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Help! No Bass Leak TL/50

K

kewpiter

New Member
I build the Leak TL/50 from scratch, point to point, following the schematic. Some of the voltages are a bit
high: EF86 165 (should be 150); 12ax7 315v (should be 300) Kt88 plates 478- cathode to plate voltage 425v.
across cathode 45v ;resistor ohms 493. The treble is wonderful but the bass is weak, very weak. I upgrade the coupling cap from .25 to .47uf, along with the screen grid cap on 12ax7. But still very little bass. Now I am a novice. the only tool I have is a multimeter. Please, no complex theory. Any help to improve the bass will be
appreciated. schematic link: http://www.44bx.com/leak/Leak/Circuits/tl50_ecc83.JPG
 
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Are you using original output transformers or clones? I just wonder if the wrong feedback values are being used? But I'm not an engineer.
 
You are bypassing the 500-ohm cathode-tied resistors on the KT-88 with 50mfd caps?


tl50_ecc83.JPG
 
Dandy said:
Are you using original output transformers or clones? I just wonder if the wrong feedback values are being used? But I'm not an engineer.
Click to expand...
It's Edcor; 5000ohms 100watts. I have experimented with different feedback values and find no problem.
 
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I calculate around 91mA cathode draw. This seems reasonable for Class A, for the KT-88.

How about the bypass C1 and C2 caps on the EF86 pentode? It is 50mfd & 0.001mfd respectively. Correct?

Feedback RC network is correct?

ECC83 phase inverter test strong?
 
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It may be that nothing is wrong. This amplifier design has a very high damping factor, which if compared to (or you are comparing to) other amplifiers of much less damping capability, will sound very bass shy by comparison indeed.

As a quick test, disconnect the NFB lead from the 16Ω tap, and ground the lead. The amplifier will be much more sensitive, but if the bass comes back with this scenario, then the high damping factor is all but proven to be the likely culprit.

Dave
 
Mr Boochie said:
I calculate around 91mA cathode draw. This seems reasonable for Class A, for the KT-88.

How about the bypass C1 and C2 caps on the EF86 pentode? It is 50mfd & 0.001mfd respectively. Correct?

Feedback RC network is correct?

ECC83 phase inverter test strong?
Click to expand...
I USED MORE THAN ONE ECC83 AND SO I KNOW THEY ARE OK. C1 AND C2 ARE OKAY. CHANGE THEM MANY TIMES.
 
dcgillespie said:
It may be that nothing is wrong. This amplifier design has a very high damping factor, which if compared to (or you are comparing to) other amplifiers of much less damping capability, will sound very bass shy by comparison indeed.

As a quick test, disconnect the NFB lead from the 16Ω tap, and ground the lead. The amplifier will be much more sensitive, but if the bass comes back with this scenario, then the high damping factor is all but proven to be the likely culprit.

Dave
Click to expand...
Wow, disconnected the NFB and the bass is much much better; the treble is wicked( When I grounded the NFB it result in poor volume and distortion). OK, what can I do about the damping factor? Let me ask, the KT88s are electroharmonix with a load
resistance of 3000ohms but the transformer is 5000ohms. Is this a problem? Thank you and everyone for helping, really appreciate it.
 
6DZ7 said:
I think this boils down to a comparison of what you are used to. If you search out info on damping factor you'll find there is nearly universal opinion that higher is better for more accurate bass production. So If you have been listening to some amps with poor or low factor then you may be hearing a difference from what you have expectations of. Removing the NFB line just exagerates all the FR deviations of the amp which are most frequently the ends of the spectrum, lows and highs. Having good damping factor but thin bass means you probably need "loudness" that doesn't exist in your system.
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Yeah, the extra damping factor maybe exposing a bass weakness in your speakers. Poor damping can cause a muddiness which makes the bass more apparent, but less defined & precise (note-wise).

What brand/model are the speakers?
 
Mr Boochie said:
Yeah, the extra damping factor maybe exposing a bass weakness in your speakers. Poor damping can cause a muddiness which makes the bass more apparent, but less defined & precise (note-wise).

What brand/model are the speakers?
Click to expand...
Eminence American Standard Beta-15A 15" Pro Audio Speaker, 300 Watts at 8 Ohms.
 
kewpiter said:
Wow, disconnected the NFB and the bass is much much better; the treble is wicked( When I grounded the NFB it result in poor volume and distortion). OK, what can I do about the damping factor? Let me ask, the KT88s are electroharmonix with a load
resistance of 3000ohms but the transformer is 5000ohms. Is this a problem? Thank you and everyone for helping, really appreciate it.
Click to expand...
I doubt if this is related to your KT88s. I think this means that you need to adjust your NFB, but I don't know how to advise you to do this.
 
Dandy said:
I doubt if this is related to your KT88s. I think this means that you need to adjust your NFB, but I don't know how to advise you to do this.
Click to expand...

Thank you for responding. I found the problem which was the Kindle Fire I used as source; it was the input. Apparently, it was not able to drive the amp to full power. I have a small preamp(solid state) DJpre 11
which I stuck between the Kindle Fire and the Leak. Oh my God, the bass almost lift the roof off.
 
kewpiter said:
Thank you for responding. I found the problem which was the Kindle Fire I used as source; it was the input. Apparently, it was not able to drive the amp to full power. I have a small preamp(solid state) DJpre 11
which I stuck between the Kindle Fire and the Leak. Oh my God, the bass almost lift the roof off.
Click to expand...

Yeah, source miss-match! That's one of the first things we all should have questioned.

Glad you found and fixed it. :thumbsup:
 
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