Dynacord Amplifiers

Re: Dynacord Amplifiers

Postby rosstiger » Sat Jan 23, 2010 9:29 pm

just checked your 2-channel schematics for the twen; doesn´t change the fact that there´s no more tremolo-circuit the basic tone of the twen? anybody who did this or a similiar mod already?
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Re: Dynacord Amplifiers

Postby Snap » Sun Jan 24, 2010 5:08 am

Yes and no. No because the tremolo works like an automatic master volume control on the power amp. If you substitute the two 330K grid resistors on the 6V6 tubes for two pots (or better a dual pot) you'll have the same effect, but manually activated. The tremolo oscillator makes the volume to change automatically. That's all.

...and yes, because the new channel affects the sound even if a guitar is plugged to the Twen channel only. But this happens in any amp mixing its channels with resistive mixer like this. Virtually any old amp without true independent and fully switchable channels. Some designs are very interactive and other doesn't interact that much. The most typical example of this is the Neil Young trick I mentioned before. The basis of his sound is a Tweed Deluxe combo, an amp with hugely interactive channels. The idea is plugging the guitar to one of the channels and set the controls to get a sound. Then by actioning the volume and tone (mainly the volume) of the other channel we can get the amp to sound juicer, or even crazily distorted as it works in these Deluxes. Young uses an automation system having four electric engines moving the four pots in the amp, controlled by a four presets pedal board. This way he can go from pristine clean to his typical crazy overdrive with two steps in between in an instant at the flick of one of the four switches.

Just try this effect in any old amp with two channels. Turn the non used channel volume pot and your sound will change. Usually the sweet spot for the max gain added by the second channel is about 2 or 3 O'clock. There are amps with reversed phase channels, like the blackface Fenders with reverb or the Vox AC30 top boost, where this effect might be detrimental due to phase cancellations, but it's just a matter of taste. I don't like it, though some other guys love it, as they would love their pickups out of phase on a guitar too. Not for me. ;)

Anyone using this mod? No idea. I conceived it a while back but never told anyone. It was just an idea I wanted to try and never or put it to work. But it's nothing crazy. Sure anyone out there has an amp close to this. In fact, the Fender 5E3 Deluxe or the 1482 have essentially the same basic topology. This was the idea behind this mod.

If you want the original Twen sound unaltered just add a DPST switch to disconnect the mixer and the 1482 channel. (And don't change the 330K plate resistor on the second stage)

Oooops! I said:

If you substitute the two 330K grid resistors on the 6V6 tubes


They are two 100K resistors tied to a 200K tied to ground. This makes the tube grids to see 300K each. The 1482 has 330K resistors instead. About the same. You can leave them in place the way they are arranged, just removing the tremolo connection from them.
Last edited by Snap on Sun Jan 24, 2010 9:04 am, edited 1 time in total.
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Re: Dynacord Amplifiers

Postby rosstiger » Sun Jan 24, 2010 8:27 am

thanks for the explanations - i really wanna do it, now! i might use the then unused vibrato-DIN-jack for switching the second channel on and off.
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Re: Dynacord Amplifiers

Postby Snap » Sun Jan 24, 2010 9:10 am

i might use the hten unused vibrato-DIN for switching the second channel on or off.


Yes, you can do it this way. In my schem the DIN socket is replaced by a conventional 1/4" jack, but you can use the two current jacks, one for each channel, or just using the inputs as they are for the Twen channel and using the 1482 as a switchable booster. This is an idea I really want to try in one of my DA15s. Using the third channel as a booster.
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Re: Dynacord Amplifiers

Postby Snap » Sun Jan 24, 2010 10:49 am

Hey, Rosstiger. One more thing I remembered. The 1482 tone circuit is quite simplistic, just a pot and a cap shunting some treble to ground (check the schem). It's not too efficient and loads a fair amount of signal. A typical solution in lo-cost small amps. In my schem I used a Garnet style low loss tone control instead. Not too different from the tone control already used in the Twen. A clever approach from the Dynacord guys. The Garnet thing might need some caps value tweaking to get it fine tuned for the channel, anyway, the values I used in the schem as an starting point should work good enough.
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Re: Dynacord Amplifiers

Postby Snap » Sun Jan 24, 2010 11:29 am

This the original Garnet tone circuit just for comparison and reference.
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Re: Dynacord Amplifiers

Postby Snap » Sun Jan 24, 2010 3:43 pm

hi snap, just noticed you know the hall jazz too; a friend of mine bought one thru ebay - he´s not too happy and offered it to me


I don't know the Hall Jazz so much and i don't have an schematic, but I guess it's about the same as a regular Jazz circuit with reverb added to one of the two channels. This amp is even closer to the 1482 than the Twen. It already has the right topology with two channels but lacking the tremolo. I think that the small and too Hi-Fi speakers don't help the sound too much if pushed into distortion. This why some many Jazz amps are updated with proper guitar speakers or just used as heads to drive guitar cabs. If you have the chance plug it to a guitar cab- I guess it would like both you and your friend this way.
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Re: Dynacord Amplifiers

Postby Snap » Mon Jan 25, 2010 8:58 am

i´d love to hear an old da 15 (the one you´re ravin about)...


You should! :mrgreen:

Dynacords are just (still affordable) well built good little amps often loaded with too Hi-Fi speakers that use to work good for clean tones, but nasty if pushed. Regular guitar speakers are tailored for a non-linear response, so they use to have a narrow response with a strong upper mids peak, not too low frequency bass response in order to keep the low end tight without flabbiness, and about nothing above 5KHz. This makes a real difference specially for distorted sounds. Hi-Fi speakers put out an excess of upper harmonics making the sound piercing, harsh and shrill when pushed. Many bass players, guitar players wanting only clean sounds or very mild crunch and acoustic guitar players use to love these quite linear Hi-Fi like speakers, But they are not the way to go for anyone wanting to use some degree of distortion. A Celestion or even better (quality/price), an Eminence Governor are sure bets for these amps to make them sound as we would expect from those worldwide acclaimed guitar amps with famous brand names in front.

The Dynacord combos have this "fault". Their speakers. It's always better replacing them. But the DA15 and 16, though actually combos with a set of tiny Hi-Fi speakers onboard, might be considered just heads, or at least I consider them this way. For me, the internal speaker (with the tweeters disconnected, please!) is only an emergency speaker or a so-so home playing solution. Better forget about the stock speakers and plug it to a 2X12" guitar cab (better a 4x12") and enjoy.

The MV15 and the Miga are real tiny heads, so no speakers problem here. Just use your favorite cab and have some fun.
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Re: Dynacord Amplifiers

Postby rosstiger » Thu Jan 28, 2010 7:08 pm

I think that the small and too Hi-Fi speakers don't help the sound too much


hi snap,
should have read your advice before testing the hall jazz - at keast with the internal speaker i didn´t like it at all: the clean sound was very nasal and knd of strange, and distortion horrible was just plain horrible - like if you use an overdrive into a home-stereo. i stick to my twen at the moment.
very interesting, by the way: i had the possibility to listen to 3 different twens - an old silver one with silver panel, a silver one with black panel, and a red one. soundwise, it´s exactly this order - the silver/silver is by far the best (fortunately, that´s the one i got); don´t know how much new elcaps helped that (i replaced them, while my friend didn´t do that with his 2 twens), or if they changed the schematics along with the cosmetics, or if it´s just components tolerances (making each amp a bit different).
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Re: Dynacord Amplifiers

Postby Snap » Thu Jan 28, 2010 7:21 pm

Sure they sound different. A 20% tolerance is a lot. The more components the more variablity from amp to amp. Every component may vary a bit the sound or dynamics so in the end the amp behaviour might be quite different. All this leaving tubes, biasing and setup apart.

Also about Dynacords and some other german amps having Neokon coupling caps, they should be changed all at once. They sound good, but age pretty bad, so are very likely to be draining current. that situation results in terrible awful sound. I don't even bother to check them I just remove them all and drop some TAD mustards or Sozo as replacements as well as silver-mica caps replacing the small ceramics. This brings some new life to these amps.
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