Moskido - Hybrid Aikido/MOSFET amplifier

[athos56]

Originally Posted by beau2317

And here is the PSU

FRED bridge rectifiers, Jensen 4 pole caps, Tube transformer from PartsConnexion

MOSFET transformer from RS Components, 500VA

Common mode filter made from some ferrite RF chokes and 0.1uF

So I made a Moskito from the original version on the TubeCad web site and was quite happy with it but I did have some hum from the Mosfet psu. Originally I tried the low dcr approch, low inductance, low dcr chokes and a few hundered uf of capacitance. In short it didn't work, so I jammed all the electrolitic caps I had in the house in the PSU and knocked the hum down to an OK level. The point is, I still had less capacitance than Beau shows here, so I bought a bunch of 4700uf caps and I'm going to put a bunch in and see how much hum I can get rid of. I'll report back when I have results.
Just as a general question how much capacitance is considered to much or to little for a SS amp? For example, I got (20) 4700uf caps I was thinking something like: a Bridge rect to one 4700uf cap to my 2 chokes (to make split rails), and then a few RC sages of parralleled caps (1 to 7 ohm resistors and 9400uf of capacitance), repeated untill I hit my target voltage (1 or 2 stages of RC per channel). Any comments??

[athos56]

Originally Posted by Her_lennon

Francois,

Thank you!!

I think to buy some of the "medium powered" line here INTERNATIONAL ALUEL. What do you think? Or do you think that is better some of the "High Powered" line. I'm trying to get a heatskins that works and and which is not so big.

I bougt 4 of the ones that looked like (Code 5075 ZD-28) and used one per Mosfet. Vertically mounted its never gotten more than luke warm, the tubes in the akidio section run hotter.

Here is what I used ( HEATSINK TO-3 PWR 50W BLK - 198540B00000G )

Its listed for the TO-3 case but I just used one of the mounting holes and it worked great.

[pgtakaka]

carbon or metal film and the Aikido..?

Dear Beau, as a long time 'Broski Follower' I'm pleased to be finally building the Broski Beau Moskido. I was lucky enough to get mail from Broski some years ago , when by pure luck I chanced upon 'cathode followers' on Broski's web site. I had tried dozens of FET and op amp circuits to buffer a Piezo pickup off my violin . Arrggggh..In desperation I tried the 'aikido' follower , with a 6C67 ( which is still on the violin. ) . I chose the bipolar circuit to eliminate the input cap. It is powered by a 6v fillament battery on the floor and runs +- 60v ( keyfob 12v cells ) . The sound , when direct into a good digital recorder is staggering . It simply 'makes music' - and spared me having to shell out 6k$ for a better violin. It sounds better than the natural sound of the violin ??? !!!

Next pre-amp will use a 1579 - just for fun . I can't image something sounding 'better ' than the 6CG7, but indeed I take your word for it . Will look pretty cool hanging off the fiddle too .. ' Octal Powered Hillbilly ' .
I discovered that yes , caps do 'color ' the sound , but that isn't necessarily a bad thing. I also discovered that any value of metal film resistor at the input caused a catastrophic loss of sound quality .
Has anyone else ever run into a problem with high values ( 5 meg ) and metal films ?
By chance , after tearing it to pieces about 6 times trying to find the cause of the problem , I replaced the part with an old 5 meg carbon and 'the sound' was back .

I learned a lot playing with this circuit - I'm convinced a significant factor in tube sound is its incredible immunity to induced noise. I prefer a Battery powered fillament . Even the most microscopic amount of fillament 'noise' will become inseparably entangled with the music and alter it - and I noted in a Broski post he mentions that he often uses a battery for knock ups and that ' it sounds better'. It does indeed and I'm prepared to be fanatical enough to use a big gel cell if need be.

I'm building this for the sound , but also so I can put ' Broski' on the front of the finished amp.. and 'thanks Bob' on the back ..
Many , many thanks
PG

[pgtakaka]

I appreciate that this is the Moskido thread , but does anyone know of a project that used the ThermalTrak Transistors John posted ? 22 October 2006 ?
" some people can't stand the sound of FETS" ?!!

It looks to be such a simple power buffer and very low cost . Any opinions as to how Transistor Buffers rate against Fet Followers ?

PG

[koldby]

pgtakaka

That buffer will not work properly as the temperature compensation is wrong!
Look at this:
RMI-FC100, a single stage audio power amplifier

Koldby

[sachi]

I have a dual mono 9 pin Aikido kit..the idea was to build a headphone amp using this with 6H30s ont he output. However I am all about hybrid amps and the morkido might be right up my alley in making a monster amp to drive my orthodynamic headphones.

Is it feasible to use 6CG7s in both input and output sections with 300V B+ (PS-1 circuit) and run 36Volt LV for the output stage?

The impedance on most of my orthodynamic (planar) headphones are about 50-120 ohms.

Could someone give me pointers if this is possible and how to go about it. I have dual transformers with 35 volt secondaries and about 300VA that i pulled from identical technics amp that i plan to use for the LV.

Appreciate any inputs.

[kacernator]

Originally Posted by sachi

I have a dual mono 9 pin Aikido kit..the idea was to build a headphone amp using this with 6H30s ont he output. However I am all about hybrid amps and the morkido might be right up my alley in making a monster amp to drive my orthodynamic headphones.

Is it feasible to use 6CG7s in both input and output sections with 300V B+ (PS-1 circuit) and run 36Volt LV for the output stage?

The impedance on most of my orthodynamic (planar) headphones are about 50-120 ohms.

Could someone give me pointers if this is possible and how to go about it. I have dual transformers with 35 volt secondaries and about 300VA that i pulled from identical technics amp that i plan to use for the LV.

Appreciate any inputs.

Hi,

I have tried building the mini low-powered moskido for headphones with SE mosfet IRF610 ouput stage and also mosfet push-pull IFR610/9610 output stage. It worked but it didnt sound good.
In the end I got it sounding very very great, but with different output stage. I am using just aikido stage with 4x6SN7, output is cap-coupled (470nF) to output transformer - Edcor XSM10K/150. But remember to invert the phase on output transformer, or it will not sound so good, because aikido already inverts the phase. My headphone amp is powerfull enough to drive 120 Ohm and 32 Ohm very very loud.

[sachi]

Thanks for the reply..

Hmm. Can you tell me what headphones you were driving ?

And the amp you are proposing, is it similar to the 6H30-OPT Aikido that JB proposes? I see he uses a 4.7uF coupling cap there however and a 10k/300R transformers. I Suppose I could go with 10k/100R

The reason I was thinking of MOSFEts is that the planar headphones love the MOSFET output stage with a low output impedance. Current drive is of the essence since the load is purely resistive.

[kacernator]

Originally Posted by sachi

Thanks for the reply..

Hmm. Can you tell me what headphones you were driving ?

And the amp you are proposing, is it similar to the 6H30-OPT Aikido that JB proposes? I see he uses a 4.7uF coupling cap there however and a 10k/300R transformers. I Suppose I could go with 10k/100R

The reason I was thinking of MOSFEts is that the planar headphones love the MOSFET output stage with a low output impedance. Current drive is of the essence since the load is purely resistive.

I am driving Koss UR29 (120 Ohm) and Creative Zen Aurvana (32 Ohm). Aikido preamp is stock aikido, no white cathode follower or any other modifications. Current drive capability - yes, thats why I tried to use mosfet output stage at first too, but it didnt sound as good as transformer output, which sounds great to me. I think mosfets sound better on higher voltages and idle currents - but then it is too much heat and power wasted just for hedphones, my opinion. But with mosfet ouput you cannot so nicely invert the phase back, which is very important to good sound. With speakers you just swap the positive and the negative connection, but with headphones you simply cant, because of the jack connector.

If you have any single ended transformer laying around, you can just try to hook it put to the aikido and listen how it sounds. I think you will be very satisified with the sound, as I am.

And be carefull with the output transformer position, so you dont pick up the hum from the power tranny.

[Itsmee]

Has anyone bolted an Aikido to Nelsons BA2 output stage
If so, how did it sound?
As a future project, I was thinking of trying a balanced input (2 Aikido's) and bridged output (2 BA2 output's) with SUSY feedback.