RMI-FC100, a single stage audio power amplifier

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ernesternest

ernesternest

Member
Joined 2007
Paid Member
Hi out there, waiting for a Groupbuy :clown:

Let me start this way: I definitly do not start a Groupbuy! I want to keep it simple for me - and for you.

I'll order 20 to 50 pcbs depending on demand. 50 boards is my personal maximum. I would order them and send to anybody, who sent an email to me and money after I know exactly the cost.

50 boards would give 25 stereos. 2 stereos for me, 2 for friends. So the maximum I could give away would be 21 stereos. I would sell them for the money they would cost me plus package plus shipping.

The first 21 will be the ones to get a pair of.

I will order by end of August, maybe later. But be sure, I'll order.

I don't want to have too much conversation, too much requests.

Neither I want to hijack this thread, nor I'll open another one. Just email me.

Price? go some posts back.

Please do not email for pcbs, if you can't accept this.

Cheers Ernst
 
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Portlandmike

Member
Joined 2006
Yet another Toriod house to consider

tryonziess said:
pzogal,
Try toroid-transformers.com they have a wide assortment of transformers from 25va up to 1.5kva. I have had very good results from their products. Tad
Click to expand...


DRZ1 said:
www.Plitron.com
Click to expand...


I find these to be decent cost effective and ship cheap at least in the US via USPS, like $10 for to 800VA ones.

More specs than most too.

http://antekinc.com/trans.html
 
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Portlandmike

Member
Joined 2006
One to many tracking diodes?

Hi,

I was just looking at the schematic for the amp, and I counted 5 bias diodes, and only 4 Vbe drops.

Is there intentionally an extra bias diode in the tracker, and if so, what was the rational.

Seems like it would defeat some of the benifit of having very fast tracking if the multiplier had 20% to much gain....

Thanks

Portland Mike
 
roender

roender

Member
Joined 2006
Re: One to many tracking diodes?

Portlandmike said:
Hi,

I was just looking at the schematic for the amp, and I counted 5 bias diodes, and only 4 Vbe drops.

Is there intentionally an extra bias diode in the tracker, and if so, what was the rational.

Seems like it would defeat some of the benifit of having very fast tracking if the multiplier had 20% to much gain....

Thanks

Portland Mike
Click to expand...

Hi Mike,

The TC of ThermalTrack transistor is different than the diode TC

http://www.diyaudio.com/forums/showthread.php?postid=1412728#post1412728
 
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pooge

Member
Joined 2003
If making new boards, why not modify them for the modifications?
I'd be interested in a couple.

Haven't looked back through the thread for a while. What is the recommended Idss for the FETs? There's a group buy in the WIKI

LSK170 group buy

There's also a group buy on the duals for these in the same group buy. Is the matching on these LSK389s tight enough, or should LSK179s be used and matched better?

LSK389 datasheet

Sorry if this has been discussed. The group buy looks to be winding up and no time to scan thread.
 
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pooge

Member
Joined 2003
OK, found the answer to Idss being greater than 9ma, so it looks like the right LSK170 in the group buy is the "C" grouping. Correct?

Also found the matching to be +/- 1mv. Wow. How many should be bought to hope to get this close?

As the LSK389 is matched to +/-20mv, they do not appear to be a good substitute. Correct?
 
roender

roender

Member
Joined 2006
pooge said:
OK, found the answer to Idss being greater than 9ma, so it looks like the right LSK170 in the group buy is the "C" grouping. Correct?

Also found the matching to be +/- 1mv. Wow. How many should be bought to hope to get this close?

As the LSK389 is matched to +/-20mv, they do not appear to be a good substitute. Correct?
Click to expand...

From 20pcs 2sk170bl you can get 4 ... 6 pcs in 1...2mV Vgs
 
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wai235

Member
Joined 2007
Is it possible to paralle the jfets?

Hi Mihai,

I like your amp. I’m going to study and build your amp. To be an audio fanatic, I want to try some mod first. For the input stage, I am thinking to parallel the jfets (i.e. a total of four jfets in the input stage) to increase the OLG for improving the THD. The THD improvement was confirmed by Ltspice. However, I could only successfully simulate parallel of BL grade 2SK170. For parallel V grade 2SK170, the simulation was failed. I followed the formulae in http://www.diyaudio.com/forums/showthread.php?postid=1574128#post1574128 for adjusting the CCS.

Can the ballasting resistor be omitted in paralleling the jfets? If yes, how close do I need to match the jfets in order to avoid ballasting resistor? How do you think in paralleling the jfets? Is there any stability problem? I’m not from the field of EE, please forgive me if I’m asking trivial questions.

Wai
 
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wai235

Member
Joined 2007
Re: Re: Is it possible to parallel the jfets?

roender said:


What's the current do you want to run in the LTP? Maybe a V grade k170 is enough ...
I don't think that you can skip resistors if you want to put in parallel more jfets

Cheers,
M
Click to expand...

Mihai,

The LTP current calculated for paralleling V grade 2SK170 is 59mA.

I found that even small ballasting resistor, say 1R will ruin the benefit of paralleling BL grade 2SK170.

Wai
 
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wai235

Member
Joined 2007
Re: Re: Re: Re: Is it possible to parallel the jfets?

AndrewT said:
? how did you workout/measure that?
Click to expand...


Hi Andrew,

From the simulation of single 2SK170V, I measured:
Id(J1) = 12.45mA
Id(J2) = 12.51mA

For paralleling 2SK170V
I5 = 2 x Id(J1) = 24.91mA
I6 = 2 x Id(J2) = 25.01mA

Adjusting I2 to 9.01mA with R19 = 22R
I1 = I2 + I5 + I6 = 58.93mA

I1 to I6 are variables of Mihai's formulae http://www.diyaudio.com/forums/showthread.php?postid=1574128#post1574128

Wai
 
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