I recently picked up a non-working Mission 776 preamp on Ebay. The problem was just with the power supply so I was able to get it working fairly quickly. It is an unusual preamp in that it runs off a 24V battery and has a built in recharging and trickle charging unit which turns on when you are not using the preamp. The other unsual thing about this preamp is that mine has a MC only phonopreamp. I was totally unaware that this existed but I must assume this particular version was introduced to match their 773MC cartridge line. I have tried emailing Mission/Cyrus but they have not responded. I have traced out the circuit and it uses fairly simple discrete circuitry using constant current sources for all the collector loads. The input is quad parallel NPN BJT CE amplifier that is direct coupled to a PNP CE amplifier. This output is then capacitor coupled to a differential pair which is direct coupled to a another CE amplifier. The output is then capacitor coupled. The RIAA circuit is through a feedback loop to the opposite side of the differential pair. The preamp sounds pretty good as is but I think that it can sound better with some component changes. This preamp came out at a time when capacitor sound was coming to the forefront. Noticably they have used different brands of coupling capacitors throughout and have bypassed these capacitors with smaller value film caps. From what I can see they are mainly polyester caps from Rifa. These polyester caps are also used to bypass the big electrolytic caps in the power supply flitering. Also the input coupling cap is a 220uF tantalum which aren't known to be sonically great. I don't know if I should just bypass this with a good polypropolene or replace it with a good electrolytic too. As for the polyester coupling caps I think polyprolene would be sonically better but I'm not sure what to use with the smaller bypass caps.
Hi tkwou,
No wonder I couldn't find it! I'll move this to Solid State for you.
Cyrus can still fix these on a "best effort" basis. I can as well. The information on these is contained in people's heads. No service manuals exist I don't think.
So, just use common sense. Replace the electrolytic types (age) and all tantalum types must go. Use your eye's and watch for bad solder joints due to age.
-Chris
No wonder I couldn't find it! I'll move this to Solid State for you.
Do one thing at a time. Lose those tantalums! They are terrible things. Use any new electrolytic and bypass it with film types. You can get 1 uF film types.
Cyrus can still fix these on a "best effort" basis. I can as well. The information on these is contained in people's heads. No service manuals exist I don't think.
So, just use common sense. Replace the electrolytic types (age) and all tantalum types must go. Use your eye's and watch for bad solder joints due to age.
-Chris
Thanks for your imput anatech
When I first examined the phono board and traced out the circuit I noticed the 220uF Tantalum used as the input coupling cap without any bypass. All other interstage coupling caps are bypassed. I read the original brochure for the 776/777 combo and it stressed the great pains they went through to minimize capacitor signature sound by using different brands and using bypass caps. The selection of passive component appears well thought out with 1% metal film resistors throughout. I don't know too much about that period of electronics (late 70's-early 80's). Were the tantalum caps thought to be "audiophile" caps at that time? It seem strange to me that they would have chosen the tantalum coupling cap unless they thought it sounded good.
When I first examined the phono board and traced out the circuit I noticed the 220uF Tantalum used as the input coupling cap without any bypass. All other interstage coupling caps are bypassed. I read the original brochure for the 776/777 combo and it stressed the great pains they went through to minimize capacitor signature sound by using different brands and using bypass caps. The selection of passive component appears well thought out with 1% metal film resistors throughout. I don't know too much about that period of electronics (late 70's-early 80's). Were the tantalum caps thought to be "audiophile" caps at that time? It seem strange to me that they would have chosen the tantalum coupling cap unless they thought it sounded good.
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Hi tkwou,
I consider this to be an unfortunate time in audio. Tantalums sounded better than the bad electrolytics possibly, but film caps clearly outclassed them. Time has corrected the situation.
One thing that did work in favour of tantalum caps in the position was the very low current leakage and small voltage applied across the capacitor. Tantalums fail to a direct short and this is not uncommon to see.
-Chris
Yes, they were in fashion,caused by many tweakers who didn't know anything. Manufacturers sometimes mus use parts that are thought to be good if they wish to sell product.
I consider this to be an unfortunate time in audio. Tantalums sounded better than the bad electrolytics possibly, but film caps clearly outclassed them. Time has corrected the situation.
One thing that did work in favour of tantalum caps in the position was the very low current leakage and small voltage applied across the capacitor. Tantalums fail to a direct short and this is not uncommon to see.
-Chris
Well I finally got around to working on the preamp. While I had it apart I decided to do a complete overhaul. I change the tantalum input cap to an electrolytic bypassed with a polypropolene cap and I changed all the coupling caps to polyprolene matching all the original cap values to within 2% of the original part. Surprising it didn't make that big of a difference. The most improved is the high end which is little clearer, more defined but certainly no earth shattering improvement. The power supply is a 24V battery filtered through 10000uF Elna, split into two supply lines and then separetly filtered by 2200uF Elna and bypasses by a Rifa 4.7uF polyester cap. How long are filter caps good for? This preamp is atleast 25 years old. Are the electrolytics worth changing if the preamp sounds fine?
I'm cetainly a strong proponent of regulated power supplies with any AC ps for preamps and even poweramps up to the VA stage but how much benefit is there with regulating a battery ps for a low current drawing component like a preamp especially if all the gain stages are all constant current source loaded? The circuit and battery are rated at over 30 hours constant use without any degradation according to the design specs.
Schemetic for Mission 776
Dear, I also came across with a vintage Mission 776 Preamp, and could not resist to buy it!!!. The set is not in working condition, I tried to search the net for its Schemetic and luckily found that you have it. Is there any possibility to get its Schemetic from you through the net?. Regards. h2o
Dear, I also came across with a vintage Mission 776 Preamp, and could not resist to buy it!!!. The set is not in working condition, I tried to search the net for its Schemetic and luckily found that you have it. Is there any possibility to get its Schemetic from you through the net?. Regards. h2o
Thank you for replying. The unit doesnt say any thing, the BALANCE control at the back is not installed by the manufacturer, I guess it is MC. It is made in Canada with high grade components. Probably, I only require Schemetic of the charging circuit board where two ICs made by Philips # LM319N are available, especially I need the two main transisters numbers. The present numbers are not eligible. I am in Karachi Pakistan, thank you once again. Regards.
Hi tkwou,
Do you have the schematic for the audio section there? That might answer the question on the balance control.
The newer Cyrus product mounts the headphone jack on the rear apron of the integrated amps. Seeing a control mounted on the rear panel would not surprise me in any way for a Mission / Cyrus product. There isn't anything wrong with doing that as this control will not be used much. It it's set off center, you probably want it to stay where it is.
-Chris
Do you have the schematic for the audio section there? That might answer the question on the balance control.
The newer Cyrus product mounts the headphone jack on the rear apron of the integrated amps. Seeing a control mounted on the rear panel would not surprise me in any way for a Mission / Cyrus product. There isn't anything wrong with doing that as this control will not be used much. It it's set off center, you probably want it to stay where it is.
-Chris
There was a provision for a balance control on the 776 but it was never implemented in the production models. Mine has the exact same missing balance control as does all the other 776's that I have seen. There is a mono button which ties the two channels together at the input to the high level board but no balance control.
Hi tkwou,
Well, I guess that answers that.
I do know that many Mission products were designs that evolved over time, and depending on who actually assembled the product. I'm talking individuals, rather than companies. I fire in their offices in England eliminated most of their documentation for older models, so getting a schematic that applies directly to any one model can be impossible. All you can really do is look a the document you have and regard that as a loose suggestion as to how a particular unit is wired.
Any documentation out there is important as there are no complete official records that I know of. The people at Mission only have a small amount of information available.
-Chris
Well, I guess that answers that.
I do know that many Mission products were designs that evolved over time, and depending on who actually assembled the product. I'm talking individuals, rather than companies. I fire in their offices in England eliminated most of their documentation for older models, so getting a schematic that applies directly to any one model can be impossible. All you can really do is look a the document you have and regard that as a loose suggestion as to how a particular unit is wired.
Any documentation out there is important as there are no complete official records that I know of. The people at Mission only have a small amount of information available.
-Chris
Hi tkwou,
If anything still exists, it will be spotty and incomplete at best.
I visited the factory (Cyrus Electronics) in 2004 where they pointed out one of these preamps in for service. They mentioned that it was a "best effort attempt" on their part as they didn't really have complete information or parts. All in all, a very responsible company for even attempting the service under the circumstances. I have repaired the odd unit over the years, but without service information. That would have made the job much easier.
-Chris
If anything still exists, it will be spotty and incomplete at best.
I visited the factory (Cyrus Electronics) in 2004 where they pointed out one of these preamps in for service. They mentioned that it was a "best effort attempt" on their part as they didn't really have complete information or parts. All in all, a very responsible company for even attempting the service under the circumstances. I have repaired the odd unit over the years, but without service information. That would have made the job much easier.
-Chris
Request
Dear, I have mailed you earlier requesting for schemetic of Mission 776. I attached 12Vx2 fully charged batteries with it but RED light is constantly remains on. The set does not go to PLay mode. The Diagram of indicators at the top cover is also not legible and rusty, though I tried to clean it but no success. Do I expect any help from you, please?. Regards, h2o
Dear, I have mailed you earlier requesting for schemetic of Mission 776. I attached 12Vx2 fully charged batteries with it but RED light is constantly remains on. The set does not go to PLay mode. The Diagram of indicators at the top cover is also not legible and rusty, though I tried to clean it but no success. Do I expect any help from you, please?. Regards, h2o
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