Dynaco A25

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Andrew
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Dynaco A25

Unread post by Andrew »

I've decided to try a pair of these when I get back to Blighty and have picked up a tidy pair to experiment with.
Naturally, I will try these in their stock form, before deciding to do anything, but I do think the crossover can only benefit from removal of the treble switch at least.

Now I'm a complete novice when it comes to electronics, but I do want to learn. Is it possible to remove everything but the tweeter capacitor? I will probably bi-amp them when done.

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I took the circuit diagram from the web and mine should be identical to the lower circuit.

The other thing I wanted to ask was in relation to the aperiodic vent on the A25. I'd like to get rid of he fibreglass and replace it with something neater but equally effective. Would black acoustic foam do the same job?

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The A25 is something I haven't ever one across, but I am curious and they were cheap enough to dabble. Apologies in advance if I'm completely off base, but I am starting from near zero knowledge.

Anyone had or even heard a pair recently?

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Dr Bunsen Honeydew
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Re: Dynaco A25

Unread post by Dr Bunsen Honeydew »

You have the 10ohm resistor in parallel it should be in series, and it is then in series with the 2.2 ohm, so just put a 12ohm ww resistor in series with the capacitor.

My advise is seal the cabinet including the resistive grid and line the cabinet internally with glued on steel plate.

Andrew
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Re: Dynaco A25

Unread post by Andrew »

Thanks, Doc. I'll give those a try. Really looking forward to dabbling!

jammy395
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Re: Dynaco A25

Unread post by jammy395 »

Look forward to yer thoughts on them, once finished Andrew...........have fun. :clap: :dance:

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howardc1951
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Re: Dynaco A25

Unread post by howardc1951 »

If my understanding of the purpose of an aperiodic vent is correct the idea is that the filling has to slow the sound waves down thus creating an apparently larger cabinet. If by black acoustic foam you're thinking of the sort of foam they use for cabinet fronts that's designed to be acoustically transparent in which case it wouldn't work.
Be interested to hear how you get on though. Have fun!

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Dr Bunsen Honeydew
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Re: Dynaco A25

Unread post by Dr Bunsen Honeydew »

Like transmission lines it just messes up the musical timing. Simplicity is best, make a simple solid sealed cabinet with no damping. All damping is is a mechanical filter.

All I do is put my opinion and experience, he can go his own way and create his own experience. If he wants to keep the Dynaco's more original then don't block the vent.

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howardc1951
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Re: Dynaco A25

Unread post by howardc1951 »

I would have thought that unblocking the vent on an aperiodic cabinet would turn it into a reflex design.

Andrew
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Re: Dynaco A25

Unread post by Andrew »

I'll certainly have fun experimenting, but my intention is to follow the Docs advice. I was planning to try acoustically absorbent foam, rather than transparent foam, but I'd only even bother if the speaker sounded worse undamped and sealed. I've tried removing damping before and the gains in liveliness were hard to believe. The issue that spoiled the experience was cabinet resonance, but steel panels should soon put a stop to that.

I like the "simple is best" approach and I've come to believe that many unnecessary and sonically damaging complexities have stemmed from both:

A: Objectivists with oscilloscopes instead of ears.
B: Marketing ploys to differentiate a product from its rivals.

The cabinet size is similar to Snell/Audionote Ks, which I love. I have always preferred sealed enclosures too. The 10 inch bass unit is something I'm excited to try and simplifying the crossover is a manageable first step for a complete novice. I love restoring things cosmetically too, so it should be all good.

I'll be sure to share my experiences, including any rookie mistakes. I'd still be interested to hear any impressions from people who have heard these. My mate (who had a pair and loved tyem) said they just sound like music, which was what interested me.

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Dr Bunsen Honeydew
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Re: Dynaco A25

Unread post by Dr Bunsen Honeydew »

Any progress Andrew.

Andrew
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Re: Dynaco A25

Unread post by Andrew »

I got them Thursday and really can't quite grasp how different they sound to anything else I've owned or heard. The closest I can come is comparing them with Isobariks. Now, 'bariks aren't to everyone's taste and they have an unusual "wall of sound" presentation that makes them sound old fashioned to some. The Dynacos don't share this quality, but they do replicate the feeling I get from Isobariks that you aren't listening solely to electronics. It's that same feeling of physical, flesh and blood musicians that they create. They are so natural and put me at ease as soon as I put them on. So much so, that I've found it impossible to sit and evaluate them. All I can say is that I've listened to music for longer spells in the last few days than I have since the early 90s when I had the system I remember as my most musically satisfying.

That leaves me with a dilemma. Do I modify them and risk changing something that already offers so much, in search of extra gains, or do I stick with them as is. I also fly back out of the UK in a few days, which doesn't leave me very long to do much at all.

I've decided to try and have my cake and eat it. Dynacos aren't exactly expensive when they appear, so I'm hoping to pick up another pair, scouring the ads whilst in away. I'll then modify one pair and keep one pair in original condition, which should actually help with any comparisons.

I'm back here for 3 weeks on July 24th. So I'm hoping to find another pair. If it takes a bit longer, I'm ok with that. I really hadn't expected to be so disarmed by these. In fact (other than any concerns about the effect on value of more expensive speakers I've owned) I can't think of another speaker that I'd be this reluctant to tamper with. I'd expected them to sound a bit "old fashioned" and diffuse. The sort of thing that might have a bit of charm to it, but would sound really dated. How wrong I was. I've not been tempted to switch things around, so I just connected them to my Puresound amp and had no urge to change. Yesterday, to try and get a handle on their sound, I tried them with Naim amps and they still sounded just as good. Again, i didn't manage any evaluation because they drew me into the music. No matter how I try to highlight differences in order to get to grips with their sound, they just seem to have this knack of switching off my analytical senses.
I'm sorry that's all I have to offer so far. Here's a couple of pics of them, so everyone can get an idea of what they look like. Whatever I do with the internals, I will smarten them up visually. Pretty they ain't but they do have a beautiful voice and I was always a sucker for that.

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