Dana Hall's VVR Install: Marshall 50 watt Plexi 1987x

[cluster]

Hello All,

My first post here. I just installed a fixed bias VVR into a 50 watt plexi (1987x circuit). The amp came to me as a pre built clone with a PPIMV already installed. I installed the VVR as per the VVR3 instructions. All the voltages track as they should (I think). However, at full VVR the lowest plate voltage I got was about 55 DCV (tracking from about 495 to 55 VDC). Not sure if it should track to 0 or not (as per the SV1 kit sold by Kevin O' Conner). Also, my guitar volume stayed the same throughout the range of VVR (very loud). PPIMV worked fine though. I mapped my VVR installation diagram to a schematic (see attached). I've included voltages as well as some changes from the original layout the previous builder made (position of the standby switch, etc..). If anyone here can see what I did wrong please let me know. If you need more data, let me know. Thanks.

Joseph

[Steve Conner]

The VVR doesn't greatly affect the gain of the amp. It mainly affects the headroom: how loud the power stage can be pushed before clipping. If you're testing the setup at a low volume at home, you may not notice a great difference.

The way to test it is to crank every knob up full except the VVR voltage control, then you should notice a big difference when you play with the VVR.

[big_teee]

Sounds like a novel idea.
But, if your using a PPIMV, I get enough vol. reduction with it.

[cluster]

The VVR doesn't greatly affect the gain of the amp. It mainly affects the headroom: how loud the power stage can be pushed before clipping. If you're testing the setup at a low volume at home, you may not notice a great difference.

The way to test it is to crank every knob up full except the VVR voltage control, then you should notice a big difference when you play with the VVR.

Thanks, but I haven't been able to get the main volume above 4 or 5 without applying PPIMV to tame it. VVR has no effect at this level. I expected the VVR to do most the grunt work in terms of volume reduction, with the PPIMV acting more as a drive control limiting the signal to the power tubes at low voltages to keep the fizz down. I haven't been able to turn everything to 10 to test your theory because my place won't allow it, but I thought the point of the VVR was to reduce volumes to at least bedroom levels. Like I said before I just installed a SV1 from KOC on a super lead and it works great. Mind u it's bigger, therefore more difficult to install and it's also more money but at least it works and he replies to his emails and answers my question. OTOH Dana hasn't replied to any of my emails regarding this issue. I don't know how his VVR circuit works but I imagine if the the voltages are tracking to his specs, then the problem is not with the VVR. What I don't understand is how setting the plates to 60 DCV in both amps, one using VVR and the other using SV1 I get a greater volume reduction using SV1 and no change in the VVR. I mean if the voltages on the plates, screens and grid are substantially reduced, you would expect a significant volume reduction going to the OT/speakers. Something is missing here.

Joseph

[big_teee]

Thanks, but I haven't been able to get the main volume above 4 or 5 without applying PPIMV to tame it. VVR has no effect at this level. I expected the VVR to do most the grunt work in terms of volume reduction, with the PPIMV acting more as a drive control limiting the signal to the power tubes at low voltages to keep the fizz down. I haven't been able to turn everything to 10 to test your theory because my place won't allow it, but I thought the point of the VVR was to reduce volumes to at least bedroom levels. Like I said before I just installed a SV1 from KOC on a super lead and it works great. Mind u it's bigger, therefore more difficult to install and it's also more money but at least it works and he replies to his emails and answers my question. OTOH Dana hasn't replied to any of my emails regarding this issue. I don't know how his VVR circuit works but I imagine if the the voltages are tracking to his specs, then the problem is not with the VVR. What I don't understand is how setting the plates to 60 DCV in both amps, one using VVR and the other using SV1 I get a greater volume reduction using SV1 and no change in the VVR. I mean if the voltages on the plates, screens and grid are substantially reduced, you would expect a significant volume reduction going to the OT/speakers. Something is missing here.

Joseph

I have the JCM800 with both Pre, and Post Master Volumes, and you can play it at any level.
I don't have the VVR.
I used to play mine through a 100 watt light bulb.
Maybe not recommended, but that tamed it some.

[Steve Conner]

Well, the most likely explanation is that you're measuring 60 volts on some place that you think is the B+ feed to the output stage, but you got things mixed up and it actually isn't. To be sure, measure the voltage right on the plate pin of one of the power tubes.

Turn the PPIMV to zero when doing this. If you did it with a signal present, the peak voltage could be too much for a cheap DVM to cope with.

[MWJB]

Thanks, but I haven't been able to get the main volume above 4 or 5 without applying PPIMV to tame it. VVR has no effect at this level. I expected the VVR to do most the grunt work in terms of volume reduction, with the PPIMV acting more as a drive control limiting the signal to the power tubes at low voltages to keep the fizz down. I haven't been able to turn everything to 10 to test your theory because my place won't allow it, but I thought the point of the VVR was to reduce volumes to at least bedroom levels. Like I said before I just installed a SV1 from KOC on a super lead and it works great. Mind u it's bigger, therefore more difficult to install and it's also more money but at least it works and he replies to his emails and answers my question. OTOH Dana hasn't replied to any of my emails regarding this issue. I don't know how his VVR circuit works but I imagine if the the voltages are tracking to his specs, then the problem is not with the VVR. What I don't understand is how setting the plates to 60 DCV in both amps, one using VVR and the other using SV1 I get a greater volume reduction using SV1 and no change in the VVR. I mean if the voltages on the plates, screens and grid are substantially reduced, you would expect a significant volume reduction going to the OT/speakers. Something is missing here.

Joseph

Just how quiet are you trying to get? Have you measured & compared AC output measured accross the OT secondary?

You seem to be saying that with the MV up, that the amp is too loud...so you turn down the MV to make it quieter. Then the VVR isn't having a noticeable impact. A 55vdc drop in B+ is very noticable...if you are dropping 440vdc there must be a massive difference.

"Bedroom levels", by my understanding are less than half a Watt.

[cluster]

The VVR doesn't greatly affect the gain of the amp. It mainly affects the headroom: how loud the power stage can be pushed before clipping. If you're testing the setup at a low volume at home, you may not notice a great difference.

The way to test it is to crank every knob up full except the VVR voltage control, then you should notice a big difference when you play with the VVR.

you were right. I cranked everything to 10 today and just used the VVR. As I applied VVR the volume dropped slightly but more importantly the tone got more compressed and distorted (PT clipping distortion) which then allowed me to reduce the PPIMV to taste and was able to get a nice "lower" guitar volume. VVR by itself (in power tube scaling mode) will not bring guitar volume down to bedroom levels (unless your bedroom is in a mansion surrounded by 10 acres). You'll need to apply PPIMV with VVR. Full VVR by itself is too loud for bedroom application. Full VVR + a good dose of PPIMV will get you there. Nice tone but comparing KOC SV1 and Dana's VVR, I would pay the extra dough and get the SV1. To me it is much more versatile as far as volume reduction goes. With SV1 I can use the PS alone to get down to bedroom levels without applying much PPIMV. As far as tone goes, I was able to get more versatile tone using the SV1 at lower volumes than the VVR. With SV1 i was playing at bedroom levels but I still had a good range of dynamics and volume range that made it more practical for me. Using VVR, I couldn't get much of a range without using the PPIMV, which defeats the purpose in my opinion. Just my 2 cents.

Joseph

[cluster]

Here is a picture of the VVR with the 2 resistors to jumper if u want to reduce the plates/screens to 0 VDC.

[GainFreak]

I'm about to install similar unit into an amp but I want to try lower the screens voltage only. I was wondering if the bias voltage will track closely the screen voltage in terms of tube bias/dissipation. Does anyone have any experience with that?

[bob p]

Some pertinent commentary about the safety of putting B+ on a front panel knob:

http://music-electronics-forum.com/t32007/#post298756

the linked thread starts off talking about a different product, but it gets hijacked with a discussion that's relevant to this thread.