Victor Chew

You still callibrate so that the servo works less hard. To calibrate I believe, you will need to remove the opa27, then power up and get both the dc offset and balance near to zero. After that, power off and put the opa27 back in. I am not sure if the servo will be able to correct a dc offset that is way off.

As far as I am aware, it responds to dc voltage errors and corrects them when the signal is inputted. Its a more accurate way of correcting the dc offset than shorting to ground, which is an unatural way, and not in use this way during normal use. Technically speaking, with the dc at zero all the time, it should therefore, make the sound better.

Looks to me like, the new additions are feedback and a servo. Additional parts should be for both these items. You should be able to get the parts from Mouser. I believe the jumper is to give you the option to use the servo or not. You can choose either local or global feedback. The terminators give you the opportunity to try out both.

Nice idea for the local and global feedback choice. Are there any sockets that can be used for the acitive parts so that when things blow its just a matter of unplugging and replacing? And perhaps aslo for higher current choices as well.

Enrique, your KGSShv came up for sale in the other forum 2 days ago. Not sure if its sold yet.

Ok. Thought it was some kind of acostic paper. Apologies.

Congratulations and awsome Enrique. Glad that the build on this amp was less stressful.. What is the white sheet at the bottom of the amp? Is it supposed to make it sound better? I too found the offboard tends to swing the balance and offset more than the onboard.

Congratulations. Nice build. What is the issue with the alpha pot?

Congratulations on the project completion Wachara! Nice neat and compact. My off board is near completion. It has been a hard build. Lining up the sand to the head sinks has been difficult and not to mention the earlier psu problems. DC offset and balance are ok. Still need to wire and doll it up.

Awsome Kerry. What level of performance did you built it to achieve? Just got my PSU for my off board working. Took me 3 attempts to get it going. In the first attempt, negative channel saw flying silicon due to fake Mosfet. Ixys10m90s and FPQF8n80c spouted silicon and also killed the 2n3904, 24v zener. After repair, blew it again when I inserted the LT1021 the other way round melting the whole zener string taking out the 2n3904s and 24v zener. Reapir done and its been on for the last hour and no explosions so far. Thanks to Kerry for pointng out that the 2n3904 also had to be changed. Positive rail is +ve502v and negative at -ve500v.

Congratulations!

SumR.

Kevin said that once you add the 1k resistors the current limit transistors won't blow up. So I guess the transistors in questions can be populated. I am halfway through my build. Faced some problems with the bom and had to reorder parts unfortunately.

What is the hv voltage you intend to use to feed the output tubes? Assuming you are using output trans, what ratio would you be using?

I have always loved the sound from the 300Bs. With an external transformer box it didn't sound quite as clear (Border patrol pre/power with my illsions); but there is to still something about it that encapsulates me even after it was sold.

Thanks alot pars.

Mouser is out of 2n3904. The order page suggests replacement with http://sg.mouser.com/search/ProductDetail.aspx?R=863-2N4401G Has anyone tried it yet? The specs are almost identical except it can take higher current at 0.6A as supposed to the 0.2A.

Very Nice build Jomat. Hope the problem will be sorted out soon and you can give us an impression of the sound. Any pictures of the PSU? Did you etch the boards yourself?

Question is whether its worth the risk putting it to real work and what is the worse case scenario.

I do that as well. Gives us the flexibility to change voltages. Perhaps 115v for the US and 230v for the UK.

Good job.

I wire my amps in the same way as posted by you, which I believe is correct.

Yes, DRV134. http://sjostromaudio.com/pages/ . At unbalanced in my B22, I was not able to get the DC offset down to zero. Infact it was way off. These days, I believe you can get many other alterative devices.

Thanks alot Marc. However, there is not alot I can do to cool it apart from blowing with an external fan.

What is the output stage current draw of the Magatron?