Novachord #346 Inspection & Initial Wakeup

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Re: Novachord #346 Inspection & Initial Wakeup

Post by Automatic Gainsay » Wed Oct 21, 2009 6:28 am

dr funk wrote:
HideawayStudio wrote: Very frustratingly the schematics sufficiently detail cap and resistor specs but not inductances. This is of particular concern in the main resonant low pass filter network where, although the chances of failure are low, if a choke were required, it would be difficult to determine it's original characteristics. I would feel happier if these chokes were characterized sooner rather than later for the record by either myself or another Novachord owner.
Have you asked Mike Fulk if he has this info? You never know, he just might...

Frank
According to many, including Fulk himself, Mike knows a very great deal about the device and has renovated many of them.
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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Wed Oct 21, 2009 8:02 pm

Automatic Gainsay wrote:
dr funk wrote:
HideawayStudio wrote: Very frustratingly the schematics sufficiently detail cap and resistor specs but not inductances. This is of particular concern in the main resonant low pass filter network where, although the chances of failure are low, if a choke were required, it would be difficult to determine it's original characteristics. I would feel happier if these chokes were characterized sooner rather than later for the record by either myself or another Novachord owner.
Have you asked Mike Fulk if he has this info? You never know, he just might...

Frank
According to many, including Fulk himself, Mike knows a very great deal about the device and has renovated many of them.
Both Mike Fulk and Phil Cirocco are Novachord legends but sadly they are both almost impossible to contact via email (at least on the subject of Novachords) these days. Sadly Marco Bacigalupo in Italy, myself and at least one other Novachord owner have tried to contact them on a number of occasions over several months with no luck.

Todays Update: Marco has very kindly measured the current loadings on each supply rail of his Novachord on which he has performed the most amazing restoration job. These measurements have been passed on to Majestic Transformers in Poole who are very kindly producing me some replica transformers for my beast.

For those who are interested the current loadings on the main positive HT rails are as follows:

270V DC (main B+ supply) 42mA
70V DC (Grid Bias) 4mA
34V DC (Control Tube Screens) 9mA

Not much is happening this evening, I'm having a bit of a rest, maybe I'll just sit in front of my keyboard and drool at the sea of components before me!

Speaking of keyboards... I still can't get over the condition of her keys - it's 70 years old!!!

Novakeys - Forget Ebony & Ivory... Try Bakelite and Plaskon!
DW_Novakeys_2.jpg
Even the Warranty card and User Instructions under the Lid are in Amazing Condition
WarrantyCard.JPG
I recently learnt that having the original cover for the rear cabinet (which I do) is -very- rare thanks to most discarding it in fear of overheating the PSU and PA units. I can send a piccy of it to anyone who needs to know what it looks like - the warning message on the inside is a nice touch....

The Rear Cover Warning on the Inside Face
DW_Novachord_Rear_Panel_Inner_Label.JPG
Automatic Gainsay wrote:One of the interesting things about that Novachord when it was working was the huge amount of noise it would generate. There was an amazingly beautiful cacophony in the background of it, which sounded like a bit of bleed from every single sound source. I loved it, but figured that it indicated that something probably needed a bit of maintenance.
This intrigues me... it will be very interesting to note whether this noise is present when she's powered up for the first time on the rebuilt PSU next month.
Last edited by HideawayStudio on Sat Oct 24, 2009 9:52 am, edited 1 time in total.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by madtheory » Thu Oct 22, 2009 12:41 pm

The keyboard looks really nice with the wood. What is it Dan? Rosewood veneer? Did you restore that too???

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Re: Novachord #346 Inspection & Initial Wakeup

Post by Automatic Gainsay » Thu Oct 22, 2009 2:40 pm

I protected those original paper aspects! I was in love with them.
As for the rear cover, I actually held on to that while the Novachord was in storage, I was so worried something would happen to it!

Ha ha, I must have contacted Fulk before he became hard to reach. I used to e-mail him all the time and he kept yelling at me to just call him. I have his phone number, I'll get it to you, Dan!

According to Hammond, the Novachord is made of American Walnut! : )
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Re: Novachord #346 Inspection & Initial Wakeup

Post by madtheory » Thu Oct 22, 2009 5:48 pm

Cool, thanks :)

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Re: Novachord #346 Inspection & Initial Wakeup

Post by Shanesaw » Thu Oct 22, 2009 7:40 pm

Looking great Hideaway!

"Both Mike Fulk and Phil Cirocco are Novachord legends but sadly they are both almost impossible to contact via email (at least on the subject of Novachords) these days. Sadly Marco, myself and at least one other Novachord owner have tried to contact them on a number of occasions over several months with no luck."

I actually spoke with Phil last month about an Arp 2600 power cord(for school). Very friendly! Give him a ring...
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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Thu Oct 22, 2009 8:21 pm

Shanesaw wrote:Looking great Hideaway!

"Both Mike Fulk and Phil Cirocco are Novachord legends but sadly they are both almost impossible to contact via email (at least on the subject of Novachords) these days. Sadly Marco, myself and at least one other Novachord owner have tried to contact them on a number of occasions over several months with no luck."

I actually spoke with Phil last month about an Arp 2600 power cord(for school). Very friendly! Give him a ring...
Now that I've tried contacting Phil via email on several occassions I'm a little nervous as I simply don't know if he's been ignoring my emails, never got them, or is so flooded with them he can't answer. It is just possible, for example, that he's tired of hearing from wannabe Novachord owners - who knows??

If anyone knows Phil I'd be really grateful if they could put in a word for me and number 346... I'm really wanting to know his opinion on exactly why so many think his beast sounds so different to less extensively rebuilt Novachords.

Many blame this on his almost 100% replacement of passives but, although this is undoubtedly the reason, it's not entirely obvious why. Much of the Novachord's function is so simplistic that any major change in function caused by new passives would render it useless. It remains to be seen whether waveform generation and filter setup are so radically altered by changing the Novachord's passives for new ones. I have a sneaking suspicion that one possibility is that new caps are producing sharper transients in the dividers which may well be producing more harmonically rich waveforms. It is also possible that modern caps are having an effect on the Q in the resonant filter network.
Last edited by HideawayStudio on Fri Oct 30, 2009 6:51 pm, edited 2 times in total.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Fri Oct 23, 2009 12:24 am

This Evening's Update:

I got curious and noting some time ago that the resonant filters on the Novachord are entirely passive I set about tapping an external audio signal into one of the divider control circuit outputs and connected the analog input of my PC audio interface to the input of the preamp channel. I then mangled up some music (can you guess what it is folks....?) and tweaked all the filter controls in time with the music. This has yielded some interesting conclusions...

1. All of the filter controls, positions and the filters themselves are working fine
2. The switch contacts are not particularly noisy (electrically) and their movement is very smooth
3. The filters themselves are quite subtle but pleasant in nature
4. It is entirely possible to kit a Novachord out with an external audio input!
5. Its a shame the filters have fixed positions as opposed to being continuously variable!
6. It's obvious where the Novachord's trademark "nasal" quality comes from!
7. In the process of trying to find an audio output I tapped into the expression pedal which clearly works beautifully!!

Here is the snippet of mangledness I came up with:

http://www.last.fm/music/D.A.Wilson/_/E ... ?autostart

The way the front panel filter controls work is as follows. You basically have 5 filter bands, the middle three are resonant, each with 3 levels of "Q". The bottom band brings in deep bass and the top band brings in the highs. There is then a control called "Full Tone" to set the amount the filters are bypassed. In position OFF the filters are 100% in the path - in position 3 the filters are fully bypassed. There are obviously no concepts of filter envelope control or adjustable tracking - you would have to wait at least a couple of decades before that kind of thing came in!!

...that said - the filter controls have no detents and, although switched, positively invite the player to adjust them whilst playing.
Last edited by HideawayStudio on Fri Oct 30, 2009 6:51 pm, edited 1 time in total.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by Automatic Gainsay » Fri Oct 23, 2009 2:52 am

HideawayStudio wrote:5. Its a shame the filters have fixed positions as opposed to being continuously variable!
They ARE continuously variable... they just require the modulation source L. Hammond and C. Williams expected every user to possess. :wink:

HideawayStudio wrote:...positively invite the player to adjust them whilst playing.
Ah, see? You possess that modulation source. :wink:
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Re: Novachord #346 Inspection & Initial Wakeup

Post by pflosi » Fri Oct 23, 2009 3:43 am

again, it's just all about the filters...

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Re: Novachord #346 Inspection & Initial Wakeup

Post by cornutt » Fri Oct 23, 2009 7:59 am

HideawayStudio wrote: 70V DC (Grid Bias) 4mA
34V DC (Control Tube Screens) 9mA
I am very impressed by those current numbers. Obviously the tubes are all in good shape and current leakage in the circuits is quite minimal.

One question... I'm a total non-expert on tube circuits, but 70V for grid bias is rather high compared to circuits that I'm familiar with. Why does it need that much?
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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Fri Oct 23, 2009 4:12 pm

cornutt wrote:
HideawayStudio wrote: 70V DC (Grid Bias) 4mA
34V DC (Control Tube Screens) 9mA
I am very impressed by those current numbers. Obviously the tubes are all in good shape and current leakage in the circuits is quite minimal.

One question... I'm a total non-expert on tube circuits, but 70V for grid bias is rather high compared to circuits that I'm familiar with. Why does it need that much?
OK a couple of things here. Firstly, although the Novachord is awash with tubes, they are configured to run at very low quiescent currents. The divider and control circuits average around 0.2mA anode (B+) current. The total current draw on the B+ rail is less than 50mA - not bad for 144 generator and 2 preamp tubes!

The second thing to note is that all of the divider tubes are not running as linear signal amplifiers but rather non linear analog monostables. In fact the way the dividers work is quite intriguing.

A Novachord Divider and Control Circuit (One Note Shown):
fig16.jpg
Often the circuit operation of the Novachord's frequency dividers is wrongly explained on the net. Strictly speaking, the Novachord doesn't divide the frequencies at all but in fact triggers on alternate cycles and fills in the gaps to achieve, seemingly, the same result. More conventional divide down chains would use bistable circuits or possibly tuned circuits but this would result in vastly more tubes being required. It's only due to the fact that the oscillator produces a fairly repeatable waveform that the following method works at all.

Each oscillator produces a sawtooth like waveform. This waveform is notable for having a rapid rise time and significant amplitude at the start of every cycle. A quiescent anode current of around 0.2mA is setup across the 1M resistor in the cathode which opposes the -192V bias supply. This leaves a net bias of around 6 volts - this is probably more what you had in mind!

Since the oscillator waveform is AC coupled to the first divider this causes a transient waveform to appear after the first blocking capacitor at the grid. This waveform is considerably larger than the 6 volts setup on the tube and thus it triggers and goes into strong conduction. Now this is the clever bit. The tube remains in it's triggered state until the voltage on cathode and grid voltages are sufficiently small that the tube can no longer stay in conduction. The time constants of the caps in this circuit are arranged in such a way that this only happens AFTER the second leading edge of the oscillator waveform comes along and thus the tube retriggers on the third rising edge. Each time the tube triggers and finally resets the output waveform of the circuit triggers another RC network to essentially fill in the gaps between trigger points thus creating a waveform of half the frequency of the input waveform. The new waveform is then passed onto the next divider and pulse skipped to give the octave below. This process continues all the way down to the bottom octave for each like note.

The Divider Operation (Service Manual)
DividerOperation.jpg
The major drawback with this form of frequency generation is that it's very reliant on all the R's and C's being of the right value otherwise the monostables will either trigger on every waveform thus producing the same octave as the one above or trigger on every fourth waveform thus producing two octaves lower than the above one. This is really where 90% of the Novachord's bad reputation stemmed from as this resulted in much reliance on very many specific values of capacitor. It's obviously made worse by the fact that if an octave divider plays up then all like notes in the octaves below will sound wrongly as well.

The beauty of this method of frequency generation is that it's analog in every sense of the word. Unlike almost all later organs and paraphonic synths each divider never triggers quite in the same place and thus the waveforms are wonderfully distorted both in symmetry and amplitude.

Incidentally I have a strong suspicion that Hammond and Williams got the idea of using monostables as dividers from early oscilloscope design where there is a very similar circuit (often called a Phantastron) to trigger the X-Axis time base. If you were to setup an analog scope, and feed a sawtooth waveform into one of it's Y channels and then setup the timebase to trigger and display two waveforms on the screen, on feeding the output of the X-Axis into an amplifier you will hear a tone of half the frequency of the input tone.

As you may have guessed, like most divide down synths, all of the note sources are running continuously. The envelope and keying circuits then take these note signals and gate/modulate them. The beauty is that, quite unlike the much younger ARP Omni, there is a dedicated envelope for each and every key globally controlled by the front panel and pedals. This means the Novachord is very capable of producing huge sustained ensembles with long release times with no fear of note starvation or triggering issues. This capability is very nicely demonstrated in many of Phil Cirocco's recordings on his impressive Novachord demo CD "Music of the Electron".
Last edited by HideawayStudio on Fri Oct 23, 2009 10:56 pm, edited 1 time in total.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by Sir Nose » Fri Oct 23, 2009 10:27 pm

It has been said before, but I'll state it again...

This project and it's blog/thread kick a*s!!!
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Re: Novachord #346 Inspection & Initial Wakeup

Post by Shreddie » Fri Oct 23, 2009 10:27 pm

Nice description Hideaway.

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Re: Novachord #346 Inspection & Initial Wakeup

Post by HideawayStudio » Fri Oct 23, 2009 10:41 pm

Sir Nose wrote:It has been said before, but I'll state it again...

This project and it's blog/thread kick a*s!!!
OK I'm glowing with embarrassment now.... but many thanks again for the kind comments :)

The light levels are not great in our living room but after another hour of running the heaters up I decided to put the top cover back on for a quick photo. I will take some better ones when I've some spare time.

Number #346 - Finally.. Lid in Place for a Quick Piccy
DW_Novachord_346_b.jpg
The 10 day wait for the new HT transformers is starting to feel like 10 months :? I really need to finish my rebuilt PSU chassis!

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