Ampeg SVT VR Head requiring at least 115 volts from wall socket

[moment15]

okay. i performed the standby mod this morning and it works PERFECT! i tested it with my variac and i ran it on 95 volts. its going with me to my gig this friday night.

here's a pic of it installed:

rather than post all the pics and info here, i created a page for the mod on my website:

http://johnkvintageguitars.homestead.com/SVT-VR.html

Many thanks to Jerrold Tiers for the tips on this mod, and thanks to those that were patient enough for me to post it.

regards,

This is SO helpful! I really appreciate the step by step instructions and pictures. It's great to know that you've got your amp working down to 95v. Definitely a big improvement in reliability.

Thanks again for all the info! I can't wait to get mine modded.

 

[MIJ-VI]

okay. i performed the standby mod this morning and it works PERFECT! i tested it with my variac and i ran it on 95 volts. its going with me to my gig this friday night.

here's a pic of it installed:

rather than post all the pics and info here, i created a page for the mod on my website:

http://johnkvintageguitars.homestead.com/SVT-VR.html

Many thanks to Jerrold Tiers for the tips on this mod, and thanks to those that were patient enough for me to post it.

regards,

Bravo!

 

[troyus]

That's great, I am going to do the same thing. Thanks guys!

 

[alfredpunkjazz]

Thaaaaaank youuuu.

This is really helpfull.

 

[Jerrold Tiers]

Just as a point of information........

Johnk_10 used the right angle type fastons, AND "kludged" them with 'extenders" to create the "male" connectors for the ends of the "Y".

But the straight type are much easier to use (cheap crimpers) and there should be room.

Also, there are straight crimp-on connectors available that have a "shielded" male connector, with an insulating sleeve to avoid any chance of shorts. I'll see if I can post a picture or link.

 

[johnk_10]

yeah, i just used what i already had in my parts box. if i had the straight connectors and the insulated males i would have used them instead, but now its done and it works great.

 

[Myth_103]

Thanks for the info! A buddy of mine (electrical engineer) said he'd mod mine for me. I sent him a link to your very informative page and he said he was down! I'm READY!

 

[johnk_10]

actually, the easiest (and probably the best) way is to use one of these 1 into 2 connectors:

that way you don't even have to make a "y" cord. just pull off J27 and plug the 1 to 2 adapter onto to the spade on the PCB, then plug J26 and J27 onto the adapter.

and you can get them here:

http://www.eagleday.com/blco.html

 

[chadds]

A BIG +1. Ampeg should come home to those who not only care about classic bass amplification, but also to those who understand 'peg's contribution to the development of North America's (and to a significant extent, the world's) pop music & culture.

For example: would the bouncy exuberance of Mr. Jamerson's bass playing have been as lively had he monitored through headphones instead of a musically responsive B-15N? Maybe. But I'd doubt it...

For now, we can only hope that Ampeg is pulled from the fire the way Fender was.

Mr. Jamerson did use headphones. He also went direct and heard himself through this no name speaker cab that sat in the studio as a monitor. He also played upright. So though I love his tone, love and played B-15s when they came out your facts are wrong. I share your enthusiasm for his, America's and Ampeg's contribution to the world's music.

 

[MIJ-VI]

Mr. Jamerson did use headphones. He also went direct and heard himself through this no name speaker cab that sat in the studio as a monitor. He also played upright. So though I love his tone, love and played B-15s when they came out your facts are wrong. I share your enthusiasm for his, America's and Ampeg's contribution to the world's music.

Darn! Another cherished sentimentality dashed!

Ahh! But were the headphones that Mr. Jamerson used made by Ampeg?

 

[MikeyB]

Should the chassis slide out the front after the 4 screws on top of the unit are removed? Or do I have to remove the screws on the bottom of the unit and take everything out from the rear?

Also, any "best practices" on the best procedure to discharge the caps?

Thanks,
-M

 

[johnk_10]

Should the chassis slide out the front after the 4 screws on top of the unit are removed? Or do I have to remove the screws on the bottom of the unit and take everything out from the rear?

Also, any "best practices" on the best procedure to discharge the caps?

Thanks,
-M

first pop off the grill cloth panel, then remove the four screws on top and slide out the preamp chassis. remember to disconnect the two multipin connectors and the two pin fan connector. then remove the chrome rear panel (with the fan). lastly, remove the 6 large screws on the bottom. (i also remove the two rear bottom corners first to make the power amp chassis slide out easier).

 

[MikeyB]

Well, let me get a number in the "modified VR" club!

I did the mod this weekend... thanks to johnk and Jerrold Tiers for all the incredibly helpful info!

-M

 

[espositod]

After gigging my brand new VR a few weeks back and experiencing the same type of 'delay blackout', I stumbled upon this extremely helpful thread and knew I just had to mod mine. This evening, I did just that. Thanks John for the extra guidance!!!

 

[attilhacks]

hello guys

I live in Europe and I'm waiting for a VR head from US. I'm looking to mod it for 230V, it should be a matter of parallel/series on the primary windings of the transformer on J17-18 and J21-22 do you confirm?

thank you very much in advance

 

[alexwittscheck]

actually, the easiest (and probably the best) way is to use one of these 1 into 2 connectors:

that way you don't even have to make a "y" cord. just pull off J27 and plug the 1 to 2 adapter onto to the spade on the PCB, then plug J26 and J27 onto the adapter.

and you can get them here:

http://www.eagleday.com/blco.html

John, if you do the mod using this method, is there a need to insulate it in any way? Just out of curiosity. I don't actually own one of these, but I may in the near future.

 

[rcarraher]

Just recently got a made in Vietnam Ampeg SVT VR- for the record, the amp sounds and looks as good as any other VR Ive seen or played through. Nails "the tone" as it should.....

However.....


The first time I plugged it in, I let it warm up for about 2 mins or so, flipped the "stand by" switch....and nothing....the light didnt turn from red to green, no volume....

after about 5 mins it did kick over. So I tried another wall outlet and this time it never kicked off of standby....even after 10 mins...I could hear some volume want to come out of it....it would come out very faint and then dissapear within 2 seconds.

I could easily return it and wait a month until the shop gets another one in, but Im not that patient....so I called Ampeg/Loud and spoke to a pretty cool tech. he said:

"These amps are extremely power hungry and require at least 115 volts out of the wall to kick off of standby. 110 volts wont do it."

So I went and bought a voltage checker from Radio Shack and checked every socket in my apartment. Every socket that was under 114.5 would not kick the amp off of standby. Many of them were in the 112-113 ranges. Two were coming in at around 116v and those two would kick the amp off of standby after 2 mins of warming up.

So...My question is....Is this normal? Has anyone else had this experience? Seems a bit inconvenient, espescially if youre at a gig and the outlets are less than 115. Should I return this head or is this truly the case with every VR out there?

The VR'smanufactured after 1994 are supposed to have a switching power supply, which means they are not as sensitive to line voltage variations. Typically they should run just fine from 90V to around 150V ac. The VR has its own seperate transformer for filament voltage instead of a tap off the main transformer, so the rest of the amp "robbing" from the filaments shouldn't happen.

I'd take it back. I don't care what the "Tech Support" person told yoou. He just didn't want to troubleshoot it. Either return it or buy a variac (variable AC Transformer) so you can dial in the precise 115V. AV power is notoriously dirty and as you found in your place, can vary greatly from outlet to outlet. Thats one of the reason switching power supplies are inside most electronic equipment since about 1980.

 

[rcarraher]

Jerrold, If you recall I PM'd you once or twice about my VR that went into standby at one place in particular. The venue is known for sketchy power (a light show once crapped out there). I took both a CL and my VR... the VR went into standby several times while playing, but the CL never did.

My question is: do you think bypassing the delay relay would also solve the problem of a VR going into standby mid-song? (i.e: after it was already powered up, off standby, and had been playing for a few minutes)? Or is that a separate section of the circuit?

And just to follow up for others interested: I haven't had the problem anywhere else but the sketchy venue. Just bothered me that the CL would tolerate the mains, but the VR would not.

Thanks much Jerrold,

-Mike

Now this makes sense, I guess I should have read the whole thread before posting. If they are employing a "safe" circuit, it could be a bot touchy and altering it so it is more tolerant of iffy line voltage would be a nice fix. I no longer have the schematics for the VR (I used to have a shop that was an authorized SLM repair center and we did warranty work on Crate, Ampeg and all the other SLM lines). The VR is the closest to the early 70's SVT's loaded with tubes and pretty close to the original design...except the power supply (this was a problem on the 70's, touchy to AC variations) The CL is more modern, but still gets that "classic" ampeg sound, but not like the VR. The CL employes a more modern design switching power supply, and doesn't have the seperate filament transformer. Thats why you don't experience the problem with your CL but occasionally do on the VR. I'll have to look for this mod on the internet as the schematics posted here are just to small for my old eyes.

 

[Tim1]

Having owned a new Vietnam VR for a little while now and deliberately thrashing it heavily I can relate no problems at all and absolutely great tone. I really have been pushing it hard to find any faults while under warranty and it has performed flawlessly. I love it. However we are on 240 volts down here.

 

[Jerrold Tiers]

The CL is more modern, but still gets that "classic" ampeg sound, but not like the VR. The CL employes a more modern design switching power supply, and doesn't have the seperate filament transformer. Thats why you don't experience the problem with your CL but occasionally do on the VR.

No it does not. it has all the same transformers as usual

The transformers and power supply are very close on CL, VR, II, HD, and even the vintage units........ The more recent ones have an extra or altered winding in filament transformer for some extra low voltage supplies.

I live in Europe and I'm waiting for a VR head from US. I'm looking to mod it for 230V, it should be a matter of parallel/series on the primary windings of the transformer on J17-18 and J21-22 do you confirm?

There is also the fan, which must be re-connected to teh center connection of the main transformer primary.

I wrote up a description on the CL which should apply to VR also, the connection board is same.

For small filament transformer You should now have wires connected to pins as follows (120V):

1) black wire connected to J17 or J18

2)White wire connected to J21 or J22

3) brown connected to J17 or J18

4) Brown/white (might be violet) connected to J21 or J22

There will also be a blue/white (may be blue/yellowstriped wire, a blue wire, and a gray wire.

One winding is black to white (the blue/white and blue are taps at 110V and 100V), the other is brown to brown/white (gray is tap at 100V)


For main transformer the wires should now be as follows (120V):

1) black wire connected to J28 or J27

2)White wire connected to J31 or J32

3) brown connected to J28 or J27

4) Brown/white connected to J31 or J32

There will also be a blue/white striped wire, a blue wire, and a gray wire.

The two windings are similar to the filament transformer.

Fan will be connected to J14 and J15

So as it is, the two transformers and fan should be connected with all windings across the mains directly

The gray, blue, etc wires are on un-connected tabs, J23,24,25 and J33,34,35


For 240V, the filament is re-connected:

Black J17

white J19

brown J20

brown white J21

The main is re-connected:

Black to J27

white to J29

brown to J30

brown/white to J31

One wire on fan is moved from J15 to J16

This connects the two windings of each transformer in series, for 240V. The fan is connected across the power transformer which provides 120V to it. The fan will now NOT RUN in standby, but this is OK.

If your voltage is 230V, use blue/white striped wire instead of black in both cases. That changes the voltages so that a 110V winding is in series with a 120V winding, for a 230V total.

Always use a variable transformer to bring up voltage slowly so that you can see if there is any abnormal current. This will help ensure that there is no problem in case some wire is different from what is expected, or is connected wrong.

A wrong connection may have bad consequences of damage or other problems.