A-25 tweeter upgrade? - Page 2 - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 10th April 2014, 03:57 AM   #11
Account disabled at member's request
 
Join Date: Mar 2011
Location: Somewhere in Quebec
The caps I used is a 4.7 uf. Can someone tell me the xo point if I select the less attenuated setting, the normal setting and the highest setting? I have no clue how to calculate that.
The crossover is suppose to be at 1.5 khz, so I guess that at the ''normal'' switch setting?

Should I change the caps to suit the new tweeter?

I just paid for a pair of seas 27tffc...

Also, the woofer of the a 25 starts to roll off at 1.7khz.

Last edited by murphythecat8; 10th April 2014 at 04:13 AM.
  Reply With Quote
Old 10th April 2014, 02:16 PM   #12
system7 is offline system7  United Kingdom
diyAudio Member
 
system7's Avatar
 
Join Date: Aug 2008
murphy, first order crossovers are incredibly rough and ready. You could fiddle with them endlessly, there is no optimum solution.

Generally speaking, -3dB crossover is determined by the RC time constant. This is the product of the capacitor value and the load resistance. In the Dynaco A25, it seems to be around 4.7uF X 18 ohms.

18 ohms comes from the typical 12R series resistance and 6 ohms DC resistance of the tweeter in series.

Now I'd guess the SEAS 27TFFC is not going to be anything like as efficient as the old SEAS H-087 tweeter. So you are going to be reducing the attenuation.

You'll be using an attenuator here after the capacitor. As the overall load impedance gets smaller, the capacitor will need to get bigger. I think you'll need about 8uF with an 8 ohm attenuator which presents an 8 ohm load to the amp. How it works is hard to say. That tweeter is being driven very low IMO.

The circuit below is the basic layout. The values are to be determined.
Attached Images
File Type: png Dynaco A25.PNG (4.8 KB, 82 views)
__________________
Well, there it is! Best regards from Steve in Portsmouth, UK.
  Reply With Quote
Old 10th April 2014, 03:00 PM   #13
Account disabled at member's request
 
Join Date: Mar 2011
Location: Somewhere in Quebec
hi
the 27tffc is said to be the exact replacement for the original tweeter. Its suppose to be a drop in replacement without really changing anything...

All I want is to cross the tweeter at 1.5khz. Isnt it possible is I select the lowest setting on the tweeter position which makes the xo around 2khz?
Quote:
Originally Posted by system7 View Post
murphy, first order crossovers are incredibly rough and ready. You could fiddle with them endlessly, there is no optimum solution.

Generally speaking, -3dB crossover is determined by the RC time constant. This is the product of the capacitor value and the load resistance. In the Dynaco A25, it seems to be around 4.7uF X 18 ohms.

18 ohms comes from the typical 12R series resistance and 6 ohms DC resistance of the tweeter in series.

Now I'd guess the SEAS 27TFFC is not going to be anything like as efficient as the old SEAS H-087 tweeter. So you are going to be reducing the attenuation.

You'll be using an attenuator here after the capacitor. As the overall load impedance gets smaller, the capacitor will need to get bigger. I think you'll need about 8uF with an 8 ohm attenuator which presents an 8 ohm load to the amp. How it works is hard to say. That tweeter is being driven very low IMO.

The circuit below is the basic layout. The values are to be determined.
  Reply With Quote
Old 10th April 2014, 03:13 PM   #14
system7 is offline system7  United Kingdom
diyAudio Member
 
system7's Avatar
 
Join Date: Aug 2008
WHO says it's an exact replacement?

It's not. It's a smaller dome for one thing. But it is a modern ferrofluid design with far less Fs resonance. So it might work well enough.

It's a bit irrelevant to talk about crossover points with the sort of gentle slopes of first order filters.

But I expect 10R series with a 4.7uF might be a good start, if what you say is right.

Have a bash. Nothing will break if you don't overdrive it. And be prepared to fiddle with the values.

FWIW, I used to have a SEAS H-087 tweeter in a B&O speaker on a second order filter. Nice sound.
__________________
Well, there it is! Best regards from Steve in Portsmouth, UK.
  Reply With Quote
Old 10th April 2014, 03:30 PM   #15
Account disabled at member's request
 
Join Date: Mar 2011
Location: Somewhere in Quebec
from madisound:

Dynaco Speaker Replacements

Dynaco A25 Tweeter
The tweeter for this speaker is no longer in production and Seas recommends using their new Sonotex fabric dome, the Seas Prestige 27TFFC (H0881).
Dynaco A25 woofer
The woofer is no longer made in this frame size. A new verison of this system is now available as the Seas Prestige A26RE4 (H1411) with modern parts.




I know Gordon from audiokarma who have restored a lot of A 25 that says its the direct replacement and that its, in his experience, the best tweeter for the job because it can handle low crossover points needed with the A-25.

Last edited by murphythecat8; 10th April 2014 at 03:34 PM.
  Reply With Quote
Old 16th April 2014, 05:31 PM   #16
Account disabled at member's request
 
Join Date: Mar 2011
Location: Somewhere in Quebec
okay! Ive changed the tweeters in my dynaco a 25 and the cap for a obbligato gold 4.7 uf. Much better! It still keep the a 25 balance, but the highs are much better, more air, more details, even the bass sounds more tight and faster. they almost disappear now, the sound stage has greatly improved.The a 25 is already a decent speaker, but this mod makes this speaker pretty good.
I got the tweeters used, so for 60$, it was worth it. I thought of selling the a 25 eventually, but I wont. it will probably go in our reading/training room. no way im selling those for 200$.

ive taken measurents and the normal setting is the most flat response. if I put it at high tweeter setting, the tweeter it a bit too elevated. I have a flat response and even at 1.2 khz, im only 4-5 db down then flat back again, so its far from the end of the world.
I'm happy, its almost like a new speaker but it still has that coherancy in the midrange that we love about the A 25

thanks for everyone!
  Reply With Quote
Old 16th April 2014, 06:02 PM   #17
spind is offline spind  Canada
diyAudio Member
 
Join Date: Feb 2003
Location: Winnipeg
The tweeters were new, never used except for testing, and the $60 included shipping, so you got a steal of a deal
  Reply With Quote
Old 16th April 2014, 06:40 PM   #18
spind is offline spind  Canada
diyAudio Member
 
Join Date: Feb 2003
Location: Winnipeg
ps. Glad they worked out for you!
  Reply With Quote
Old 16th April 2014, 06:48 PM   #19
Account disabled at member's request
 
Join Date: Mar 2011
Location: Somewhere in Quebec
yeah, they are breaking in, the sound much is better then yesterday. thanks for the deal!
the a25 dont sound like boxed speaker, they almost disapear. the midrange is particularly sweet and musical and fun to hear, not the most detail, but so pleasing. and the highs are now sparkling and clean and detailed.
im happy

and im finishing my jeff bagby continuum today!
  Reply With Quote
Old 21st April 2014, 12:11 AM   #20
bonejob is offline bonejob  United States
diyAudio Member
 
Join Date: Apr 2014
Location: Madison, WI USA
Quote:
Originally Posted by murphythecat8 View Post
hi
I have a pair of vintage dynaco A-25.
I have already replced teh cap in the crossover and thought about maybe getting a better tweeter. I think the direct replacement is the seas 27tffc
The Madisound Speaker Store

anyone done this mod? Should I do it and would it be a direct replacement or I should modify the xo?
Yes, I've done this mod and I highly recommend it. The SEAS 27TFFC (H0881) is an upgrade over the OEM tweeter. Besides being a drop-in-fit replacement, it doesn't fundamentally change the tonal balance of the A-25, about which far more is right than is wrong. The end result still sounds like a Dynaco A-25, but with just a little more sparkle and detail on the high end. On the OEM, high percussion - cymbals etc. - could sound a little closed, a little papery. The new tweeter has more high-end extension (flatter response in the 12,000 Hz and higher region) - cymbals sound more open, dynamic and natural, violins and other acoustic strings have more air.

More important (at least to me), the imaging and soundstage seem much better - most likely due to superior high-frequency dispersion. With the OEM tweeter, upper midrange could display a certain closed-in boxiness on some material. But with the replacement tweeters, the boxes seem to entirely disappear. Very natural and musical presentation.

In my opinion, no major modifications of the crossover are called for. I just replaced the cap with a new high quality one of the same value from ClarityCap. I also replaced the 40-year-old resistors with new and better ones, but I kept the values the same.

In my room, the normal setting sounds best to me, and output from a calibrated microphone in my listening environment pretty much confirms that. But of course your results in your room may be different.

In sum, the upgrade was well worth the modest cost - a bargain and a half.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
CeraDome Tweeter - flat from 1200 Hz - 25 kHz otto88 Multi-Way 36 19th August 2008 03:59 AM
seas TWEETER 25 TAFN/G NEEDED Thomas Giz Swap Meet 2 20th October 2005 06:03 PM
Good tweeter for less than USD 25.00 each? tcpip Multi-Way 83 20th September 2005 02:03 PM
Tweeter upgrade ? jim Multi-Way 2 22nd November 2003 06:49 PM


New To Site? Need Help?

All times are GMT. The time now is 12:34 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2