Vox Cut and Matchless Parallel Triode V1 and More

[fiftynine]

First off, if you have space for a dedicated cathode cap and resistor on V1, is there any point doing it? Will it sound the same as if the 2 stages were still sharing the 25uF/1.5K?
 
Also, I notice Matchless use parallel triodes on V1 (DC30 C1, Lightning). Was this just to simplify the Vox input arrangement, do away with the normal side and not leave a redundant triode? Or, does it actually improve the Top Boost circuit? I hear the gain is increased by doing this but does it change the feel?

Finally, if I chose to remove the cut circuit from the AC30, can I just omit the cut pot and 0.0047 cap assembly seen here and leave the rest of the circuit as is? Will it sound the same as just having the cut pot fully anti-clockwise?

Looking at the cut circuit, does it just work by cancelling out the opposing signal by bleeding across depending on the position of the pot?

Cheers Gents.

[kagliostro]

First off, if you have space for a dedicated cathode cap and resistor on V1, is there any point doing it? Will it sound the same as if the 2 stages were still sharing the 25uF/1.5K?

some people like to have two different response from the two intake of V1

so they put two different resistors and cap values for each cathode

sometime one is in Fender Style and the other in Marshall Style

--

The paralleled V1 will give a more "fat" sound

also that way V1 stage is less sensible to noise

many people like that paralleled sound

about the tone cut, you can omit it simply, you must get off the pot and the cap

the cap in that position act as a filter for high frequency, the pot give less or more effect on what the cap is doing

few days ago there was an interesting thread about the use of a cap in that position (without the in series pot)

Kagliostro

[HotBluePlates]

Finally, if I chose to remove the cut circuit from the AC30, can I just omit the cut pot and 0.0047 cap assembly seen here and leave the rest of the circuit as is? Will it sound the same as just having the cut pot fully anti-clockwise?

Yes, that works. Sounds same-as Cut control in the full "non-Cut" position.

Looking at the cut circuit, does it just work by cancelling out the opposing signal by bleeding across depending on the position of the pot?

Yes, exactly. 1 + (-1) = 0

If the cap value stays small, only the highest frequencies are cancelled. As the cap is made bigger, you begin cancelling high-mids, etc.

First off, if you have space for a dedicated cathode cap and resistor on V1, is there any point doing it? Will it sound the same as if the 2 stages were still sharing the 25uF/1.5K?

There is a point if you determine there is a point.

If you were going to parallel the two triodes, I wouldn't give each half their own resistor and cap, because the electrically-same thing can be done with 1 resistor and 1 cap (saves money/space).

If each triode were being used in different channels, with different voicing, then there might be a good reason to make one brighter/darker and/or biased differently. That depends on your objectives though. Taste-testing is highly encouraged here.

First off, if you have space for a dedicated cathode cap and resistor on V1, is there any point doing it? Will it sound the same as if the 2 stages were still sharing the 25uF/1.5K?
 
Also, I notice Matchless use parallel triodes on V1 (DC30 C1, Lightning). Was this just to simplify the Vox input arrangement, do away with the normal side and not leave a redundant triode? Or, does it actually improve the Top Boost circuit? I hear the gain is increased by doing this but does it change the feel?

Parallel triodes (for a typical 12AX7 stage and component values) will yeild about 30% more gain. That's enough to be audible without being overwhelming. Whether that's better than simply turning up the volume another 3-5 notches is again your call.

It's also your call as to whether that triode can be better-used some other way.

For example, I'm working up an amp build now, and tweaking the original design somewhat. There were two inputs, each with their own volume in the original amp.Following the sperate inputs stages/volumes, the signals move on to a shared path for the remainder of the preamp.

I have tweed-copy amps with 3 input jacks that will likely never get used; the extra channel is therefore meaningless to me. But, I don't want to change the stock gain of the amp I'm copying (not yet anyway), so paralleling doesn't make sense for me. Instead, I'm choosing to replace the input 12AX7 with a 7-pin socket and a 6AV6 or 6AT6 (1-triode version of the 12AX7 and 5751, respectively). Oddly, I may also add an extra 7- or 9-pin socket further downstream for an effects loop, but I want that extra triode positioned somewhere else in the chassis.

I apologize if this answer seems non-committal, but I think the information will serve you best long-term.

[The_Gaz]

Finally, if I chose to remove the cut circuit from the AC30, can I just omit the cut pot and 0.0047 cap assembly seen here and leave the rest of the circuit as is? Will it sound the same as just having the cut pot fully anti-clockwise?

Yes, that works. Sounds same-as Cut control in the full "non-Cut" position.

No, that's not correct. Too mimic the Cut control in the off position, you'd need a 250k resistor in series with a .0047uf cap. That would re-create the pot set all the way off.

[fiftynine]

No, not non-committal at all. Thanks for all the replies.

I guess there's one easy way to see if it's removal makes any appreciable difference. Same with the parallel triodes. It's just that I'm a bit tight for space at the design stage and don't actually have the amp yet to experiment on.

[HotBluePlates]

No, that's not correct. Too mimic the Cut control in the off position, you'd need a 250k resistor in series with a .0047uf cap. That would re-create the pot set all the way off.

I know what you're thinking, but the pot is wired as a variable resistor, not a voltage divider. Therefore, the pot in "non-cut" position looks like 1M.

The 0.0047uF cap looks like a 1M resistor at 33Hz, smaller at higher frequencies. So with the full 1M in series, the cap is effectively out of the circuit.

[The_Gaz]

No, that's not correct. Too mimic the Cut control in the off position, you'd need a 250k resistor in series with a .0047uf cap. That would re-create the pot set all the way off.

I know what you're thinking, but the pot is wired as a variable resistor, not a voltage divider. Therefore, the pot in "non-cut" position looks like 1M.

The 0.0047uF cap looks like a 1M resistor at 33Hz, smaller at higher frequencies. So with the full 1M in series, the cap is effectively out of the circuit.

Now I don't know who's confused. It was my understanding that the stock pot was 250KA wired as a variable resistor as you said. With the pot 'off', it would be 250k in series with the .0047uf cap, no?

[HotBluePlates]

I'm the one confused.

The AC30, as well as Doug's drawing, has a 250k pot. I've been imagining there was a 1M pot, hence my answer. I've been so sure in my fantasy  that I got a 1M pot for the Cut control I'm putting in an amp build I have in progress.

I think I must have been equating Matchless' Cut control (which uses a 1M pot) with Vox'. Has anybody compared the two?

[fiftynine]

Here's the Ceriatone DC-30 which uses a 0.0022uf but looks the same as the Vox otherwise.

[HotBluePlates]

What I had in mind was the Matchless Clubman.

[sluckey]

I think I must have been equating Matchless' Cut control (which uses a 1M pot) with Vox'. Has anybody compared the two?

I haven't compared the two but I did install the Clubman MV and cut (1M controls) in my Lightning. I don't like either control. Both are very hard to dial in and the MV is almost useless in the bedroom (kinda all or nothing). They may act quite differently in a gigging situation though but I can't say.

[HotBluePlates]

What kind of taper did you use on the Cut? If you could, tell me more about what made it hard to dial in.

I'm asking because I'm planning on putting a cut-style control in the Standel-build (mechanical/final schematic planning phase) to help shave some of the very top end, if needed given the D-130.

I used to own a Matchless Clubman 35, but that was maybe 15 yrs ago... I can't remember if the Cut control was fiddly or not. Funny though, my general memory is while I enjoyed the Clubman, I recall thinking the Lightning was shrill and harsh (at least at polite guitar shop volumes) when I tried one around the same time. The funny thing is "shrill and harsh" often records much better than "full and round" which gets lost in a mix.

[sluckey]

The MV and cut (or brilliance if you prefer)were interactive. Touch one and you would likely need to touch the other. The cut does exactly what you expect, but the MV interaction would drive me nuts. I always felt I had to tweak both pots just to change volume levels and keep the same tone. And the crossline MV was the s#!ts! It was all or nothing, kinda like having an audio taper pot wired backwards. I used Alpha 1MA pots for both.

Maybe all this would react differently in a club situation. I don't know. But I was not pleased with it in my bedroom. I built the Lightning in January, 2009. Played with it about 2 weeks. Added a typical Vox EF86 preamp. No joy there either. After about a month, the Lightning went to the back of the top shelf in a storage cabinet. It hasn't been out since.

Maybe I just didn't give it enough time. But the time I did give it was used more for knob twisting than groovin' to the tone! It totally turned me against the simplistic crossline MV.

[The_Gaz]

@ HBP

I find a 250k linear taper to work the best. To me, an audio taper does absolutely nothing until about "8" on the dial, then jumps in. Linear of course means more attenuation at the "noon" position, but has a much smoother/finer response. The only problem with 250k is that even all the way off there is still some attenuation happening, whereas with a 1M it would be practically negligible. This is probably okay in most cases if the amp is already real bright to begin with. The only problem with a 1M linear is that at noon it's already cutting a lot more highs than with the 250k. Still I prefer 250K Lin, which was used in a couple Matchless designs, in fact. I think with a PEC pot (which I believe is a 30% taper), a log pot would be OK.

[HotBluePlates]

The MV and cut (or brilliance if you prefer)were interactive. Touch one and you would likely need to touch the other. The cut does exactly what you expect, but the MV interaction would drive me nuts. I always felt I had to tweak both pots just to change volume levels and keep the same tone.

Thanks for the report! Fortunately, my situation will not use a master of any type, so interaction will not be an issue.

@ HBP

I find a 250k linear taper to work the best. To me, an audio taper does absolutely nothing until about "8" on the dial, then jumps in. Linear of course means more attenuation at the "noon" position, but has a much smoother/finer response.

Thanks for the head's up!

This may work fine for me, as the phase inverter in the Standel is using a 12AU7, so the output impedance is very much smaller than the 250k pot. I think I can envision why a linear taper would work best.

The PEC RV4 audio taper is very likely 10% (or close). That's more of a true log taper, whereas the 30% taper is being sold nowadays as an "upgrade" but really mimics older, cheaper model pots that fake a true log taper. I'm not sure it will matter either way, since it seems the general wisdom is that a 250k linear works best.