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Modifying a Coincident Dynamo Mk1

Hello all,

Have been modifying my Coincident Dynamo Mk1 for some time and I could use a helping hand from more experienced users.

If I understood correctly, looking at the image attached the 2 Epcos 22uf/500v are the filter caps which come after the rectifier (in my case the 5AR4) and these have to take into the account the rating of the tube and capacitance limit which is 60uf?

If my ramblings prove to be true can this position be improved on with better caps and/or a slightly larger caps?

Looking at the, what I think to be the power supply cap, which is a 470uf/500v, would there be a benefit in putting a larger cap without causing other issues? For instance the Mk2 Dynamo has much bigger caps in that position but I suppose the transformers are different as well. Id be looking to get more bass and mid bass and some readings say this is the place which can yield some results.

I have done several modifications already with mixed results so if anyone is interested I can share the details but Im trying to learn more about the positions and parts and their relative role. Any ideas and suggestions are welcome.

Link to insides below.

Thanks in advance!

https://ibb.co/JqW6JDb

P.S. For some reason the picture did not want to upload via the insert photo, sorry for the link.

neverlast
noromance's avatar
noromance
9,907 posts
 

I do not have a Coincident amp but have worked on other tube amps. I would leave the rectifier caps alone. You could double the reservoir cap by adding another in parallel. Check with Israel to make sure it won’t impact the choke rating (unlikely). I would add a bypass VCap of 0.1ųF/630vdc. Also replace the green Solen coupling caps with VCaps. There are a few other electrolytic caps that could be changed to good quality film like Clarity Caps. Note that film caps need 20+ hours to lose the slight plastic coloration. Check size and clearance before ordering. Do it in stages.

neverlast OP
15 posts
 

@noromance, thanks for the suggestions! At the time being I have the power supply cap bypassed with a polypropylene Solen 4,7uF and small 0,1uf PPE Solen on top of it. This was a good change but it does not increase the reservoir by much.  After reaching out to Israel on the matter his reply was that he does not recommend any other modifications and I have the feeling that he does not want to get into it, which is understandable. Heard excellent things on the VCap but the prices are a bit too dear for my current budget and also taking into account the value of the amp being modified. What I did do was use a pair of Mundor Supreme caps instead of the Solens with great results.

imhififan's avatar
imhififan
2,211 posts
 

I would leave the rectifier caps alone.

+1.

To improve sound quality, my suggestion is change the volume control pot to a stepped attenuator like a Gold point, Khozmo or even a Eizz from Aliexpress.

 

neverlast OP
15 posts
 

Regarding the volume control, I had the chance to hear it can have a dramatic effect in the amp. I have read about these attenuators and they get good reviews the only problem is they are either very expensive or too large to fit, or both. Does anyone have any experience with the Audio Note basic 100k pot or TKD pots?

imhififan's avatar
imhififan
2,211 posts
 

No experience with Audio Note basic pot, TKD is good but expensive. If you are not using the volume control and always set it to maximum, my suggestion is to use a resistor to ground instead of the volume control potentiometer.

 

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