Arkless Electronics
Trade: Amp design and repairs.
One may try this but I suspect it will be found a retrograde step in SQ which is why I didn't do this in the original schematic... experiment away though
A valve line pre amp for the DIY fishy
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One may try this but I suspect it will be found a retrograde step in SQ which is why I didn't do this in the original schematic... experiment away though
snowman_al
pfm Member
Well I tried the revisions Jez suggested in post #104 a couple of days ago. 47ks in place of 180ks, added 1000uF across the 220ufs and as I only had 2.2uF Orange Drop caps in my spares box, added another to each original Wimas (so 4.4uF total).
As I expected the bass to be different I went straight to some bass tracks for an initial try out. Ummm, yes there was a slight improvement, hard to put a finger on, but more control and a touch extra thump in the chest at a lower volume setting. A subtle difference though, but yes better.
So then I switched some more balanced music.
I noticed two things immediately, some of the life had gone from the presentation. Very difficult to describe, but maybe the mid range is suppressed. It could be that it is flatter, but the pleasing character the original had right from the start was somehow missing. The second was that the treble had become 'edgy'. (For example, REM's Monty got a raw deal upper strings gained a fuzzy / blurry sound and on Kyle's On a night like this the vocals and strings were really grainy/smeary when the mix becomes complicated.) So I let it play for 3 or 4 hours to see if it warmed up a bit.
The next day it still sounded the same so I went back a step at a time.
First I removed the extra 2.2uF Orange Drop caps. The treble and fuller sound of the original was restored. Clearly the output caps have a very significant effect on SQ...
Next I removed the 1000uFs and it is very difficult to say if they have any effect. I have swapped back and forth since and I'm still not sure.
I haven't gone back to the 180ks yet. It would take too long to do A / B testing. But my subjective impression is its fine.
So now I have run out of junk box bits and have ordered 2 different makes of 10uF polyprops. Fingers crossed they sound better.
Also as the lash ups are getting very untidy now and the new caps will require a change in layout, I'm going to build a 2nd chassis. And perhaps do some A / B testing.
Addictive?
As I expected the bass to be different I went straight to some bass tracks for an initial try out. Ummm, yes there was a slight improvement, hard to put a finger on, but more control and a touch extra thump in the chest at a lower volume setting. A subtle difference though, but yes better.
So then I switched some more balanced music.
I noticed two things immediately, some of the life had gone from the presentation. Very difficult to describe, but maybe the mid range is suppressed. It could be that it is flatter, but the pleasing character the original had right from the start was somehow missing. The second was that the treble had become 'edgy'. (For example, REM's Monty got a raw deal upper strings gained a fuzzy / blurry sound and on Kyle's On a night like this the vocals and strings were really grainy/smeary when the mix becomes complicated.) So I let it play for 3 or 4 hours to see if it warmed up a bit.
The next day it still sounded the same so I went back a step at a time.
First I removed the extra 2.2uF Orange Drop caps. The treble and fuller sound of the original was restored. Clearly the output caps have a very significant effect on SQ...
Next I removed the 1000uFs and it is very difficult to say if they have any effect. I have swapped back and forth since and I'm still not sure.
I haven't gone back to the 180ks yet. It would take too long to do A / B testing. But my subjective impression is its fine.
So now I have run out of junk box bits and have ordered 2 different makes of 10uF polyprops. Fingers crossed they sound better.
Also as the lash ups are getting very untidy now and the new caps will require a change in layout, I'm going to build a 2nd chassis. And perhaps do some A / B testing.
Addictive?
Arkless Electronics
Trade: Amp design and repairs.
Interesting stuff! The output cap is indeed where I expected the biggest differences and of course the negative feedback goes via this cap.
It may be worth trying a resistor of about 100R after the output cap... ie between the output of the amp and the output phono socket, feedback still comes from the end of the cap and the 100R is added to the output impedance.
It's a pity everyone seems to want it with no gain as this rules out potential for changes in sound due to the amount of feedback.
It may be worth trying a resistor of about 100R after the output cap... ie between the output of the amp and the output phono socket, feedback still comes from the end of the cap and the 100R is added to the output impedance.
It's a pity everyone seems to want it with no gain as this rules out potential for changes in sound due to the amount of feedback.
snowman_al
pfm Member
Yes!
My cheaper 10uF polies arrived this morning and I fitted them half an hour ago. That's better all round. You just know straight away.
Better bass, yes more solid and faster. Sweet mids still, yes nice, no real difference. Treble is improved, smoother is not right, but it is as if a 'grainy layer' has been removed. Also vocal siliblance is handled really nicely now. And more 3 dimensional now with greater back to front depth as well as L to R separation.
Here is lash up No. 5.
Fully valve rectification (another mains TX), 800uF of cathode bypass caps (trying better quality ones), 10uF polies, 47k resistors and 100 ohms added to the outputs.
My cheaper 10uF polies arrived this morning and I fitted them half an hour ago. That's better all round. You just know straight away.
Better bass, yes more solid and faster. Sweet mids still, yes nice, no real difference. Treble is improved, smoother is not right, but it is as if a 'grainy layer' has been removed. Also vocal siliblance is handled really nicely now. And more 3 dimensional now with greater back to front depth as well as L to R separation.
Here is lash up No. 5.
Fully valve rectification (another mains TX), 800uF of cathode bypass caps (trying better quality ones), 10uF polies, 47k resistors and 100 ohms added to the outputs.
Arkless Electronics
Trade: Amp design and repairs.
Its all gravy.Lovely mains transformer there BTW.
Arkless Electronics
Trade: Amp design and repairs.
Now we need a matching phono.
That's not going to happen.
russel
./_dazed_and_confused
Now we need a matching phono.
I have a copy of the World Audio Designs phono stage article, looks a reasonable design, not too complex, pm me if you cannot find it on the web.
Arkless Electronics
Trade: Amp design and repairs.
Not DIY but I am considering putting out a cheap MM valve or hybrid phono stage soon.. emphasis on cheap, say £400 or so. It would be kept cheap by no attempt being made to have it look nice... no writing on it (not even "Arkless Electronics" or "input, "output" etc") cheap case etc. so the money can be spent on the innards. I'll have to get some feedback on that from people as I'm expecting it to be "we don't care how good the VFM is, it has to look good"... in which case I won't be going ahead with it.
I have one of those with a number of mods ,its very good,there is a similar design in Morgan Jones as well.
russel
./_dazed_and_confused
Why don't you offer an upgrade option for the "laser etched Arkless box". Then you get a viable business model where you cater for what your customers want rather than what you think they should have.
Arkless Electronics
Trade: Amp design and repairs.
Sorry but I don't know what you are referring to... "laser etched Arkless box"??
Arkless Electronics
Trade: Amp design and repairs.
Ah right... it seemed like you were referring to some other item I already make...
No I'm intending it to be a budget unit and the cost of making it look nice is prohibitive.
No I'm intending it to be a budget unit and the cost of making it look nice is prohibitive.
Dowser
Learning to bodge again..
Lordy, I am rubbish at metalwork...but at least I have started now
Line in and out;
AC power umbilical connector;
Volume and selector (I really want to mount these at back of chassis, close to connectors, but this will have to do for a first stab, I've no idea how to extend with rods from front panel to rear of chassis reliably at this stage!);
Loads of space - rectifier over to the left, stage on the right;
Line in and out;
AC power umbilical connector;
Volume and selector (I really want to mount these at back of chassis, close to connectors, but this will have to do for a first stab, I've no idea how to extend with rods from front panel to rear of chassis reliably at this stage!);
Loads of space - rectifier over to the left, stage on the right;
Arkless Electronics
Trade: Amp design and repairs.
That's the worst of it over then.. plain sailing now
Dowser
Learning to bodge again..
That's the worst of it over then.. plain sailing now
Well, easier than metalwork anyhow
Quick question Jez - you say location of 6.3v heater 2x 22Rs to earth don't really matter - is there a technical preference? If not, I'm going to join them to the earth from the HT rectifier, and from there to the proper star ground, just to make things a bit tidier. But both options would work, I have quite a lot of space to play with;
Thanks! Richard
Arkless Electronics
Trade: Amp design and repairs.
Well, easier than metalwork anyhow
Quick question Jez - you say location of 6.3v heater 2x 22Rs to earth don't really matter - is there a technical preference? If not, I'm going to join them to the earth from the HT rectifier, and from there to the proper star ground, just to make things a bit tidier. But both options would work, I have quite a lot of space to play with;
Thanks! Richard
Their physical location doesn't matter but don't do what you're proposing with the ground no. Everything should preferably go to star ground separately and very definitely in all areas of the power supply. In the case you propose there are high (ish) current spikes from the rectifiers which will get straight on to the heaters..
You can create local star grounds for each channel at the point where the cathode resistor, cathode bypass cap and vol control connect together.
Be very wary of spoiling it by going for visual neatness and symmetry etc rather than short direct connections and good grounding practice
Dowser
Learning to bodge again..
Their physical location doesn't matter but don't do what you're proposing with the ground no. Everything should preferably go to star ground separately and very definitely in all areas of the power supply. In the case you propose there are high (ish) current spikes from the rectifiers which will get straight on to the heaters..
You can create local star grounds for each channel at the point where the cathode resistor, cathode bypass cap and vol control connect together.
Be very wary of spoiling it by going for visual neatness and symmetry etc rather than short direct connections and good grounding practice
Thanks, understood!
Arkless Electronics
Trade: Amp design and repairs.
I suggest you start another thread....