[DBaldock9]

Oh and just an idea I had, would it be possible to replace the 100K volume pot with two fixed resistors, one for each channel?

That way I could install resistors to provide the volume level I most commonly use on the pot (about 10 o'clock) whilst adjusting it on the DAP, and hopefully gaining a big increase in sound quality as I've read in so many places that volume pots, particularly cheap ones, are great for killing sound quality. I could install a stepped-attenuator but there's really only one volume level my pot is ever set to, two fixed resistors would be far cheaper and possibly sound better.

I think most modern amps have a 10K input impedance, which is a good load for a line output, as well as for an earphone output.

 

[Bosk]

I think most modern amps have a 10K input impedance, which is a good load for a line output, as well as for an earphone output.

Does that mean I’d need to substitute the volume pot with two 10k resistors, or could I say measure the resistance of the pot when set to my typical listening position and use two resistors of that value?

sorry if that’s an awkward way of wording the question, bottom line is I’m happy to do some experimenting providing it doesn’t blow up another B4-X.

 

[DBaldock9]

Does that mean I’d need to substitute the volume pot with two 10k resistors, or could I say measure the resistance of the pot when set to my typical listening position and use two resistors of that value?

sorry if that’s an awkward way of wording the question, bottom line is I’m happy to do some experimenting providing it doesn’t blow up another B4-X. ☺

Since the Input potentiometer is isolated from the rest of the circuit with a capacitor - you can replace it with two resistors that equal the values you measure across the pot.
I guess if they're using a 100K pot, the DC input resistance (R1 + R2) = 100K.
Pin 1 (Input)
\
R1 = ?
/
Pin 2 (Wiper - to Coupling Cap and Tube Input)
\
R2 = ?
/
Pin 3 (GND)

 

[Bosk]

Since the Input potentiometer is isolated from the rest of the circuit with a capacitor - you can replace it with two resistors that equal the values you measure across the pot.
I guess if they're using a 100K pot, the DC input resistance (R1 + R2) = 100K.
Pin 1 (Input)
\
R1 = ?
/
Pin 2 (Wiper - to Coupling Cap and Tube Input)
\
R2 = ?
/
Pin 3 (GND)

Ahhhhh so the sum of the two resistors should equal the value of the pot then, thanks for that.

I might buy some cheap resistors to experiment, and if all goes well then replace them with Z-foils. I can't imagine any stepped attenuator let alone potentiometer being able to match that sound quality, and all the high-end attenuators are worth far more than the stock amp itself. Happy to make do without the convenience if it means a more pristine signal for those spectacular Tidal MQAs.

 

[Bosk]

The mod has been performed!

I wanted to test it out before buying any expensive resistors and so purchased some 8k metal film resistors from my local electronics shop. They sell mostly Chinese junk so the quality is probably bargain basement, but of the 10 I at least used the two that measured closest.

Very noticable improvement. The soundstage has opened up and feels substantially broader, imaging has also improved and detail levels have increased, yet there's less digital glare & fatigue. The amp sounds phenomonal now, my main complaint with performance was always the narrow soundstage but suddenly that's no longer an issue.

The mod does involve cutting the traces between the 3.5mm input and the potentiometer, then the traces from the potentiometer to the 2.2k input resistors, but other than that its basically soldering a resistor to two contact points - about as easy as it gets. A strongly recommended this mod as the loss of convenience is totally worth the improvement. I suspected that tiny pot was constricting the sound and its proven correct. When I replace these cheap resistors with Z-foils it should sound even better.

 

[DBaldock9]

The mod has been performed!

I wanted to test it out before buying any expensive resistors and so purchased some 8k metal film resistors from my local electronics shop. They sell mostly Chinese junk so the quality is probably bargain basement, but of the 10 I at least used the two that measured closest.

Very noticable improvement. The soundstage has opened up and feels substantially broader, imaging has also improved and detail levels have increased, yet there's less digital glare & fatigue. The amp sounds phenomonal now, my main complaint with performance was always the narrow soundstage but suddenly that's no longer an issue.

The mod does involve cutting the traces between the 3.5mm input and the potentiometer, then the traces from the potentiometer to the 2.2k input resistors, but other than that its basically soldering a resistor to two contact points - about as easy as it gets. A strongly recommended this mod as the loss of convenience is totally worth the improvement. I suspected that tiny pot was constricting the sound and its proven correct. When I replace these cheap resistors with Z-foils it should sound even better.

Why did you need to cut traces, rather than just soldering the fixed resistors to the 3 holes for each channel of the pot?

 

[Bosk]

Why did you need to cut traces, rather than just soldering the fixed resistors to the 3 holes for each channel of the pot?

The traces were already cut from the previous mod I did to replace them with silver wire. I mentioned it since unless I'm mistaken they would need to be cut if this mod were performed from scratch and the pot not removed (I've kept mine in place for now) as the signal would otherwise automatically flow through it via the traces.

Not sure if that makes sense or I'm getting confused.


On another topic, in your DIY journeys have you noticed much effect bypassing electrolytics with smaller film caps? I've done it previously and haven't noticed much change, but was thinking of doing it with all my B4-X's electrolytics.

 

[DBaldock9]

The traces were already cut from the previous mod I did to replace them with silver wire. I mentioned it since unless I'm mistaken they would need to be cut if this mod were performed from scratch and the pot not removed (I've kept mine in place for now) as the signal would otherwise automatically flow through it via the traces.

Not sure if that makes sense or I'm getting confused.


On another topic, in your DIY journeys have you noticed much effect bypassing electrolytics with smaller film caps? I've done it previously and haven't noticed much change, but was thinking of doing it with all my B4-X's electrolytics.

I thought you were removing the pot, but if you're leaving it on the board, then some traces will have to be cut.

For the capacitors - do you mean adding film caps to both the power supply bulk caps, and the series coupling caps?

 

[Bosk]

I thought you were removing the pot, but if you're leaving it on the board, then some traces will have to be cut.

For the capacitors - do you mean adding film caps to both the power supply bulk caps, and the series coupling caps?

I'm thinking of bypassing the 6x B4-X electrolytics with smaller film caps. Its a pretty common practise in DIY and I'm curious to hear your thoughts on the practise.

 

[ledzep]

Nice to see this thread still going, have I missed anything ?

 

[elvispreasley]

My "portable" setup with little bear is almost finished) Really enjoying the sound!

 

[asatiir]

My "portable" setup with little bear is almost finished) Really enjoying the sound!

That's a neat setup, could you give use a breakdown what is connected to what?

 

[DBaldock9]

My "portable" setup with little bear is almost finished) Really enjoying the sound!

Can you describe the signal path, for those of us who don't recognize the devices that you're using? Thanks!

 

[elvispreasley]

Ok, let me explain you how everything works) Tento OCUB DAC/AMP working as as DAC. Then B4x connected with ALO SCX22, serving as an AMP for Tento. Then Beaglebone Black is there for digital transporting purpose, as the best transport at all (IMHO). As the Beaglebone needs to be powered with external power source - it powers from the powerbank, located on the very bottom. Also the Beaglebone need to get the internet signal with LAN cable, so it connected to the tiniest Wi-Fi router on market - Microtik mapLite which is powering also by the powerbank. Also I'm using USB to COAX converter with galvanic isolation, which is not draining the power from the powerbank through Beaglebone like a straight USB connection (also the SQ is noticeably better with this converter).
In the end I'm getting exactly setup I love: multibit DAC with tube AMP and the oportunity to stream content with Tidal Connect and UpNP protocols, fully powered from batteries.

 

[Barndoor]

That's quite a stack.
What are the advantages of this system compared to using a small dnla capable DAP such as the Hiby R2?

Edit: just from a transport perspective - e.g. R2 - DAC - B4