(Really Basic) Questions on Helios Mic Pre
- Thread starter Lerok
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Help Support GroupDIY Audio Forum:
My 15C1s are positive, but I have seen the schematics you are talking about. Positive grounds on the negative version certainly have a mysterious wow factor and probably stem from the germanium amp cards that we have all heard about from Olympic.Squeaky said:
Thanks for that clarifying info on the 15C1s. I also thought it probable that the rails selection was the result of an evolution from the (famous) germanium amp cards, which are oft-quoted as sounding much more betterer.
Rocinante
Well-known member
Yes you are right they were all used in the summing stage. With my own eyes (via pics) I saw the 22113 used as the summing stage.
Rocinante
Well-known member
Have you guys ever seen the 2 x 22113 boards ? I'd be very interested in your thoughts regarding those. I'm certain I have a pic in my stuff of one, I'll look to see.
ruffrecords
Well-known member
Rocinante said:
Can you share these pic please?
Cheers
Ian
Rocinante
Well-known member
Gotta find the pics but as soon as I do I certainly well. The pics were taken by a recently acquired and proud owner of a Helios console. I had emailed him a lot of questions regarding the console in outs and various pcb's of which there is a lot of circuits and amp cards that are very specific (send return, foldback, monitor, etc,,,,) as well as the general do it all circuits like the 2128 and 22113.
I'll look for the email. The owner was an engineer and knew a ton about the console.
I'll look for the email. The owner was an engineer and knew a ton about the console.
This is probably old news, but on another forum I read an interesting post or two, from a few years ago, by a (very) divisive but apparently talented engineer who was "poking around" in Strawberry and Manor Mobile modules. He stated that both the Strawberry and Manor Mobile microphone/line equalisers contained the 2128 mic amp and 22113 line amp cards . There was also mention of the filter stage on the cards (sometimes present sometimes not). The standing current of the output stage of the 22113 was measured at about 4.5mA - 5mA.
I'd love to see some information about how the bus sum amps were configured in Helios consoles. I was thinking of using a switched gain pair of 2128s for makeup from the main 2-bus followed by a stereo fader and then 22113 line drivers into the main L-R output transformers. Possibly also using something like a pair of CMM1-7Cs before the 2128s as inter-stage transformers in a Neve style? I am considering a main L-R bus onto which drops on 16 channels, 4 returns and the output. I've been stewing on this forever and maybe in 5 or 10 years I'll know enough to actually commit to something. Never mind the grounding puzzle.
I have used my own diy 2128-22113 mic pre recently in line level mode (my version also has a 10k:10k line input transformer) and I had to add a 20dB pad at the line input, which is still probably not enough, double that might be better (more added noise there). I think the 22113 in my diy version is set for about 20dB of makeup for the eq section (too much, I think that only 16dB is required). I used a 1:2 output transformer (more gain I didn't need). The 22113-type PCBs I had made up have provision for a feedback resistor trim pot, which I can play around with to try and get the gain set where I want it. I'll also look at 1:1 output transformers. So maybe tame the gain a bit and add a 0-20-40dB switchable pad on the line input is the way forward. Or just reassess the line input. There is a fair bit to work out (at least for me) to get everything running as I want it to. Cuts into my fishing time as well. And the dog needs walking. And the kids I suppose.
This is the stereo 22122/3 pic that I found.
I'd love to see some information about how the bus sum amps were configured in Helios consoles. I was thinking of using a switched gain pair of 2128s for makeup from the main 2-bus followed by a stereo fader and then 22113 line drivers into the main L-R output transformers. Possibly also using something like a pair of CMM1-7Cs before the 2128s as inter-stage transformers in a Neve style? I am considering a main L-R bus onto which drops on 16 channels, 4 returns and the output. I've been stewing on this forever and maybe in 5 or 10 years I'll know enough to actually commit to something. Never mind the grounding puzzle.
I have used my own diy 2128-22113 mic pre recently in line level mode (my version also has a 10k:10k line input transformer) and I had to add a 20dB pad at the line input, which is still probably not enough, double that might be better (more added noise there). I think the 22113 in my diy version is set for about 20dB of makeup for the eq section (too much, I think that only 16dB is required). I used a 1:2 output transformer (more gain I didn't need). The 22113-type PCBs I had made up have provision for a feedback resistor trim pot, which I can play around with to try and get the gain set where I want it. I'll also look at 1:1 output transformers. So maybe tame the gain a bit and add a 0-20-40dB switchable pad on the line input is the way forward. Or just reassess the line input. There is a fair bit to work out (at least for me) to get everything running as I want it to. Cuts into my fishing time as well. And the dog needs walking. And the kids I suppose.
This is the stereo 22122/3 pic that I found.
Attachments
ruffrecords
Well-known member
The idea that the EQ gain make up amp is a 22113 is quite reasonable. It makes sense as it can drive plenty of pre-fader sends as well as the fader itself. The only block diagram for a type 69 channel amp I have seen just calls the two amplifiers card 1 and card 2. They could be anything.
The other big question is what type of mixing did Helios use? Was it passive like Neve or was it virtual earth? Helios started making mixers in the late 60s and the NE5534 did not appear until the about 1974 and the 741 appeared in 1969. So it is not clear to me if virtual earth mixing was used by anybody at that time.
Cheers
Ian
The other big question is what type of mixing did Helios use? Was it passive like Neve or was it virtual earth? Helios started making mixers in the late 60s and the NE5534 did not appear until the about 1974 and the 741 appeared in 1969. So it is not clear to me if virtual earth mixing was used by anybody at that time.
Cheers
Ian
ruffrecords
Well-known member
P.S. The earliest form of virtual earth mixing I know of n the UK is in the EMI TG12345 mixer.
Cheers
Ian
Cheers
Ian
When would have it been?ruffrecords said:
ruffrecords
Well-known member
The design spec was apparently drawn up in 1967 and it was delivered in time for the recording of Abbey Road by the Beatles which was released in September 1969. So presumably some time in 1969.abbey road d enfer said:
Cheers
Ian
I was at school then; the concept of opamps was relatively new. My teachers considered only their use in analog computers; anyway, audio was frowned at ("music boxes").ruffrecords said:
ruffrecords
Well-known member
abbey road d enfer said:
I had just left school and started my apprenticeship (at British Aerospace) just before going to university. Part of the apprenticeship involved spending a couple of weeks in different departments. At the time Abbey Road was released two of us were spending two weeks in the wages department, mostly filling wage packets with cash. We both knew the album by heart and we used to sing it all the way through every day. Heaven knows what the 'old folks' working in that department thought of us.
In 1970 I began university and returned to work at BAe in the summer vacation. I was working on a chopper stabilised dc amplifier using uA709 op amps. I learnt a lot about the practical operation of op amps which was good because we covered op amps the following term.Cheers
Ian
I couldn't find a schematic for TG12345, but I've found a manual that explains the design. Injection into the bus is done via voltage-to-current converters, an idea JR and I had discovered (separately) several years later ;D. These current sources where far from perfect, but were equivalent to a 6.8k resistor but loaded the bus with 27k (reducing the noise gain of the summing amp by factor 3). And the litt definitely mentions "virtual earth".
Hi,
yesterday I scanned the full tech docs I have for the Helios Musicland console so I could help in the "stay at home type 69 project" thread here:
https://groupdiy.com/index.php?topic=74779.msg948062#msg948062
I'm posting the individual docs in the Tech Docs section.
Hope it can be helpful for you and future projects
Best Regards
yesterday I scanned the full tech docs I have for the Helios Musicland console so I could help in the "stay at home type 69 project" thread here:
https://groupdiy.com/index.php?topic=74779.msg948062#msg948062
I'm posting the individual docs in the Tech Docs section.
Hope it can be helpful for you and future projects
Best Regards
Whoops said:
I wonder if you have the same docs as I do. Schematic #12 is missing in my book, it's the patchbay. There are three schematics for the power supply, and yes MMC is used as a sort of buffer amp on the subgroups.
It came with the console when I bought it. Lots of parts missing and I have been in the process of collecting parts and restoring it for seven years.
Strat96 said:
Hi,
were you the buyer of the Ebay auction?
If so Im happy you have that console
How is the restoration going on?
