Bushmaster MKI & MKII Venom-4 ultimate headphone mod

[StanleyB]

I have been promising to put this mod up for some time now, and many people have emailed me to ask if I can get it up quickly. So here it is. This mod and the V3 mod are both suitable for the MKI and MKII. Just that some part numbers on the PCBs are different. If anyone needs a cross reference let me know and I shall put one up.

For the MKI the part numbers to note are:
R31 - R41
MEC2 - MEC4
R32 - R42

http://www.homehifi.co.uk/images/mods/7530/hp_org.jpg

This mod changes the gain for different types of headphones impedance.
For 32 to100 Ohms headphones, R32/R42 can be about 10K to 12K. The larger value means it will be louder.
For 300 Ohms headphones, you can use 15K or 18K. For larger 300 drivers (like the HD800), you can even go up to 22K

MEC2/MEC4/R32/R42 changes the frequency feedback gain. For deep bass ( recommended for bass light headphones and people who want deeeeep bass) use 22nF for MEC2/MEC4.
R32/R42 should be 22K.
If you want to maintain the bass level as stock, then MEC2/MEC4 = 33nF. And R32/R42 is 33K.
Caps are WIMA 2.5mm leg spacing type.
Resistors are 0.25 or 0.5 Watt.

http://www.homehifi.co.uk/images/mods/7530/hp_mod.jpg


When soldering in the new components, I recommend that you solder in the capacitor last. That way you reduce the chance of burning the case of the capacitors.

[RAZRr1275]

So basically this sort of thing changes components in the amp in order to suit different headphones better?

Also just curious - is there a way that this sort of thing could be done via a switch? For example all of the caps/resistors are on the pcb and switches enable/disable them?

[istari_knight]

Thanks Stan :thumbsup:

[StanleyB]

So basically this sort of thing changes components in the amp in order to suit different headphones better?
You got it:).



Also just curious - is there a way that this sort of thing could be done via a switch? For example all of the caps/resistors are on the pcb and switches enable/disable them?
That will be my forthcoming headphone amp :eyebrows:.

[RAZRr1275]

You got it:).


That will be my forthcoming headphone amp :eyebrows:.

Oooh - If you're serious about that being your next project you can basically sign me up to buy it. I owned a tube amp like that in the past by Garage1217 and loved the ability to tweak it.

[ZebuTheOxen]

Headphone amp? :eek: Yes please.

Will it need a separate DAC?

[PeteC]

Not quite sure about this mod Stan, maybe you could give a little clarification.

"For 32 to100 Ohms headphones, R32/R42 can be about 10K to 12K. The larger value means it will be louder.
For 300 Ohms headphones, you can use 15K or 18K. For larger 300 drivers (like the HD800), you can even go up to 22K

MEC2/MEC4/R32/R42 changes the frequency feedback gain. For deep bass ( recommended for bass light headphones and people who want deeeeep bass) use 22nF for MEC2/MEC4. R32/R42 should be 22K. If you want to maintain the bass level as stock, then MEC2/MEC4 = 33nF. And R32/R42 is 33K."

So if I want to mod my BM2 for use with my HD650s, ending up with a with a flat response, should I just change R32/R42 to perhaps 20K to change the gain, or, referring to the last line of the quote, perhaps it should be MEC2/MEC4 = 33nF. And R32/R42 is 33K. Assuming that stock means flat.

Which components would give the best result?

Thanks.

[StanleyB]

Headphone amp? :eek: Yes please.

Will it need a separate DAC?
The first release is designed for use with a separate DAC, or analogue source. But I am also considering an additional version with a DAC built in. It all depends on how the analogue only version is received. If all goes to plan, the HPA could be ready in July. But don't expect a conventional design. This baby has adjustments to cater for personalized tuning of your headphone.

[StanleyB]

Not quite sure about this mod Stan, maybe you could give a little clarification.

"For 32 to100 Ohms headphones, R32/R42 can be about 10K to 12K. The larger value means it will be louder.
For 300 Ohms headphones, you can use 15K or 18K. For larger 300 drivers (like the HD800), you can even go up to 22K

MEC2/MEC4/R32/R42 changes the frequency feedback gain. For deep bass ( recommended for bass light headphones and people who want deeeeep bass) use 22nF for MEC2/MEC4. R32/R42 should be 22K. If you want to maintain the bass level as stock, then MEC2/MEC4 = 33nF. And R32/R42 is 33K."

So if I want to mod my BM2 for use with my HD650s, ending up with a with a flat response, should I just change R32/R42 to perhaps 20K to change the gain, or, referring to the last line of the quote, perhaps it should be MEC2/MEC4 = 33nF. And R32/R42 is 33K. Assuming that stock means flat.

Which components would give the best result?
The MKII has already been set up for the HD650 as standard. What exactly are you trying to increase or reduce in the HD650 response?

[PeteC]

I was just looking for a bit more gain. When playing CDs of many older recordings the level is a lot lower than more recent made since the "loudness wars" began. Normally the volume control might be at about 11 o'clock, but sometimes it's up to quarter past or more. The frequency response is fine. I would just like a bit more in reserve, it seems wrong to drive something so hard.

[StanleyB]

I was just looking for a bit more gain. When playing CDs of many older recordings the level is a lot lower than more recent made since the "loudness wars" began. Normally the volume control might be at about 11 o'clock, but sometimes it's up to quarter past or more. The frequency response is fine. I would just like a bit more in reserve, it seems wrong to drive something so hard.
The first 60 odd percent of the rotation of the volume control is on a log scale and covers about 50% of the output level. This is to take into account low impedance headphones. The higher output level that is required for high impedance headphones also requires that the volume control is turned up far higher in order to get an equivalent output level as a low impedance headphone. It is one of the reason why I am designing an alternative headphone amp. The basic headphone amps on the market, and headphone amps circuits fitted to DACs, have to cater for a wide range of cans. But low and high impedance headphones don't have their equivalent sound output level in the same location on the volume dial.
So you are not actually driving the headphone section hard. It is merely a perception created by the difference in position of the volume control position that is required by differing headphone impedance settings.
But of you want to move the dial position a bit lower for the equivalent gain, you can use 22K for the resistors if you got a HD650.

[StanleyB]

Based on some queries with regards to extended low down bass, one update to note:

For the MKII, R53/R54 = 10K for 32 Ohms headphones. 15K for 300 Ohms like HD650. Or 22K for HD800.

This is based on:
R55/R56 = 22K
C53/C54 = 22nF

The same applies for the equivalent MKI circuit.

[istari_knight]

Based on some queries with regards to extended low down bass, one update to note:

For the MKII, R53/R54 = 10K for 32 Ohms headphones. 15K for 300 Ohms like HD650. Or 22K for HD800.

This is based on:
R55/R56 = 22K
C53/C54 = 22nF

The same applies for the equivalent MKI circuit.

Your calcs are spot on Stan. I use 32R headphones & fitted 12K/22nF. There's been not only an appreciable increase in the extreme low end but greater usable range on the volume pot too.

[John]

James was kind enough to do the Venom mods. Thanks
A further improvement in SQ seems to add more depth and detail
I love to hear where the DAC is now against other DACs

[StanleyB]

I love to hear where the DAC is now against other DACs
You can always pass by and we can compare it to the CaimanII. You only heard the headphone output. We can try them out on speakers this time.

[John]

Sounds fun I try and come over soon I PM you latter

[StanleyB]

Hi John, it was nice to catch up with you again yesterday. I hope that you enjoyed the BMII versus CaimanII demo. Especially the mp3 versus FLAC versus WAV comparison from the Touch digital output. My past comments about FLAC, when compared to WAV, should make a lot more sense now ;).

[John]

Yes great session
Please put me on the list for the Caiman when it released

[wee tee cee]

mmm....new caiman? Please tell me more.

[nat8808]

and many people have emailed me to ask if I can get it up quickly.

Tell me about it! I get a lot of spam too.. :rolleyes:

[StanleyB]

mmm....new caiman? Please tell me more.
Not much to say at this stage Tony, except to say that the legend that is the Caiman is further enhanced:). It is mainly aimed at the music connoisseur who is looking for concert hall clarity, detail, and openness. But you do need a reasonably good amp and speaker combination with the ability to convey that kind of performance. On my budget test system I can't tell an obvious difference that consistently stands out with the CaimanII when compared to the BM. But on my reference system anyone who has passed by to listen to it could tell the difference in less than a minute. I don't expect to sell as many of them as the original Caiman though. The far higher price is likely to deter the casual buyer and user, and cause the more avid performance seeker to take a far closer and longer look at the state of his or her wallet.

[pitadavespa]

Stanley,

What is the main difference between them?
The variable pre-out?

[StanleyB]

Yes it does have a fixed/variable output, as well as a USB input.

[slate]

Battery support?

Hmm time to start a dedicated thread?

[pitadavespa]

Yes it does have a fixed/variable output, as well as a USB input.

Thanks Stanley.

How about sound quality?
Is the Caiman II as good as the Bushmaster II working with battery?

[John]

If you wish I give my thoughts via pm as its not in production and would be just based on what I heard on Stan's reference system

[pitadavespa]

If you don't mind, I'd appreciate it, since I'll be buying one or another in a (I hope) near future.

Thanks. :thumbsup:

[StanleyB]

If you don't mind, I'd appreciate it, since I'll be buying one or another in a (I hope) near future.
Just keep in mind that the CaimanII is going to set you back around 50 to 60% more price wise.

[wee tee cee]

With usb that off sets the cost of a converter. Variable output could take a pre out of the equation. Will a headamp still feature? I trust Johns ears if its an improvement on the BM2 then I would be happy to stump up for one as I cant fault what I have at the moment.
If its a standalone DAC then the additional headphone amp Stan is planning would make a nice pairing in a bundle......

[pitadavespa]

Just keep in mind that the CaimanII is going to set you back around 50 to 60% more price wise.

Thanks.
That's good and bad news...

[StanleyB]

With usb that off sets the cost of a converter. Variable output could take a pre out of the equation. Will a headamp still feature? I trust Johns ears if its an improvement on the BM2 then I would be happy to stump up for one as I cant fault what I have at the moment.
If its a standalone DAC then the additional headphone amp Stan is planning would make a nice pairing in a bundle......
I shall cover that and more in a dedicated thread sometime next week. Just waiting for one of the production boards to arrive with FEDEX so I can make sure there are no quality problem between it and the pre-production board.