Yes Sebastian ,you are right,I did not notice that there were elco in the signal path.
These should be shot on sight.
It still surprises me how many manufacturers of high quality equipment still use elcos as coupling caps.Moreover most of the time they are huge (e.g. 100uf output coupling caps in my TEAC vrds 25 )when 1uf polyprop would do assuming you have a normal preamp input impedance.
I still think there are other options for the opamps apart from the 627 which is probably the mose expensive ´´hi-end´´ opamp.I like AD8610 quite a lot and they are 1/4 the price.When you have to change 13 opamps it adds up.
I don´t agree with using big expensive BG caps as coupling caps.I still think a good 1-2uf WIMA polyprop or similar quality will sound better and be cheaper as long as you can fit it.
These should be shot on sight.
It still surprises me how many manufacturers of high quality equipment still use elcos as coupling caps.Moreover most of the time they are huge (e.g. 100uf output coupling caps in my TEAC vrds 25 )when 1uf polyprop would do assuming you have a normal preamp input impedance.
I still think there are other options for the opamps apart from the 627 which is probably the mose expensive ´´hi-end´´ opamp.I like AD8610 quite a lot and they are 1/4 the price.When you have to change 13 opamps it adds up.
I don´t agree with using big expensive BG caps as coupling caps.I still think a good 1-2uf WIMA polyprop or similar quality will sound better and be cheaper as long as you can fit it.
I think the smd Sebastian mentioned must be much smaller in size obviously.These are probably the headphone output coupling caps.Without knowing the circuit I would say that you could probably do without them completely.The output to the headphones is probably opamp buffered and it is unlikely you will get much DC from any opamp likely to hurt headphones.Usually it is in the single digit mv range- if that .If you are worried that a malfunction may burn your expensive ´phones then you could bypass them with some high quality poly caps.marinsimina said:
marinsimina said:
Dear all,
Yes this are the nasty caps! But there are two smaller caps in bypass with them. One of them is the white one, and there is a smaller one. I'm not on the office now, but tuesday I can look up the location numbers on the print and provide a more detailed picture. If you can not wait... well it is not that difficult to play a test cd with an 1 Khz. tone and search in the circuit with a scope yourself
I advice there the 47uF NXhiq caps from blackgate.
Best regards,
Bas
protos said:
Deare Protos,
No this are not the headphone coupling caps! This are the coupling caps after the second buffer opamp in the circuit. This are the only coupling caps! Removing them and bypass them will destry your headphone! The DC offset without is +/= 200mV on that location. After the headphone amp (wich adds more gaing) with the volume turn open this can be gained tot more then 1 volt DC!
So you really need a DC servo or caps.
Best regards,
Bas
Salas and Protos, C13 and C14 are the only (SMD) coupling caps in the audio signal. If you follow the circuit traces, you will see that they connect the output of 1/2 opamp to the input of the other 1/2 opamp. In a previous message (dated 12-21-2006), Bas explained why they are necessary (to tune out the remaining 200mV DC offset of the DAC chip).
Bas avoided to specify the caps numbers since there are many revisions of DAC1 (and the numbers may be different). I suggest we use the numbers in the latest version, since the current manual can be downloaded from Benchmark: DAC1 Manual. The component layout is given on page 14 (you need to zoom to see all the component numbers).
Marin
Of course if the dc is that high there is no question you need some caps there.What I meant by bypass is that you can parallel some high quality small value cap over the elco.This the dc left over from the I/V stage I guess.So there are no other output coupling caps-great.
Do you need 47uf though?What is the impedance of the next stage?
Anyway I will not make any more suggestions here because without a schematic it is like prescribing medicine without examining the patient.
Sebastian obviously has studied the circuit and knows.
Do you need 47uf though?What is the impedance of the next stage?
Anyway I will not make any more suggestions here because without a schematic it is like prescribing medicine without examining the patient.
Sebastian obviously has studied the circuit and knows.
DAC1 mods so far
I compiled a list of the mods discussed so far:
Part| Replace by| Remarks/Replaces
C13, C14 BlackG NX Hi-Q 47uf/6.3V coupling cap
C109, C110 remove coupling cap
C15, C16 remove coupling cap
SPDIF Input Cap BlackG NX Hi-Q 0.1uf/50V or WIMA MKP2 0.1uf (might not fit)
C27, C28, C29, C30 WIMA FKP2 220pf feedback loop (see AD1853)
C34, C35, C36, C37 WIMA FKP2 330pf feedback loop (see AD1853)
U7 LT1085CT-5 7805A JRC
Aditionally, audioengr uses good poly caps for:
C108 (seems to be on SPDIF input)
C54 BlackG NX Hi-Q 0.1uf/50V or WIMA MKP2 0.1uf (see AD1853)
I compiled a list of the mods discussed so far:
Part| Replace by| Remarks/Replaces
C13, C14 BlackG NX Hi-Q 47uf/6.3V coupling cap
C109, C110 remove coupling cap
C15, C16 remove coupling cap
SPDIF Input Cap BlackG NX Hi-Q 0.1uf/50V or WIMA MKP2 0.1uf (might not fit)
C27, C28, C29, C30 WIMA FKP2 220pf feedback loop (see AD1853)
C34, C35, C36, C37 WIMA FKP2 330pf feedback loop (see AD1853)
U7 LT1085CT-5 7805A JRC
Aditionally, audioengr uses good poly caps for:
C108 (seems to be on SPDIF input)
C54 BlackG NX Hi-Q 0.1uf/50V or WIMA MKP2 0.1uf (see AD1853)
Could the THS4130 sub for the I/V OpAmps?
Hope someone could advise on this.
Would the THS4130 be a good
substitute for the I/V opamps ?
The last opamp, OP275, might also
be subbed by a THS4130 to
drive a balanced output if needed?
Not sure if the Vocm input would
null the offset negating the need
for a DC blocking capatitor?
Has anyone drawn up a schematic
from the dac outputs to RCA outputs
{and balanced outputs} ?
ref: Post #61 for original schematic
http://www.diyaudio.com/forums/showthread.php?postid=1087454#post1087454
Hope someone could advise on this.
Would the THS4130 be a good
substitute for the I/V opamps ?
The last opamp, OP275, might also
be subbed by a THS4130 to
drive a balanced output if needed?
Not sure if the Vocm input would
null the offset negating the need
for a DC blocking capatitor?
Has anyone drawn up a schematic
from the dac outputs to RCA outputs
{and balanced outputs} ?
ref: Post #61 for original schematic
http://www.diyaudio.com/forums/showthread.php?postid=1087454#post1087454
Attachments
Re: Could the THS4130 sub for the I/V OpAmps?
You may want to take a look at the following opamp list.
For many other opamps, you will also have to change the 7818/7918 regulators. I intend to try LM340T-15/LM7915CT (National Semiconductor) or LT317AT/LT337AT by using Eddie's adaptors. Does anyone have better alternatives (need to accept 30V input)?
Marin
ichiban said:
You may want to take a look at the following opamp list.
For many other opamps, you will also have to change the 7818/7918 regulators. I intend to try LM340T-15/LM7915CT (National Semiconductor) or LT317AT/LT337AT by using Eddie's adaptors. Does anyone have better alternatives (need to accept 30V input)?
Marin
Marin, as I have suggested before, I would just measure current draw and use an R drop like we do in tube circuits.
Lets say you lift 3rd reg pin and restore the circuit with your multimeter in current mode, you get the draw in mA. If it is 100mA for example, a 30R in place of the multimeter, will drop 3V. You get 15V, plus a time constant is formed with the following capacitor already installed there that further filters PSU by several dB. Passive, noiseless and easy. 2W resistors will do fine. Rdrop=I(A)*R(Ohm).
Lets say you lift 3rd reg pin and restore the circuit with your multimeter in current mode, you get the draw in mA. If it is 100mA for example, a 30R in place of the multimeter, will drop 3V. You get 15V, plus a time constant is formed with the following capacitor already installed there that further filters PSU by several dB. Passive, noiseless and easy. 2W resistors will do fine. Rdrop=I(A)*R(Ohm).
Salas, I will try your suggestion if I will find the resistors. DAC1 draws about 190mA (very easy to check by removing JP1 or JP5), so I need something around 15.78ohm. But I might end up paying almost as much as for new regulators
I looked for capacitors at digikey.com and I found the following:
Cornell Dubilier SMD mica capacitors
338-1112-ND 220pf (size 1210 SMD) $1.4
338-1126-ND 330pf (size 1812 SMD) $1.93
I was wondering if these are good alternatives to WIMA FKP2 (to be used in the feedback loops). Also, I was wondering if it is worth replacing the .1uf opamp decoupling caps with Panasonic PPS ECH-U1H104GC9 (and add a small blackgate PK 47uf/25V in parallel):
PCF1166CT-ND Panasonic PPS SMD .1uf/50V $.72
Marin
I looked for capacitors at digikey.com and I found the following:
Cornell Dubilier SMD mica capacitors
338-1112-ND 220pf (size 1210 SMD) $1.4
338-1126-ND 330pf (size 1812 SMD) $1.93
I was wondering if these are good alternatives to WIMA FKP2 (to be used in the feedback loops). Also, I was wondering if it is worth replacing the .1uf opamp decoupling caps with Panasonic PPS ECH-U1H104GC9 (and add a small blackgate PK 47uf/25V in parallel):
PCF1166CT-ND Panasonic PPS SMD .1uf/50V $.72
Marin
KIWAME- 66141 16R 2 Watt $1.10 $1.05 $0.99
From Parts Connexion. Do not cost much.
As for small caps you mention, I would not go there before I could listen to each step of upgrading. Too many variables to change at a time.
190ma per polarity must be with OPA627 everywhere as you did by now? How is your sound by now?
From Parts Connexion. Do not cost much.
As for small caps you mention, I would not go there before I could listen to each step of upgrading. Too many variables to change at a time.
190ma per polarity must be with OPA627 everywhere as you did by now? How is your sound by now?
Yes, I have 190mA with OPA627 everywhere. I definively have more midrange and bass (more "layered" and detailed sound as well), but the OPA627 get very hot. You cannot keep the finger on a chip for more than 5 seconds, so I avoided to use it for a long time lately. I intend to do some more "mainstream" upgrades (e.g., change rectifiers and improve power delivery to opamps). However, power delivery got complicated by using the brown dog adaptors since the .1uf caps are not so close to the opamps. I am looking for solutions to this problem.
Marin
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