[legopart]

Hi Legopart,

This is a web page http://muamp.com/uAmp-energiser.html that I wrote a while back. The info' has has been published on Head-Fi by me in the past. At the bottom of the web page, it shows two different ccts for bias from the mains, I prefer the second one as it has fewer components, although the first one allows you to adjust the bias voltage to what ever you want by changing the potential divider resistors to different values . Both have mains isolation transformers but still need you to be electrically competent.

http://muamp.com/images/MuampPhotos/uAmp-energiser/BiasII.JPG
about the last one,
What the size of the elements that requires?
- What diodes (IN4007 1A 1000V) and capacitors (uF and Voltage) to use?
- How much Watt acceptance use for the Resistors ?

 

[bui501-tech]

So do you suggest not to mess with the SRD-7 ?
Or can I buy some ready board and use it for the bias?

When I decided to go into this hobby, I started out by purchasing an old Stax SRM-1 MK-2 that I modified using procedures that have been well documented online to be able to drive pro-bias (580v boas) headphones. The version I have can drive pro-bias from one jack and the normal (230v) bias from the 2nd jack. It was noisy as hell compared to modern designs, but it was reliable and it got me started with DIY electrostatic headphones.

I’ve since moved on and built several Kevin Gilmore-designed amps, but I still have the original Stax SRM-1 mk-2 I used at the beginning to test and drive my early diy drivers.
(Legopart, PM me if you’re interested in purchasing the srm-mk2. I’m currently using it as my electrostatic headphone amp for my home computer when I’m working at my desk.)

 

[lkos98]

So do you suggest not to mess with the SRD-7 ?
Or can I buy some ready board and use it for the bias?
I renewed the solder on each of my vintage amps, as the Stax Srm-1 pro, I re-solder all the connection and test all of the Capacitors and they fine. But I still plan to recap it.
And set-off the DC voltage by this guide for SRM-1 https://www.head-fi.org/threads/stax-srm-1-mk2-re-cap.648596/

I really interested in DIY projects, and I still try to re-film/ Strech the diaphragm on some broken Stax headphones, and I want to create some electrostatic driver by myself.


I asked if it possible to create the bias voltage for SRD-7. if not then I guess that it useless for me.
I bought the SRM-1 because I found SRD-7/sb not quality enough with delays, and I found it as bad idea to buy another SRD-7 mk2 pro because it rare and have high price

I'm not familiar with SRD-7, but it appears it runs on audio transformers only and the bias is created from the mains with multiplier. It's a non-isolated multiplier, which is never a good idea as ulfar4 and muamp said. Otherwise it should be quite easy to connect a separate bias to this - the principle is the same for all types of energizers - the gnd of the bias goes to the middle point of the audio transformers (or the ground point of an amplifier) and the positive (or negative) bias wire is connected to the 2.2Mohm resistor (as per the posted by you schematic). But the bias voltage must be ISOLATED!
This is exactly how I ran my ESHs for a long time - audio transformers and separate bias. Very uncomfortable - heavy amplifier and on top, heavy energizer + a lot of wires. On the other hand it's very safe and reliable - no amp oscillations, no high voltage power supply (except for the bias), accepts heavy loads, etc.

 

[legopart]

What do you mean by ISOLATED bias?

 

[lkos98]

What do you mean by ISOLATED bias?

I'm not sure how exactly is it called, but it means it has to be isolated from the mains power socket. Meaning there should be insulation transformer usually 220x220 VAC, so there is no electrical connection between the bias circuit and your power socket.
Explanation is simple - your power socket has Live and Neutral. When you plug into the socket, you never know which is which and you may get LIVE connected to your schematics GND. Since this is usually a common ground you may get electrocuted (not even mentioning the damage to that it can do to your equipment). For example you connect your phone as audio source with a 3.5mm jack socket - L,R and GND - hence your phone chassis is now connected to the LIVE from the mains. You don't want to hold with your hand the LIVE from the mains?
https://www.quora.com/Where-and-why-are-isolation-transformers-used

 

[Ulfar4]

I have some update for my phone. I printed fully new enclosure for drivers, because I found out that the previous were little bended. For this I buy 3d printer for myself, so i can print anything anytime, which is great.

Now it is playing great more than month and half. So I am happy that I achieved this. I think that I will not modificate this headphones anymore. But I will create new one with larger diameter active area and print enclosure with PETG instead of PLA material.

 

[chinsettawong]

I have some update for my phone. I printed fully new enclosure for drivers, because I found out that the previous were little bended. For this I buy 3d printer for myself, so i can print anything anytime, which is great.

Now it is playing great more than month and half. So I am happy that I achieved this. I think that I will not modificate this headphones anymore. But I will create new one with larger diameter active area and print enclosure with PETG instead of PLA material.

Very nice! Congratulations! Look forward to seeing your new headphones.

 

[legopart]

do I have to spray the membrane from the both sides?

 

[chinsettawong]

You only need to coat one side of the diaphragm.

 

[legopart]

My last try to reglue and strach the membrane on broken STAX LAMBDA Normal

dast filters

I use some wood fram and glue the the membrane with streching it.

Unfutualy, after all tryies and unglueing its destroys and deform the shap of the parts (and the distance between the plates) so the work done very badly
Unfutualy the cable is for normal bias , and this headphones works better with pro
I unfutuatly think that the membrane touching one of the plates and it makes this headphones to function as electret, even without the bias voltage (I will try it.)
on normal bias they having some distortion on the high volume but on pro bias they not having any distortion.

they sound somehow, I think that they not so bad.

hop to build some electrostatic headphones by myself in the futur.

 

[chinsettawong]

What glue did you use for gluing the diaphragms? What glue did you use for gluing the pieces of the driver together?

 

[legopart]

Something like this one https://www.ebay.com/itm/50ML-Yello...054674?hash=item5b3c619f52:g:eL8AAOSwtYxZgsBq
I bough several years ago some "speakers glue"


For other parts I used B7000 the known glue https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=B7000&_sacat=0

 

[Ulfar4]

legopart: I think that your glues is not strong enough for mylar.

 

[legopart]

legopart: I think that your glues is not strong enough for mylar.

please inform me which glue to use next time ?

 

[Ulfar4]

legopart: I am using Pattex chemoprene extreme