Thanks for the re-assurance on the board pedigree. All seems to work now on the bench (once I jumpered the 12v trigger terminals...)
Works good in my system! A couple of things I noticed.
1. Gain is too high, I use only the minimal beginning of the volume control. Other than using attenuators for the input is there a more "elegant" way of reducing the gain of one or more op-amps?
2. Balance control does not fully attenuate the muted channel when rotated all the way. I assume this is by design?
1. Gain is too high, I use only the minimal beginning of the volume control. Other than using attenuators for the input is there a more "elegant" way of reducing the gain of one or more op-amps?
2. Balance control does not fully attenuate the muted channel when rotated all the way. I assume this is by design?
Gain reduced, I changed the values of R42 and R45 from 3.3k to 1k for unity gain on A7a and A7b.
The preamp still has some gain it seems. What is the overall gain?
Could I reduce gain further by changing R21 from 2.2k to say 1k?
The preamp still has some gain it seems. What is the overall gain?
Could I reduce gain further by changing R21 from 2.2k to say 1k?
With the gain reduced as above, I get an overall gain of the preamp at just slightly over 1. Obviously I don't want to reduce the gain further. What made me think it still has too much gain is the volume control operation.
As I recall, it is spec'd as a linear taper. An audio taper may be a better choice.
As I recall, it is spec'd as a linear taper. An audio taper may be a better choice.
"As I recall, it is spec'd as a linear taper. An audio taper may be a better choice."
You don't want to use a linear tapered pot for the volume control. Doug Self designed the volume control as an 'active volume control'. Only a linear pot will work in that circuit.
You don't want to use a linear tapered pot for the volume control. Doug Self designed the volume control as an 'active volume control'. Only a linear pot will work in that circuit.
Knocked this up on QuickPanel. If anyone wants the file please just ask. Looks like it will cost about 70eur. This is 350x60 iirc but you can tweak the model yourself to suit. The scales aren't ent quite right but I got fed up messing about with them!
Hi DIY, back for more. 2 things : About the volume choice, I currently use an audio taper because I wanted it to be motor driven and couldn't find it linear. Works perfectly and remember it's just a resistance variation but logarythmic. And second I tested the devinyliser proposed by m.Self in Linear Audio - Volume 11 and found problems of matter. Works fine when both channel are driven by same signal but when signals are different or even absent in one of the 2, the signal present in one channel will also reflect on the other channel in opposite phase and a bit smaller amplitude. Meaning you could lost the stereo picture and it will cut the dynamic at the speaker since one speaker will be pushing while the other will be pulling. Has anyone experience on the devinyliser? I took great care on matching parts as stated on the book!! Aside that, it really works goods on the 5-10Hz area.
I have an extra 5k linear motorized pot. It is Bourns PRM162-K415K-502B1.
Can you share the link for a log motorized pot? As I mentioned in an earlier response this needs a log pot.
Can you share the link for a log motorized pot? As I mentioned in an earlier response this needs a log pot.
Well I bought 2 Alps 'Blue Beauty' motorized and log pot that are 20K which will give double gain at output of Doug's preamp. They're still available at HiFi Collective UK and are affordable. And the magnitude of voltage will not make pot becomes hot. There's not enough energy, no big current consumption! None of the pots on the precision preamp will get hot.
I just realized that I failed to proof read my post in #2165. Here what I intended to post ...
"You don't want to use a LOGORITHMIC tapered pot for the volume control. Doug Self designed the volume control as an 'active volume control'. Only a LINEAR tapered pot will work in that circuit.". Sorry for my error.
The Bourns PRM162-K415K-502B1 linear pot is an excellent part for those wanting to build a volume that is remote controlled. I have a version of the PCB that is designed to accept the part.
"You don't want to use a LOGORITHMIC tapered pot for the volume control. Doug Self designed the volume control as an 'active volume control'. Only a LINEAR tapered pot will work in that circuit.". Sorry for my error.
The Bourns PRM162-K415K-502B1 linear pot is an excellent part for those wanting to build a volume that is remote controlled. I have a version of the PCB that is designed to accept the part.
Has anyone ever tested to se how the front panel center frequencies compare with the actual center frequency of the output? Ditto with the DB scale
I am actually building a second preamp and it's a good test that should be ran, those frequencies response. And for the volume type, my actual preamp run with a motorized logarythmic 20K since jan.2021. I intend to use my second one for this new preamp. And for questions about the balance, the configuration is made of a non-inverting op-amp. Gain will equal (Rf/Rin) +1. So minimum gain would be +1 or 0.74dB while the maximum gain on the other channel would be 1.9 or 5.57dB with actual design. M.Self give +/-6dB which is quite that. I change it to be +/-9dB but in the end when centered both will give approx.1.13dB. And this choice from m.Self, I believe, is the high impedance at the input that's fix by the 470K and the low impedance at the output to drive the rest of the preamp.
I did not read m.Self's comment on log pot but I must admit that the response slope is different. In logarythmic, the change will mostly appear from 2/3 to maximum while in linear pot it's smoother and linear. Again my choice was to have it motorized. I just don't have time to hook a gear to a linear pot shaft with motor but believe me, it's feasible... and I must share that despite that limitation of control area, sound is incredible!
That was on my mind last night, as I'm getting into vinyl for a fun of it. Because of the manner in which the devinyliser removes unwanted rumble based on antiphase from vertical stylus movement, I think it's normal operation. Today, most music is mastered with bass panned to mono and there is no issue. Older recordings made in true stereo, or those deliberately placing instruments separate on each channel, may undergo an inversion like you mention.marc2009 said:
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Anyone using XY capacitors across the mains, and two in a Y formation to chassis ground?
Maybe we don't need mains filtering, but I do have a SMPS running on the same power bar.
What happens if a 2k or 10k pot is substituted for the usual 5k bass/treble gain pot? Not that I'm going to try it, just curious.
Maybe we don't need mains filtering, but I do have a SMPS running on the same power bar.
What happens if a 2k or 10k pot is substituted for the usual 5k bass/treble gain pot? Not that I'm going to try it, just curious.
Changing pot value will just boost or cut audio level differently. Lower pot= lower gain or cut. Higher pot = higher gain or boost. In the center they're all the same with no cut and no boost. Also going much higher could bring more noise!!
And for the devinyliser,my point of view is that if you pay expensive for let's say a moving coil that gives a channel separation of an amount of dB, well you're expecting a sound image at the cost you pay... Like I wrote before based on measurements, it does the job expected of cancellation of common sub-bass but I intend to preserve the channel separation over the remainig 20 to 20kHz and in respect with my investment. Experiencing with devinyliser was interesting but I bypass it from my PCB. It becomes a personnal choice$!
And for the devinyliser,my point of view is that if you pay expensive for let's say a moving coil that gives a channel separation of an amount of dB, well you're expecting a sound image at the cost you pay... Like I wrote before based on measurements, it does the job expected of cancellation of common sub-bass but I intend to preserve the channel separation over the remainig 20 to 20kHz and in respect with my investment. Experiencing with devinyliser was interesting but I bypass it from my PCB. It becomes a personnal choice$!