. Phasing is critical, so be careful. Look at the schematic or service manual.
Click to expand...
Yes in a lot of cases, but on the Sansui in question it has a Plug and Socket arrangement which can be plugged in and lined up with the appropriate voltage.
The only way there could be an error is from the factory, or if someone has rewired the socket for some unknown reason.
The voltage options are 100/220/120/240, there are as best as I ca recollect, two primary windings with taps as well to achieve the 4 different voltages.
 
All good good advice and thank you for that! I will verify this before I make any changes. On a 40 year old receiver you never know what may have been done.

This will have to wait to this weekend, jhave to travel to Mexico for work. Will update when I get back. i
 
ghazzer said:
Wouldn't it be wise to at least measure the rail voltages before making any changes?
Click to expand...
A sensible piece of advice in my opinion, and the easiest and safest way for someone possibly not familiar with mains voltage selectors and associated wiring to establish whether a change needs to be made.
DougBrewster said:
I guess we're a all taken aback by how well it appears to be functioning at half rail voltage. Have you run it at high output without detecting distortion? I certainly don't suggest you do that until this question is resolved, but have you run it at high output without distortion on the present setting?
Click to expand...
Exactly this, for it to be set to 230V operation and apparently work fine when 120V is applied is very strange. Checking that the transformer installed is possibly a 'single voltage type' is simple enough, and could explain why the selector appears to be in the wrong position, or simply not functional because of a historic transformer change to single voltage.

The sort of scenario that could have happened is the cap of the selector may have broken off or been removed for some purpose, and then glued back on in the wrong position.
 
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Hyperion said:
A sensible piece of advice in my opinion, and the easiest and safest way for someone possibly not familiar with mains voltage selectors and associated wiring to establish whether a change needs to be made.
Exactly this, for it to be set to 230V operation and apparently work fine when 120V is applied is very strange. Checking that the transformer installed is possibly a 'single voltage type' is simple enough, and could explain why the selector appears to be in the wrong position, or simply not functional because of a historic transformer change to single voltage.

The sort of scenario that could have happened is the cap of the selector may have broken off or been removed for some purpose, and then glued back on in the wrong position.
Click to expand...
Yes for sake of simplicity, we really need a reading on the Main DC rails and a clear picture of the voltage selector....
 
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