I am using a single +/-53v SMPS for my VHEX and I use a small CRC filter between the SMPS and each channel to give a little more isolation between the two channels and find that improves stereo separation tremendously. Each CRC consists of 4x9600uF caps with a 10W 0.47R resistor on each rail.
On my amps with linear PSU’s - preventing hum is best done by using two separate transformers, one for each channel. I found that paralleling two PSUs designed for dual secondaries (like in sketch above), I still had residual hum that was obvious only after both RCA inputs are connected as ground loop went through the source cable shield/gnds which are common at the source.
However, with two separate transformers (4 separate secondaries) each going through a CL60 on the primary windings, and a common ground loop breaker, I had no hum or noise at all.
The most important thing is to control all your connections between earth ground and 0v power ground and analog input ground. Don’t let any inadvertent connections on ground get made. Define them all and define them as only star connections.
It’s a tricky business.
On my amps with linear PSU’s - preventing hum is best done by using two separate transformers, one for each channel. I found that paralleling two PSUs designed for dual secondaries (like in sketch above), I still had residual hum that was obvious only after both RCA inputs are connected as ground loop went through the source cable shield/gnds which are common at the source.
However, with two separate transformers (4 separate secondaries) each going through a CL60 on the primary windings, and a common ground loop breaker, I had no hum or noise at all.
The most important thing is to control all your connections between earth ground and 0v power ground and analog input ground. Don’t let any inadvertent connections on ground get made. Define them all and define them as only star connections.
It’s a tricky business.
Using dual supplies with dual bridge rectifier per supply with a single transformer will eliminate hum also, but that can be tricky to get right as well. This only works for an amplifier with a lifted ground on the input, otherwise there may be issues with supplies returning through the wrong channel through RCA grounds.
I've never noticed or have been able to measure any improvement using a CRC supply. This might possibly improve things when using a single bridge in each power supply though.
I've never noticed or have been able to measure any improvement using a CRC supply. This might possibly improve things when using a single bridge in each power supply though.
By a lifted ground at the input you mean a balanced input or using a 10-15R resistor to ground, creating an audio ground?
I was backreading when I found this.
I wasn’t aware Albert posted it here. Here’s the completed build. The amplifier sits on a pair of stainless steel drawer handles.Attachments
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I was backreading when I found this.
Hi Rough512,
Thank you for sharing - a beautiful build! Solid PSU, nice compartment
Cheers,
Valery
Rough's build will be battling it out with other local DIYers this coming Nov. It is a HiFi Show with a special participation of a DIY Amp Shootfest organized by a local Audiophile community. Top contenders are tube builders and some hybrids.
I wish you all the luck VHex+ and Rough go for the win!
I wish you all the luck VHex+ and Rough go for the win!
Has anyone built VHEX+ tube yet? If not, I guess I'll be the g.p.
Valery, just for testing, I'm going to put the tube heater on its on circuit, with 20 second delay before rails energize. Just worried about tubes picking up noise in my tight chassis. I'm probably going to have to rotate the board up 90 degrees, the tubes sticking out of the lid.
Cheers,
Greg
Valery, just for testing, I'm going to put the tube heater on its on circuit, with 20 second delay before rails energize. Just worried about tubes picking up noise in my tight chassis. I'm probably going to have to rotate the board up 90 degrees, the tubes sticking out of the lid.
Cheers,
Greg
Hi Greg!
Some time ago Terry has tested the front-end - exactly this one - with some other OPS (mini-slew, I think) - it played nicely. 20 seconds for the filaments pre-heating is good. I don't think the tubes picking up some noise are going to be a problem, especially being placed vertically as you just mentioned.
CHeers,
Valery
VHex vSingle Lateral Retro
Dear Valery,
Using the latest Topology of current subtraction instead of Voltage subtraction, your Vsingle is ideally suitable for Retro mod. Please see the files enclosed. Is the project viable ? Can you please check the stability of my scheme? Any values to be changed ?
I am particularly interested in your comments on values of R7, R12 & C5.
--gannaji
Hello All,
A very simple front-end desidn, based on the same principle, as the first VHex front-end. The critical, most non-linear piece is a single-transistor transconductance stage at the input (Q4). All the rest is driven by the current - highly linear current conversions.
Open loop 1KHz THD is less than 0.05%, with 40db NFB it comes down to 0.0005%, showing around 0.001% in combination with VHex+ OPS (2-nd picture is showing the Fourier analysis at 50W @ 8 ohm, +/-50V rails). 2-nd and 3-rd harmonics are dominant, all the rest are significantly lower.
Simple light compensation, good stability margins.
The VAS output stage can be easily adapted to any swing (OPS rails) - just adjust the value of R16 for having around 3mA through it.
PSRR is lower than the one, shown by the balanced designs, so I recommend to use regulated +/-15V supply (or at least having the good cap multipliers).
The layout is going to be rather simple - a good exercise for somebody who'd like to try
Cheers,
Valery
Dear Valery,
Using the latest Topology of current subtraction instead of Voltage subtraction, your Vsingle is ideally suitable for Retro mod. Please see the files enclosed. Is the project viable ? Can you please check the stability of my scheme? Any values to be changed ?
I am particularly interested in your comments on values of R7, R12 & C5.
--gannaji
Attachments
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Hi Gannaji,
Sorry for delay
I like the idea of such a simple configuration
I need to redraw the schematic in multisim to be able to see the stability margins and other performance parameters - it will take some time but I plan to do it.Cheers,
Valery
Hi vzaichenko,
I saw your vSingle front-end (post #409 of this thread) and liked the idea so I experimented with it, changed it somewhat and built a nicely working prototype of 8/16 W (at 8/4 R) amplifier.
The amp is very tame and stable (capacitive load test - 3R3 || 1uF). R6/R5 sets the gain (~20dB) and D7 biases the OPs (Lateral MOSFETs) at about 200mA. TL071 holds the the output DC offset at 2mV. PSRR is not bad either - ear to the speaker detects no noise so I guess output noise is about 100uV or less.
PSU has 4 x 12Vac/200VA toroid, schottky rectifier and two 22,000 uF caps.
As for the sound, I built just one channel so I listened mono only. Nevertheless, the presentation is surprisingly pleasant, tonally coherent and clean - very enjoyable (even large orchestra) and that's why I'm reporting the build.
I won't develop it further or build the stereo version (many projects are waiting) but it's nice to know that this topology performs well.
Best regards
I saw your vSingle front-end (post #409 of this thread) and liked the idea so I experimented with it, changed it somewhat and built a nicely working prototype of 8/16 W (at 8/4 R) amplifier.
The amp is very tame and stable (capacitive load test - 3R3 || 1uF). R6/R5 sets the gain (~20dB) and D7 biases the OPs (Lateral MOSFETs) at about 200mA. TL071 holds the the output DC offset at 2mV. PSRR is not bad either - ear to the speaker detects no noise so I guess output noise is about 100uV or less.
PSU has 4 x 12Vac/200VA toroid, schottky rectifier and two 22,000 uF caps.
As for the sound, I built just one channel so I listened mono only. Nevertheless, the presentation is surprisingly pleasant, tonally coherent and clean - very enjoyable (even large orchestra) and that's why I'm reporting the build.
I won't develop it further or build the stereo version (many projects are waiting) but it's nice to know that this topology performs well.
Best regards
Attachments
Excellent work, juma.
This is one of the greatest virtues of current driven TIS. This is why VHEX+ is one of my favorite amp. Are you planning to build it with a higher supply voltage?
This is one of the greatest virtues of current driven TIS. This is why VHEX+ is one of my favorite amp. Are you planning to build it with a higher supply voltage?