Tuning-tips Dynavox VR-70e

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#1 erstellt: 27. Mai 2005, 11:36

Here are some of the (cheap and simple) modifications I did to my Dynavox VR-70E.

My general experience has been that capacitors play a big role in the overall sound. The standard capacitors in this amp are bad sounding cheap junk. That said, all the other parts also play a big role in the soundquality

1) Remove input capacitors = first capacitor of each channel after the volume poti. Replace it with a straight wire: Improvement: big! Much deeper bass and clearer sound. These caps have no function but to filter out dc from the cd-player, but the output stage of your cd-player has output caps with the same function, so they really do nothing except mess up your music!

2) Replace coupling capacitors (0.47µF) with high quality types, best are paper-in-oil (you can find them cheap if you search a little on ebay): improvement: huge: much clearer sound, deeper and more controlled basses (even with the same value replacement). There's no real use in replacing with higher values.

3) Replace decoupling capacitors with high quality types, best are paper-in-oil

4) Replace the lousy standard Chinese EL34 with =SED= El34: biggggggg improvement: terrible floppy bass is gone, sound has much more air etcetera

5) Replace the Chinese 6f2 with other type ECF82 = 6U8A. I found the standard chinese not so bad, but a little laid-back midrange. I've tried several makes of ECF82 and EI are in my opinion the best: airy, flowing sound + you can see their construction is top quality

6) Remove the lid (Haube) that covers the transformers: this opens up the sound (the cover shields them magnetically, which has certain advantages, but also results in a more 'closed' sound)

7) Replace the standard diodes (needless to say they are junk) with (Ultra) fast soft recovery diodes. I just did this an hour ago and am surprised with the result: much more airy sound and more controlles basses, music comes more in the room instead of staying in the speakers, huge authority!!!

Future modifications:
- replacing the very very crap volumepoti with a stepped attenuator with 1% tolerance RN military spec metalfilm resistors: this should give a much better imaging (I'm really not happy at all with the imaging at the moment, no pinpoint at all!!! + much clearer sound). A good quality carbon pot like Alps is also good, but imo 20k is a difficult value to find

-replacing the cheap elkos in the power supply with paper-in-oil should also be a big step forwards

-Maybe replacing all the resistors with high quality carbon types (allen bradley). I haven't disected the standard resistors yet, but am pretty sure they are cheap metalfilm type. Expected improvement: warmer, less sharp sound

- replacing all the capacitors with better quality types

My opinion about this amp is that the most expensive parts (= power transfomer and outputtransformers) are of good quality, especially considering the ridiculous price, and I like the schematic. If you spend a little time and change the components with higher quality types (what the amp comes with is really cheap junk and this literally messes up your music) you can bring it to a MUCH higher level + it's a wonderful experience to solder, replace and then hear the improvement!!!

I'm not talking about marginal differences, each of these tweaks is clearly audible for ANYONE. Try it and thank me later!!!

Don't hesitate to ask if you have any questions or if you'ld like me to mail you a copy of the schematic.
#2 erstellt: 27. Mai 2005, 13:34
Hi Simonix,

it seems that you did a great job :D, have you made some pictures of the modification steps?:)

But there ist one thing that i don't understand: Why do you prefer the EI ECF82s?:? I tested these tubes too, but i wasnt't very satisfied. I've replaced them by some Philips NOS and i would say, they sound much better than the Tubes from EI...

Okay, i must say at this point that i use JJ-Tubes in the output stage, maybe they harmonise much better with the pre stage tubes made by Philips.....whatever

There ist still one Question that I still have: Do you, or should I better say, did you have a very low hum in one speaker channels before the modification?


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#3 erstellt: 27. Mai 2005, 23:54
Hi Nils,

Sorry, no pictures, but there really isn't much to see except some bigger metallic caps and a few bigger diodes!

I had hum when I bought the amp, and still have hum now, although less. I don't think the tweaks have lessened the hum, but the difference is clearly audible when switching driver tubes, in my experience the Ei's are most silent. You could reduce hum by mounting the transformers on rubber or damping material. Also the power supply is very basic: no resistor, no choke, only 2*470µF/250v in series which makes 235µF/500V, plus the bypass cap. I have switched this cap with a paper in oil type and behold: decays and fine details are better audible (I'm starting to bore myself)! The hum doesn't really bother me and I will have to build a bigger chassis soon so will mount the trafos on rubber than. My fridge makes more noise anyway.

As for my choice of the EI's: I have compared (all nos) GE, Sylvania FAA, El Menco Jan (made by a daughter-company of Mullard), Telefunken, RCA and Motorola. Of these I clearly prefered the RCA's (I had the type with blackplate triode section). The sound was much more open and airy then with the other tubes. Then I changed to EI and heard immediate improvement - and more importantly, my girlfriend was friendly enough to confirm that (normally she's sceptical about all this audio-thing...)! Another factor, as I mentioned before, is the buildquality: I believe that a tube which looks well-built will probably also sound better, and the EIs look wonderful (ofcourse the soundtest is what really counts!). Well, it's not easy to compare (+subjective) and I can follow you when refering to the different output tubes you play.

Well, hope you try something out, and another thing I forgot to mention: be careful with those lethal voltages!!! Safest way is to measure the voltage across the two big caps and unload them with a resistor of 10k (or something, doesn't really matter) to under 20volts.

#4 erstellt: 05. Jun 2005, 14:06
Hi Simonix,
as i had a little spare time today, i opened my VR70 and adopted your 1.st tuning tip (removement of the input-caps)and replaced them with solid silver-wires.
The performance has really made a step forward, i am very happy with this little modification.

thx for that tip
In the further steps i want to replace some of the other caps.
What do you think, which of the caps i should replace first ?

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#5 erstellt: 05. Jun 2005, 15:34
Hello Azeg,

Nice to hear a second opionon about that tweak !

I'ld suggest to replace the coupling capacitors next, in my amp they were 0.47µ and I replaced them with paper-in-oil. Theoretically the value of these caps is responsible for the low-end extension, but this is allready well below the 25hz that I think will be the lowest the output transformers will go (and probably also your speakers), so what it comes down to here is quality. I think you won't miss any bass when you replace them with lower F caps (say 0.27µ) (In theory this would cut off the bass a little higher).

I can also heartilly recommend changing the diodes: this created a much more 'stable, steady' sound + amazing results in the bass-department (much tighter). I bought mine with conrad; search for 'fast recovery diode'.

If you really want to experience the difference between standard MKP and paper-in-oil caps, change the caps in your speaker filter (if you have one!) with pio only in one speaker, then hear the difference the result is amazing!!! You'll be surprised how much a standard quality MKP distorts the sound. I did find that at first the pio's sounded terribly 'slow', lifeless, but this seems to have disappeared after a while. Others report that the best way to go is to combine pio (colour, emotion of the sound) with MKP (exactness of the sound) for best results. One writer compares it with spicing you meal: a little of every spice being giving a better balance than using only a lot of pepper.

Good luck and keep us posted on the results!

[Beitrag von Simonix am 05. Jun 2005, 15:35 bearbeitet]
#6 erstellt: 04. Jul 2005, 14:48
Hi Simonix,

I´ve read your tuning tipps which I also want to introduce after changig tubes.
What I realized when measuring the amp. Values do not corespond to how the tubes work proper.The Bias Level was set ( or not set!!!) to 245 mV and 270 mV.
It would be great if you can measure power on Anode !
The Anode is powered with 420 V, this permitts 300mV (cold) and 420mV (hot).
U should set it on a good midrange which is 360 mV.

That´s also a good tweak.

#7 erstellt: 04. Jul 2005, 16:59
Hi CLutsi,
Having adjusted the correct Bias for the tubes is the premise and the first step before making changes as simonix described.

#8 erstellt: 11. Sep 2005, 13:42
I am really happy to have found this forum.I recently acquired the Dynavox VR-70E amplifier (under the name Audio Institute VR-70E ).

I will do immediately the first tweak of Simonix, to throw away the input capacitors. But I was wondering if the wire I replace the capacitors is important? Is a solid wire better than a multi stranded wire? The diameter of the wire?! Should it be insulated?

I apologize, my questions are probably below the level of the people who participate in this forum.

Thank you very much
#9 erstellt: 11. Sep 2005, 13:51

zuheyr schrieb:
But I was wondering if the wire I replace the capacitors is important? Is a solid wire better than a multi stranded wire? The diameter of the wire?! Should it be insulated?

Hi Zuheyr,

i don't think it's a good idea to replace these capacitators by wire, imagine what's happening when something is going wrong with one of the imput-tubes.......it's not only dangerous for yourself, your CDP will also be destroyed....


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#10 erstellt: 11. Sep 2005, 14:29

I recently sold my Dynavox (I found out I prefer SE) and the buyer told me he would replace the wire with input caps again, affraid to destroy his cd-player.

My electronical background is scarce, but I read on several occacions that both cd-player and amp have caps to block dc from entering the other unit. So it wouldn't do any harm to remove either (but never both!) the cd player's output caps or the amplifiers input caps.

I just took a look at a few schematics made by respected tube-amp designers (triodedick, diyparadiso, andrea ciuffoli etc.). I couldn't find one input cap on any of their schematics. Think that says enough

Keep in mind that a cap is the worst component for the signal to be passing through. In a well-designed tube-amp the signal only passes through very few components, and in most of the cases only one capacitor. The dynavox only has two capacitors in the signal-path: the useless input cap and a usefull coupling cap. I wouldn't hesitate for a moment and get the damn input caps out
#11 erstellt: 11. Sep 2005, 23:42

I also checked an Audio Note amplifier schematics and there are no input caps there. I did the Simonix tweak No 1
(with some serious help from Simonix) and the sound **DOES** improve. The improvement is in the clarity and bass (if they are seperate aspects)... It is really worthwhile. My public thanks to Simonix.

Now I will try to figure out the second best tweak.

Regards and thanks all of you,
#12 erstellt: 13. Sep 2005, 13:31

Könnte jemand das technische Englisch übersetzen? Was ist ein input capacitor? Was ist ein coupling capacitor? Was ist ein de-coupling capacitor?

#13 erstellt: 13. Sep 2005, 14:45
Capacitator -> Kondensator
input-> Eingang
coupling capacitor > Koppel Kondensator

...Letzteres sollte man besser nicht im Eingang des Dynavox überbrücken auch wenn einige Experten hier im Forum dies bereits getan haben...


#14 erstellt: 13. Sep 2005, 15:49
Und ein de-coupling capacitor wäre ein Entkopplungskondensator? Gibt es sowas?

Danke und Gruß
#15 erstellt: 13. Sep 2005, 17:32

abozny schrieb:
Und ein de-coupling capacitor wäre ein Entkopplungskondensator? Gibt es sowas?

Danke und Gruß

Ja, sowas gibt's - auch bekannt als Bypass- bzw. Abblockkondensator. Dient vornehmlich in Digitalschaltungen zur hochfrequenten Verblockung von Versorgungsspannungsleitungen.


#16 erstellt: 17. Sep 2005, 09:37
Hello Simonix!

I am so glad I have found your tips- I'm expecting my Dynavox to arrive (I've just paid for it, ebay,) and I expect it to arrive soon.

I listened to the amp for just one day (borrowed) and it was enough to go for it:) I was more than happy to hear the sound- I'd never have imagined such quality for THE price!

However, I would be greatful if you sent me a copy of the schematic (my e-mail: rpaprocki@gmail.com): I've already spoken about improving the amp with my father (who happens to know much more than me, though) and I was excited to report your priceless experience with it to him! (which means some work on the gear as soon as it arrives...)

My system now (in case you wanted to suggest some changes): NadC540, MissionM51 loudspeakers (wires replaced with 'Sextet' Straight Wire), Straight Wire 'Chorus' cables, VDH 'The First' interconnects and...HK620, for sale at the moment:)


Rafał, Poland
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#17 erstellt: 29. Sep 2006, 00:24
Eine Frage zu dem Amp:
Gibt der Netztrafo irgendwelche Geräusche von sich?
Ich meine nicht im Audio-Pfad, sondern direkt akustisch.
(Ich bin immer skeptisch, wenn ein Gerät keinen Ringkerntrafo im Netzteil hat ...)

#18 erstellt: 01. Nov 2011, 16:09
Hey there guys! Thanks for you terrific informative posts! It was great to follow this thread!
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