Absolutely agree; it’s excellent value for money. Out of interest, what bias voltage/current have you set?
Thanks.
Hi everyone.
I have Audio Institute VR-70E, which is British model not German branded by different company. It seems to be exactly same model, as both are in the same chassis, same topology - I guess one Chinese factory made.
It doesn't to be derated, but set in Triode mode I guess. The max power will be 25Watts per channel in class A. It is very simple to do which can be seen on the photos below.
First photo is in triode mode, if you look to the right corner of PCB you will see P1 and SG1 are connected together and SG1 wire disconnected - Triode mode:
On second mode SG1 was disconnected from P1 again and the wire back on there - back to Ultra Linear mode (2x40W in class A):
On the last photo you can also see whole modification I've done so far. Together with 6CA7-Z Shuguang Treasure Black it is became a serious game changer. Imagine what would happen there with some nice (bot unfortunately way to expensive) NOS valves
Great pictures and you're absolutely right; it looks simple to convert to triode operation. I have this amp and will get round to checking for myself soon; you never know, one of the previous owners may well have done this. Have you also taken out the input capacitors? My unit certainly sounds excellent and considering I only paid £200 for it, good value for money.
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Cheers buddy!
Yes, input caps are removed, which you can see on the second pic in my post above. Still shown on the first photo - near to the middle, top of PCB, brown coloured. First, very audible change that was
I've paid £255.00 for mine. Serviced at Affordable Valve Company (maker), untouched by previous owner - still sealed at the bottom, safety cage also sealed. After Bias adjusting (slightly low on all valves) sounds pretty nice, however after all mods I've done sounds far better. Way better.
And the whole thing is all mods are safe, and very easy if someone is a bit keen with soldering iron. All done under "over the web" suggestions and supervision of another guys from some Polish Forum.
If you guys interested I can open new topic with all modifications presented
And this is how this beauty looks like today, all that innocent look gone, this is not the sleeper any more:
Going back to the mods; what is the second PCB for in the lower picture and what's been swapped over to make room for it? I am intrigued!
So you showed me yours; now here's mine! Very clean in there and looks to be wired up in UL mode with the input caps replaced by a couple of humungous looking caps! So still a bit of mystery why this amp was 'derated' to 2 x 20W and how that was done
. It can go pretty loud if I ask it to! So I might try triode mode sometime and also some of your other mods. Thanks for sharing.Attachments
"derated ?" Have you measured the power using 1000hz sine and power resistors ?
So you showed me yours; now here's mine! Very clean in there and looks to be wired up in UL mode with the input caps replaced by a couple of humungous looking caps! So still a bit of mystery why this amp was 'derated' to 2 x 20W and how that was done
Hi mintymiller, I was split your questions to be sure you got all answers neat - hope you don't mind
• bit better sound stage, position & separation of instruments in Triode;
• bit better micro- and macro dynamics in UL.
Still consider to insert switches to have both ways on demand
Their website looks quite dodgy like sites from over fifteen years behind (seems to be not updated for a while to me):
Valve Amplifiers
But this amp is still for sale by German company called Dynavox - with some upgrades (source selector in mkII) and newer versions. You can easily find them on eBay
Thanks, once I find a bit of time I will start the topic about those mods
Tried Triode somewhere between modifications - in that time I liked it. More jobs inserted there shows that the UL it isn't outstanding much to Triode - both have their good points:
• bit better sound stage, position & separation of instruments in Triode;
• bit better micro- and macro dynamics in UL.
Still consider to insert switches to have both ways on demand
350mV.
Honestly? I doubt it if they still exists or if they do - they selling any amps.
Their website looks quite dodgy like sites from over fifteen years behind (seems to be not updated for a while to me):
Valve Amplifiers
But this amp is still for sale by German company called Dynavox - with some upgrades (source selector in mkII) and newer versions. You can easily find them on eBay
Yellow small PCB is a Soft Start circuit. Preventing sudden start peak while the Amplifier is turning on. Good stuff for delicate anodes mesh. In other words - increase lifespan of valves, which is always a good thing
Why PCB has landed there I will describe in new topic, but I think the photo explains it anyway. I moved diodes of 6.3V circuit with their capacitor. Mounted after with the same screw exactly in the same place on the other side - the hole was already there
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You welcome! I see few changes - caps, pot and of course resistors in some sensitive places
So you showed me yours; now here's mine! Very clean in there and looks to be wired up in UL mode with the input caps replaced by a couple of humungous looking caps! So still a bit of mystery why this amp was 'derated' to 2 x 20W and how that was done
Now, I have some good and bad news.
The bad news is potentiometer - it's a blue Alps isn't it? I had one in this AMP and it is worse than silly, not hermetic pot originally fitted in this Amp... Bad channel balance on lowest settings, dry midrange and vocals. In my opinion of course
Not very expensive Audio Note AN-100K in that place and you'll stay shocked, I bet. Again IMHO
But the good news will make your smile back now - it is not "derated", set to Triode etc. It is running in Ultra Linear mode so it is produces his designed 2x40W. I cannot see anything on your PCB, that could affect the output power mate - so no wonder it goes loud
Not very expensive Audio Note AN-100K in that place and you'll stay shocked, I bet. Again IMHO
Actually, I've not noticed any audible degradation of the sound quality through this pot but I may change it to a better one at some point.
I cannot see anything on your PCB, that could affect the output power mate - so no wonder it goes loud
Thanks for confirming the UL wiring of my amp (as I thought). Looking forward to learning more about your mods. You're in Stoke I see; my niece and her family live there and I visit them quite a lot from Leeds. Maybe we can meet up for a pint somewhere? Judging by your handle, I think you're Polish as is my wife?!
So that's quite a bit lower than my settings (~500 mV) which I get with a setting at ~40mA. Probably valve dependent; your power valves do look a bit different to mine.
You'll do yourself a favour, I bet
Yep, not far off from Leeds down to Stoke, you are very welcome to visit me while you get to the Potteries. Not for a beer only, we can also arrange listening session with JD included for example
Just let me know on PM and we sort it out mate
Yes, I am Polish so I am saying sorry for any confusions in front, haha
Not judging, but have you consider to get rid of those Audio Note caps in input? No idea why someone spend a nice few pounds there, plus some time if best results you'll get without any there. They only filtering out DC voltage from the source, but all sources have them as well in outlet for sure - so both doing the same job. Following the rule - best caps are no caps is very simple there!
Good God, are you using this one as the fireplace in winter? You need 35mA, which that is 350mV in measure point - using multiply of 10 Ohm Resistor. If you treat your Valves with ca. 500mV (500mV / 10 Ohm = 50mA) you simply reducing their lifespan and nothing else - I suppose...
If you are using EL34 Tubes they look totally different to mine, as they are 6CA7 Valves, not EL34. 6CA7 you can find in two shapes of glass - some of them look like EL34, and others look like those ones I have - which is quite similar shape to KT88 Tubes for example
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6CA7 you can find in two shapes of glass - some of them look like EL34, and others look like those ones I have - which is quite similar shape to KT88 Tubes for example
Supposedly yours' are the 'American' BPT version of the 6CA7, while the others resemble the European EL34 as true pentodes. Are yours' made by EH?
Best regards!
HaHa! I was going by the plate voltage (I haven't actually measured it myself but based it on previous owner's reading at 450). I calculated that with 70% of 24W (typical max EL34 output) being 17, then the current I needed was 17/450 or ~38mA. Switching to voltage on my meter, 38mA reads 520mV not the expected 380mV but I'll need to check it again. Either the plate voltage is higher or my meter's rubbish! You must be running at about 65% of full output?
You'll do yourself a favour, I bet
Yep, not far off from Leeds down to Stoke, you are very welcome to visit me while you get to the Potteries. Not for a beer only, we can also arrange listening session with JD included for example
Just let me know on PM and we sort it out mate
Yes, I am Polish so I am saying sorry for any confusions in front, haha
I'd love a listening session! Not had one of those since the Harrogate HiFi show last year and many years before that. Let's fix something up when the weather's a bit better and the days a bit longer. I'll PM you about it.
No idea mate, all I know they are Chinese and how they sound for me - what else I need for happy hearing at this price
No, they aren't Electro Harmonix, Like a I wrote sometime earlier (however there's always nice to remind it) they are Shuguang Treasure 6CA7-Z Valves
All I found before and it's fair enough for me is that this Amplifier's Bias should be set at 350-360mV and that's why I am stick to that
Looked for it somewhere over the web
Looking forward to it, invitation is open!
Anyway if you like Audio Shows, there is next one in February in Bristol - which I will be there definitely
Hey guys!
I've just started new topic, where I will describe my mods of that big/little Amplifier:
My mods of Audio Institute VR-70E
Everyone welcome there!
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