Cool, thanks for that. I was just a bit concerned when the voltages weren't over 10v as mentioned. Didn't think there could be too much wrong as it's doing everything right.
Still evaluating but from what I'm hearing I'd say it's added more accuracy to the music, placement is more precise and there seem to be more micro details coming through which adds a lot of nouonce to vocals ect. Hasn't really done much to the sound stage, this was already very good.
Happy so far.
Thanks to everyone for making this available.
Only minor issue is a small amount of hum, I've got 95db bass speakers and it's just audible right up close. The transformer is well away from the board so I don't think placement is an issue.
Is a toridal better than a normal"box" transformer?
Is a toridal better than a normal"box" transformer?
High left channel offset?
Just managed to get around to building the mezmerize board.
All seems ok so far, I get +10.39V and -10.13V at the DC test points on the board, with a 15v transformer.
Right channel has offset of -0.5mv
Left channel has offset of -5.3mv
Is there any way to reduce the left channel offset, or is this acceptable?
Thanks,
geoff.
Just managed to get around to building the mezmerize board.
All seems ok so far, I get +10.39V and -10.13V at the DC test points on the board, with a 15v transformer.
Right channel has offset of -0.5mv
Left channel has offset of -5.3mv
Is there any way to reduce the left channel offset, or is this acceptable?
Thanks,
geoff.
Mutually exchange places between the higher offset channel's JFET pair, maybe you will get lucky and they will reduce. Else you can't do anything more than finding a better pair to replace them or accept their now mV figure. 5mV is not the end of the world but that depends on the power amplifier too. If its DC input coupled and has high voltage gain it may amplify that to a level that is going to change its output bias somewhat. Usually its either blocked by an input capacitor in the amp or its inconsequential.
Thanks Salas,
I tried swapping the JFETs over (as per post 1945), I now get:
Left +2.8mv
Right -2.3mv
Sounds fine on test, not hooked it up to my main system yet for a proper listen.
Thanks,
geoff.
I tried swapping the JFETs over (as per post 1945), I now get:
Left +2.8mv
Right -2.3mv
Sounds fine on test, not hooked it up to my main system yet for a proper listen.
Thanks,
geoff.
Err, good question!
At the moment, it's going to be a Neurochrome Modulus-86 (lm3886 composite), but looking to build a F5-Turbo in the near future.
Thanks for the great build, I learned a lot from this!
geoff.
At the moment, it's going to be a Neurochrome Modulus-86 (lm3886 composite), but looking to build a F5-Turbo in the near future.
Thanks for the great build, I learned a lot from this!
geoff.
You are welcome. Just look to have enough voltage gain in the system for your speakers sensitivity to express alive dynamics, since a buffer preamp won't add to that, the source and the amp will contribute all signal voltage there is.
Salas, your suggestion was pure genius and showed uncanny intuition. Many thanks and take a bow. You saved me from dismantling the board. You were right I had not put in the earth link in the middle of the board! It is the old Mesmerize Black version by crt. From the beginning I somehow got the idea it was an optional connection if you got earth hum. Maybe the blue version?
Anyway the picture shows it just works now to specification and I need to try it with music.
Dropbox - Black Mes works!.JPG
Thank you
Anyway the picture shows it just works now to specification and I need to try it with music.
Dropbox - Black Mes works!.JPG
Thank you
In blue boards you may enhance those links with wire for lowest resistance, especially the long one associated with the AC rectification area, but there is copper film already underneath those two white linking lines because blue are double sided so its just optional and not that important. But the old black board is single sided so to actually make the links with wire jumpers on it is necessary.
Congratulations for completing your build and let us know your impressions with music.
Congratulations for completing your build and let us know your impressions with music.
My 2010 Black Mez DCB1 plays music
Wired up and connected. No DC protection so I have only used a 2.5in speaker from a pc tower! There is however music from R and L channels.
Next step is proper speakers, should I wait till some DC protection modules arrive? My impression is that danger occurs switching the preamp on and off, providing I make sure the power amp is off and powered down completely first I am reasonably safe?
Thank you, I have really enjoyed this project and can't wait to hear how it sounds in the full set up.
Wired up and connected. No DC protection so I have only used a 2.5in speaker from a pc tower! There is however music from R and L channels.
Next step is proper speakers, should I wait till some DC protection modules arrive? My impression is that danger occurs switching the preamp on and off, providing I make sure the power amp is off and powered down completely first I am reasonably safe?
Thank you, I have really enjoyed this project and can't wait to hear how it sounds in the full set up.
Its prudent to have DC protection relay modules on the power amp's output. Any power amp if without transformer or capacitor coupling to a speaker, i.e. the majority, can self fail at a point in its service life or due to mishandling and pass strong DC anyway. Does not even need other gear connected to it in order to do that. One of its output transistors can fail because its been not passing heat well due to imperfect mounting or getting abused by imbalance of characteristics and current hogging for instance.
If the full chain is DC coupled, long term accidents probability increases of course. A one side rail failure in any of the system's components for example. On the other hand the very low DC offset level achieved in your DCB1 won't affect anything and when the heat sinking of its PSU works well, also when taking precaution for the right power on/off order between amp and preamp, it could be safe to proceed. What level of safety measures against disaster scenarios are enough is always an individual user's decision. Ultimately nothing is 100% safe in life 🙄
If the full chain is DC coupled, long term accidents probability increases of course. A one side rail failure in any of the system's components for example. On the other hand the very low DC offset level achieved in your DCB1 won't affect anything and when the heat sinking of its PSU works well, also when taking precaution for the right power on/off order between amp and preamp, it could be safe to proceed. What level of safety measures against disaster scenarios are enough is always an individual user's decision. Ultimately nothing is 100% safe in life 🙄
Here is the DCB1 I built for a friend.
That case looks great!!!
Can you tell me what it is?
Which parts are used to make the extension of the attenuator shaft?
How is it mounted at the front panel?
How is the attenuator secured in the box?
How is it mounted at the front panel?
How is the attenuator secured in the box?
A 6mm brass rod, and a 6mm coupling.
There is a ball bearing in the front panel the rod goes though.
The pcb and attenuator are mounted on a sheet of acrylic, the attenuator is bolted in from underneath.
Is this a Khozmo kit or your own invention with ball bearing in the front panel?
I need to find a solution for the 10mm front panel I have for the BA-3 pre. The easy solution would be to just get a 3mm panel and mount the attenuator as usual.
I need to find a solution for the 10mm front panel I have for the BA-3 pre. The easy solution would be to just get a 3mm panel and mount the attenuator as usual.
My own solution, with parts from ebay.
It would work with just a hole in the front panel and a bushing of some kind, but I decided a ball bearing would work better.
Their pre amplifiers are much the same High Quality Passive Preamplifiers