Rebuilt Quickie: "The Bonze"

[Bonzo]

To calculare bass rolloff (cutoff frequency) you can apply the same formulae for a simple RC high pass-filter.
You can use this calculator, for example http://sim.okawa-denshi.jp/en/CRhikeisan.htm
Use power amp's impedance for "R" and output cap's value for "C"; please bear in mind that when you use two caps in parallel you have to sum their capacitance value and use this value for "C".
Hope it helps!
Ciao

 

[Grainger49]

Also, if you have a bleeder resistor after the output cap it is in parallel with the amp's input.  So get the parallel equivalent first then plug into the formula.

With just two resistors product over sum works.  (R1)*(R2)/R1+R2

 

[aragorn723]

Hi,

Thanks for the ideas, just realized why there was no bass.  Before adding the bypass caps, I set the eq in itunes to treble booster, which makes the bass flat.  After turning off the eq, bass is back!  Oops!  lol.

Dave

 

[Bonzo]

Ok, some feedbacks for the big tubes
Tubes #1: metal base
The gain is really high..I think you can expect 3db more gain from the quickie, but you'll also pick up a lot of hum.
It's not so simple to enjoy music with them, you have to use an amplifier with low gain (absolutely less than 20db)
Tubes #2: normal plastic base
A touch less gain (very strange, they are supposed to be te same model!), so you can use them with a normal amplifier

How do they sound? As they exhibit more gain, they seem to sound better (i.e. louder), but once you balance the volume you'll hear some bass rolloff. I use fostex fullrange, so I don't need a bass-shy preamp!
Midrange is really good, detailed and a bit sharp, voices are really good
Highs are a good.
Soundstage is good too, a bit flat but good nonetheless...

Did I tell you there is also the "glow factor"?!?  ;D

 

[Bonzo]

Some more updates:
Still wondering how can a simple tube swap made the quickie almost twice as powerful (but I suspect the distortion is double too...).
In any case I recommend this particulare "tube swapping": not only the look is really cool, but the mod maintains the sound signature of the Quickie.
I would have kept this setup if I hadn't a pair of Telefunken 

Ciao!

 

[Bonzo]

ok,
some free time and some monster cap to play with: what do you think if I use 37uf PIO western electric caps for cathode bypass?
I red somewere minimum value should be 47uf...how much bass rolloff would I experience?

Thank you very much for any help!

 

[Bonzo]

Hi everybody, a little bump for my question:
do anyone here can give me some ads about using 37uf PIO western electric caps for cathode bypass?

I red somewere minimum value should be 47uf, but I also red there could be no caps too, albeit there would be less gain.

Thank you very much for your help!

 

[Bonzo]

This is another quote from PJ:

I think around 40uF should be satisfactory. The 1000uF is just something big enough to not lose on the workbench  :^)  seriously, at that low a voltage the cap is very cheap.

So maybe 37uf is ok, BUT having red this article http://www.rfcafe.com/references/popular-electronics/bypass-capacitor-jan-1962-popular-electronics.htm it seems the smallest value to achieve a good reactance (1/20 of Rk) and a 10Hz bottom freq. is 380uf.

Mmmmhhh....

 

[Bonzo]

A little bump for my old question...
The point is the PIO caps I have are really huge, and to try them means to rebuild my quickie once again, so before made this huge amount of work I'd like to know in advice if the value of the caps is ok.

From what I red in the forum 47/40 uf is ok (so 37uf should be ok too), but from the formulae I found on the net it seems not...
Obviously I trust the man who designed the Quickie  ;D but, as I said, the huge amount of work involved in the mod makes me think twice...  :

Ciao!

 

[Paul Joppa]

There are numerous different formulations of the "proper" cathode bypass capacitance. They differ because they each use different criteria and/or different simplifications of the circuit. As far as I know, nobody has published or posted real-world subjective comparisons, so the various theories remain untested. For example, the article quoted suggests a reactance 1/10th or 1/20th of the cathode resistance at the lowest frequency - which would be -0.1dB or -0.022dB. This is IMHO overkill. If you make it 1/2 of the cathode resistance you are down 1dB at the lowest frequency and the cap is 5 or 10 times smaller. You would be hard pressed to hear a 1-dB difference at 20Hz. For what it's worth, the Quickie output cap, feeding the lowest recommended load resistance of 10K, will be down about 1dB at 20Hz.

I recommend you get some clipleads to temporarily insert the caps in your current working Quickie, and do some listening to see what differences there may be. Remember that a small loss of deep bass will usually bring out the midrange, which may make it sound better at first, but a little weak eventually.

 

[Bonzo]

When I was about to try out the new NOS coupling capacitor, my quickie started to behave strangely.
I was listening to a piano solo cd when all of a sudden it seemed there was a snare drum near the piano, with the snare sizzling on every loud note palyed.
I came nearer the loudspeakers and I heard a sort of high pitch hum, that increase ad the music got louder.
After some time I started hearing loud pops, like someone turned on and off the quickie.
I double checked each solder joint, tested continuity, cleaned the sockets with dry contact cleaner, cleaned pins of the tubes but it seems I cannot get rid of the sizzling and, during the first 10minutes of playing, some loud pops.

Any help is really appreciate!

 

[mcandmar]

Battery voltages ok?

 

[Bonzo]

Yes, plenty of voltage, alco checked continuity of the battery holders... 

 

[mcandmar]

Is it on both channels?  Does it go away with the inputs disconnected?

 

[Bonzo]

The sizzle is on both channels, the pop only on one channel (also swapping tubes the channel is the same).
It's the same with inputs disconnected, and also changing inputs it remains the same.

 

[cpaul]

For battery voltage, you checked both filament and plate supplies?

 

[Bonzo]

Yes, checked both filament and B+ and they are both good (1,4 v filament and 32v b+).

Another weird thing happened yesterday night: I removed the Quickie from the system and turned it upside down to inspect soldering once again. Everything was fine so I switched it on trying to ear any strange noise while gently touch components.
I was using the quickie as headphones aplifier for this task (I built Edcor transformer in a separate case).
No noises, no sizzling, just music.
Put the pre back into the system and...no more sizzling nor pops... 

I will investigare further this evening...

 

[Doc B]

It's most likely a damaged capacitor or it could be a loose piece of wire or something that fell out when you turned the preamp over.

 

[Bonzo]

It's most likely a damaged capacitor or it could be a loose piece of wire or something that fell out when you turned the preamp over.

Thank you all for the help, I really cannot understand what's wrong!
I think the problem is still something related to sockets: now after some more cleaning and tube swapping the sizzling is less evident, and the pops stopped within 30 seconds after turning on.

Quickie's output caps are russian K75, big as a grenade, I don't tink they are damaged, but I'll change them just to be shure.

ATM I'm using the quickie with a class D amp which has big electrolytic output capacitors, maybe is a good idea to check if they are damaged too, and maybe bypass them with good teflon ones?

Thank you all again! 

 

[Doc B]

I was working under assumption that you were sure the noise was coming from the preamp. If you haven't already, you will want to isolate which piece of gear the noise is coming from before changing out any parts.