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?
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?
the weird things Ive noticed, no matter the position on the switch, theres no difference in sound. what could be the cause? i have to see if I may have put the wrong cap value when I did the recap.
As you start with 12 ohm and go up to 20 ohm in 4 steps that is a reduction of less than 3 dB in 4 steps so less than 1 dB per step that can be hard to hear.
The bigger problem with the crossover is that the croosover is a shallow 6dB octave at a very low 950 Hz with minimal attaneuation and down to 650 Hz with all resesistorns in line. So the attenuation of the tweeter is counteracted by a lowering of the crossover frequency. With no serial resistors at all the the crossover is at 2 kHz still pretty low and shallow but usable with a dome with good power handling and a fundamental resonnance that is low in Q and Fr. I have several H-87 I might measure them.
The bigger problem with the crossover is that the croosover is a shallow 6dB octave at a very low 950 Hz with minimal attaneuation and down to 650 Hz with all resesistorns in line. So the attenuation of the tweeter is counteracted by a lowering of the crossover frequency. With no serial resistors at all the the crossover is at 2 kHz still pretty low and shallow but usable with a dome with good power handling and a fundamental resonnance that is low in Q and Fr. I have several H-87 I might measure them.
The Seas I have is from two different batches or vintages so Fr is different but the pair matching is good. The Q is kind of middle value, but what happen with a singel cap in series?
Correction: 5 micro and 8 ohm is 4 kHz so the crossover with 20 ohm added in series the crossover is down to 1100 Hz and that is way to low.
Here we have a Philips dome with the same total Q value but with a lower electrical A and higher mechanical Q.
With a small cap in series. The tweeter is 6 dB down at 4 kHz and 12 dB down at 2 kHz from a 7-8 kHz crossover, textbook stuff so far. But then hell breaks loose and at a 700-100 Hz the attenuation is not 18-24 dB as it should but less than 5 dB.
Use an 8 ohm L attenuator and tune in the attenuation you want to have then if needed measure the serial and parallell resistances and replace with fixed resistors. The parallell resistor will flatten the impedence peak of the dome and improve the working conditions of the cap.
Correction: 5 micro and 8 ohm is 4 kHz so the crossover with 20 ohm added in series the crossover is down to 1100 Hz and that is way to low.
Here we have a Philips dome with the same total Q value but with a lower electrical A and higher mechanical Q.
With a small cap in series. The tweeter is 6 dB down at 4 kHz and 12 dB down at 2 kHz from a 7-8 kHz crossover, textbook stuff so far. But then hell breaks loose and at a 700-100 Hz the attenuation is not 18-24 dB as it should but less than 5 dB.
Use an 8 ohm L attenuator and tune in the attenuation you want to have then if needed measure the serial and parallell resistances and replace with fixed resistors. The parallell resistor will flatten the impedence peak of the dome and improve the working conditions of the cap.
We have had a thread recently about the updated similar SEAS A26 speaker. I do suspect that there is no exactly optimum setup with this type of low crossover speaker.
EaZy used the SEAS 27TBFC/G as a replacement for the expensive modern T35C002 unit that SEAS fit. He was pleased with the results, but changed the crossover a little. I have seen DIY versions of this crossover with 2.2R in series with 8uF, and a 10R resistor shunted across the tweeter too, which might be good.
http://www.diyaudio.com/forums/multi-way/229231-seas-a26-speaker-kit-5.html
He felt it had the right low frequency toleration needed. It doesn't look much different to the 27TFFC TBH, but is a metal dome. So, yes, I think your 27TFFC is a decent idea if that famous old SEAS H-087 tweeter is past it. Hope it helps anyway. Worst that happens is you refit the original I suppose.
EaZy used the SEAS 27TBFC/G as a replacement for the expensive modern T35C002 unit that SEAS fit. He was pleased with the results, but changed the crossover a little. I have seen DIY versions of this crossover with 2.2R in series with 8uF, and a 10R resistor shunted across the tweeter too, which might be good.
http://www.diyaudio.com/forums/multi-way/229231-seas-a26-speaker-kit-5.html
He felt it had the right low frequency toleration needed. It doesn't look much different to the 27TFFC TBH, but is a metal dome. So, yes, I think your 27TFFC is a decent idea if that famous old SEAS H-087 tweeter is past it. Hope it helps anyway. Worst that happens is you refit the original I suppose.
Last edited:
the recommended tweeter replacement by SEAS is the SEAS Prestige 27TFFC , so i will go with that.
do you think its a good idea to go with the 27tffc?
if I understand correctly, if I select the highest tweeter setting, this bypass the serial resistors and gives me 12 ohm so 2 khz crossover?
And if I select the lowest tweeter setting, the xo is at 1100 hz?
http://www.seas.no/index.php?option=com_content&view=article&id=81&Itemid=105
Ideally, with the replacement tweeter, it seems to be flat from around 1.5khz, so my best bet is to put the tweeter pot at the highest setting for a 2khz xo?
Last edited:
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.
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:
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.
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.
Attachments
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?
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?
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.
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.
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.
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.
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:
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!
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!
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!
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!
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.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.