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Old 5th August 2015, 04:54 PM   #2031
Rothor is offline Rothor  Sweden
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Couldn't arrange to have the Bonnecs picked up in time, so I missed that opportunity... =(
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Old 5th August 2015, 08:21 PM   #2032
Danger Mouse is offline Danger Mouse  Germany
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Quote:
Originally Posted by wengtech View Post
hello again,
i have 4pcs Rcore single 32vac 180va each.
(that will be 2x32vac 360va for one channel)
if i separate the supply for gain stages.
is it okay to supply for the output stages?

thanks.
why not try the cascode from F5 Turbo V3 this cascode should also work for the BA3 frontend

So you could easyly use the transformers

Or i`m wrong?
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Old 6th August 2015, 02:06 AM   #2033
wengtech is offline wengtech
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Hi Danger Mouse,
Yes that is one solution using cascoded for a higher voltage rails.
But since the jfets k170 j74 very likes a low voltage, I think I have to make separate PSU for the gains rails.
And keep the voltage as low as possible without the help of cascode transistors.

Also, cascode and without cascode will "sound" quite different, and I like without.

18-20v is sweet enough for the jfets.

Last edited by wengtech; 6th August 2015 at 02:16 AM.
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Old 6th August 2015, 03:09 AM   #2034
Russellc is offline Russellc  United States
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Originally Posted by wengtech View Post
Hi Danger Mouse,
Yes that is one solution using cascoded for a higher voltage rails.
But since the jfets k170 j74 very likes a low voltage, I think I have to make separate PSU for the gains rails.
And keep the voltage as low as possible without the help of cascode transistors.

Also, cascode and without cascode will "sound" quite different, and I like without.

18-20v is sweet enough for the jfets.
I'm finding 31 volt rails pretty darn sweet. Of course mine is complementary, not single ended.

Taken from 6L6's build thread:

Complimentary output, 24V rails - 25WPC, 8ohm. More into 4ohm
Complimentary output, 32V rails - 40WPC, 8ohm. More into 4ohm.
Single-ended output, 24V rails - 25WPC, 8ohm. Less into 4ohm.

I guess you can go higher rails with single ended?

Russellc
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Last edited by Russellc; 6th August 2015 at 03:14 AM.
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Old 6th August 2015, 01:51 PM   #2035
stormfrontier is offline stormfrontier  United States
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Quick question: The single-ended bias boards only have P1, so I'm assuming that there is no "offset," and that the only thing that needs to be set for the outputs is the bias itself?

Also, the FE gets biased to 1V, or a little under. Do the output boards get biased to the same amount?
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Old 6th August 2015, 03:03 PM   #2036
coils is offline coils  United States
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Originally Posted by stormfrontier View Post
Quick question: The single-ended bias boards only have P1, so I'm assuming that there is no "offset," and that the only thing that needs to be set for the outputs is the bias itself?

Also, the FE gets biased to 1V, or a little under. Do the output boards get biased to the same amount?
Hi storm, I built the se version, the pot on the bias board zeroes the dc offset on the output terminals, the bias is fixed.
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Old 6th August 2015, 03:13 PM   #2037
stormfrontier is offline stormfrontier  United States
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Originally Posted by coils View Post
Hi storm, I built the se version, the pot on the bias board zeroes the dc offset on the output terminals, the bias is fixed.
Do you remember what the bias is fixed at for the outputs?
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Old 6th August 2015, 03:24 PM   #2038
Russellc is offline Russellc  United States
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Originally Posted by stormfrontier View Post
Do you remember what the bias is fixed at for the outputs?
I dont know if this helps, but with my complimentary BA-3, while the FE board biased like you say, from .900's to 1.000, the output stage, depending on room, circulation and so forth in a 5U chassis was limited to .46 or .50. Maybe this winter ( or with a babysitter ) a little higher. At this level the heatsink was reaching 52 degress centigrade.

Perhaps if someone with an up and running would measure across one of the resistors on the output board they could tell you, but if it is fixed, I guess it is fixed. I dont remember the BA-3 article mentioning it, but it may have escaped me as I was going complementary.

Anyone out there running a single ended BA-3 that wouldn't mind measuring this for stormfrontier?

Russellc
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Last edited by Russellc; 6th August 2015 at 03:27 PM.
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Old 6th August 2015, 06:34 PM   #2039
coils is offline coils  United States
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Originally Posted by stormfrontier View Post
Do you remember what the bias is fixed at for the outputs?
I built it per spec with +- 25 volt rails, and 1 ohm source resistors. Bias is .58 amps per quasi comp pair. I have 6 pairs for 3.5 amps bias. I only use the se outputs and bias boards, I don't use the front end.
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Old 6th August 2015, 10:01 PM   #2040
coils is offline coils  United States
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You can decrease the bias with the addition of R219 on the bias board. My final build does not use it.
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