Valve compressor and mains voltages

[wave1]

Hi all - a friend of mine is using a Thermionic Culture Phoenix valve compressor on the stereo bus at his studio, and complains that when he recalls a mix, the compressor often sounds different despite the settings on the Phoenix being the same. Could this be caused by fluctuations in mains voltage at different times of day affecting the valves? Is there a simple and cheap tool to measure mains voltage (other than sticking the probes of a multimeter into the socket which he doesn't feel comfortable doing) and if this does measure a fluctuation is there anything we can do about it? The Phoenix has recently been back to TC for a checkup, so I don't think the hardware is the issue....

Thanks in advance!

[Jack Ruston]

That's Thermionic Culture gear I'm afraid. It sounds WONDERFUL. But it's 'organic' to the point of being a bit different as the week goes on in my experience. All I can suggest is that he lets it warm up for a good while before trying to recall it. And rather than rely on knob positions, use tone where possible to get an exact line up. But this is the reason I stopped using a Culture Vulture I had for mixing. It was just too inconsistent. One day it would sound one way, and then next one side would be noisy, or half a dB down, or just...different. I sent mine back a couple of times to get it checked but that's just the way it always was. It's a shame because the way I work does rely on reliable recalls these days, and I'd have Thermionic gear in my racks if it wasn't for these sorts of problems. I don't know if some of the later designs are better in this respect. Whatever they're doing it sounds really nice. I just don't know if they'd be able to make it more consistent without affecting the cost in a major way. For example using switches instead of those (frankly totally useless) detented pots would be good, but it would add hundreds to the cost of each unit. I think a lot of the weird inconsistencies could be down to some sort of valve related stuff...current, bias whatever.

J

[ef37a]

Well, I know nothing of the equipment save what I have read in SoS but perhaps someone should send the makers a copy of Nelson Jones' Valve Amplifiers!

Making stabilized heater, bias and HT supplies using modern ICs is pretty simple and would add little to the cost of the units.
Bugger! Were I 30 years younger! I can see an nice little earner there! Will, want a lucrative sideline modding vulture giblets?

I know people want the "sound" of valves but surely the challenge is to keep the sound but use modern techniques to overcome their many shortcomimgs and extend their life?

Dave.

[Hugh Robjohns]

...when he recalls a mix, the compressor often sounds different despite the settings on the Phoenix being the same.

They all do that, Sir! I concur with Jack; the Thermionic stuff sounds great, but it can be quite variable over time as it warms up and the biasing drifts.

Could this be caused by fluctuations in mains voltage at different times of day affecting the valves?

Possible, but not that likely. I'm not sure how the power supply is configured, but I'd be surprised if the rail voltages vary much.

The Phoenix has recently been back to TC for a checkup, so I don't think the hardware is the issue....

Au contraire -- if you dig around you'll find similar observations from a lot of users. The Thermionic stuff is wonderfully musical, but you have to use it 'in the moment' and print what you get because getting back to exactly the same place might prove tricky, frustrating and time consuming!

hugh

[ef37a]

"Possible, but not that likely. I'm not sure how the power supply is configured, but I'd be surprised if the rail voltages vary much."

Oh I don't know Hugh? Say 300V as a good guess for the HT supply for a nominal 230V in that gives 330 and 290 max/min for a 10% mains shift.

Then the heaters will be affected as well tho' I would be MOST suprised if kit of that quality had raw AC heaters!

Continuous converting UPS as an answer perhaps?

Dave.

[Hugh Robjohns]

The continuous UPS idea is a good one, Dave, if the mains supply volts really do vary a lot in the studio and if the anode HT really does vary with it. But there are several 'ifs' there and I'd want to hard figures on the incoming mains variation and the anode HT variation before making that kind of investment in a continuous UPS.

The Thermionic stuff is quite old-school in mnay ways -- inherently so -- but I think I've seen some solid-state power supply regulation in them for at least some rails -- although I wouldn't swear to it!

I think the sonic variation is more likely to be an issue of thermal drift... but it's only a guess and I'm not a valve man, really. I gladly defer to your far greater experience.

hugh

[ef37a]

Greater experience Hugh?
Only with guitar amps and NOBODY ever complains about mains variations!

I bit of thought brings me to conclude that a SMPSU as fitted to much high end solid state studio gear now (thus banishing the wall rats I know you love!) is the best solution but 230in 300V ish out supplies are remarkably hard to find.

Dave.

[zenguitar]

Greater experience Hugh?
Only with guitar amps and NOBODY ever complains about mains variations!
Dave.

Apart from Neil Young apparently. His tech's report that that he can hear his Fender Deluxe in a new venue and accurately identify the voltage at the drop down transformer. However, it is the exception that proves the rule

Andy

[. . . Delete This User . . .]

yeah, and eric johnson can hear the difference between nickel jack plugs and brass jack plugs.

[ef37a]

yeah, and eric johnson can hear the difference between nickel jack plugs and brass jack plugs.

Who was the guy said he could tell the difference between brands of PP3 pedal batts?

Dave.

[zenguitar]

yeah, and eric johnson can hear the difference between nickel jack plugs and brass jack plugs.

Who was the guy said he could tell the difference between brands of PP3 pedal batts?

Dave.

That's Eric Johnson too. And again apparently confirmed in blind tests. However, both Neil Young and Eric Johnson are VERY familiar with their set-ups and have put them together over many years of experimenting. It's more that they know exactly how their full signal chain sounds and responds to their playing and can hear very subtle differences if anything is changed from what they know. Not sure if that's a blessing or a curse to be honest

Andy

[wave1]

Thanks for the contributions, chaps - any suggestions for a handy (and idiot proof)gizmo for measuring mains voltage?

[chris...]

Something like this:

http://www.maplin.co.uk/plug-in-mains-power-and-energy-monitor-38343

should do - tho' not sure how accurate.

Whether this is your problem is another matter!

[Hugh Robjohns]

I use the very same thing to keep an eye on both incoming mains volts and to measure power consumption and that kind of thing. Seems very accurate and reliable. Mains volts here only seems to vary a few volts either side of 230. Don't think I've seen it lower than about 228 or higher than 233... But the legal supply tolerances allow much greater range.

hugh

[Folderol]

Got one of those mains voltage/current jobbies myself. Quite useful.

Don't underestimate the effect of supply changes on valve kit. As far as I've seen only fairly recent top quality kit has done serious control, and if the mains voltage rises you get a multiplying effect as higher anode/screen voltage gives more gain, but changes the working point of the valves, and at the same time higher heater voltage increases the emission, so again changes the working point.

UK supply voltage used to be quoted as 240V +6% - 10%, but now is European 'harmonised' 230V +- 10% which effectively means the supply companies can get away with lower voltages

[ef37a]

Something like this:

http://www.maplin.co.uk/plug-in-mains-power-and-energy-monitor-38343

should do - tho' not sure how accurate.

Whether this is your problem is another matter!

That should be as accurate as you can be with mains volts Chris. I don't know whether you have ever monitored the mains but it is never still! I had to set it to 230V for spec' tests with a Variac and everytime I glanced at the meter it was 231 or 229!

Dave.

[chris...]

That should be as accurate as you can be with mains volts Chris.

I'm glad to hear it.

I had to set it to 230V for spec' tests with a Variac and everytime I glanced at the meter it was 231 or 229!

Right, but of course that in itself doesn't tell us much about the meter's accuracy...

[Hugh Robjohns]

Right, but of course that in itself doesn't tell us much about the meter's accuracy...

No, it doesn't... but if you go to that Maplin Link and then click on SPECIFICATIONS you'll see the rms AC voltage accuracy is quoted as typically 0.002V and maximum 0.01V.

Hugh

[Folderol]

Good Lord! Whatever for? Switch on your washing machine and the figures will be flapping about all over the place.

[ef37a]

Good Lord! Whatever for? Switch on your washing machine and the figures will be flapping about all over the place.

Verily! And that is why if I paid £2k+ for a compressor I would expect it to have fully regulated supplies, all of 'em!

I don't know about the RNC but the RNP has quite sophisticated power management I understand? And that at 1/4 the price.

Dave.

[Hugh Robjohns]

You seem to be assuming that the thermionic culture products don't have regulated supplies... Is there anything to substantiate that?

Hugh

[ef37a]

You seem to be assuming that the thermionic culture products don't have regulated supplies... Is there anything to substantiate that?

Hugh

Well that's where we came in wasn't it Hugh? The compliant that the devices have an inconsistant performance day to day. Valves, especially small signal valves are pretty stable devices (assuming TC don't use bottom draw Russkies!)so the most likely explaination for the wandering parameters IS supply variation, just keeping the heater supply stable is probably 75% of the battle. In fact my experience is that put ECC83s on a 7812 regulator and the damn things last for ever!

Didn't anyone notice when they popped the cans for the photos?

Dave.

[ef37a]

I am so slow these days!
There is no longer any need for makers of valved devices such as preamps, EQ etc to get into conventional HT supplies!

I have in front of me a pcb, 150x110mm containing a pos and neg 15volt supply, part of which feeds a heater and a UC3843AN chip driving a FET that produces 304volts at about 2mA but that can be made to supply 400V* and beefed up for more current. The whole circuit is powered from a 24V DC supply which could be a conventional 50Hz job or, as in this case, an external 24V SMPSU.

The pcb is part of two others in a pedal that sells for less than £200 for the top product (psu pcb is common to the range). So there really is no excuse for unregulated heater and HT supplies in anything but the cheapest Bellringer crap!

*I have one modded for 48V spook juice.

Dave.

[The Korff]

Here's a little Bustard... There might be more gut shots of TC gear knocking around.

[ef37a]

Here's a little Bustard... There might be more gut shots of TC gear knocking around.

I can't get a big enough image with good enough resolution to tell much. There does seem to be two bridge rectifiers so the heaters could well be DC but regulated?

Oh FCS! the image has now got better as I review the post! No, not a bridge and there are some (limply!)twisted wires that could be heaters and that suggests bog standard AC.

Dave.