Cheers James, all files runs OK. Also congrats and wish you enjoy that Amp and its potential as much I do. This little device makes me sure that I am never go back to Solid State. I am already have those original Dynavox schematics, but thanks anyway. The modified one with Grid Stoppers added surely will be very useful here. Nice one matey.
Oh no, good job you explaining the purpose - for me and for all people that never get that far yet 🙂
The question I have about Grid Stopper Resistors is do they affect upper frequency range somehow? I believe they not, but rather be sure.
The purpose of using 47pF Caps (I am personally recommend Charcroft Silver Mica - outstanding ones) instead of factory value 100pF in negative feedback circuit was to increase frequency range for more airy sound 😉
Oh no, good job you explaining the purpose - for me and for all people that never get that far yet 🙂
The question I have about Grid Stopper Resistors is do they affect upper frequency range somehow? I believe they not, but rather be sure.
The purpose of using 47pF Caps (I am personally recommend Charcroft Silver Mica - outstanding ones) instead of factory value 100pF in negative feedback circuit was to increase frequency range for more airy sound 😉
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Yes you are right they are a low pass filter and do limit high frequency, but they are sized that it's around 30kHz upwards, so no loss of any music signal
J
J
OK, this is it - I am getting to the most recent changes now. Sorry for it was taking a while 🙄
First change was done couple a months before Amp was broke down. It's about removing transformer cover. The result? However it was expected (as I found this tip over Internet) still was very surprising. The sound becomes more open, for me it was like dropping down the blanket off the speakers! Really worth try - I'll say 🙂
Now if the main transformer is tend to humming you have to consider pros and cons unfortunately. Mine does humming quietly, however that is very low audible - hear it only when I am sitting by the desk, next to the audio rack and doesn't bother me at all. From my listening position is completely inaudible.
OK how did the Amplifier look after? In my opinion much more serious, please take a look:
At the time I was waiting for replacement 10Ω 2W Resistors I was finally done some mods planned months ago. So I soldered small 10nF 2kV Caps by 420V Diodes to get rid of sibilants. That also makes vocals nicely smooth, which is always a good thing.
Another job was changing wiring for Tube Valve glowing for twisted ones (or more twisted if was present). Obviously for EMI reduction. Below is the most recent photo inside - new 10Ω 2W Resistors, 10nF 2kV Caps and wiring:
Final thoughts.
This cheap PP Class A Tube Valve Amplifier doesn't sound like chip component anymore. It's "grown up" inside and outside, it is now taking the music more seriously - by getting deeper inside. Expression of soundstage, resolution, background tones and clarity are really increased. Both micro- and macro dynamics (which are a good sides of this equipment already) have improved somewhat since the mods, causing pleasant creeps while listening 🙂
There is no way to produce any treble harshness, they are sweet, sparkling but away from domination. That job belongs to midrange, which is on the first place, smooth, clear and nicely presented, with loads of information provided. This area is very connected to the low frequencies, which is supported by them. I like that way of presentation with big correspondence between mid & low. That results the midrange sounds very serious - if I can say that way.
The bass in my opinion doesn't have much from EL34 reputation. Deep and very various. Oh, forgot about something very important - punctuality. You will be very surprised how easily this Unit can move, but more importantly how it can now stop bass speaker cones. I'd never expect that from cheap Tube Valve Amplifier. Partially this is thanks to Shuguang Treasure 6CA7-Z Vacuum Tubes, as they are much more confident from Chinese "No name" EL34's originally fitted there.
Was it worth to put some money there. I never thought I will ask that myself, but yes it was worth at all. I am pretty sure, that it sounds better than any EL34 based Amplifier for that money - bought and modified.
I am not going to promise that this one will stay with me forever. That may change even by the end of this month (you'll never know), but one thing I am sure - it's increased my level of expectations from Tube Valve Amplification for a lot!
First change was done couple a months before Amp was broke down. It's about removing transformer cover. The result? However it was expected (as I found this tip over Internet) still was very surprising. The sound becomes more open, for me it was like dropping down the blanket off the speakers! Really worth try - I'll say 🙂
Now if the main transformer is tend to humming you have to consider pros and cons unfortunately. Mine does humming quietly, however that is very low audible - hear it only when I am sitting by the desk, next to the audio rack and doesn't bother me at all. From my listening position is completely inaudible.
OK how did the Amplifier look after? In my opinion much more serious, please take a look:
At the time I was waiting for replacement 10Ω 2W Resistors I was finally done some mods planned months ago. So I soldered small 10nF 2kV Caps by 420V Diodes to get rid of sibilants. That also makes vocals nicely smooth, which is always a good thing.
Another job was changing wiring for Tube Valve glowing for twisted ones (or more twisted if was present). Obviously for EMI reduction. Below is the most recent photo inside - new 10Ω 2W Resistors, 10nF 2kV Caps and wiring:
Final thoughts.
This cheap PP Class A Tube Valve Amplifier doesn't sound like chip component anymore. It's "grown up" inside and outside, it is now taking the music more seriously - by getting deeper inside. Expression of soundstage, resolution, background tones and clarity are really increased. Both micro- and macro dynamics (which are a good sides of this equipment already) have improved somewhat since the mods, causing pleasant creeps while listening 🙂
There is no way to produce any treble harshness, they are sweet, sparkling but away from domination. That job belongs to midrange, which is on the first place, smooth, clear and nicely presented, with loads of information provided. This area is very connected to the low frequencies, which is supported by them. I like that way of presentation with big correspondence between mid & low. That results the midrange sounds very serious - if I can say that way.
The bass in my opinion doesn't have much from EL34 reputation. Deep and very various. Oh, forgot about something very important - punctuality. You will be very surprised how easily this Unit can move, but more importantly how it can now stop bass speaker cones. I'd never expect that from cheap Tube Valve Amplifier. Partially this is thanks to Shuguang Treasure 6CA7-Z Vacuum Tubes, as they are much more confident from Chinese "No name" EL34's originally fitted there.
Was it worth to put some money there. I never thought I will ask that myself, but yes it was worth at all. I am pretty sure, that it sounds better than any EL34 based Amplifier for that money - bought and modified.
I am not going to promise that this one will stay with me forever. That may change even by the end of this month (you'll never know), but one thing I am sure - it's increased my level of expectations from Tube Valve Amplification for a lot!
Cheers mate. Is lowering that Resistors value a bit does have any sense? I reckon with 47pF it goes up to 40kHz and love to keep that way. However I am not keen on this - I have been told about, no idea how far the freq. goes, as I don't have oscilloscope and not sure that I could even operate one lol 😀
It is just the "curiosity question" as 30kHz is not very far away from there 😉
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Morning
No worries about not posting for a bit, I haven't even got any speakers at mo as most of my stuff is stored somewhere else, so I can't even listen yet never mind mod !! I'm very excited about the amp thou after what you have said.
Couple of things - hum in transformers can be caused by DC voltage on the mains that saturates the core. This effectively reduces the 'size' of the transformer as it reduces the core efficiency. I'll look into DC blocking caps for the mains, I am planning on fitting an IEC socket somewhere down the line that has RFI/EMI filters fitted.
The negative feedback capacitor/resistor is not connected to the 'miller' capacitance issue. The 'miller' capacitance is unseen, it is inside the valve. The resistor at 1k Ohm is normal size for these valves both Menno van der veen and the late great Allan Wright (RIP) both used this value in their amp's. It's use when fitted close to the valve socket is to stop oscillation at around 200k-300kHz it won't effect audio, the 30kHz I said earlier is just roughly where the filter starts to become effective.
J
No worries about not posting for a bit, I haven't even got any speakers at mo as most of my stuff is stored somewhere else, so I can't even listen yet never mind mod !! I'm very excited about the amp thou after what you have said.
Couple of things - hum in transformers can be caused by DC voltage on the mains that saturates the core. This effectively reduces the 'size' of the transformer as it reduces the core efficiency. I'll look into DC blocking caps for the mains, I am planning on fitting an IEC socket somewhere down the line that has RFI/EMI filters fitted.
The negative feedback capacitor/resistor is not connected to the 'miller' capacitance issue. The 'miller' capacitance is unseen, it is inside the valve. The resistor at 1k Ohm is normal size for these valves both Menno van der veen and the late great Allan Wright (RIP) both used this value in their amp's. It's use when fitted close to the valve socket is to stop oscillation at around 200k-300kHz it won't effect audio, the 30kHz I said earlier is just roughly where the filter starts to become effective.
J
Oh, I do worry, as I know haw to be without the music when need 😀
But at least you've got the motivation to gather everything to one place and start having good time 🙂
I would say that's the transformer quality rather than DC in mains in my case, as there is no change between plugging straight to mains and to the mains conditioner. But like I said before that hum is very quiet and the low speed fans in my PC on the other side of the desk are more audible - and still quiet anyway 🙂
Sound, thanks for explanation mate. I will add 1k 2W to de basket on next shopping at hificollective, which is soon 😉
But at least you've got the motivation to gather everything to one place and start having good time 🙂
I would say that's the transformer quality rather than DC in mains in my case, as there is no change between plugging straight to mains and to the mains conditioner. But like I said before that hum is very quiet and the low speed fans in my PC on the other side of the desk are more audible - and still quiet anyway 🙂
Sound, thanks for explanation mate. I will add 1k 2W to de basket on next shopping at hificollective, which is soon 😉
Thanks for the info as I didn’t know what they’re for. I’ll have to see how straightforward it is to add these components.
Minty, I don't know what you figured so far with their placement, but I think about permanent change - track cutting in the right place and insert resistor above that place...
1k 2W Resistors should be on my way from tomorrow 😉
If the benefits are that good as James mentioned I don't see the reason for saving the "return to stock" option 🙂
1k 2W Resistors should be on my way from tomorrow 😉
If the benefits are that good as James mentioned I don't see the reason for saving the "return to stock" option 🙂
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I've skip mentioning testing stage, just get straight to "after satisfactory results" mate 😉
Just don't want to build a bridge from part to part to avoid the track 🙂
Just don't want to build a bridge from part to part to avoid the track 🙂
Hi mintymiller,
Yes, it is done now. There's no negative side effects - I am not discover anything added to the Amp's signature and also I didn't found any affection to the "airy sound", no change at all. Which is very good 🙂
That mod is now left for permanent, with tracks cut - so there is no circuit hanging "in the air", means no temporary tracks & risky soldering inside. This is how it looks inside now:
Other changes can be seen above - I've swapped Anode Resistors for 200R 5W Kiwame Resistors. I have feeling that opens the sound a bit, especially in midrange area.
I've also put back input Caps. The reason is that my DAC had really crap electrolytic ones in output, with not much space for any decent replacement. So I was made the decision to remove them from there, and put some decent ones in Amplifier - where is much more space for improvement. I used 0.1uF Miflex Copper Foil Capacitors (KPCU range).
Anyway, there is no other mods planned with this one currently, as I am really enjoying the big sound from this little unit. Currently I am preparing hi-fi equipment to accommodate different Tube Valve Amplifier, which is already with me - Class A SET on 6C33C Valves.
On the end of the day there will be only one left here with me. My only concern is the question of cooperation with my speakers. Sensitivity of my speakers is only 88dB, and my DAC have quite low output. Soon I'll grab a preamp, which should helps. How much in the fact? Don't know yet. Once I sort those things out I've made comparison and decide where to go 😉
Yes, it is done now. There's no negative side effects - I am not discover anything added to the Amp's signature and also I didn't found any affection to the "airy sound", no change at all. Which is very good 🙂
That mod is now left for permanent, with tracks cut - so there is no circuit hanging "in the air", means no temporary tracks & risky soldering inside. This is how it looks inside now:
Other changes can be seen above - I've swapped Anode Resistors for 200R 5W Kiwame Resistors. I have feeling that opens the sound a bit, especially in midrange area.
I've also put back input Caps. The reason is that my DAC had really crap electrolytic ones in output, with not much space for any decent replacement. So I was made the decision to remove them from there, and put some decent ones in Amplifier - where is much more space for improvement. I used 0.1uF Miflex Copper Foil Capacitors (KPCU range).
Anyway, there is no other mods planned with this one currently, as I am really enjoying the big sound from this little unit. Currently I am preparing hi-fi equipment to accommodate different Tube Valve Amplifier, which is already with me - Class A SET on 6C33C Valves.
On the end of the day there will be only one left here with me. My only concern is the question of cooperation with my speakers. Sensitivity of my speakers is only 88dB, and my DAC have quite low output. Soon I'll grab a preamp, which should helps. How much in the fact? Don't know yet. Once I sort those things out I've made comparison and decide where to go 😉
Hi Tommek. Interesting that you put input caps back in! I've done no mods so far, mainly because I'm quite happy with the sound the amp makes as it is. But I'm keen to modify when I have more time. I bought a pair of Mission 760 SEs recently, oststensibly for my son; but I liked them so much, I kept them attached. They are 25 years old, tiny and rated at 89dB, so quite sensitive. They go loud enough with the VR70! Anyway, perhaps I'll bring over the amp in the summer some time and you can help me out with some of the mods?! David
Just realised, that removing input caps also have more sense if volume pot is removed completely. Why? Just imagine potentiometers are made with different quality - actually most of them will give unexpected noise and crackling, audible as not unfiltered by those caps. I was lucky with Audio Note AN100K, as it is quiet, however that definitely will be changed during everyday operation.
Sensitivity of 89dB (or 88dB - like my speakers, or even 86dB of previous ones) is not a hard work for this Amp at all. I am calling this one "Volcano of Dynamics" 😀 It will run those speakers with ease, if we not trying to fill quite large rooms with loud music - definitely not to try with little monitors like those Mission's 😉
Let's talk mods.
Let me know what are planning and how deep you want to go with make-over. I can provide list of all elements used, together with sources to buy. If you also willing to engage softstart, I can get the same one I have from Poland - cost around 10 Quid + delivery.
Or might be an idea to grab your Amp and get over to me while you in Stoke next time, make a one to one comparison, which that would help you with planning and final decision?
Having this sorted I will definitely help you with - all soldering with lead promised 😀
Sensitivity of 89dB (or 88dB - like my speakers, or even 86dB of previous ones) is not a hard work for this Amp at all. I am calling this one "Volcano of Dynamics" 😀 It will run those speakers with ease, if we not trying to fill quite large rooms with loud music - definitely not to try with little monitors like those Mission's 😉
Let's talk mods.
Let me know what are planning and how deep you want to go with make-over. I can provide list of all elements used, together with sources to buy. If you also willing to engage softstart, I can get the same one I have from Poland - cost around 10 Quid + delivery.
Or might be an idea to grab your Amp and get over to me while you in Stoke next time, make a one to one comparison, which that would help you with planning and final decision?
Having this sorted I will definitely help you with - all soldering with lead promised 😀
Hi all, been following this thread with interest as I've just got me an AI VR-70E off ebay for 250 quid. The vendor said it had been professionally serviced recently and it seems so. When it arrived the first thing I did was have the base open, surprise - surprise, the right hand channel 10 ohm resistors have been replaced with new ones !
So with that checked out I was keen to give it a try. Used for playing me vinyl collection. Previous amp was a valve hi-bird, what an astounding difference this amp makes. It's had a set of quad matched KT77's plugged into it and strangely enough a pair of 6GH8A's in the first stage, but no complaints the sound is great. Running a set of Q Audio 1030's off the amp.These are 6 ohm speakers so have them connected to the 4 ohm terminals and for average sound level the volume control is only at around 25%, 50% and the next door neighbour can enjoy the music too !
Following on from the thread I have also spent a good few quid with Hifi Collective and have all the bits ready to upgrade the amp. This should resolve the one issue I have with the amp and this is a slight hint of roughness when a high pitched vocal note is played.
Ahh well, just waiting for me new de-soldering tool to arrive and then I'll see if I can tear meself away from listening to the music to trying to improve it 🙂
So with that checked out I was keen to give it a try. Used for playing me vinyl collection. Previous amp was a valve hi-bird, what an astounding difference this amp makes. It's had a set of quad matched KT77's plugged into it and strangely enough a pair of 6GH8A's in the first stage, but no complaints the sound is great. Running a set of Q Audio 1030's off the amp.These are 6 ohm speakers so have them connected to the 4 ohm terminals and for average sound level the volume control is only at around 25%, 50% and the next door neighbour can enjoy the music too !
Following on from the thread I have also spent a good few quid with Hifi Collective and have all the bits ready to upgrade the amp. This should resolve the one issue I have with the amp and this is a slight hint of roughness when a high pitched vocal note is played.
Ahh well, just waiting for me new de-soldering tool to arrive and then I'll see if I can tear meself away from listening to the music to trying to improve it 🙂
I also have a VR70E that I purchased ten years ago. I have been using it with a passive pre with a 20k impedance volume control, but because of impedance mismatch i use an inline attenuator. I have just bought a powered pre that can have its gain altered. Does anyone know what the original input impedance is for this amp ? As can been seen from the photo I had the amp rebuilt, apart from the power supply. Valve biasing no longer needed
Attachments
Just scrolled through my past emails from the chap who rebuilt the amplifier .........input impedance 220k
Old post I know but have done most of the mods as listed and very pleased with the results on the VR 70...had a buffer stage lying around.. just something that I made up a year ago . big power supply in it with cascaded transistors.. that confusion when complex passages occur seems to have been cleaned up significantly plus the slightly bloated bass that is a characteristic of this amp has also been cleaned up.. individual bass notes are effortlessly heard now. So maybe it's something that others may benefit from.. probably thou depending on which buffer stage and preamp..but again transforming. Imaging has improved as well with dynamics in the midrange benefitting. I am using Quad ESL63's so is easy to hear any changes..preamp is a NZ brand made in the 80s ...very updated tho..McLaren . Great blog this one and has been very helpful to getting to where I am with this RV-70.. excellent.
This is the buffer stage made between the pre amp and the dynavox VR70..all AliExpress and great value..had a extremely small amount of DC out...0.126 v so installed caps which didn't impact on the sound quality. Have just changed the input valves on the VR 70 to some Yugo SGH8 and am aware that this particular valve is not that reliable but this has perked up the detail and midrange definition a bit over the 6f2s so was worthwhile.. If they fail I will get the western reliable equivalents.. the 6f2s were ok and in reality the buffer stage was about 200 percent more improvement rather then the valve change..