Bottlehead Crack - A Custom Headphone Amp!
- Thread starter Mikey
- Start date
Grainger49
New member
Mike,
Excellent work ! I particularly like the beveled skirt at the bottom of the base. It is a distinctive touch. It reminds me of the old Dual bases. I still have one with a 1219 in it.
Excellent work ! I particularly like the beveled skirt at the bottom of the base. It is a distinctive touch. It reminds me of the old Dual bases. I still have one with a 1219 in it.
Hi Gang,
It's been a while since I've tinkered with this amp, I've been too busy enjoying it in its existing condition!
However, the modification bug finally got the best of me, and I decided to upgrade the output capacitors
and add a choke to the power supply.
I removed the last RC stage from the power supply filter. In place of the resistor, I installed a Triad C-7X
choke. This allowed me to use a smaller (physically larger!) cap in the last position. I had a Solen 22uF
film cap in my parts box, so that's what I used.
The choke was mounted on some 1" tall nylon standoffs, and the Solen cap was mounted to an additional
terminal strip that I mounted near the output tube socket:
A little bit of rewiring was necessary around the surrounding area, but nothing too difficult.
Now that the power supply was improved, I could turn my attention to the output caps...
It's been a while since I've tinkered with this amp, I've been too busy enjoying it in its existing condition!
However, the modification bug finally got the best of me, and I decided to upgrade the output capacitors
and add a choke to the power supply.
I removed the last RC stage from the power supply filter. In place of the resistor, I installed a Triad C-7X
choke. This allowed me to use a smaller (physically larger!) cap in the last position. I had a Solen 22uF
film cap in my parts box, so that's what I used.
The choke was mounted on some 1" tall nylon standoffs, and the Solen cap was mounted to an additional
terminal strip that I mounted near the output tube socket:
A little bit of rewiring was necessary around the surrounding area, but nothing too difficult.
Now that the power supply was improved, I could turn my attention to the output caps...
I decided to take a slightly different approach to mounting the giant Dayton output caps
in my amplifier. I chose to attach four terminal posts to the underside of the chassis plate,
and run short wires back to the appropriate points in the circuit:
These terminal posts would also serve to firmly mount the output caps without resorting to
tie wraps or any other means of attachment:
Everything just barely fits inside the confines of my shorter base!
Sonically, the film caps add a bit of smoothness, and get rid of a bit of 'hash' in the highs.
I suspect the sound will improve with a bit of break in...
Mike
in my amplifier. I chose to attach four terminal posts to the underside of the chassis plate,
and run short wires back to the appropriate points in the circuit:
These terminal posts would also serve to firmly mount the output caps without resorting to
tie wraps or any other means of attachment:
Everything just barely fits inside the confines of my shorter base!
Sonically, the film caps add a bit of smoothness, and get rid of a bit of 'hash' in the highs.
I suspect the sound will improve with a bit of break in...
Mike
Grainger49
New member
Very, very neat work! Most of my Bottlehead equipment doesn't look that good.
Good job on mounting the Daytons, having those physical connections to the chassis is important for good reliability.
Heck, it even looks like you have a little room left to add the Speedball down the road.
I also thought I'd mention that when I've used the PEC stereo pots, sometimes the tracking on the bottom range of the pot is a little off from channel to channel. If you find yourself in this range a lot, you can add a 100k resistor in series between the center pin of your input RCA jacks and the potentiometer (with some heatshrink over to keep the clean look).
-PB
Heck, it even looks like you have a little room left to add the Speedball down the road.
I also thought I'd mention that when I've used the PEC stereo pots, sometimes the tracking on the bottom range of the pot is a little off from channel to channel. If you find yourself in this range a lot, you can add a 100k resistor in series between the center pin of your input RCA jacks and the potentiometer (with some heatshrink over to keep the clean look).
-PB
NightFlight
New member
Inspiring build! I generally don't care what it looks like underneath, as performance is key. But this build is simply stunning.
mcandmar
New member
They used to be available on eBay in blue, brown, and white. These are the only ones i know of that are reasonably priced.
http://www.ebay.co.uk/itm/Teflon-4-40-Double-Turret-Terminal-Qty-10-/321221461849?pt=LH_DefaultDomain_0&hash=item4aca4a8759
http://www.ebay.co.uk/itm/Teflon-4-40-Double-Turret-Terminal-Qty-10-/321221461849?pt=LH_DefaultDomain_0&hash=item4aca4a8759
Mikey said:
Expressing my ignorance here, but does the above mean that replacing the final resistor with a choke that I can substantially drop the capacitance needed for the final PS capacitor? Is it safe using a 22uF capacitor? I have a Triad choke en-route and was planning on using a 220uf / 250V Mundorf MCap, but the Crack will get crowded. If I can save some real estate by using a smaller cap(56uf to 100uf) it would definitely be helpful.
Gunter, that's the way I understand it.
A while back, PB posted about this modification to the power supply....that's where I got my information.
His post(s) should be in the archives if you want to dig for them.
Even with a 22uF cap as the final filter cap, the amplifier is as quite as a tomb...
Mike
A while back, PB posted about this modification to the power supply....that's where I got my information.
His post(s) should be in the archives if you want to dig for them.
Even with a 22uF cap as the final filter cap, the amplifier is as quite as a tomb...
Mike
JamieMcC
New member
A simulation of the PSU using Duncan Amps shows stock the Cracks ripple is around 1.5068m
With the C7 choke and keeping the stock capacitors this is reduced to 66.546u
A simulation with 10uf in place of the last 220uf with the choke fitted shows as 1.4929m closer to the original specification.
I don't know how low would be wise to go and how a lower value such as 10-20uf might effect the sonics perhaps someone else will chime in who is more knowledgeable as I am really just pulling the figures of the psu program and suspect there might be a industry rule of thumb of some kind for correct ratio's.
From my own experiments I have run a Cack with choke and at different times 50uf, 100uf an 200uf capacitors fitted in the last spot there where subtle differences mostly bass impact seems to be a little punchier and more dynamic moving up from 50uf to 100uf and I could not with any certainty say this was again noticeable going from 100uf to 200uf.
It would be interesting to hear some thoughts from the resident gurus...
edit it would be interesting to try a higher quality lower value capacitor such as the a Mundorf supreme or Jantzen in place of a budget film.
With the C7 choke and keeping the stock capacitors this is reduced to 66.546u
A simulation with 10uf in place of the last 220uf with the choke fitted shows as 1.4929m closer to the original specification.
I don't know how low would be wise to go and how a lower value such as 10-20uf might effect the sonics perhaps someone else will chime in who is more knowledgeable as I am really just pulling the figures of the psu program and suspect there might be a industry rule of thumb of some kind for correct ratio's.
From my own experiments I have run a Cack with choke and at different times 50uf, 100uf an 200uf capacitors fitted in the last spot there where subtle differences mostly bass impact seems to be a little punchier and more dynamic moving up from 50uf to 100uf and I could not with any certainty say this was again noticeable going from 100uf to 200uf.
It would be interesting to hear some thoughts from the resident gurus...
edit it would be interesting to try a higher quality lower value capacitor such as the a Mundorf supreme or Jantzen in place of a budget film.
Mikey, thanks for clarifying. I did a quick search, but will do a more thorough one later today...thanks for the feedback on the mod although my primary concern is more avoiding fireworks. I am hoping that having the proper voltage rating will avoid that.
The plus side of this is that, by using for example 47uf for the coupling caps and a 47uf for the last power supply cap, I can get a lot further with the real estate available in my Crack. I ordered some 100uf / 400V Jantzen Cross Caps and was quite surprised at just how much space they need. Not sure if I can fit those and the Speedball in the stock base.
The plus side of this is that, by using for example 47uf for the coupling caps and a 47uf for the last power supply cap, I can get a lot further with the real estate available in my Crack. I ordered some 100uf / 400V Jantzen Cross Caps and was quite surprised at just how much space they need. Not sure if I can fit those and the Speedball in the stock base.
Gunter,
Take a look at this post by Paul Joppa mentioning that the last capacitor in the power supply is also in the output current loop.
http://bottlehead.com/smf/index.php?topic=3498.msg30955#msg30955
That may help you make a decision on what value to use as a replacement for the power supply's last capacitor.
Richard
Take a look at this post by Paul Joppa mentioning that the last capacitor in the power supply is also in the output current loop.
http://bottlehead.com/smf/index.php?topic=3498.msg30955#msg30955
That may help you make a decision on what value to use as a replacement for the power supply's last capacitor.
Richard
Mike - Apologies for having this discussion on your gallery thread.
Richard - Thanks, that was helpful. So, I will use 47uFs on the output caps since I won't really lose much low-end, and use 100uF on the last PS cap in order to have at least double the capacitance over the output caps.
Richard - Thanks, that was helpful. So, I will use 47uFs on the output caps since I won't really lose much low-end, and use 100uF on the last PS cap in order to have at least double the capacitance over the output caps.
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