dayton wright st300a matching / bias trnsformer unit

[krmaudio]

hi guys,

Has anyone got any service or user manuals for a dayton wright st300a electrostat bias matching transformer?

It has had a few "mods" done to the input wiring, i would like to know how it should be!

thanks in advance

[bear]

dunno about the input xfmr, but if these are the classic Dayton-Wrights that I recall, they had an inert gas inside the bag, and horrific piezo tweeters.

If you can lose the piezos, assuming the gas is still in the bag, and go with an external HF source, you'd be doing well, imho.

_-_-bear

[krmaudio]

hello,

Thanks for your reply, i have not seen the speakers yet,

The bias transformer matching unit looks like all the inpit circuitary
has been bypassed, im think it has been used with a low power vale amp or pre amp as an input at some point.....

thanks again

[ticknpop]

hi
In all likleyhood the input 8 or 10 ohm /700 UF R/C network was bypassed which was there to protect early solid state amplifers from low impedance loads tripping the amp's protection networks and tuning the amp off - but had it'sonic detriment and was often bypased as later amplifers could handle driving them directly. The input R/C network only affected the low frequency load seen by the amp. The XG 8's are still a fairly low impedance load in the midrange whether the input network is there or not ( bypassing the input R/C netwrok was called the Threshold mod for the ST 300 I believe ).
The ST300 schematic is fairly similiar to the IM 10 that the XG 10 mk 1 used . you can locate the IM 10 schematic in the manauls for the XG 10 mk 1 at http://www.dayton-wright.com/

This input network was bypassable by a switch in the XIM 11 interface that the final XG 10 mk 11.

Unless your amp has a delicate output stage which doesn't like a low impedance load in the low end I would leave the input network bypassed as it sounds better - it seems this has likley been done already on your ST 300.

[krmaudio]

Thanks for your info, im not that practiced with electrostatics!

the 0.15 ohm input impedance frightened me! and my power amp!

Great to have some help, i wasnt too sure what had gone on, but i thought it had been bypassed for a reason, people sometimes go mad inside amps and the like, it does my head in! so to speak!

cheers buddy

[ticknpop]

The input impedance doesn't fall to .15 ohms, but to about 2 ohms or so in the midrange. I have used Japanese recievers, tube amps, and solid state power amps to drive Dayton Wright's so don't fear your amp not being able to drive them - just don't overdrive a small amp trying to do it. Figure 50 watts from an amp with a good power supply and output stage at an absolute minimum from a nice class A power amp and 200 watts or more would be prefffered
You get better sonics from the higher powered products with good power supplies - Bryston 4Bs, Thresholds, and Krell's were good matchs at the time. Most of today's products will drive them, but again better amps will have higher output and better sonics.

Tube power amps have been good matches for electrostatics even with their output ransformer driving the step-up transformer of the elctrostsic, Mike Wright figured about 75% of the distortion in the electrostatics was from the stepup transformer ( and the Dayton Wrigth step-up transfomer (Hammond) for each channel weighs 39 pounds ) in the ST 300 interface, hence it's 110lbs total weight - no-one used bigger step ups for high tolerance to saturation . The theory exists for direct driving them as the Accousts model X did, but in practice this requires the speaker manufactruer to also design the power amplifier which generally hindered sales. Mke also worked on an error correction drive with a second power amp to over come the step transformer limitations - I still have several pairs around which I will canibalize make into a staked set of when time permits

Nelson Pass ( Pass Labs) in a recent DIY article ( ZEN 7 or so ) looked at driving the Dayton Wright ST 300 transfomer directly from a DIY project amp, despite it's limited power would probabaly drive them quite well. I am considering trying it when the speakers are up and running. Restoring and working on the Dayton Wright's is not an easy task. They were built with SF 6 gas, but can run in air with less output if the gas has leaked just watch out for the crackle and hiss of dischaging cells which mean damage over the long run.

[bentoronto]

I drove my Dayton-Wrights with a high voltage Sanders-like amp for many years. Dramatically cleaner than using an amp plus the D-W matching transformers.

I'm into elder-person decline as a listener and so currently get along OK with the matching transformers and a '70s high-power JVC receiver to drive them. But the difference is like tap water versus Brita filtered water.

[bentoronto]

PS. I can get away with using the undistinguished JVC receiver because I am driving the stock D-Ws only in the easy-to-drive middle 5 octave range, 140-3500 Hz.

[MarkSel]

Does anyone out there have the circuit diagram to modify the ST 300 interface? Also, are there any DW e stat users in the GTA who would like to share information with a new DW owner?

TIA

Mark

[bentoronto]

I'm going to start a thread to gather intelligence about the D-W speakers.